Immune response of a heat killed Brucella abortus vaccine in guinea pig

Background: Brucellosis is an endemic disease in Bangladesh which has economic impacts attributable to humans and animals. To control bovine brucellosis two types of vaccines are available- vaccine S19 and vaccine SRB51 but they have some adverse effects. On the other hand the heat killed vaccine produces less immunity but no adverse effect. Vaccination against brucellosis in Bangladesh has not yet been initiated and not recommended in subsistence management systems due to very low level of prevalence. But in commercial management systems the prevalence is reported to be higher and vaccination may be initiated. Before importing live vaccine which have some adverse effects locally prepared killed vaccine can be tested for its immune response. Hence this study was undertaken to evaluate the immune response of heat killed vaccine prepared from local isolate in guinea pig. Methods: Brucella abortus recently isolated from aborted fetal membranes (unpublished data) was used for vaccine production. Pour plate technique was used by tenfold serial dilution of the isolate to count cfu (colony forming unit)/ml of Brucella abortus for dose calculation of heat killed vaccine. Bacterial pellet was prepared by centrifugation of 200ml of the cultured broth at 10,000 rpm for 10 mins. The bacterial pellet was mixed with required amount of PBS (phosphate buffer saline) to obtain 40×1010 cfu organisms in 2ml dose for guinea pig inoculation. Then heat killed vaccine was prepared by heating the organism at 80˚C for 90 minutes and the prepared vaccine was inoculated subcutaneously 2ml (4×1010cfu) in each of the guinea pig. The sera of guinea pigs were collected at 1st, 2nd, 4th, 6th and 9th week after inoculation to determine the reciprocal antibody (Ab) titre by Rose Bengal test (RBT) and to examine the rise of antibody level by Enzyme-Linked Immunosorbent Assay (ELISA). Results: The antibody level started to rise significantly (p<0.01) from the 2nd week (OD value 0.2287, Reciprocal Ab titre 1:120) and reached a peak level at 4th week (OD value 0.2842, Reciprocal Ab titre 1:800) and then started to decline significantly (p<0.01) from 6th week (OD value 0.1832, Reciprocal Ab titre 1:35) to 9th week (OD value 0.1015, Reciprocal Ab titre 0). Conclusions: Heat killed vaccine without adjuvant induces immune response in guinea pigs which persists for a maximum period of 6 weeks. A further study to investigate the immune response of killed vaccine with adjuvant is recommended.