Experimental Toxoplasmosis in Chickens

The chicken is a natural host of Toxoplasma gondii. The parasite has been reported from birds with paralytic or spastic symptoms (Hepding, 1939; Fankhauser, 1951) and has also appeared in epizootics among flocks in Norway (Ericksen and Harboe, 1953). Experimental infections in chickens have been studied by Levaditi and Schoen (1928) who found only young chicks susceptible, by Jacobs and Jones (1950) who studied parasitemias, and by Harboe and Erickson (1954). The latter authors were not able to duplicate, in their experimental birds, the symptoms found in the flock in which they discovered epidemic toxoplasmosis in spite of the fact that they used parasites isolated from a sick bird. According to Siim (1956) Dr. Biering-Sgrensen has found an acute spontaneous infection in hens in Denmark and has demonstrated toxoplasmas in the ovaries and in eggs of some birds. Gibson and Eyles (1957) reported finding infected chickens in an area neighboring the home of a case of human toxoplasmosis in Memphis, Tennessee. Especially in view of the widespread distribution of Toxoplasma, it is necessary to evaluate the potentialities for its spread among individuals of each host species and from one species of host to another. The importance of the demonstration of parasites in chickens and in hens' eggs requires evaluation as to how frequently such localization of Toxoplasma occurs. In addition, the flesh of the chicken, as a food for man, requires study as to the frequency with which it harbors toxoplasmas. Furthermore, the parasitemia is of interest in regard to the possibility of arthropod transmission. In addition to these motives for further investigation, base line studies on the chicken were desirable to see if it would be useful in chemotherapeutic trials. Incidental to such work, dye test titers have been obtained on chickens with experimental infections, with the view to evaluating the usefulness of serological tests in surveys of flocks. The studies to be reported here were performed in 2 Sections of this Laboratory. The results are combined to give a more complete picture of the findings.