The use of statistical and simulation modelling as decision support tools in veterinary public health

In this thesis, the Ecuadorian case of two livestock-related neglected zoonoses (brucellosis and cysticercosis) is treated. We tried to find and evaluate their relationships with components of food security, such as livestock populations, adequate sanitation and biological variability within livestock species. Generally, in extensive and small-holder livestock systems in developing countries, there is a carelessness when it comes to the evaluation and assessment of risks related to problems in animal husbandry and as such in the prevention of health problems in human and livestock populations. Data provided by a passive surveillance system, generated in Ecuadorian hospitals were used for the analysis and non-specific epilepsies were used additionally to support neuro-cysticercosis data. We state that this kind of surveillance provides critical information for monitoring community and livestock health statutes with relation to those zoonoses in a relatively cheap way. This strategy may help to cover larger areas, to gain insights in zoonotic diseases and to prioritise areas of intervention. In the case of human brucellosis several clusters were found in time and space, and later on several of our hypotheses were verified in the Northern and central parts of the country and in some regions in the coastal part of the country. For farmers, the rationale for the elimination of this disease is often found in benefit-cost calculations providing them with the incentives for prevention and eradication of the disease. A mathematical model for the transmission dynamics of brucellosis in cattle was developed, allowing estimation of losses in cattle farms due to brucellosis. Losses were estimated in terms of abortions and milk yield losses that result from a reduction in the cattle farm population or from delays in the production due to abortions. It was estimated that, in the absence of control measures, brucellosis in cattle is an economically catastrophic problem because of noticeable lack of female replacements and as a consequence an inefficient production systems. The model predicts that brucellosis in a dairy herd is an eradicable disease. Strict vaccination of female calves an biannual testing half the population and culling the seropositive animals can reduce the true prevalence in cattle to negligible levels with minimum economic losses. In neurocysticercosis (NCC), traditional and previously recognised endemic zones were identified as higher risk zones, but recent, new clusters of epilepsy have appeared. Overall, an increasing trend for the incidence of hospitalised cases (IHC) of epilepsy and a decreasing trend for the IHC of NCC were observed over time; oddly enough, within municipalities a significant positive linear relationship between both disorders was confirmed. Risk models demonstrated that rates of epilepsy and NCC in hospitals were related to the presence of systems for eliminating human excreta. On the other hand, but in the same vein, the increasing demand for food of animal origin has tended to favour international high-output breeds over local breeds. Consequently, there has been a worldwide tendency to reduce the effective size of populations under selection. Animal genetic diversity is a critical factor for food security, and it may also reduce the risk of disease threats in livestock. In this document, a methodology to estimate the effective population size is given. It can be applied when partial information of family sizes is known in a beef cattle population. Additionally, this genetic structure of livestock populations must be taken into account when statistical data analyses are performed for features with genetic backgrounds, because of genetic resemblance. The use of statistical and modelling tools in the epidemiology of livestock-related neglected zoonoses still plays an important role when advising decision makers in public health.