Estimating the prevalence rate of a disease is crucial for controlling its spread, and for planning of healthcare services. Due to limited testing budgets and resources, prevalence estimation typically entails pooled, or group, testing where specimens (e.g., blood, urine, tissue swabs) from a number of subjects are combined into a testing pool, which is then tested via a single test. Testing outcomes from multiple pools are analyzed so as to assess the prevalence of the disease. The accuracy of prevalence estimation relies on the testing pool design, i.e., the number of pools to test and the pool sizes (the number of specimens to combine in a pool). Determining an optimal pool design for prevalence estimation can be challenging, as it requires prior information on the current status of the disease, which can be highly unreliable, or simply unavailable, especially for emerging and/or seasonal diseases. We develop and study frameworks for prevalence estimation, under highly unreliable prior information on the disease and limited testing budgets. Embedded into each estimation framework is an optimization model that determines the optimal testing pool design, considering the trade-off between testing cost and estimation accuracy. We establish important structural properties of optimal testing pool designs in various settings, and develop efficient and exact algorithms. Our numerous case studies, ranging from prevalence estimation of the human immunodeficiency virus (HIV) in various parts of Africa, to prevalence estimation of diseases in plants and insects, including the Tomato Spotted Wilt virus in thrips and West Nile virus in mosquitoes, indicate that the proposed estimation methods substantially outperform current approaches developed in the literature, and produce robust testing pool designs that can hedge against the uncertainty in model inputs.Our research findings indicate that the proposed prevalence estimation frameworks are capable of producing accurate prevalence estimates, and are highly desirable, especially for emerging and/or seasonal diseases under limited testing budgets. / Doctor of Philosophy / Accurately estimating the proportion of a population that has a disease, i.e., the disease prevalence rate, is crucial for controlling its spread, and for planning of healthcare services, such as disease prevention, screening, and treatment. Due to limited testing budgets and resources, prevalence estimation typically entails pooled, or group, testing where biological specimens (e.g., blood, urine, tissue swabs) from a number of subjects are combined into a testing pool, which is then tested via a single test. Testing results from the testing pools are analyzed so as to assess the prevalence of the disease. The accuracy of prevalence estimation relies on the testing pool design, i.e., the number of pools to test and the pool sizes (the number of specimens to combine in a pool). Determining an optimal pool design for prevalence estimation, e.g., the pool design that minimizes the estimation error, can be challenging, as it requires information on the current status of the disease prior to testing, which can be highly unreliable, or simply unavailable, especially for emerging and/or seasonal diseases. Examples of such diseases include, but are not limited to, Zika virus, West Nile virus, and Lyme disease. We develop and study frameworks for prevalence estimation, under highly unreliable prior information on the disease and limited testing budgets. Embedded into each estimation framework is an optimization model that determines the optimal testing pool design, considering the trade-off between testing cost and estimation accuracy. We establish important structural properties of optimal testing pool designs in various settings, and develop efficient and exact optimization algorithms. Our numerous case studies, ranging from prevalence estimation of the human immunodeficiency virus (HIV) in various parts of Africa, to prevalence estimation of diseases in plants and insects, including the Tomato Spotted Wilt virus in thrips and West Nile virus in mosquitoes, indicate that the proposed estimation methods substantially outperform current approaches developed in the literature, and produce robust testing pool designs that can hedge against the uncertainty in model input parameters. Our research findings indicate that the proposed prevalence estimation frameworks are capable of producing accurate prevalence estimates, and are highly desirable, especially for emerging and/or seasonal diseases under limited testing budgets.

Little is known about the tick populations found within the central Appalachian/southwestern region of Virginia. The main focus of this research was to better assess local tick communities in the central Appalachian-Southwestern region of Virginia, which was addressed by determining species diversity, habitat associations, seasonal phenology, pathogen prevalence, and ecological factors that influences tick presence and abundance. A field study was conducted from June 2019 - November 2020 across 8 counties and 3 habitat types. Forested habitats exhibited greater tick species diversity than pasture and urban habitats. Each tick species was observed to be associated with particular habitats. The presence of B. burgdorferi sensu stricto (causative agent of Lyme disease), the human variant of A. phagocytophilum (causative agent of human granulocytic anaplasmosis), and Powassan virus (the causative agent of Powassan encephalitis) were detected in collected field specimens, suggesting a significant threat to public health. The detection of Powassan virus RNA in local Ixodes scapularis ticks is the first evidence of this viral pathogen within the region. The overwintering abilities of ticks, whose populations are expanding or becoming more invasive, including Haemaphysalis longicornis, Amblyomma americanum, and Amblyomma maculatum, were examined through a combination of laboratory and field experiments. Amblyomma americanum and H. longicornis nymphal ticks had a lower supercooling temperature than adult ticks, suggesting their potential to overwinter better; A. maculatum nymphs had similar average supercooling temperatures as the other two species at nymphal stage. Via a field experiment, A. americanum, H. longicornis, and A. maculatum were subjected to natural elements of a Virginian winter in a two-factor design investigating elevation and potential insulation coverage. Elevation and insulation coverage were found to have no significant impact on the overwintering survival of H. longicornis and A. americanum. However, the life-stage of the tick was determined to be a significant factor that dictated the survival of ticks of these species. Overwintering survival of Amblyomma maculatum nymphs was influenced by insulation (proxied by leaf litter); which may be attributed to this tick's preference of drier climate. Low overwintering survival suggests that a tick may not be able to establish a permanent population within the area. / Master of Science in Life Sciences / Ticks can transmit many pathogens, bacteria or viruses that cause disease, to both humans and animals. Diseases associated with ticks can include Lyme disease, Human Anaplasmosis, Ehrlichiosis, Rocky Mountain spotted fever, as well as viral illnesses. The pathogens that cause these diseases are vectored by specific tick species. Currently, there are no published reports of tick species present within the central Appalachian/southwestern region of Virginia. A study to determine local tick populations presence and the factors influencing their maintenance in the environment was conducted. Additionally, field collected specimens were screened to assess pathogen prevalence within the region. I confirm the presence of Borrelia burgdorferi sensu stricto (causative agent for Lyme disease), Anaplasma phagocytophilum (causative agent for Human Granulocytic Anaplasmosis), and Powassan virus within Ixodes scapularis, commonly referred to as black-legged ticks. Habitat (forest, urban, pasture) was a significant influencing factor on the presence of I. scapularis, Amblyomma americanum, and Haemaphysalis longicornis (e.g., the latter species was predominantly found in pasture habitats). Secondly, I investigated how well three sympatric tick species would overwinter within the region. Survival of a tick is heavily dependent upon their ability to withstand desiccation, obtain a blood meal from a host, mate, and reproduce. Certain ticks may be limited to certain regions based on elevation, temperature, and relative humidity. I investigated the influence of elevation and insulation coverage (presence of leaves vs. no leaves) on A. americanum (Lone star tick), H. longicornis (Asian longhorned tick), and A. maculatum (Gulf Coast tick). Elevation and insulation coverage had no significant impact on the overwintering survival of the Lone star and Asian longhorned ticks. Tick survival was mainly dictated by what life-stage they were in; Lone star ticks survived better as adult than at other life stages. Asian longhorned ticks survived better as nymphs than larva and adults. Insulation coverage influenced the overwintering survival of the Gulf Coast tick. These ticks survived better with no leaves, which may be associated with their preference of drier climates.

Population numbers of bumblebees has been on a steady decline leading to the endangerment of several species that are critical to the growth and pollination of crops and plants. Varying factors have contributed to this situation, one key factor being pathogens wiping out colonies. Studying pathogens that diminish bumblebee populations is vital to understanding how to combat the decline of these important species effectively. The aim of this study was to analyse five of the most common pathogens that exist in the abdomen of five different species of bumblebees. This was achieved by extracting DNA, from 176 previously acquired frozen samples, through homogenisation and varying washing steps before an analysis of the resulting nucleic acids. The analysis was done with quantitative polymerase chain reactions to quantify the amounts of each pathogen, as well as a passive reference nucleic acid, to then be able to calculate the absolute total -amount of pathogen carried by each individual bumblebee. The results showed that almost half of the bumblebees were infected by Nosema, one sixth were infected by Crithidia and Apicystis while only a small number of individuals had been infected by Bombus Densovirus and the Apis Mellifera Filamentous Virus. Bombus Lapponicus was the most infected species. The conclusion based on the results is that future research could put a focus on the more commonly found parasites Nosema, Crithidia and Apicystis. Additional research should also be undertaken into the factors contributing to the less common pathogens Bombus Densovirus and the Apis Mellifera Filamentous Virus.

This scoping review aimed to determine, what empirical research currently exists about disablist hate crimes, targeted violence and hostility and what gaps in research can be identified. Digital databases were examined to identify studies published in English from 2000 onwards. This field is new and emerging with most research from 2010 onwards. In total 48 studies were identified in the UK, Australia, Ireland, Norway, USA, Iceland, Spain and Sweden. The studies provide information on: the prevalence and experiences of disablist hate crime, sex-related offences, online hate speech, space and place, ‘mate crime’ and the reporting and responding to disablist hate crime. Despite disablist hate crimes being recognised by legislation, it has been found that it is still widely unprioritised compared to other protected characteristics. Further investigation into disablist hate crime is required to focus on disability-specific aspects of experiences

The diploma thesis deals with the issue of ADHD among clients treated in therapeutical communities for users of illegal addictive substances. The issue of ADHD is explored in the point of view of prevalence, influence on a person and in the point of view of complications during the treatment. Information concerning this issue are absented in the Czech Republic. Research studies about dual diagnosis substantiate the influence of associated co morbid for use of addictive substances in the point of view of an ability of one to cope with normally adjusted medical schedule and make profit out of it. Lingering of ADHD in adultery even with subliminal Symptomatology presents a burden in fields of executive and behavioral abilities of a person. Well- timed and proper diagnosis is vital for an adjustment of optimal medical schedule. The goal of the thesis was to find whether there are clients with ADHD diagnosis in therapeutical communities and what is the influence of a defect on a person and on complications during the treatment. The occurence of ADHD clients of therapeutical communities was found out in childhood and in the present, characteristics of ADHD clients were tracked and a degree of occurence of complications in comparision with clients without diagnosis during the process of the treatment was...

Reproductive health and induced abortion in Latin America and the Caribbean Abstract The objective of this study is to give a comprehensive overview of the reproductive health of the population living in Latin America and the Caribbean, and to evaluate the level of induced abortion in the region at the same time. In the theoretical part of the study the term reproductive health is defined and indicators evaluating its level are described. As well the difference between safe and unsafe abortion is explained and the state of abortion law is expounded in this part. Next part is devoted to the promotion of family planning programs. In the analytical part Latin American and Caribbean countries are divided into four groups by using cluster analysis. Within each group one selected country is characterized in more detail. Indicators entering into the analysis show the level of reproductive health, the level of fertility and the economic performance of countries in the early 21st century. In the part related to the induced abortion rate in the region is discovered that despite the fact that in Latin America and the Caribbean there is one of the highest levels of contraceptive prevalence, there is also the highest level of induced abortion in the world. In the last part of the study the relationship between level of...

INTRODUÇÃO E OBJETIVOS: Distúrbios miccionais são freqüentes em pacientes com doença de Parkinson, mas sua associação com parâmetros como idade do paciente, gênero, gravidade do comprometimento neurológico e duração da doença não é bem conhecida. Neste estudo, avaliamos prevalência e características dos sintomas miccionais em pacientes com doença de Parkinson e examinamos sua associação com parâmetros clínicos com potencial impacto sobre a disfunção miccional. MÉTODOS: Avaliamos prospectivamente 110 pacientes, incluindo 84 homens (76,4%) e 26 mulheres (23,6%), com idade média de 61,8 ± 9,6 anos. Os critérios de inclusão foram doença de Parkinson idiopática e idade acima de 40 anos. Pacientes com outras doenças neurológicas, história de cirurgia e radioterapia pélvica foram excluídos. A duração média da doença foi 12,3 ± 7,2 anos. O comprometimento neurológico foi avaliado pelas escalas Hoehn-Yahr (HY) e Escala Unificada de Avaliação da Doença de Parkinson (UPDRS). Os sintomas miccionais foram avaliados pelo questionário da Sociedade Internacional de Continência para Homens, incluindo uma questão de qualidade de vida relacionada a sintomas miccionais. Consideramos sintomáticos os pacientes que queriam tratamento para sua disfunção miccional. Estes foram avaliados com análise de urina, creatinina sérica, PSA, ultra-sonografia do aparelho urinário e urodinâmica. Avaliamos a associação da disfunção miccional com idade, gênero, tempo de duração da doença, grau de comprometimento neurológico, impacto na qualidade de vida e achados urodinâmicos. RESULTADOS: A avaliação neurológica demonstrou média de 3,0 ± 0,8 na escala de HY e 70,0 ± 31,1 na escala de UPDRS. A média do escore miccional foi de 11,9 ± 9,3 e os sintomas mais comuns foram noctúria em 89 (80,9%) pacientes, urgência em 40 (36,3%) e aumento da freqüência miccional em 39 (35,4%) pacientes. A duração média dos sintomas miccionais foi de 3,8 ± 3,4 anos. A prevalência da disfunção miccional aumentou significativamente com o aumento no grau de comprometimento neurológico, mas não com a idade nem com a duração da doença. A qualidade de vida relacionada aos sintomas miccionais foi afetada pela severidade da disfunção miccional e os sintomas de freqüência e noctúria são os de pior impacto na qualidade de vida. Sessenta e três pacientes (57,2%) eram sintomáticos e 54 (43 homens e 11 mulheres) completaram a avaliação. Os pacientes sintomáticos apresentaram disfunção neurológica mais severa (HY médio 3,2 ± 0,8 vs 2,8 ± 0,9 para os assintomáticos; p=0,035). A idade, a duração da doença e dos sintomas miccionais não diferiram entre sintomáticos e assintomáticos. O volume médio da próstata foi 30,3 ± 10,7 cc. Os achados urodinâmicos foram obstrução infravesical em 38 (70,3%) pacientes, hiperatividade detrusora em 27 (50,0%), e hipocontratilidade detrusora em seis (11,1%) pacientes. O grau de comprometimento neurológico não se associou com nenhum padrão urodinâmico. Na comparação entre homens e mulheres sintomáticos a única diferença observada foi a maior gravidade dos sintomas de esvaziamento nos homens. CONCLUSÕES: A maior parte dos pacientes com doença de Parkinson apresenta disfunção miccional significativa e a gravidade da doença neurológica é o principal fator preditivo para a ocorrência de disfunção miccional. Obstrução infravesical e hiperatividade detrusora são os achados urodinâmicos mais comuns, mas não estão associados com o grau de comprometimento neurológico. Homens e mulheres são similarmente afetados pelos sintomas miccionais e não demonstraram distinção quanto aos achados urodinâmicos. / INTRODUCTION AND OBJECTIVES: Voiding dysfunction often occurs in patients with Parkinsons disease, but its association with patients age, gender, degree of neurological impairment, and disease duration is not fully known. In this study, we assessed the prevalence and characteristics of lower urinary tract symptoms (LUTS) in patients with Parkinson\'s disease and examined their association with those clinical parameters that could have an impact on voiding dysfunction. METHODS: We prospectively evaluated 110 patients, of which 84 were men (76.4%) and 26 were women (23.6%), with a mean age of 61.8 ± 9.6 years. The inclusion criteria were: idiopathic Parkinsons disease and age > 40 years. Patients with other neurological diseases and history of pelvic surgery and radiotherapy were excluded. Mean duration of the disease was 12.3 ± 7.2 years. The neurological impairment was assessed by the Hoehn-Yahr scale (HY) and the Unified Parkinson Disease Rating Scale (UPDRS). Lower urinary tract symptoms were assessed by the International Continence Society male questionnaire, which included a question about quality of life related to LUTS. Those patients who wanted to be treated for their voiding dysfunction were considered as symptomatic. They underwent urine analysis, serum creatinine measurement, PSA, urinary tract imaging and urodynamic study. We examined the association between voiding dysfunction and age, gender, disease duration, degree of neurological impairment, impact on quality of life, and urodynamic findings. RESULTS: The neurological assessment showed a mean HY score of 3.0 ± 0.8 and a mean UPDRS score of 70.0 ± 31.1. Mean LUTS score was 11.9 ± 9.3, and the most prevalent symptoms were nocturia in 89 (80.9%) patients, urgency in 40 (36.3%), and frequency in 39 (35.4%). Mean duration of LUTS was 3.8 ± 3.4 years. The prevalence of voiding dysfunction increased significantly with the degree of neurological impairment, but not with patients age or disease duration. Quality of life was affected by the severity of the voiding dysfunction, and the symptoms with the worst impact on quality of life were frequency and nocturia. Sixty-three patients (57.2%) were symptomatic and 54 (43 men and 11 women) concluded the evaluation. Symptomatic patients had more severe neurological dysfunction (mean HY 3.2 ± 0.8 vs 2.8 ± 0.9 for asymptomatic patients; p=0.035). Symptomatic and asymptomatic patients did not differ as to age, disease duration and LUTS. Mean prostate volume was 30.3 ± 10.7 cc. The urodynamic findings were bladder outlet obstruction in 38 (70.3%) patients, detrusor overactivity in 27 (50.0%), and detrusor underactivity in 6 (11.1%). The degree of neurological impairment was not associated with any urodynamic pattern. The only difference observed between symptomatic men and women was that the voiding symptoms were more severe in men. CONCLUSIONS: Most patients with Parkinsons disease have significant voiding dysfunction, and the severity of the neurological disease is the main predictive factor for the occurrence of voiding dysfunction. Bladder outlet obstruction and detrusor overactivity are the most common urodynamic findings, although not associated with the degree of neurological impairment. Men and women are equally affected by LUTS and show similar urodynamic findings.

Um dos estudos observacionais mais difundidos e usados em epidemiologia veterinária é o estudo do tipo transversal. Sua popularidade ocorre por fatores como baixo custo e rapidez comparados com outros tipos de estudos, além de ajudar a estimar a prevalência de uma doença (desfecho) e postular fatores associados com o desfecho, que poderão ser confirmados como fatores causais em outros tipos de estudos epidemiológicos. Porém, este tipo de estudo apresenta dois importantes desafios: a dependência dos dados, muito frequente dada a típica estrutura populacional de animais dentro do mesmo rebanho ou fazenda e a escolha da medida de associação para desfechos binários, tão frequentes neste modelo de estudo. Com o objetivo de contribuir com a compreensão global da epidemiologia do aborto bovino associado à Neospora caninum tendo em conta a estrutura populacional, construiu-se um modelo misto com os dados de um estudo transversal realizado em duas regiões do Rio Grande do Sul. Usaram-se dados de 60 propriedades amostradas em duas regiões (noroeste e sudeste) e 1256 bovinos. A percentagem de aborto dentro de cada rebanho variou entre 1% e 30%. Vacas soropositivas tiveram 6,63 vezes mais chances de ter histórico de aborto (IC 95%: 4,41-13,20). As chances de uma vaca ter histórico de aborto foram 5,18 vezes maiores na região noroeste em relação à região sudeste (IC 95%: 1,83-20,80). Um coeficiente de correlação intraclasse de 16% foi estimado, indicando que 16% da variação da ocorrência de abortamentos não explicados pelos efeitos fixos foram devido as fazendas. Já na segunda parte deste trabalho, uma revisão sistemática foi realizada considerando um conjunto diverso de revistas e jornais com o objetivo de verificar os métodos estatísticos usados e a adequação das interpretações das medidas de associação estimadas em estudos transversais na área de medicina veterinária. Um total de 62 artigos foi avaliado. A revisão mostrou que, independentemente do nível de prevalência relatado no artigo, 96% deles empregou regressão logística e, portanto, estimaram razão de chances (RC). Nos artigos com prevalência superior a 10%, 23 deles fizeram uma interpretação adequada da RC como uma “razão de chances” ou simplesmente não fizeram uma interpretação direta da RC, enquanto 23 artigos interpretaram de forma inadequada a RC, considerando-a como risco ou probabilidade. Entre os artigos com prevalência inferior a 10%, apenas três interpretaram a RC como uma “razão de chances”, cinco interpretaram como risco ou probabilidade e em um, apesar de ter estimado a razão de prevalências (RP), foi interpretado de forma inadequada. Paralelamente, com o objetivo de exemplificar o uso de métodos estatísticos que estimam diretamente a razão de prevalências (RP), medida mais adequada para os estudos transversais, um conjunto de dados obtidos a partir de um estudo transversal sobre a ocorrência de anticorpos (AC) contra o vírus da diarreia viral bovina (BVDV) foi usado. Os AC foram medidos em amostras de tanque de leite de rebanhos leiteiros localizados no estado do Rio Grande do Sul, em que os possíveis fatores associados puderam ser avaliados. Entre os métodos utilizados, as maiores discrepâncias nas medidas de associação estimadas foram observadas com a regressão logística tomando-se como referência a regressão log-binomial. Finalmente, é importante que este tipo de desafio seja atendido pelos pesquisadores que realizam estudos transversais, ou seja, considerar a estrutura das populações nas análises, cuidado ao escolher o tipo de modelo estatístico empregado para desfecho binário e interpretação dos estimadores. / The commonest study design used in veterinary epidemiology is the cross-sectional study. Its popularity lies on the fact of the short time needed and low costs compared with other types of studies; moreover, this type of study estimates prevalence and associated factors, which may be elucidated as causal in another type of epidemiological studies. However, this type of study presents two major challenges: a very common dependence between data given the typical structure of the animal population, i.e., animals within herds or farms and the choice of measure of association for binary outcomes, frequently used in this type of study. In order to contribute to the understanding of the epidemiology of bovine abortion associated with Neospora caninum, a mixed model accounting for the hierarchical structure of cattle population using data from a cross-sectional study conducted in two regions (northwest and southeast) of Rio Grande do Sul was made. Data from 60 dairy herds and 1256 sampled cattle were used. The percentage of abortions in each herd ranged between 1% and 30%. Seropositive cows were 6.63 times more likely to have a history of abortion (95% CI: 4.41 to 13.20). The chances of a cow have a history of abortion were 5.18 times higher in the northwest comparing with the southeast region (95% CI: 1.83 to 20.80). An intraclass correlation coefficient (ICC) of 16% was estimated which means that 16% of the variation in abortion occurrence not explained by the fixed effects is due to farms. In the second part of this work, a systematic review was conducted considering a range of journals and newspapers in order to verify the statistical methods used and the adequacy of the interpretations of the measures of association estimated in cross-sectional studies from the veterinary medicine field. A total of 62 articles were revised. The review showed that, regardless of the reported prevalence, 96% of them employed logistic regression, therefore estimating odds ratio (OR). From the articles that reported prevalence rates above 10%, 23 of them did a proper interpretation of OR as an odds ratio, or simply did not make a direct interpretation of the OR, while 23 articles interpreted improperly the OR as a risk or probability. Among the articles that reported prevalence rates lower than 10%, only three interpreted the OR as an odds ratio, five interpreted as a risk or probability and only one, despite the estimated prevalence ratio (PR), it was improperly interpreted. Meanwhile, in order to exemplify the use of statistical methods to estimate directly the PR, the more appropriate measure of association in cross-sectional studies, a data set obtained from a cross-sectional study to estimate the occurrence of antibodies (AB) against bovine viral diarrhea virus (BVDV) in milk was used; AB were measured in bulk tank samples from dairy herds located in the state of Rio Grande do Sul, Brazil, and also possible associated factors were estimated. Among the methods used, major discrepancies in the measures of association estimated were observed with the logistic regression, comparing with the log-binomial regression. Finally, it is important that such challenges are met by the researchers that undertake cross-sectional studies.

INTRODUCTION Taenia solium cysticercosis (CC) and taeniosis are zoonotic diseases mainly occurring in developing countries of Asia, Africa and Latin America. Humans are the only definitive host of the parasite harbouring the adult tapeworm in the small intestine (taeniosis). Gravid proglottids containing thousands of eggs are daily shed with the faeces in the environment. The pig intermediate host, through its coprophagic behaviour, may consume contaminated human faeces and consequently, ingest eggs that will further develop into the larval stage of the parasite in the muscles and the brain (cysticerci), causing porcine CC. Humans acquire infection with the adult tapeworm by consumption of undercooked or raw pork infected with cysticerci. Humans can also become infected by the cysts by accidental ingestion of T. solium eggs and develop human CC. In humans, cysts may lodge in muscles, subcutaneous tissues, eyes and/or central nervous system causing ocular CC and neurocysticercosis (NCC) in the two latter cases, respectively. While mainly asymptomatic in pigs, CC and particularly NCC may be responsible of severe health disorders in humans, seizures and epilepsy being the most common ones. In the last decade T. solium became the study target of research groups throughout the world and is now more in the focus of international health and animal health organizations. However, the disease remains neglected and many data gaps still hinder a comprehensive estimation of its burden. Therefore, the general objective of this thesis is the development of tools to estimate the impact of T. solium CC on both public health and veterinary public health in regions where the parasite occurs. For this purpose, four specific objectives are followed focusing on taeniosis, porcine and human CC in different endemic areas of the world. Firstly, a stochastic model is developed allowing the estimation of the monetary and health (disability adjusted life year, DALY) burden of CC in three endemic provinces of Cameroon and the identification of data gaps increasing the uncertainty around the disease burden estimates (Objective 1). Secondly, because there is incomplete knowledge on many CC burden assessment parameters, two protocols are designed to study specific factors that may affect the transmission dynamics of the parasite, and possibly, the disease burden estimation. Because the latter estimation may depend on the age of diseased individuals, a community-based study aims at determining the occurrence of human CC and at studying the age-related infection and transmission patterns of the parasite among a population living in an endemic area of Ecuador (Objective 2). The objective of a second field study conducted in the Democratic Republic of Congo is to determine the occurrence of porcine CC at different levels of the pig trade chain in order to detect any variation in the apparent prevalence figures of the disease (Objective 3). Finally, because none of the available tests for the diagnosis of human CC is a gold standard limiting the estimation of the disease occurrence to the apparent prevalence, and since sensitivity and specificity of the diagnostic tests have only been evaluated in clinical settings, i.e. infected diseased versus uninfected non-diseased individuals, a Bayesian approach is used to estimate the true prevalence of human CC and the performances of available immunological tools for its diagnosis in the framework of an epidemiological study (including uninfected and infected diseased and non-diseased individuals) (Objective 4). RESULTS 1. Development of a stochastic model for the estimation of the economic and health (DALY) burden of T. solium cysticercosis The first experimental section of this thesis aims at developing a stochastic model for the estimation of the monetary and health (DALY) burden of CC, taking 3 endemic provinces of Cameroon as example. Both cost and DALY estimations are applied. All necessary parameters are collected and imported in R software. Different probability distributions are used according to the type of information available for each of the parameters. Monte Carlo simulation techniques allow drawing a set of parameters from the underlying distributions through serial iterations. The number of people with NCC-associated epilepsy represents 1.0% of the local population, whereas the number of pigs diagnosed with CC corresponds to 5.6% of the local pig population. The total annual costs due to T. solium CC in West-Cameroon is estimated at 10,255,202 Euro (95% CR 6,889,04814,754,044), of which 4.7% are due to losses in pig husbandry and 95.3% to direct and indirect expenses associated with human CC. The average number of DALYs lost is 9.0 per thousand persons per year (95% CR 2.820.4; meaning that 9 years of life in perfect health per thousand inhabitants of this area are lost due to CC). This study provides the first estimates of the impact of CC in Cameroon and allows identifying the related economical, clinical and epidemiological necessary parameters and related data gaps. Moreover, the stochastic approach developed here allowed quantifying the uncertainty around the estimates due to the lack of knowledge on this neglected disease. 2. Study on the age-related infection and transmission patterns of human CC in an endemic area The second experimental part of this thesis aims at estimating the apparent prevalence of human CC in an endemic area of Ecuador using both serological antigen and antibody detection methods. Besides a high exposure to the parasite (25% of the sampled population had antibodies directed against T. solium cysticerci) contrasting with a low level of active infection (2.9% had circulating parasite antigens), this study shows that positivity patterns of both diagnostic tests strongly depend on the age of the subjects. The proportion of individuals showing antibodies directed against the larval stage of the parasite significantly increases till the age of 40 to become stable later. Simulation models incorporating insights from cohort study data and basic immunology principles are developed to explain the variations in antibody detection positivity pattern and to reflect the dynamics of exposure to the parasite. The simulations suggest a continual exposure to the parasite through all age categories but a variation of the rate of seroreversion depending on the number of exposures, or in other words, on the immunological status of the individuals. The models also indicate that at least 14% of the population of the community is yearly exposed to the parasite. On the other hand, the proportion of individuals infected by living cysticerci is significantly higher in the elderly. These findings agree with clinical observations in Mexico and Brazil. Immunosenescence could explain such an observation since a weaker immune system in the elderly would facilitate the establishment and maintenance of viable cysticerci in the muscles and in the brain in comparison with fully immunocompetent younger individuals. Our findings indicate that age-related CC infection may influence the CC burden estimates. 3. Occurrence of porcine cysticercosis at different levels of the pig trade flow in a suspected endemic area Based on the use of the enzyme-linked immunosorbent assay for the detection of circulating antigens of T. solium metacestodes (B158/B60 Ag-ELISA), the third experimental section of this thesis reports an apparent prevalence of about 40% of active CC in a pig population in a rural area of Bas-Congo (where pigs are reared) and in a pig population in different markets of Kinshasa (where pork is sold). This work also indicates that the marketing of cysticercotic pig may influence the transmission of the parasite. Indeed, while no significant difference is found in the proportion of active infections between the two sites, the intensity of infection is significantly higher in pigs sampled in the villages in Bas-Congo as compared to those in the markets in Kinshasa. It seems that massively infected animals are excluded at a certain level in the pig trade chain. Preliminary informal surveys on common practices in pig husbandry and pig trading indicate that pig farmers and/or buyers select the low infected animals and exclude those who are positive by tongue inspection at village level. More heavily infected pigs are subsequently used for villagers own consumption or sold at local (clandestine) markets. The influence of the cysticercotic pig marketing should be considered when estimating the animal disease burden. Accurate burden estimates will allow establishing and implementing effective food safety policies and regulations or improving the existent ones in order to control and prevent CC and taeniosis. 4. Estimation of the performances of available immunodiagnostic tools for the diagnosis of human CC in the framework of an epidemiological study The last experimental section of this thesis focuses on the use of Bayesian models to estimate the true prevalence of infection with and exposure to T. solium, and the characteristics of serological tests, namely the enzyme-linked immunosorbent assay for the detection of circulating antigens of the metacestode of T. solium (B158/B60 Ag-ELISA), the enzyme-linked immunoelectrotransfer blot assay (EITB) for the detection of antibodies directed against 7 specific T. solium glycoprotein antigens, and the ELISA for the detection of antibodies directed against crude cyst fluid extracts (Ab-ELISA), used in an epidemiological study setting (including uninfected and infected diseased and non-diseased individuals) in an Ecuadorian endemic area. The EITB and B158/B60 Ag-ELISA sensitivity and specificity estimates in the latter conditions are comparable to the same estimates in clinical settings. However, the present study demonstrates the importance of clearly defining a case when conducting such an exercise. Indeed, the sensitivity and specificity of EITB and B158/B60 Ag-ELISA are high for estimating the true prevalence of exposure to (proportion of individuals who have been in contact with the parasite during the precedent year, with or without development of cysticerci, and with or without (cured individuals) current infection with living cysticerci) and infection with T. solium (proportion of individuals currently infected with living cysticerci), respectively, but drop the other way around. In conclusion, since no gold standard test for human CC diagnosis is available, this study provides a tool for estimation of the true CC prevalence, which is essential for the disease burden assessment. CONCLUSIONS AND PERSPECTIVES Even though the World Health Organization (WHO) already drew the map of the global distribution of T. solium, data remain very limited in several parts of the world. Through a literature review and four experimental sections, this thesis shows that the burden of human and porcine CC may be non negligible and deserves a more global assessment. Moreover, this work allows depicting the disease data gaps more precisely and proposes some tools to deal with the lack of knowledge on this neglected zoonosis. The threat of misusing limited data is a fact and one could reject more global burden estimates based hereon. However, this should not be the main issue. The main concerns should rather focus on how to obtain estimates when only fragmentary data are available. For this purpose, two approaches may be considered: (1) a prospective approach aiming at developing more accurate taeniosis and CC diagnostic tools and at collecting more standardized data from different endemic areas of the world; (2) a retrospective approach aiming at using existing data in innovative ways, such as simulation, Bayesian and stochastic models and expert elicitation, may be a valid alternative. In conclusion, the development of new diagnostic and estimation tools is in progress to compensate for the lack of knowledge on taeniosis/CC and for the diagnostic test and study design limitations (including financial, technical and ethical restrictions). Efforts should be made to increase their availability to developing countries and to standardize study designs in order to produce reliable estimates to assess the global burden of T. solium CC. Once burden estimates are available, the cost-effectiveness of prevention and control programs can be tested and help national and international policy- and decision- makers in setting priorities in public health and veterinary public health policy, services and research. INTRODUCTION La cysticercose (CC) et la taeniose dues à Taenia solium sont des maladies zoonotiques sévissant principalement dans les pays en voie de développement dAsie, dAfrique et dAmérique Latine. LHomme est le seul hôte définitif du parasite, infesté par le ver adulte au niveau de lintestin grêle (taeniose). Des proglottis gravides, contenant des milliers dufs sont quotidiennement évacués avec les matières fécales humaines dans lenvironnement. Le porc, hôte intermédiaire coprophage, peut consommer ces matières fécales contaminées et, par conséquent, ingérer des ufs qui se développeront en stade larvaire au niveau des muscles et du cerveau (les cysticerques), causant ainsi la CC porcine. LHomme, en consommant de la viande de porc infestée (de cysticerques) crue ou mal cuite, sinfeste par le ver adulte bouclant ainsi le cycle. LHomme peut également sinfester par ingestion accidentelle dufs et développer la CC humaine. Chez ce dernier, les cysticerques peuvent se loger dans les muscles, le tissu sous-cutané, les yeux et le système nerveux central, causant, dans ces deux derniers cas, respectivement, la CC oculaire et la neurocysticercose (NCC). Alors que la CC est généralement asymptomatique chez le porc, la CC et tout particulièrement la NCC peuvent être responsables daffections sévères chez lHomme, les convulsions et crises dépilepsie étant les plus fréquentes dentre elles. Durant les dernières décennies, T. solium est devenu le sujet détude principal de plusieurs groupes de recherche à travers le monde ainsi que dorganisations internationales de santé publique et de santé animale. Cependant, le manque de données épidémiologiques et cliniques empêche toujours une estimation précise de son impact réel sur la santé. Cest pourquoi, lobjectif principal de cette thèse est de développer des outils permettant destimer limpact de la CC due à T. solium sur la santé publique et la santé publique vétérinaire. Dans ce but, quatre objectifs spécifiques sont fixés. Premièrement, un modèle stochastique est développé pour estimer limpact économique de la CC due à T. solium et son impact sur la santé (« disability adjusted life year », DALY) dans trois provinces du Cameroun. Cette première étude vise également à identifier les données lacunaires qui augmentent lincertitude autour des estimations (Objectif 1). Sur cette base, deux études épidémiologiques sont conduites dans des communautés endémiques dAfrique et dAmérique Latine, focalisées sur certains facteurs pouvant avoir une influence sur la transmission du parasite, et ainsi sur son impact sur la santé. Puisque lestimation de limpact de la CC sur la santé peut dépendre de lâge des individus malades, une étude de terrain a pour but détudier les relations entre la prévalence apparente de la CC et lâge des individus exposés et infestés dans une zone endémique dEquateur (Objectif 2). Une seconde étude de terrain vise à déterminer loccurrence de la CC porcine à différents niveaux de la filière de production et de commercialisation de la viande de porc dans une zone suspectée endémique de la République Démocratique du Congo (RDC) afin de détecter déventuelles variations de la prévalence apparente de la maladie (Objectif 3). Finalement, vu que la sensibilité et la spécificité des tests pour le diagnostic de la CC humaine ont uniquement été évaluées dans le cadre détudes cliniques, cest-à-dire chez des patients souffrant de CC versus des individus non infestés et asymptomatiques, et vu quaucun de ces tests nest un test parfait (test ayant une sensibilité et une spécificité de 100%), une approche bayésienne est appliquée pour estimer les performances de tests immunologiques disponibles dans le cadre dune étude épidémiologique, incluant des individus non infestés et infestés avec ou sans symptômes (Objectif 4). RESULTATS 1. Développement dun modèle stochastique pour lestimation de limpact économique et de limpact sur la santé (DALY) de la cysticercose due à T. solium Le coût monétaire et le nombre dannées de vie en bonne santé perdues en raison dune mortalité prématurée et/ou de la morbidité dues à la cysticercose (CC) (DALY) sont tous deux estimés dans trois provinces de lOuest du Cameroun. Tous les paramètres épidémiologiques et économiques nécessaires sont collectés et importés dans le logiciel R. Différentes distributions de probabilité sont utilisées en fonction du type dinformation disponible pour chacun dentre eux. Des techniques de simulation de Monte Carlo permettent les estimations finales sur la base des distributions de probabiltés. En tenant compte dune prévalence dépilepsie de 3,6%, le nombre dindividus souffrant dépilepsie associée à la NCC sélève à 1,0% de la population locale. Dautre part, le nombre de porcs diagnostiqués comme infestés correspond à 5,6% de la population porcine locale. Le coût annuel total associé à la CC à lOuest du Cameroun est estimé à 10255202 Euros (95% de la région de confidence (RC) : 6889048-14754044 Euros), desquels 4,7% sont dus aux pertes liées à la production porcine. Le coût par cas de CC humaine séleve à 194 Euros (95% RC : 147-253 Euros). Le nombre moyen de DALYs perdus par 1000 personnes et par an est de 9,0 (95% RC : 2,8 20,4). Cette étude permet une première quantification de limpact de la CC au Cameroun, recense les paramètres économiques, cliniques et épidémiologiques nécessaires à cette fin et le manque de données leur étant lié. De plus, lapproche stochastique utilisée ici permet de quantifier lincertitude autour de ces estimations due au manque de connaissance de cette maladie négligée. 2. Etude de la relation entre la prévalence et la transmission de la cysticercose et lâge des individus exposés et infestés La seconde section expérimentale de cette thèse a pour objectif destimer la prévalence apparente de la CC humaine dans une région endémique de lEquateur en utilisant des techniques sérologiques de détection dantigènes et danticorps. En plus dune exposition élevée au parasite (25% des individus ont des anticorps dirigés contre les cysticerques) contrastant avec une faible proportion dindividus infestés par des cysticerques vivants (3% des individus ont des antigènes circulants de cysticerques), cette étude montre que la positivité aux tests sérologiques dépend de lâge des individus. En effet, la proportion dindividus montrant une réaction humorale dirigée contre le stade larvaire du parasite augmente significativement jusquà lâge de 40 ans pour se stabiliser ensuite. Des modèles de simulation intégrant des données issues dune étude longitudinale ainsi que des principes de bases dimmunologie sont développés dans le but dexpliquer ces variations et de refléter certains aspects de la dynamique dexposition au parasite. Ces simulations suggèrent un taux dexposition au parasite stable à travers les différentes catégories dâge, mais une variation du taux de séroréversion dépendant du nombre de contacts préalables avec le parasite ou, en dautres mots, du statut immunologique des individus. Les modèles indiquent également quau moins 14% de la population sont annuellement exposés au parasite. Dautre part, la proportion des individus infestés par des cysticerques vivants est significativement plus élevée chez les personnes âgées de plus de 60 ans. Limmunosénescence pourrait expliquer ce phénomène, puisque un système immunitaire plus faible chez les personnes âgées pourrait faciliter létablissement et le maintien de cysticerques vivants au sein des muscles et du cerveau. Nos observations indiquent que lâge des individus malades pourrait influencer lestimation de limpact de la CC. 3. Occurrence de la cysticercose porcine à différents niveaux de la filière de la production de viande porcine dans une zone suspectée endémique Sur la base de lutilisation dun test immuno-enzymatique (« enzyme-linked immunosorbent assay », ELISA) pour la détection dantigènes circulants de cysticerques (B158/B60 Ag-ELISA), la troisième section expérimentale de cette thèse permet destimer une prévalence denviron 40% de CC active au sein dune population de porcs élevés traditionnellement dans une zone rurale de la province du Bas-Congo (RDC) et dans une population de porcs vendus et abattus sur différents marchés de Kinshasa (RDC). Ce travail démontre aussi linfluence du commerce de la viande de porc infestée sur la transmission du parasite. En effet, alors quaucune différence significative nest observée entre les proportions de porcs infestés sur les des deux sites détude, lintensité de linfestation est significativement plus élevée chez les porcs des villages que chez les porcs des marchés. Il semble ainsi que les animaux hautement infestés sont exclus à un certain stade de la filière de production et de commercialisation de la viande de porc. Des enquêtes préliminaires réalisées auprès des éleveurs de porcs et des vendeurs de viande de porc indiquent que les éleveurs et/ou les acheteurs de porcs sélectionnent les animaux faiblement infestés et excluent les animaux positifs au langueyage (inspection de la langue) dans les villages. Les porcs hautement infestés sont, par conséquent, consommés par les villageois ou vendus sur des marchés clandestins. Linfluence possible de la filière de la production et de la commercialisation de la viande porcine sur la prévalence apparente de la CC observée dans cette étude devrait être prise en considération lorsque lon évalue limpact de la maladie sur la santé et la production animale. Des estimations précises de cet impact permettront la mise en place de mesures de contrôle et de prévention adéquates de la CC et de la taeniose. 4. Estimation des performances doutils sérologiques pour le diagnostic de la cysticercose humaine dans le cadre dune étude épidémiologique La dernière section expérimentale de cette thèse vise lutilisation de modèles bayésiens pour lestimation de la prévalence réelle dinfestation par et dexposition à T. solium, et des caractéristiques (sensibilité et spécificité) de trois tests sérologiques, à savoir , un ELISA pour la détection dantigènes circulants de cysticerques de T. solium (B158/B60 Ag-ELISA), un autre test immuno-enzymatique (« enzyme-linked immunoelectrotransfer blot assay », EITB) pour la détection danticorps dirigés contre sept glycoprotéines spécifiques à T. solium, et un ELISA pour la détection danticorps dirigés contre le liquide vésiculaire brut de cysticerques (Ab-ELISA), appliqués dans le cadre dune étude épidémiologique (incluant des individus non infestés et infestés avec ou sans symptômes) dans une région endémique de lEquateur. Les performances de lEITB et du B158/B60 Ag-ELISA sont comparables à celles obtenues dans le cadre détudes cliniques. Cependant, cette étude démontre limportance dune définition claire de ce quest « un cas » lorsque lon sadonne à un tel exercice. En effet, la sensibilité et la spécificité de lEITB et du B158/B60 Ag-ELISA sont élevées lorsquil sagit destimer la prévalence dexposition à T. solium (proportion dindividus ayant été en contact avec le parasite durant lannée précédente, avec ou sans établissement de cysticerques et, avec ou sans présence concomitante de cysticerques vivants) et dinfestation par le parasite (proportion dindividus actuellement infestés par des cysticerques vivants), respectivement, mais chutent dans le cas contraire. En conclusion, vu quaucun test parfait nest disponible à ce jour pour le diagnostic de la CC humaine, cette étude propose un outil destimation de la prévalence réelle de la maladie. Cette estimation est essentielle pour lévaluation de limpact de la CC. CONCLUSIONS ET PERSPECTIVES Même si lOrganisation Mondiale de la Santé (OMS) a déjà dressé une carte de la distribution globale de la CC due à T. solium, les données concernant celle-ci restent limitées et incomplètes dans beaucoup de régions endémiques du globe. A travers une étude de la littérature et quatre sections expérimentales, cette thèse montre que limpact de la CC porcine et humaine peut être non négligeable. De plus, ce travail permet de décrire de façon quantitative le manque de connaissance sur la maladie et propose quelques outils permettant dy pallier. Le risque de mal interpréter ou dextrapoler à tort des données incomplètes existe. Il pourrait donc être légitime de rejeter toute estimation plus globale de limpact dune maladie qui serait basée sur ces données. Cependant, le manque de données ne devrait pas signifier « estimation impossible » mais devrait plutôt soulever la question suivante: « Comment pouvons-nous y pallier? ». Pour cela, deux approches sont envisageables : (1) une approche prospective visant à développer des techniques plus performantes pour le diagnostic de la taeniose et de la CC et à permettre la collecte de données standardisées dans différentes zones endémiques du monde ; (2) une approche rétrospective ayant pour but dutiliser les données existantes de manière innovatrice, cest-à-dire en utilisant par exemple des modèles de simulation, des modèles bayésiens ou l« élicitation dexpert ». En conclusion, de nouveaux outils diagnostiques et techniques destimation sont en développement et en cours de validation pour pallier au manque de connaissances, aux limitations des protocoles détudes de recherches scientifiques (incluant les restrictions financières, techniques et éthiques) et/ou aux limitations des tests diagnostiques mais, de considérables efforts devraient être fournis afin de mettre ces outils à la disposition des pays en voie de développement et de standardiser les protocoles de recherche pour permettre une estimation globale de limpact de la CC. Une fois disponible, cette estimation pourra aider les décideurs politiques et les bailleurs de fonds à fixer les priorités en termes de lois, services et recherche scientifiques en santé publique et santé publique vétérinaire.

Um dos estudos observacionais mais difundidos e usados em epidemiologia veterinária é o estudo do tipo transversal. Sua popularidade ocorre por fatores como baixo custo e rapidez comparados com outros tipos de estudos, além de ajudar a estimar a prevalência de uma doença (desfecho) e postular fatores associados com o desfecho, que poderão ser confirmados como fatores causais em outros tipos de estudos epidemiológicos. Porém, este tipo de estudo apresenta dois importantes desafios: a dependência dos dados, muito frequente dada a típica estrutura populacional de animais dentro do mesmo rebanho ou fazenda e a escolha da medida de associação para desfechos binários, tão frequentes neste modelo de estudo. Com o objetivo de contribuir com a compreensão global da epidemiologia do aborto bovino associado à Neospora caninum tendo em conta a estrutura populacional, construiu-se um modelo misto com os dados de um estudo transversal realizado em duas regiões do Rio Grande do Sul. Usaram-se dados de 60 propriedades amostradas em duas regiões (noroeste e sudeste) e 1256 bovinos. A percentagem de aborto dentro de cada rebanho variou entre 1% e 30%. Vacas soropositivas tiveram 6,63 vezes mais chances de ter histórico de aborto (IC 95%: 4,41-13,20). As chances de uma vaca ter histórico de aborto foram 5,18 vezes maiores na região noroeste em relação à região sudeste (IC 95%: 1,83-20,80). Um coeficiente de correlação intraclasse de 16% foi estimado, indicando que 16% da variação da ocorrência de abortamentos não explicados pelos efeitos fixos foram devido as fazendas. Já na segunda parte deste trabalho, uma revisão sistemática foi realizada considerando um conjunto diverso de revistas e jornais com o objetivo de verificar os métodos estatísticos usados e a adequação das interpretações das medidas de associação estimadas em estudos transversais na área de medicina veterinária. Um total de 62 artigos foi avaliado. A revisão mostrou que, independentemente do nível de prevalência relatado no artigo, 96% deles empregou regressão logística e, portanto, estimaram razão de chances (RC). Nos artigos com prevalência superior a 10%, 23 deles fizeram uma interpretação adequada da RC como uma “razão de chances” ou simplesmente não fizeram uma interpretação direta da RC, enquanto 23 artigos interpretaram de forma inadequada a RC, considerando-a como risco ou probabilidade. Entre os artigos com prevalência inferior a 10%, apenas três interpretaram a RC como uma “razão de chances”, cinco interpretaram como risco ou probabilidade e em um, apesar de ter estimado a razão de prevalências (RP), foi interpretado de forma inadequada. Paralelamente, com o objetivo de exemplificar o uso de métodos estatísticos que estimam diretamente a razão de prevalências (RP), medida mais adequada para os estudos transversais, um conjunto de dados obtidos a partir de um estudo transversal sobre a ocorrência de anticorpos (AC) contra o vírus da diarreia viral bovina (BVDV) foi usado. Os AC foram medidos em amostras de tanque de leite de rebanhos leiteiros localizados no estado do Rio Grande do Sul, em que os possíveis fatores associados puderam ser avaliados. Entre os métodos utilizados, as maiores discrepâncias nas medidas de associação estimadas foram observadas com a regressão logística tomando-se como referência a regressão log-binomial. Finalmente, é importante que este tipo de desafio seja atendido pelos pesquisadores que realizam estudos transversais, ou seja, considerar a estrutura das populações nas análises, cuidado ao escolher o tipo de modelo estatístico empregado para desfecho binário e interpretação dos estimadores. / The commonest study design used in veterinary epidemiology is the cross-sectional study. Its popularity lies on the fact of the short time needed and low costs compared with other types of studies; moreover, this type of study estimates prevalence and associated factors, which may be elucidated as causal in another type of epidemiological studies. However, this type of study presents two major challenges: a very common dependence between data given the typical structure of the animal population, i.e., animals within herds or farms and the choice of measure of association for binary outcomes, frequently used in this type of study. In order to contribute to the understanding of the epidemiology of bovine abortion associated with Neospora caninum, a mixed model accounting for the hierarchical structure of cattle population using data from a cross-sectional study conducted in two regions (northwest and southeast) of Rio Grande do Sul was made. Data from 60 dairy herds and 1256 sampled cattle were used. The percentage of abortions in each herd ranged between 1% and 30%. Seropositive cows were 6.63 times more likely to have a history of abortion (95% CI: 4.41 to 13.20). The chances of a cow have a history of abortion were 5.18 times higher in the northwest comparing with the southeast region (95% CI: 1.83 to 20.80). An intraclass correlation coefficient (ICC) of 16% was estimated which means that 16% of the variation in abortion occurrence not explained by the fixed effects is due to farms. In the second part of this work, a systematic review was conducted considering a range of journals and newspapers in order to verify the statistical methods used and the adequacy of the interpretations of the measures of association estimated in cross-sectional studies from the veterinary medicine field. A total of 62 articles were revised. The review showed that, regardless of the reported prevalence, 96% of them employed logistic regression, therefore estimating odds ratio (OR). From the articles that reported prevalence rates above 10%, 23 of them did a proper interpretation of OR as an odds ratio, or simply did not make a direct interpretation of the OR, while 23 articles interpreted improperly the OR as a risk or probability. Among the articles that reported prevalence rates lower than 10%, only three interpreted the OR as an odds ratio, five interpreted as a risk or probability and only one, despite the estimated prevalence ratio (PR), it was improperly interpreted. Meanwhile, in order to exemplify the use of statistical methods to estimate directly the PR, the more appropriate measure of association in cross-sectional studies, a data set obtained from a cross-sectional study to estimate the occurrence of antibodies (AB) against bovine viral diarrhea virus (BVDV) in milk was used; AB were measured in bulk tank samples from dairy herds located in the state of Rio Grande do Sul, Brazil, and also possible associated factors were estimated. Among the methods used, major discrepancies in the measures of association estimated were observed with the logistic regression, comparing with the log-binomial regression. Finally, it is important that such challenges are met by the researchers that undertake cross-sectional studies.