Seroepidemiologic study on the prevalence of Toxoplasma gondii and Trichinella spp. infections in black bears (Ursus americanus) in Pennsylvania, USA

Authors: Dubey, Jitender; BROWN, JUSTIN - Pennsylvania Game Commission, Bureau Of Wildlife Management; TERNENT, MARK - Pennsylvania Game Commission, Bureau Of Wildlife Management; VERMA, SHIV - Non ARS Employee; Hill, Dolores; CEZAR, CAMILA - Non ARS Employee; Kwok, Oliver; CALERO-BERNAL, RAFAEL - Non ARS Employee; HUMPHREYS, JAN - Indiana University Of Pennsylvania

Submitted to: Veterinary Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/18/2016
Publication Date: 10/15/2016
Citation: Dubey, J.P., Brown, J., Ternent, M., Verma, S., Hill, D.E., Cezar, C., Kwok, O.C., Calero-Bernal, R., Humphreys, J. 2016. Seroepidemiologic study on the prevalence of Toxoplasma gondii and Trichinella spp. infections in black bears (Ursus americanus) in Pennsylvania, USA. Veterinary Parasitology. 229:76-80.

Interpretive Summary: Human toxoplasmosis, caused by single-celled parasite, Toxoplasma gondii, continues to be a significant public health problem in the United States. Pregnant women and their fetuses are exposed to elevated health risks. Cats (pets and wild) are the main reservoirs of infection because they are the only hosts that can excrete environmentally resistant stage (oocyst) in their feces. Humans and animals can acquire toxoplasmosis by ingesting food and water contaminated with oocysts. In the present study authors found antibodies to T. gondii in 87.6% (206/235) adult bears from Pennsylvania. Epidemiologic investigations indicated that bears become infected with T. gondii after birth, and bears are good indicators of environmental contamination of T. gondii. Seven of these bears were also infected with Trichinella sp. humans can become infected with both Toxoplasma and Trichinella infections by eating undercooked meat, including game. In Pennsylvania approximately 3500 bears are hunted every year, and their meat is also consumed by humans.These results will be of interest to biologists and parasitologists.

Technical Abstract: The protozoan Toxoplasma gondii and the metazoan Trichinella spp. infect virtually all warm-blooded animals, including birds, humans, livestock, and marine mammals. Both parasitic infections can cause serious illness in human beings and can be acquired by ingesting under-cooked meat harbouring infective stages. Approximately 3500 black bears are legally-harvested each year in Pennsylvania during the November hunting season. Among animals found infected with T. gondii, the prevalence of T. gondii is the highest among black bears in USA; however, little is currently known of epidemiology of toxoplasmosis in this species. Serum samples were collected during the winters of 2015 and 2016 from adult female bears and their nursing cubs or yearlings while they were still in their dens. Additionally, archived sera from bear samples collected throughout the year, including hunter-harvested bears in November and trapped bears in the summer, were serologically tested. Antibodies to T. gondii were assayed by the modified agglutination test (MAT, cut-off 1:25) and antibodies to Trichinella spp. were assayed using a commercial enzyme-linked immunosorbent assay (ELISA). Overall, T. gondii antibodies were found in 87.6 (206/235) of adults, 44.1% (30/68) of yearlings. In March 2015/2016 sampling, antibodies to T. gondii were found in 94% (30/32) adult female bears while in their den. Antibodies were detected in 5% (3/66) of the nursing cubs in the dens of these sows. One positive cub had a MAT titer of 1:160 and two were positive at the 1:25 dilution but not at 1:50. The adult females of these cubs had MAT titers ranging from 1:400 to 1:3200 Antibodies to Trichinella spp. were found in 3% (6/181) adults, and 3.6% (1/28) yearlings; these 7 bears were also seropositive for T. gondii. No antibodies to Trichinella spp were detected in the sera of 44 nursing cubs tested. The finding of T. gondii antibodies in only 3 of 66 cubs, and higher antibody titers in their respective sows indicates that the colostrally-acquired antibodies wane to undetectable levels by 8-10 weeks, while the cubs are still in the den. The results indicate that there is no transplacental transmission of T. gondii, that antibodies acquired from colostrum are largely undetectable by the time cubs emerge from the den, and nearly 50% of bears acquire infection postnatally by 10 months of age. This is the first report of disappearance of transcolostral antibodies of any infection in bears.