Africa is uniquely vulnerable to the occurrence of drought. A rise in temperatures over Southern Africa occurs at almost twice that of the global rate. South Africa has begun to experience an increase in the frequency of drought, particularly in the Western and Eastern Cape. Droughts are associated with several health effects. The direct and indirect risks of climate change to human health have become a global concern. The most recent systematic review available on the adverse health effects associated with drought was published in 2013, and as such, an up-to-date review focusing on Africa is needed to inform a Cape Town specific health vulnerability index. This study aims to provide a review of available research exploring the association between drought and adverse health effects in Africa. The rationale for this study is to provide a solid research foundation from which a drought-specific health vulnerability index for Cape Town can be developed. A narrative review of original studies and published reviews was conducted. An extensive electronic literature search was performed using a combination of keywords, Medical Subject Heading (MeSH) terms and free text words. The Critical Appraisal Toolkit (CAT) was used to assess the quality of included studies. A total of 1922 publications were identified, of which twenty-four articles were included in this review. The main drought-related health effects that emerged were divided into 4 main categories: (1) drought and nutritional health including malnutrition, poor childhood health outcomes (wasting, stunting and underweight), mortality, anaemia, and nutritionrelated disability; (2) drought and food consumption including micronutrient deficiencies and motor neuron diseases; (3) drought and water-borne, water-washed and water- related diseases including cholera outbreaks, diarrhoeal diseases, protozoa parasite transmission, scabies outbreaks, trachoma, vector-borne disease outbreaks and malaria-related mortality; and (4) drought and health behaviours including health perceptions and health-seeking behaviours, HIV prevention and care behaviours and family planning practices. There was generally limited evidence in all health categories with several limitations. These limitations include studies with methodological weaknesses (e.g. a lack of comparison to a non-drought period), the singularity of published studies on health effects associated with drought and studies which did not account for potential confounders. While the evidence from the included studies is limited, this study highlights gaps in literature to encourage further research into understanding the direct and indirect impacts of drought on health, particularly in vulnerable groups. Furthermore, the results of this study emphasized the contextual factors which lower an individual's adaptive capacity and identified key indicators that can be used to begin to develop a broad framework for a vulnerability index

This thesis focuses on the molecular characterization of tick-borne parasites of dogs in South Africa. Emphasis is placed on Babesia, Erhlichia, incidental and novel parasite infections that may cause morbidity or mortality in infected dogs. An outbreak of canine babesiosis in the Netherlands is also reported in this thesis. Molecular techniques were employed to isolate, amplify and characterize genomic DNA of these parasites to species level. During preliminary screening of blood samples collected from various sites in the country, that included the Onderstepoort Veterinary Academic Hospital, SPCAs and private clinics throughout seven provinces in South Africa, it was discovered that domestic dogs harboured a wide variety of tick-borne pathogens. The most frequently encountered parasites in South Africa were Babesia rossi, a novel Theileria species of dogs, B. vogeli and Ehrlichia canis respectively. The parasites occurred as single or mixed infections. Incidental infections that included B. gibsoni and Trypanosoma congolense were also detected using PCR. Although it was anticipated that zoonotic Ehrlichial infections of dogs would be detected, none were found. Babesia vogeli was reported for the first time in South Africa although, without any clinical significance. An outbreak of autochthonous canine babesiosis in the Netherlands was confirmed to have been caused by Babesia canis. Dermacentor reticulates was implicated in the transmission of the parasite to naïve dogs. Clinical significance of B. rossi and the novel Theileria sp. of dogs was evaluated. Babesia rossi was found to be of significant clinical importance. Genotyping of B. rossi isolates revealed that parasite genotypes could be correlated to disease phenotype. Additionally, specific genotypes could also be associated with fatalities. Although the characterization of the Theileria sp. in dogs was a first report in South Africa, the clinical significance of this infection in dogs appeared to be poorly resolved. The dangers of having non-endemic species becoming established in South Africa was highlighted with the incidental finding of a B. gibsoni infection in an imported dog. The results of this thesis have shown therefore that populations of dogs that live in tickendemic areas are exposed to single or multiple tick-borne pathogens. These pathogens continue to cause morbidity and mortality in susceptible dogs. Correct diagnosis (supported by molecular diagnostic tools) followed by appropriate treatment offers a better understanding and management of these tick-borne pathogens. Preventative measures should be fully evaluated and applied to prevent these tick-borne pathogens from adversely affecting the canine population in South Africa and elsewhere. / Thesis (PhD)--University of Pretoria, 2008. / Veterinary Tropical Diseases / unrestricted

QC 20110617

No description available.

Mathematical modeling is a powerful tool to study and analyze the disease dynamics prevalent in the community. This thesis studies the dynamics of two time since infection structured vector borne models with direct transmission. We have included disease induced death rate in the first model to form the second model. The aim of this thesis is to analyze whether these two models have same or different disease dynamics. An explicit expression for the reproduction number denoted by R0 is derived. Dynamical analysis reveals the forward bifurcation in the first model. That is when the threshold value R0 < 1, disease free-equilibrium is stable locally implying that if there is small perturbation of the system, then after some time, the system will return to the disease free equilibrium. When R0 > 1 the unique endemic equilibrium is locally asymptotically stable. For the second model, analysis of the existence and stability of equilibria reveals the existence of backward bifurcation i.e. where the disease free equilibrium coexists with the endemic equilibrium when the reproduction number R02 is less than unity. This aspect shows that in order to control vector borne disease, it is not sufficient to have reproduction number less than unity although necessary. Thus, the infection can persist in the population even if the reproduction number is less than unity. Numerical simulation is presented to see the bifurcation behaviour in the model. By taking the reproduction number as the bifurcation parameter, we find the system undergoes backward bifurcation at R02 = 1. Thus, the model has backward bifurcation and have two positive endemic equilibrium when R02 < 1 and unique positive endemic equilibrium whenever R02 > 1. Stability analysis shows that disease free equilibrium is locally asymptotically stable when R02 < 1 and unstable when R02 > 1. When R02 < 1, lower endemic equilibrium in backward bifurcation is locally unstable. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2020. / FAU Electronic Theses and Dissertations Collection

This study was conducted to understand the occurrence, diversity and epidemiology of tickborne diseases (TBDs) in a transhumant pastoral area of Karamoja Region, Uganda. We used participatory epidemiology (PE), involving focus group discussions (n = 24) with livestock keepers, 30 key informant interviews, review of previous surveillance data, clinical examinations, and laboratory confirmation of cases of TBDs, to define and prioritise cattle diseases, evaluate current control activities, and identify constraints to the control of TBDs. The livestock keepers regarded TBDs, particularly East Coast fever (ECF) and anaplasmosis, as the most important health problems in their cattle, based on morbidity and mortality rates, rates of transmission, treatment costs, difficulty in accessing the correct treatment, difficulty to control, and inadequate knowledge to manage the diseases. The main constraints to the control of TBDs were inadequate knowledge, inadequate veterinary services and limited availability of drugs. Hand picking of ticks was done by all pastoralists while hand spraying was done with under-strength acaricides, often at irregular intervals and with little acaricide wash. We determined the endemic status of TBDs in 20 randomly-selected cattle herds by estimating the proportion of annual ECF and anaplasmosis cases in different age groups of cattle using participatory approaches and clinical examinations, determining the diversity and abundance of ticks (161 cattle in 20 herds), and establishing the seroprevalence of antibodies to Theileria parva and Anaplasma marginale among cattle (n = 397 in 20 herds). Clinical examinations and informant interviews showed that TBDs affected all age groups of cattle. Two-thirds of the cattle were infested with moderate (37.3%, 11-50 ticks) to abundant (28.6%, > 50 ticks) numbers of ticks. Out of the 10,923 ticks collected, Rhipicephalus appendiculatus (54.4%) was the most abundant species followed by R. decoloratus (17.7%), Amblyomma variegatum (12%) and A. lepidum (11.6%). We collected tick species that are either rare in Uganda (A. lepidum, Hyalomma truncatum, A. gemma) or were not known to be present in the country (R. pulchellus). The true seroprevalence of antibodies to A. marginale was high (95.1%, 95% confidence interval [CI] 91.3% - 98.5%), while that of T. parva was low (16.5%, 95% CI 12.9% - 19.6%). We determined the presence of tick-borne haemoparasites among cattle and the prevalence of infections using reverse line blot (RLB) hybridisation and quantitative real-time polymerase chain reaction (qPCR), and characterised Theileria and Babesia species by sequence and phylogenetic analyses of the full-length 18S rRNA gene. The RLB hybridisation assay demonstrated the presence of tick-borne haemoparasites in most cattle (99.6%), mostly as mixed infections (97.5%). The most frequently-detected species were Theileria mutans (88.3%, 95% CI: 84.6-92.1%), A. marginale (73.8%: 68.3-79.2%), T. velifera (71.3%: 65.8-76.7%) and Anaplasma sp. Omatjenne (63.3%: 57.5-68.8%). Other virulent pathogens, namely Babesia bigemina (5.0%) and T. parva (2.9%), were also detected with RLB, but Ehrlichia ruminantium was not detected. The proportions of qPCR positive samples were 82.9% (A. marginale), 12.1% (A. centrale), 3.3% (T. parva), and 1.7% (E. ruminantium). Variations (5 to 9 nucleotides) in the 18S rRNA gene sequences of B. bigemina were identified as compared with previously published sequences. We assessed the 16S rRNA gene phylogeny of Anaplasma species from cattle and analysed the msp1α gene sequences of A. marginale to identify genotypes. There was genetic heterogeneity within A. marginale in cattle in the study area. Most A. marginale sequences (16/19) were closely related (99- 100% identities) and clustered with A. marginale strain Veld from cattle in South Africa, with strong bootstrap support, while three sequences clustered (100% identity) with A. marginale strain from Virginia, USA. The A. centrale sequences were closely related (100% identity) and clustered with the Israel vaccine strain. We found four different kinds of MSP1a tandem repeat sequences (UP39-F-M2-3) that correspond to one A. marginale strain unique to Uganda. One tandem repeat (UP39) was unique to Karamoja cattle. The findings from this study provide knowledge on the diversity and epidemiology of TBDs, which can be used to support diagnosis and strategic control of TBDs, and consequently improve cattle productivity and the livelihoods of pastoralists. More effective control and prevention measures against ticks and TBDs should urgently be implemented in the region. There is need to facilitate and promote immunisation of cattle against ECF. Given the scarcity of veterinarians in the region, the activities of community-based animal health workers [CAHWs] should be strengthened. The local governments in Karamoja Region should facilitate a more favourable business environment to attract private companies, who could scale-up veterinary drug supplies to the region. Pastoralists should be sensitised to improve their ecological knowledge of the seasonal activity of ticks for strategic tick control. / Thesis (PhD)--University of Pretoria, 2017. / Agricultural Technology and Agribusiness Advisory Services (ATAAS) / The National Agricultural Research Organisation (NARO) of Uganda / Veterinary Tropical Diseases / PhD / Unrestricted

The state of Florida is the third most populous state in the United States of America, with six (6) of its metropolitan areas dubbed as the fastest growing in the entire country. A mosquito bite may mean the transmission of a virus or disease which might be fatal. Hence, there is a need for the state to control mosquitoes through the various Departments of Mosquito Control in each of its sixty-seven (67) counties. Six locally acquired mosquito-borne viruses which affect humans and animals in the state of Florida were considered. This thesis used statistical methods to examine data for rainfall, population estimate, as well as, the data on six (6) arboviruses, over the course of thirteen (13) years, namely 2002 to 2014. The first hypothesis that was tested, was that greater precipitation increased the likelihood of a greater number of arbovirus cases. It was important to also examine the relationship that this growing human population had with mosquito-borne diseases, and so the second hypothesis that was tested, was that, an increase in the human population would increase the likelihood of a greater number of arbovirus cases. Subsequently, an analysis was done for eleven (11) of Florida*s 67 counties with the greatest cumulative occurrence of human and animal arbovirus cases combined. Of the eleven counties, seven exhibited a weak associated between the size of the human population and the spread of animal and human arbovirus cases; three exhibited a somewhat moderate association; and one – Osceola County – had a strong negative association. This indicated that, as the size of the human population increased in Osceola County, the combined number of human and animal arbovirus cases decreased, which refuted the second hypothesis of this thesis. A linear regression model for the data for Osceola County was derived and that model was used to simulate what will occur in future years with the use of population projection data. In each simulated year, the number of combined human and arbovirus cases was negative. This prediction meant that, as the projected population increased from year to year, then the number of cases should be zero in each year. The reliability of these predictions are questionable, since Osceola County does not exist in a vacuum and it cannot be isolated from the surrounding counties which may be experiencing an outbreak of arboviruses.

No description available.

Vector-borne diseases (VBDs) cause significant harm to humans, plants, and animals worldwide. For instance, VBDs are very difficult to manage, as they are governed by complex interactions. VBD transmission depends on the pathogen itself, vector-host movement, and environmental conditions. Mosquito-borne diseases are a perfect example of how all these factors contribute to changes in VBD dynamics. Although vectors are highly sensitive to climate, modeling studies tend to ignore climate effects. Here, I am interested in the arthropod small vectors that are sensitive to climate factors such as temperature, precipitation, and drought. In particular, I am looking at the effect of temperature on vector traits for two VBDs, namely, dengue, caused by a virus that infects humans and bluetongue disease, caused by a virus that infects ruminants. First, I collect data on mosquito traits' response to temperature changes, this includes adult traits as well as juvenile traits. Next, I use these traits to model mosquito density, and then I incorporate the density into our mathematical models to investigate the effect it has on the basic reproductive ratio R0, a measure of how contagious the disease is. I use R0 to determine disease risk. For dengue, my results show that using mosquito life stage traits response to temperature improves our vector density approximation and disease risk estimates. For bluetongue, I use midge traits response to temperature to show that the suitable temperature for bluetongue risk is between 21.5 °C and 30.7 °C. These results can inform future control and prevention strategies. / Doctor of Philosophy / Infectious diseases are a type of illness that occurs when microorganisms spread between hosts. Some infectious diseases are directly transmitted and some require indirect transmission such as vector-borne diseases (VBDs). Each VBD requires the presence of a vector for the disease to be transmitted. For example, dengue that puts 40% of the world population at risk, requires mosquitoes to transmit the disease between humans. My research aims to investigate how the main climate factor, temperature, influences the spread of VBDs. I develop mathematical and statistical models that explain the effect of temperature on vector traits of a mosquito-borne disease (dengue) and a midge-borne disease (bluetongue) and investigate modeling formulas to improve our estimates for dengue mosquito densities. My results can be used to inform future prevention and control strategies.

Mosquito-borne viruses, such as dengue virus (DENV), Zika virus (ZIKV), chikungunya virus (CHIKV), yellow fever virus (YFV), Japanese encephalitis virus (JEV), and West Nile virus (WNV) are major threats to global public health resulting in millions of infections and hundreds of thousands of deaths annually. The presence of these viruses and their increasing emergence/spread continues to escalate. Notably, Usutu virus (USUV; Genus: Flavivirus; Family: Flaviviridae) is one such pathogen currently causing mass die-offs of avian hosts throughout Europe. USUV is categorized in the Japanese Encephalitis virus (JEV) antigenic complex and thus shares many antigenic and pathologic characteristics with fellow members, such as JEV and WNV. Respective to human infections, USUV cases are generally asymptomatic; nonetheless, acute cases have been reported. These acute cases typically cause mild symptoms, such as fevers and rashes; however, more severe cases can result in neurologic diseases, such as encephalitis and/or meningoencephalitis. In addition to these pathologic similarities, USUV shares several ecological and geographical traits with WNV, a pathogen responsible for several outbreaks during its spread from Africa, to Europe, and eventually the United States. Currently, WNV is considered endemic in areas across the United States due to its transmission via Culex spp.; mosquitoes that are ubiquitous in the United States. These parallels suggest the possible emergence of USUV into the United States and therefore, it is imperative to broaden our knowledge of USUV and assess its potential to become a major global health concern. The overall goal of this thesis was to characterize USUV and evaluate its emergence potential in the United States by: (1) developing infectious clones of recent European and African USUV isolates as tools for characterization and analysis of USUV and (2) assessing the transmission potential of several species of North American mosquitoes. In Aim 1, we show that the aforementioned infectious clones infect and replicate similarly to their parental strains in vitro in both vertebrate and invertebrate models, as well as in transiently immunocompromised CD-1 and IFNAR-/- murine models, and thus serve as useful tools for future molecular studies focusing on USUV. Furthermore, in Aim 2, we describe the ability of field-caught (Southwest Virginia, USA) Culex spp. and Aedes spp. mosquitoes to become infected with a recent European isolate of USUV; although, we report an overall limited potential for these species to transmit this virus. Altogether, these studies form a foundation for understanding the potential emergence of USUV in the United States as well as provide necessary tools needed to aid future research on USUV emergence, transmission, and pathogenesis. / Master of Science / Usutu virus (USUV) is an emerging mosquito-borne virus that was first isolated from a mosquito in 1959 in South Africa, and since then, has become a major problem throughout Africa and Europe causing acute to severe infection in dozens of patients. Additionally, this virus is causing massive die-offs in Eurasian blackbird populations. This is particularly problematic because birds play a critical role in ecosystems as they act as forms of pest control, pollinators, and seed dispersers. Depletion of these species could lead to an imbalance and, eventually, collapse of our natural ecosystem. Additionally, there is a growing concern of USUV making its way into the United States, following a similar track of emergence to WNV's introduction in New York in 1999 and its subsequent spread throughout the states. WNV's introduction to the United States was detrimental to native bird populations and humans, and has caused tens of thousands of infections and thousands of deaths since this introduction. Research has shown USUV causes similar disease symptoms to WNV. The self-limiting illness from these viruses typically includes fever and rashes but some infections can result in more severe cases causing inflammation of the brain and surrounding areas. Like many other prominent mosquito-borne viruses, there is no specific treatment or vaccine for WNV or USUV. Because USUV is so closely related to WNV, and their similar characteristics may point towards similar emergence in the United States, it is essential to garner more information on USUV. The overall goal of this thesis was to establish a reliable tool(s) for further characterization of USUV and demonstrate the potential for USUV emergence in the United States. We first developed molecular tools, known as viral clones, that are valuable to the scientific community which allows the manipulation of USUV genetic material to perform further downstream studies. Our objective for this initial study was to create a molecular tool that would behave similarly to their natural, or "parental", virus. The results from this study suggest we have successfully produced these tools. Furthermore, we sought to determine the potential for field-caught mosquitoes from Southwest Virginia, USA to transmit a recently isolated strain of USUV. These data suggest that while these mosquitoes do have the ability to become infected with USUV, they have a limited potential to transmit this virus to animal hosts. Altogether, these studies have allowed us to expand our knowledge on USUV's potential emergence in the United States and develop powerful tools to continue this essential research.