A participatory approach to marsh deer (Blastocerus dichotomus) morbidity and mortality passive surveillance in Argentina: first results

Background: The comprehensive approach to diseases in broad ecological contexts appears as a new challenge for global health. Winter mortality of marsh deer ( Blastocerus dichotomus ) was historically described in Argentina even though field difficulties prevented their in-depth study. Results: Between May 2014 and April 2017, we investigated marsh deer morbidity and mortality through passive surveillance in the two largest populations in Argentina using a participatory approach. The latter spanned a network of researchers, field partners (veterinarians, park rangers, and local community), and decision makers. We sampled dead deer during as well as outside mortality events. A total of 44 marsh deer with different body condition scores were evaluated. We obtained reference haematology and biochemistry values from animals with good body condition score. Marsh deer with poor body condition had a high burden of the ticks Amblyomma triste and Rhipicephalus microplus . Vector-borne agents (VBAs), such as Theileria cervi , Trypanosoma theileri, Trypanosoma evansi, Ehrlichia chaffeensis, Anaplasma platys, Anaplasma odocoilei, Anaplasma marginale , and Candidatus Anaplasma boolense were also found. Haemonchus spp., Ostertagia spp., and Trichostrongylus spp. were the most frequent gastrointestinal parasites in deer with poor body condition. A Multiple Correspondence Analysis reinforced a possible association of winter period with lower body score condition, high tick loads, infection with E. chaffeensis , and presence of harmful gastrointestinal parasites. Conclusions: Our approach allowed the establishment of a participatory surveillance network of marsh deer morbidity and mortality in Argentina. We report and analyse the first data obtained opportunistically within the framework of this network, providing information on the infectious and parasitic agents in marsh deer populations. The occurrence of Fasciola hepatica and Leptospira interrogans serovar pyrogenes is reported for the first time in wild marsh deer from Argentina. The histopathological findings in succumbed animals allowed us to distinguish lesions associated with their body condition from those that were unrelated. Our data will be useful to improve the interpretation of future mortality events. The field implementation of a surveillance network is key to a holistic approach to wildlife diseases.