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Since 1996 a mysterious epidemic has been sweeping across the island of Tasmania, threatening the Tasmanian devil (Sarcophilus harrisii) with extinction. The species is endemic to the island which is part of Australia and lies south of Melbourne. Being endemic to the island the devils are of particular risk of extinction. Not only has the risk of losing the world’s largest extant carnivorous marsupial aroused great interest, but also the disease itself, has received much attention from the world of oncology due to its unusual trait of being a contagious cancer.

Contagious bovine pleuropneumonia (CBPP) is a bovine bacterial disease of major economic importance in sub-Saharan Africa. Vaccination has been recommended to control the disease in endemic areas such as the Maasai ecosystems of Kenya and Tanzania; however, the currently used live attenuated vaccine has been reported to have poor vaccine safety and efficacy. To compare standard (current) and an improved (buffered) version of the live CBPP-vaccine, several epidemiological studies were carried out in Maasai cattle in Kenya between 2006 and 2008. Specifically, the aims were to estimate CBPP seroprevalence at herd and animal level; to identify risk factors for seroprevalence at both levels; to investigate the spatial distribution of seroprevalence; to compare post vaccination adverse events in cattle vaccinated with a standard and a buffered vaccine, and finally to compare efficacy of the two vaccines to induce seroconversion and to prevent development of clinical signs suggestive of CBPP. A cross-sectional study was carried out in 6872 cattle in 175 randomly selected herds from Loita and Mara divisions. A competitive ELISA revealed that 85% of the herds in the area had at least one seropositive animal and that seropositive herds were harbouring 11% seropositive cattle. A complement fixation test revealed that 46% of the herds had at least one seropositive animal and that seropositive herds were harbouring 4% seropositive cattle. A multivariable logistic regression analysis of the seroprevalence indicated that previous vaccination against CBPP, a history of CBPP outbreaks in the herd, animal age and the location of the herd in the division of Mara were positively correlated to seroprevalence. To investigate the observed difference in herd seroprevalence between the two divisions further, a spatial analysis was conducted. A SatScan test revealed clusters in Mara in areas identified by veterinary personnel as CBPP ‘hot spots’. A logistic regression using spatial information identified that location in the midland agro-ecological zone or close to a river and vaccination were positively associated with seroprevalence. To compare safety and efficacy of a standard and a buffered vaccine, two cohorts of approximately 40,000 cattle were used. The study showed that within 100 days post vaccination, 6.2 cattle per 1000 vaccinates developed adverse events, 4.1 of which were specifically attributable to vaccination and ranging from swelling of the tail to the tail sloughing off. This study revealed a slightly higher incidence of adverse events in cattle vaccinated with the buffered vaccine compared to the standard vaccine. A comparison of the efficacy of the two vaccines revealed that cattle vaccinated with the buffered vaccine had higher odds of seroconversion and lower odds of developing symptoms of CBPP, three and twelve months post vaccination respectively. The epidemiological studies conducted clearly show wide spread seroprevalence in the Maasai cattle. Given the (spatial) heterogeneity observed, control measures should probably be targeted in areas of increased risk (clusters). However, positive association of vaccination and seropositivity call for better diagnostics tests that can differentiate vaccinated from infected animals. Vaccination with buffered vaccine resulted in increased seroconversion, decreased clinical signs indicative of CBPP post vaccination and low seroprevalence post ‘outbreak’. Nevertheless, the increase in adverse events related to the buffered vaccine calls for further research into safer CBPP vaccines.

Four families of contagious distributions--generalized Poisson distributions, generalized binomial distributions, generalized Pascal distributions, and generalized log-zero distributions--are investigated in this thesis. The family of generalized Poisson distributions contains five distributions: the Neyman Type A, the "Short," the Poisson binomial, the Poisson Pascal, and the negative binomial. The family of generalized binomial distributions contains eight distributions: the binomial Poisson, the binomial binomial, the binomial Pascal, the binomial log-zero, the Poisson with zeros, the binomial with zeros, the Pascal with zeros, and the log-zero with zeros. The family of generalized Pascal distributions contains four distributions: the Pascal Poisson, the Pascal binomial, the Pascal Pascal, and the Pascal log-zero. The family of generalized log-zero distributions contains four distributions: the log-zero Poisson, the log-zero binomial, the log-zero Pascal, and the log-zero log-zero. For each family of contagious distributions, the common probability generating function based on a biological model is derived by application of Feller's compound distribution theorem and Gurland's generalized distribution terminology. The common recurrence relation and the common factorial moments or cumulants are derived from the common probability generating function by using the successive differentiation method. Then for each distribution within this family, the particular probability generating function, recurrence relation, and factorial moments or cumulants are easily obtained from common ones. The equations of factorial moments or cumulants are solved. The maximum likelihood equations are derived for some distributions which have been shown to provide a good or excellent moment fitting. These equations are solved by an iteration procedure, Except for the Neyman Type A distribution and the "Short" distribution in which the maximum likelihood equations are derived from the probability generating functions and solved by the method of scoring, the maximum likelihood equations a re derived from the probability functions and solved by the Newton-Raphson method. Forty sets of biological and accident data classified into five types have been collected from various sources. A Fortran program has been written for fitting each distribution and a numerical example is given to illustrate the fitting procedure. In comparing the fits among these distributions, the chi-square goodness- of-fit values have been calculated and tabulated. The results suggest that the binomial distribution with zeros and the Pascal distribution with zeros be used if one is to describe the empirical data arising from populations having a contagious character. This is not only due to the fact that the two distributions have provided better fits to all five types of data, but also the fact that their maximum likelihood estimate procedures have no common disadvantages of other distributions. These disadvantages are that not every moment estimate can allow the iteration process to converge and that the probabilities must be recalculated after each iteration.

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Thesis (MMedVet (Production Animal Studies)--University of Pretoria, 2007. / Includes bibliographical references.

abstract: Although many examples have demonstrated the great potential of a human crowd as an alternative supplier in creative problem-solving, empirical evidence shows that the performance of a crowd varies greatly even under similar situations. This phenomenon is defined as the performance variation puzzle in crowdsourcing. Cases suggest that crowd development influences crowd performance, but little research in crowdsourcing literature has examined the issue of crowd development. This dissertation studies how crowd development impacts crowd performance in crowdsourcing. It first develops a double-funnel framework on crowd development. Based on structural thinking and four crowd development examples, this conceptual framework elaborates different steps of crowd development in crowdsourcing. By doing so, this dissertation partitions a crowd development process into two sub-processes that map out two empirical studies. The first study examines the relationships between elements of event design and crowd emergence and the mechanisms underlying these relationships. This study takes a strong inference approach and tests whether tournament theory is more applicable than diffusion theory in explaining the relationships between elements of event design and crowd emergence in crowdsourcing. Results show that that neither diffusion theory nor tournament theory fully explains these relationships. This dissertation proposes a contatition (i.e., contagious competition) perspective that incorporates both elements of these two theories to get a full understanding of crowd emergence in crowdsourcing. The second empirical study draws from innovation search literature and tournament theory to address the performance variation puzzle through analyzing crowd attributes. Results show that neither innovation search perspective nor tournament theory fully explains the relationships between crowd attributes and crowd performance. Based on the research findings, this dissertation discovers a competition-search mechanism beneath the variation of crowd performance in crowdsourcing. This dissertation makes a few significant contributions. It maps out an emergent process for the first time in supply chain literature, discovers the mechanisms underlying the performance implication of a crowd-development process, and answers a research call on crowd engagement and utilization. Managerial implications for crowd management are also discussed. / Dissertation/Thesis / Doctoral Dissertation Business Administration 2017

Viral infections account about 80 % of all infections that preschool children suffer from. Many researches have shown that infectious diseases spread easily in environments where many individuals live in a limited space at the same time. Coronavirus disease 2019 (Covid19) is a new virus discovered in Wuhan city of China, that can cause serious respiratory problems and the infection can easily spread between people. The Swedish Public Health Authority has developed hygiene recommendations to reduce the risks of infection and limit the spread of the coronavirus by having good hygiene routines as well as social distance. The purpose of my study was to highlight hygiene and infection prevention work in preschools from different parts of Sweden. The study examined similarities and differences between the southern, the central and the northern part of the country regarding hygiene work in preschools during the pandemic. To answer the questions, a survey about hygiene work was sent to pedagogues at preschools in different municipalities. The results of the survey showed both similarities and differences between preschools in different parts of the country and indicated that the knowledge among pedagogues is high when it comes to general hygiene practices. The study showed deficiencies in the use of disinfectant by preschool children. Maintaining the same level of hygiene in preschools may have good effects and can reduce infections caused by pathogenic microorganisms other than coronavirus

Outbreaks of contagious ecthyma (CE) have been reported in vaccinated sheep and studies were undertaken to investigate the causes of these vaccination failures. The vaccination procedure was very effective in inducing a lesion at the site of vaccination, but a proportion of sheep (17 percent) were not fully protected when reinoculated with CE virus 4 weeks later. The size of the primary vaccination lesions, virus neutralizing antibody titers and virus-specific lymphocyte stImulation indices could not be used to predict the degree of protective immunity. Measurement of the neutralizing antibody and virus-specific lymphocyte transformation responses suggested that there was a minimal systemic immune response following CE virus inoculation. Higher levels of systemic immunity may be induced by parenteral administration of live CE vaccines compared to the current procedure of inducing a localized skin infection. Replication of CE virus in buffy coat cells in vitro suggested that the virus may replicate in macrophages and therefore parenteral administration of vaccines may be feasible. Occurrence of CE in vaccinated sheep raised questions about possible variation of antigenic types of CE virus. It was found that cross-neutralization and delayed-type hypersensitivity tests could not be used to classify the CE viral isolates. However, analysis of the structural polypeptides of CE virions revealed differences among the isolates in the position of distinct polypeptide bands in the molecular weight region of 37,000-44,000 daltons, allowing the isolates to be classified into four groups. The polypeptides which varied among the different groups were shown to be located in the surface component of the virion. Unilateral cross reactions detected in cross-neutralization tests were found to correlate with classification of the isolates based on the position of the distinct polypeptide bands. Cross-immunity tests were performed in lambs using two isolates which did not cross-react in the cross-neutralization tests and in which differences in the polypeptide profiles were detected. Reinoculation with virulent sheep-passaged CE viruses overcame the immunity of the lambs. By contrast, there was protection against the less virulent cell culture-passaged CE viruses with cross-protection between the two isolates. These results suggest that virulent CE viral isolates may be responsible for the occurrence of CE in vaccinated animals rather than differences in antigenicity. Two epidemiological aspects of CE infection of sheep were also studied. Latent CE infections were investigated by treating CE-inoculated sheep with corticosteroids. Treatment induced recrudescence of lesions at sites of previous CE virus inoculation, but virus could not be isolated from these lesions. Hence, the existence of latent infections could not be confirmed, but it is unlikely that latent infections are important for the initiation of CE disease outbreaks. Importance of colostral immunity was investigated with ewes vaccinated 6 months prior to parturition. This vaccination did not result in sufficient colostral immunity to protect lambs from subsequent exposure to CE virus, however, the severity of the CE lesions may have been reduced. / Ph. D.