Comparison of the clinical signs, pathological and immuohistochemical findings in visceral organs of chickens experimentally infected with Salmonella Zega through three routes

Salmonella Zega isolated from natural outbreaks that were characterized by high mortality in poultry farms in three Southwestern States of Nigeria was used to inoculate two week-old chicks through different routes in order to determine and compare the clinical signs, pathological and immunohistochemical changes in each route of infection. The birds were divided into 4 groups of 25 each as groups A (orally inoculated), B (intraperitoneally inoculated), C (inoculated per cloaca) and D (uninoculated control). All the birds were inoculated with 0.2 ml of 1 × 10^{8} cfu of the bacteria. Clinical signs were observed and recorded according to the route of infection, and with the days post-infection from day 0 till day 10 post-infection. Two birds from each group were sacrificed every 24 h and examined for gross lesions, which were described and scored according to the route of infection and days post-infection. Samples of visceral organs were collected for bacteriology, histopathology and immunohistochemistry. Clinical signs in chicks infected orally and intraperitoneally were weakness, anoraexia lethargy, somnolescence, yellowish diarrhoea observed from 4 days till day 10 post infections. Mild sign of weakness was observed in chickes infected per cloaca, from day 3 to 7. The gross lesions were congestion, oedema and enlargement and necrosis in visceral organs from day 4 to 10 post infection in orally and intraperitoneally infected chicks, but mild vascular changes were observed in chicks infected per cloaca, except in the caecum were lesions of necrosis and infiltration of inflammatory cells were moderate to severe. Microscopic lesions were necrosis of host cells and infiltration by lymphocytes, heterophils and macrophages in multiple organs observed from day 4 to 10 post infection in orally and intraperitoneally infected chicks. Immunoreactions were observed in all the visceral organs examined. Clinical signs, pathological and immunohistochemical findings were mild in chicks infected per cloaca, except caecal lesions. Salmonella Zega isolated from an outbreak in poultry farms in Abeokuta, Nigeria was highly pathogenic in chicken and produced similar findings in oral and intraperitoneal infections; while per cloacal infection showed a localized infection of the caecum.