In this study twenty four isolates of Pasteurella multocida were collected from field out breaks of Haemorrhagic septicaemia (H.S) in cattle and buffalo from various regions of the country from 1991-2001. The isolates were subjected to detailed cultural, biochemical and pathogenicity test in albino mice. The stereotyping was done by indirect haemagglutination test for determination of their capsular antigen. Serologically all the isolates were classified on the basis of their capsular antigen as Carter Type B. All the twenty four isolates produced oxidase, catalase and indole and reduced nitrate. They did not produce urease. All the isolates fermented fructose, glucose, sucrose and sorbitol and mannitol with the production of acid whereas dulcitol, lactose, silicon were found negative. Variable results were found among isolates on the fermentation of arabinose and maltose. It was concluded that all the isolates were serologically and immunologically homologous to H.S. vaccine strain produced in the institute.

Two studies were performed in order to test the relative ability of different strains of porcine reproductive and respiratory syndrome virus (PRRSV) to replicate and cross the placental barrier in pregnant gilts. Study 1 comprised 6 nonvaccinated gilts. Study 2 comprised 8 nonvaccinated gilts and 12 gilts that were vaccinated twice before conception. On, or about, gestation day 90 all gilts were simultaneously exposed to 20 field strains of PRRSV (all strains were distinguishable by restriction fragment length polymorphism (RFLP) patterns). Gilts of study 1 were euthanized on day 7 postpartum. Gilts of study 2 were euthanized on, or about, gestation day 111. All gilts, pigs, and fetuses were tested for the presence and type of strain of PRRSV. Of 128 samples shown to contain PRRSV, 118 contained a single strain, 4 contained 2 strains, and 2 contained a strain or strains for which the RFLP pattern was undecipherable. Only 8 of the 20 strains were isolated from nonvaccinated gilts and their litters. And only 2 of the 20 strains (notably 2 of the same strains isolated from nonvaccinated gilts and their litters), were isolated from vaccinated gilts and their litters. Moreover, 1 of the 2 strains accounted for most (31 of 37; 84%) of the isolates from the vaccinated group. Collectively these results indicate that strains differ in their ability to replicate in pregnant gilts and cross the placental barrier. And they suggest that maternal immunity, although sometimes insufficient to prevent transplacental infection, can exert additional selective pressure.