Experimental Infection of Domestic Chickens (Gallus gallus) with Genetically Distinct Strains of Toxoplasma gondii

Abstract

Infection by Toxoplasma gondii is one of the most widespread zoonoses in the world, and the microorganism is probably the most frequent protozoa affecting human and animal populations, including birds. Due to the fact that toxoplasmosis clinical and pathological behavior in birds has not been fully elucidated, the aim of this experimental study was to assess the variation in clinical and pathological toxoplasmosis pattern in birds inoculated with different strains of T. gondii. Six groups of 36 days old Cobb hens were divided as follows: G2, submitted to oral inoculation with 100 tissue cysts of strain ME49 (genotype II); G3, submitted to oral inoculation with 1,000 oocysts of M7741 strain (genotype III) and G1, the uninoculated control. Animals were evaluated daily for the development of clinical signs. Cloacal temperature was checked daily in the first week. Animals were weighed weekly up to 63 days post-infection (dpi) and blood samples were also drawn weekly for the determination of anti-Toxoplasma antibodies using of the modified agglutination test (MAT). At 63 days after infection, birds were killed by cervical displacement. Two G2 hens showed neurological changes in the course of the experiment. The most frequent sign of Toxoplasma infection was diarrhea, mainly in the group that received oocysts (G3). The weight of the birds increased in all groups until the end of the experiment, with no significant differences between the groups. Weekly weight gain was around 300 to 500 grams in the first five weeks of observation. Although there were no significant differences between the groups from the sixth week on, G2 and G3 birds had the smallest weight gains, and G3 birds even lost body mass. Serum antibodies titers increased in G2 and G3 birds from the 14 dpi on. From the 28 dpi on, mean G3 titer was significantly greater than that of G2. Both groups showed a peak in antibodies at 35 dpi, with a continuous decrease until 63 dpi. In G2, parasites were isolated from pooled brains and hearts of all six birds. Toxoplasma was also isolated from four G3 birds.