Mode of vertical transmission of Salmonella enterica sub. enterica serovar Pullorum in chickens

The mode of vertical transmission was studied with local isolate of Salmonella pullorum in hens and cocks. Twenty (20) hens and five cocks were experimentally infected by the oral route with 2 × 10 (CFU) dose of S. pullorum organisms at 21 weeks of age in hens and 29 weeks in cocks and in control (20 hens and five cocks) no bacteria was given. The used methods were reisolation of S. pullorum from different organs, blood, eggs and newly hatched chicks, and detection of S. pullorum by PCR from testicular tissue at different time intervals of experimental period. Five birds (four hens and one cock) randomly selected and sacrificed on 6 h before inoculation (BI) and one, two, three and four weeks of post-infection (PI) from infected and control group. S. pullorum was reisolated from 50% eggs of experimentally 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 one to three weeks PI from testicular tissues. It was clear 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 different organs and produced 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.