Isolation of viable Toxoplasma gondii, molecular characterization, and seroprevalence in elk (Cervus canadensis) in Pennsylvania, USA

Authors: Dubey, Jitender; BROWN, JUSTINE - Pennsylvania Game Commission, Bureau Of Wildlife Management; VERMA, SHIV - Non ARS Employee; CEZAR, CAMILA - Non ARS Employee; BENEFIELD, JERMEY - Pennsylvania Game Commission, Bureau Of Wildlife Management; Kwok, Oliver; YUGING, YING - University Of Maryland; MURATA, FERNANDO - Non ARS Employee; PRADHAN, ABNI - University Of Maryland; SU, CHUNLEI - University Of Tennessee

Submitted to: Veterinary Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/31/2017
Publication Date: 8/30/2017
Citation: Dubey, J.P., Brown, J., Verma, S., Cezar, C., Benefield, J., Kwok, O.C., Yuging, Y., Murata, F., Pradhan, A., Su, C. 2017. Isolation of viable Toxoplasma gondii, molecular characterization, and seroprevalence in elk (Cervus canadensis) in Pennsylvania, USA. Veterinary Parasitology. 243: 1-5. http://dx.doi.org/10.1016/j.vetpar.2017.05.030.

Interpretive Summary: Human toxoplasmosis, caused by single-celled parasite, Toxoplasma gondii, accounts for an estimated one-fifth of all diagnosed foodborne infections in the United States, and one fifth of the economic costs attributable to any foodborne pathogen. Pregnant women and their fetuses are exposed to elevated health risks. The ingestion of under cooked infected meat, including venison is considered an important source of toxoplasmosis in humans. The Elk is one of the largest species within the deer family and mature animals can weigh up to 750 pounds. In the present study, the authors found Toxoplasma specific antibodies in 221 of 317 (69.7%) elk hunted in Pennsylvania. Viable T. gondii was isolsated from the hearts of 2 elk; the first time from this host.Hunted elk are gutted in the forest and viscera of infected deer could be a source of infection for wild cats that in turn can shed oocysts and spread infection. An infected elk could be a source of Toxoplasma infection in many persons if meat is consumed undercooked. The results will be of interests to parasitologists, public health workers and biologists.

Technical Abstract: Toxoplasmosis is a worldwide zoonosis. The ingestion of uncooked/undercooked meat and consumption of water contaminated with Toxoplasma gondii oocysts excreted by felids are the main modes of transmission of this parasite. Thousands of wild cervids are hunted or killed in traffic accidents yearly but little is known of toxoplasmosis in elk in USA. In the present study, antibodies to T. gondii were determined in serum by the modified agglutination test (MAT, cut-off 1:25); 221 of 317 (69.7%) had MAT titers of 1:25 in 19, 1:50 in 28, 1:100 in 34, and 1:200 or higher in 140; thus most (44.1%) had high titers. Seropositivity was slightly higher in males (76.9%) than females (67.5%). Seroprevalence was higher in adults (76.5%) than in yearlings (46.4%), and in calves (21.7%); indicating post-natal transmission of T. gondii. Seroprevalence was relatively stable and ranged from 66.6% to 72.2% ([72.2%-26 of 36 in 2013], [74.1%-63 of 85 in 2014], [66.7% - 60 of 90 in 2015], and [70.3% 71 of 101 in 2016]). Of the 101 elk harvested in 2016, tissues were available for bioassay from 91 elk; most (76%, 54 of 71) of the seropositive elk in 2016 had a titer of 1:200 or higher. In total, hearts were bioassayed from 20 elk and tongues were bioassayed from 56. Viable T. gondii was isolated from hearts of two female elk, one of these was adult seronegative by serum testing and the other was a calf with no serum available. Both T. gondii isolates were cultivated in cell culture and DNA derived from tachyzoites was characterized using the PCR-RFLP markers including SAG1, SAG2 (5’-3’SAG2 and altSAG2), SAG3, BTUB, GRA6, c22-8, c29-2, L358, PK1, and Apico. One belongs to ToxoDB PCR-RFLP genotype #2 and the other is #5. Both genotypes are frequently identified in animals in North America.