Simon R. Ruegg Institute of Parasitology, University of Zurich, Zurich, Switzerland Title Biology and Epidemiology of Equine Piroplasmoses in Takhin Tal (Mongolia) Abstract Equine piroplasmoses, caused by Theileria equi and Babesia caballi, have been identified as presumptive causes of mortality in newly reintroduced Przewalski’s horses (Equus ferus przewalskii) in the Dzungarian Gobi (Mongolia). To quantify the risk of infection for these horses, the parasites’ epidemiology has been investigated in the local domestic horse population. The prevalences of the two pathogens were determined in 510 domestic horses in the reintroduction area by indirect immunofluorescence antibody test (IFAT) and multiplex PCR. The data was analysed by fitting non-linear mathematical transmission models to the field data with the Maximum Likelihood method to determine the transmission parameters and selecting the best fitting model by conducting a Monte Carlo simulation study. The selected optimal model indicates that antibodies have no significant influence on the infection dynamics of T. equi. The maximum likelihood estimates of the parameters indicate that infection is expected approximately 2 yrs after first exposure and then persists lifelong. For B. caballi, the infection rate of susceptible animals is age-dependent with a much higher infection rate for young animals than for adults (1.58 vs. 0.05 per annum). We assume that this is a result of the increasing resistance to ticks with rising age. Maternal antibodies appear to be protective and immune animals are unlikely to be re-infected. The parasites are eliminated after approximately 2 yrs. Because the Przewalski’s horses have not been exposed to Mongolian ticks, they are expected to become infected rapidly with B. caballi and T. equi after their arrival in Mongolia. The outbreak of clinical piroplasmosis is related to the virulence of the infecting strain and the general immune status of the horse. Especially latter is suppressed by stress, and it is therefore recommended to apply a preventive treatment of imidocarb at arrival on the reintroduction site. This will protect the animals during the stressful reintroduction period for approximately 3 weeks. Secondly it is advisable to transport the animals after the main tick season in order to allow a longer acclimatization period prior to exposure. Nevertheless, further infections and clinical cases of piroplasmoses are to be expected after the animals have been released into the field because the endemic equilibrium is not reached until approximately 10 years after the last introduction. CV Education 1982 – 1991 Primary and Secondary School, Fribourg, Switzerland 1991 – 1995 High School, Fribourg, Switzerland 1993 High School (AFS Exchange Year), Mudgee, NSW, Australia 1995 – 2000 Faculty of Veterinary Medicine, Berne, Switzerland Languages Research 2001 - 2003 Doctoral thesis (Dr med vet): “Mortality Causes and Equine Piroplasmoses at the Reintroduction site of Przewalski’s horses in Takhin Tal, Mongolia” At the Institute of Animal Pathology, Center for Fish and Wildlife Diseases, University of Bern and the International Takhi Group (ITG) Supervision: Dr. Nadia Robert (Bern) and Dr. Chris Walzer (ITG, Research Institute for Animal Ecology, Vienna) Including 6 months of fieldwork in Mongolia, laboratory analyses, statistical evaluation and modelling. 2003 – 2007 PhD: “Biology and epidemiology of equine piroplasmoses in Takhin Tal, Mongolia” At the Institute of Parasitology, University of Zurich, Switzerland Supervision: PD Dr. Alexander Mathis (molecular biology), Dr. Paul Torgerson (veterinary epidemiology), Prof. Andrew Barbour (mathematics) Including grant applications, 3 months of fieldwork in Mongolia, laboratory analyses, statistical evaluation and mathematical modelling. Formal training in laboratory animal science, laboratory safety course, and examinations in vector biology and incrimination, immunology, cell biology, epidemiology, biomathematics Publications S.Ruegg, C.Walzer, N.Robert, M.Doherr, K.T. Friedhoff. Disease Risk Assessment: Piroplasmosis at the reintroduction site of the przewalski horse (Equus caballus przewalskii) in the dsungarian gobi, Mongolia. Proceedings of the annual conference, EAZWV 2002. S.R. Ruegg. Mortality causes and equine piroplasmoses at the reintroduction site of Przewalski's horses (Equus ferus przewalskii) in Takhin Tal, Mongolia, veterinary doctoral thesis at the Institute of Pathology. 2002, University of Berne S.Ruegg. Forschungsreportage: Wenn Zecken heisse Köpfe machen. Unipress, Bern November 2002 S.Ruegg, C.Walzer, N.Robert, K.T.Friedhoff, R.Böse. Significance of Piroplasmoses at the reintroduction site of the Przewalski’s horse in Mongolia. Proceedings of the 41st International Symposium on Zoo and Wild Animals, IZW 2003. N. Robert, C. Walzer, S.R. Ruegg, P. Kaczensky, G. Oyunsaikhan, C. Stauffer. Pathological investigations at the reintroduction site of the Przewalski's horse (Equus caballus przewalskii) in Mongolia - What can we learn? Journal of zoo and wildlife medicine, 2005. 36(2): p. 273-85. S. Ruegg, A. Mathis, P. Torgerson, R.Böse, C. Walzer, P. Deplazes. Development of equine piroplasm infections in a horse population in SW Mongolia. Proceedings of the 22. Jahrestagung der Deutschen Gesellschaft für Parasitologie, 2006: p. 94 S.R. Ruegg, P. Torgerson, M.G. Doherr, P. Deplazes, N. Robert, C. Walzer. Equine piroplasmoses at the reintroduction site of the Przewalski’s horse (Equus ferus przewalsii) in Mongolia. Journal of Wildlife Disease, 2006. 42(3): 518-526. S.R. Ruegg, P. Torgerson, P. Deplazes, A. Mathis. Age-dependent dynamics of Theileria equi and Babesia caballi infections in southwest Mongolia based on IFAT and/or PCR prevalence data from domestic horses and ticks. Parasitology, 2007. 134: 939-947. Rüegg SR, Heinzmann D, Mathis A, Torgerson P. Use of mathematical transmission model to determine the risk of Przewalski’s horses to acquire equine piroplasmosis during their reintroduction. Proceedings of the 43rd International Symposium on Zoo and Wild Animals, IZW 2007: p. 54 S.R. Ruegg, D. Heinzmann, A.D. Barbour, P. Torgerson. Estimating the transmission dynamics of Theileria equi and Babesia caballi infections in horses. Parasitology, 2007 submitted in revision. S.R. Ruegg. Biology and epidemiology of equine piroplasmoses in Takhin Tal (Mongolia). PhD thesis at the Vetsuisse Faculty of Zurich, in preparation. Institution address S.R. Rüegg Institute of Parasitology, University of Zurich, Zurich, Switzerland