Abstract
A pathogenesis study was undertaken with local isolate of Salmonella Pullorum in poultry birds of different age groups (pullets, chicks, hens and cock). S. Pullorum (Isolate No. 5) was reconfirmed by conventional methods as well as by PCR. The experiments performed were necropsy and histopathology, reisolation of bacteria, staining and biochemical test, rapid plate agglutination test (RPA), ELISA and PCR. The percentage and severity of clinical signs, gross and hisopathology, RPA, ELISA and reisolation rate were variable in different age groups of birds at different time intervals in all experiments. The cumulative highest recorded gross lesion was button-like ulcer in the ceca (80%) and the lowest was white nodules in lungs (1.25%) in pullets. S. Pullorum was reisolated from crop, liver, lung, heart, spleen, bile, duodenum, ceca and blood from different age groups of birds in all experiments. The highest titre was found at day 14 of inoculation in all infected groups in pullets. The highest histological lesion was focal necrosis with infiltration of inflammatory cells in 80% spleen and the lowest histological lesion was nodule formation in 16% liver of chicks. Twenty percent chicks showed RPA at 72 hrs postinfection and 100% chicks showed positive agglutination from 2 wks PI to 4 wks PI. The antibody titre increased gradually and the highest titer was 7275.7175087.24 at 4 wks PI in chicks. All liver and lung samples showed 284 bp band from 48 hrs PI to 2 wks PI by PCR in chicks. The highest mean CFU/ml of Salmonella Pullorum from blood was 13.55 x 103 at 1 wk PI and the lowest was 13 x 102 at 4 wks PI in hens. The highest gross lesion was 93.75% spleen swollen and congested; and the lowest lesion was 56.25% necrotic foci in the liver in hens. Microscopically, the liver showed (81.25%) congestion; hepatitis, infiltration of inflammatory cells, and nodule formation with the infiltration of heterophils, lymphocytes, macrophages and plasma cells in (12.5%) liver in hens. In rapid plate agglutination test, the positive result was found from 1 wk PI with the sera of infected hens. The overall seropositive was 80% in hens. The antibody titres of infection group increased significantly (p<0.01) in hens and cocks. S. Pullorum was reisolated from ovary, ovarian follicle, oviduct, uterus and vagina of female reproductive organs after experimental infection. S. Pullorum was reisolated from 50% eggs of experimentally infected hens. The mean egg production reduced significantly (p<0.01 and p<0.05) in infected hens. Twenty percent hatchability was lost due to experimental S. Pullorum infection. Piped chicks were 20% and embryo mortality was 15%. S. Pullorum was isolated from 66.66% chicks. Seventy five percent testes were positive for S. Pullorum by culture and biochemical test. S. Pullorum was detected by PCR at 1 wk to 3 wks PI from testicular tissues. From the above experiments, it was cleared that after oral route of infection with infective dose of S. Pullorum, the bacteria invaded digestive epithelia and ultimately entered into blood inducing bacteremia and ultimately infected liver, lung, spleen, kidney, different parts of reproductive tracts of hens and testes of male and other tissues producing pathological lesions. It was also confirmed that the bacteria invaded ovary and egg follicles, and this infection persisted in ovary and egg follicles and transmitted into laid eggs then to hatched chicks.