Clinical, serological and histopathological signs of toxoplasmosis in broiler chickens (Gallus domesticus) after experimental infection

Abstract

To identify the features of experimental toxoplasmosis in broiler chickens (Gallus domesticus), a total of 48 birds aged 25 days were randomly assigned to one of four groups of 12 birds each. Tachyzoites of Toxoplasma gondii were injected intraperitoneally at doses of 5 × 10⁵ (group A), 1 × 10⁶ (group B) and 1.5 × 10⁶ (group C), and chickens in group D were treated with an injection of saline only (control). Before and after experimental infection, serum samples from all chickens were tested for antibodies against T. gondii with the Sabin–Feldman reaction. After infection, the clinical signs in all the chickens were recorded daily, and blood smears were prepared to determine parasitemia. Paraffin-embedded tissue sections were used for semi-nested polymerase chain reaction (PCR) to detect the T. gondii B1 gene. Half of the chickens in each group were killed 25 days and half were killed 35 days after infection. All serum samples from chickens in groups A, B and C contained titers of T. gondii antibodies. However, there were no clinical signs suggesting toxoplasmosis. On day 15, the protozoan was observed in blood smears in groups A, B, and C. Analysis by PCR was negative. Microscopic lesions were observed in the brain, heart, liver, pancreas, kidney, spleen, skeletal muscle, proventriculus and lungs, but not in the eyes. Although chickens in group A were exposed to the lowest dose of T. gondii tachyzoites, lesions in this group were relatively more severe than those observed in groups B and C, which were exposed to higher doses of tachyzoites. Group B showed acute signs of toxoplasmosis with few microscopic lesions, whereas group C showed no lesions. Although no stages of the parasite were found in histopathological sections of skeletal muscle, the potential risks of infected chicken meat for public health cannot be disregarded.