Date of Award
Doctor of Philosophy
Comparative and Experimental Medicine
John Schaefer, Chunlie Su, Marcy Souza
Toxoplasma gondii is an important zoonotic protozoan parasite that infects all warm-blooded animals including humans and birds. Wild birds are an intermediate host of the parasite and an important prey item of the Felidae family which are the only animal capable of producing T. gondii oocysts. We investigated T. gondii prevalence in various wild bird species to better understand the parasite epidemiology and ecology. We tested 27 wild bird species for T. gondii infection using modified agglutination test (MAT) or polymerase chain reaction (PCR) or mice bioassay or combination tests. We detected a T. gondii prevalence of 27.4% (308/1124) in various wild bird species using different methods. We had a prevalence of 78.3% (18/23) in Charadriiforms, 48.4% (178/368) in Anseriformes, 20.5% (78/381) in Galliformes, 44.8% in Falconiformes (13/29), 75% in Strigiformes (15/20) and 3.8% in Ciconiiformes (4/106) using MAT. We molecularly examined the brains of 197 Columbiformes and only two birds (1%) were T. gondii sequence positive. We successfully isolated viable T. gondii tachyzoites from one red-shouldered hawk (Buteo lineatus) and genotyped it using PCR-RFLP of ten genetic markers (TgHawkFL1, ToxoDB PCR-RFLP genotype #28). We also experimentally infected twenty-five, four-weeks old, female domestic turkeys (Meleagris gallapavo) intraperitoneally with Toxoplasma gondii tachyzoites of two different stains and doses (105 and 108 tachyzoites/ml PBS) to investigate the seroconversion, feed conversion rate (FCR), weight gain pattern and parasite tissue tropism in relation to the parasite dose and virulence. We recorded an increase in FCR and a decrease in bird weight gain and survival rate with increase of T. gondii dose and virulence. The group infected with 108 tachyzoites/ml PBS of the virulent T. gondii strain seroconverted earlier than the other groups and had a significantly higher antibody titers as tested by MAT. Gross and histological findings were also discussed. We documented the presence of T. gondii infection in various wild birds which represents an important host for the maintenance of T. gondii life cycle, and we investigated the progress of the infection in experimentally infected turkeys which support our understanding of the parasite life cycle and pathogenesis.
Ammar, Sawsan, "Transmission and ecology of Toxoplasma gondii in various wild bird species. " PhD diss., University of Tennessee, 2019.