Toxoplasmosis in sentinel chickens (Gallus domesticus) in New England farms: Seroconversion, distribution of tissue cysts in brain, heart, and skeletal muscle by bioassay in mice and cats.

Free-range chickens are a good indicator of soil contamination with oocysts because they feed from the ground and they are also an important source of infection for cats that in turn shed oocysts after eating tissues of intermediate hosts. Little is known of the epidemiology of toxoplasmosis in chickens. In the present study 90 Toxoplasma gondii seronegative, sentinel chickens were placed on three (30 each) swine farms in New England in November, 2003. Chickens were bled monthly and their sera were tested for T. gondii antibodies by the modified agglutination test (MAT, cut-off 1:25). Chickens that seroconverted were euthanized and their tissues were bioassayed in mice, cats, or both. Over the course of the experiment (7 months), 31 of 71 chickens seroconverted (MAT 1:100 or higher). Tissues of 26 seropositive chickens were bioassayed in both cats and mice; viable T. gondii was isolated, by bioassay in mice, from hearts (whole) of all 26 chickens, brains (whole) of 3 chickens and leg muscles (25 g) of 11 chickens; 21 of 26 cats fed 250 g of muscle from seropositive chickens excreted T. gondii oocysts. Results indicated that the density of T. gondii in poultry muscle is low but heart is the tissue of choice for isolation of viable parasites.