Is Toxoplasmosis a Potential Emerging Disease for Wildlife, Domestic Animals and Humans in Mongolia?
William F. Swanson1, DVM, PhD; Bariushaa Oyuntuya2, MS; Meredith Brown3, DVM, PhD; Martin Gilbert4, BVMS, MRCVS; Amanda E. Fine4, VMD, PhD; Steve Ross5, PhD; Kurt Volle6, DVM; Jill Van Milligen7; Tsatsralt-Od Bira8, MD, PhD; Bariushaa Munkhtsog9, PhD
1Center for Conservation and Research of Endangered Wildlife, Cincinnati Zoo & Botanical Garden, Cincinnati, OH, USA; 2National University of Mongolia, Ulaanbaatar, Mongolia; 3Laboratory of Genomic Diversity, National Cancer Institute, Frederick, MD, USA; 4Wildlife Conservation Society, Ulaanbaatar, Mongolia; 5Bristol University, Bristol, UK; 6Buffalo Zoo, Buffalo, NY, USA; 7Utah’s Hogle Zoo, Salt Lake City, UT, USA; 8National Center for Communicable Diseases, Ulaanbaatar, Mongolia; 9Mongolian Academy of Sciences, Ulaanbaatar, Mongolia
Read the Spanish translation: ¿La Toxoplasmosis es una Enfermedad Emergente Potencial Para la Vida Silvestre, los Animales Domésticos y los Humanos en Mongolia?
The Pallas’s cat (Otocolobus manul), a small-sized felid native to Central Asia, is uniquely susceptible among cat species to mortality caused by toxoplasmosis, possibly as a consequence of its evolutionary history. In our earlier research in Mongolia, we identified two wild Pallas’s cats (2/15, 13%) that were seropositive for Toxoplasma exposure, but found no seropositive individuals among sampled domestic cats (0/15) and wild rodents (0/45).1 In this follow-up study, we have expanded our survey in Mongolia to include humans and domestic hoof stock as well as wild birds and additional Pallas’s cats and rodents. Serum samples from native Mongolians (n=300) were obtained opportunistically from citizens providing blood for routine health exams. Blood samples also were collected from domestic sheep and goats (n=300) in herds located at our primary field site in central Mongolia and on the grassland steppes of eastern Mongolia. Serum samples from two migratory bird species (bar-headed geese, Anser indicus; swan geese, A. cygnoides; n=189) were collected in north-central Mongolia as part of the WCS-USAID Global Avian Influenza Network for Surveillance (GAINS) program. Additional rodent (n=45) and Pallas’s cat (n=19) blood samples were obtained at the primary field site. Serum samples were assessed for Toxoplasma antibodies at a single titer (1:16–1:64, depending on species) using a latex agglutination test (Toxotest MT, Tanabe USA, Inc., San Diego, CA, USA).
Results indicated that only two of the sampled Mongolians (0.7%; 2/300) had antibodies to Toxoplasma, while none (0%; 0/45) of the tested rodents and just a few (1.2%; 4/300) of the hoof stock had anti-Toxoplasma titers. Although only 1/19 (5.3%) adult Pallas’s cats were seropositive, these findings, combined with our earlier data, confirm the existence of some undefined nidus for Toxoplasma exposure. Because migratory waterfowl had a very high seroprevalence (104/189 positive, 55.0%), we suspect that Pallas’s cats may be exposed sporadically via ingestion of tissue cysts in these potential prey items or from other migratory bird species. These new findings support our contention that Toxoplasma is not truly an endemic parasite of Mongolia but is likely a transient pathogen, perhaps as an intracellular stowaway in wild birds. The combination of an extremely cold and arid climate, high altitude, very few domestic cats and limited numbers of wild felids may compromise the ability of Toxoplasma to complete its natural life cycle. These results reinforce the importance of managing Pallas’s cats, especially breeding age females, in a Toxoplasma-free environment in zoos to prevent fatal toxoplasmosis in newborn kittens. In a broader context, these findings may have major public health implications for both pregnant women and the livestock industry in Mongolia if Toxoplasma exposure increases due to changes in cultural practices (e.g., increased ownership of domestic cats) and global climate (e.g., warmer winter temperatures affecting Toxoplasma oocyst survival). Initiation of surveillance programs for susceptible human and animal populations in Mongolia could be warranted.
The assistance of Jamsran Gantulga, Galsandorj Naranbaatar, Enkhtuvshin Shiilegdamba and other field staff in Mongolia and Donna Stringer at the WCS is gratefully acknowledged.
1. Brown, M., M.R. Lappin, J.L. Brown, B. Munkhtsog, and W.F. Swanson. 2005. Exploring the ecologic basis for extreme susceptibility of Pallas’ cats (Otocolobus manul) to fatal toxoplasmosis. J Wildl Dis. 41:691–700.