Location: Animal Parasitic Diseases LaboratoryTitle: Isolation and genetic characterization of Toxoplasma gondii from mute swan (Cygnus olor) from the USA Author
Submitted to: Veterinary Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/9/2013
Publication Date: 6/1/2013
Citation: Dubey, J.P., Choudhary, S., Kwok, O.C., Ferreira, L., Oliveira, S., Verma, S., Marks, D., Perdersen, K., Mickley, R., Randall, A., Arsone, D., Su, C. 2013. Isolation and genetic characterization of Toxoplasma gondii from mute swan (Cygnus olor) from the USA. Veterinary Parasitology. 195:42-46. Interpretive Summary: Toxoplasma gondii is a single-celled parasite of all warm-blooded hosts worldwide. It causes mental retardation and loss of vision in children, and abortion in livestock. Cats are the main reservoir of T. gondii because they are the only hosts that can excrete the resistant stage (oocyst) of the parasite in the feces. Humans become infected by eating under cooked meat from infected animals and food and water contaminated with oocysts. Little is known of the circulation of Toxoplasma in wildlife. Mute swans (Cygnus olor) are protected species. In the present study scientists found Toxoplasma in mute swans for the first time. Isolation of T. gondii from feral swan indicates that the local waters were contaminated by T. gondii oocysts, and that mouse T. gondii virulent strains are circulating in wildlife. The results will be of interest to biologists, parasitologists, and public health workers.
Technical Abstract: Little is known of the genetic diversity of Toxoplasma gondii circulating in wildlife. In the present study, antibodies to T. gondii were determined in serum samples from 632 mute swans (Cygnus olor) collected from different areas of the USA. Sera were tested by T. gondii modified agglutination test; 54 (8.5%) of 632 samples were seropositive with titers of 25 in 28 sera, 50 in 22 sera, 100 in three samples, and 1:200 or higher in one swan. Hearts from 14 seropositive swans were bioassayed in mice and viable T. gondii (designated TgSwanUs1 to 3) were isolated from the hearts of three. These three T. gondii isolates were further propagated in cell culture, and DNA isolated from culture-derived tachyzoites was characterized using 11 PCR-RFLP markers (SAG1, 5’- and 3’-SAG2, alt.SAG2, SAG3, BTUB, GRA6, c22-8, c29-2, L358, PK1 and Apico). Results of genotyping revealed that two strains (TgSwanUs1, TgSwanUs2) were Type III (ToxoDB PCR-RFLP genotype #2), and TgSwanUs3 was a new genotype designated here as ToxoDB PCR-RFLP genotype #216. Pathogenicity of oocysts derived from these three strains was determined in Swiss Webster (SW) outbred mice. All mice infected with oocysts and tachyzoites of the atypical isolate (TgSwanUs3) died of acute toxoplasmosis, irrespective of the dose. Oocysts of the remaining two isolates were less pathogenic but differed from each other; 10 oocysts of the TgSwanUs1 killed all inoculated mice whereas 1 million oocysts of the TgSwanUs2 were needed to kill all infected mice. Isolation of T. gondii from feral swan indicates that the local waters were contaminated by T. gondii oocysts, and that mouse T. gondii virulent strains are circulating in wildlife. Mute swan is a new host record for T. gondii.