Abstract

Anthrax is a fatal disease that strike almost all warm-blooded animals and caused by a gram-positive bacterium Bacillus anthracis. The disease is common in farm ruminants, causes regular mortality. The disease is commonly prevented by using vaccine. The Sterne strain F-34 vaccine has been using in ruminants for more than five decades in Bangladesh but there is little work describing the efficacy of the vaccine. This study was aimed to evaluate efficacy of F-34 Sterne strain Anthrax vaccine in mice model. Anthrax vaccine vials containing F-34 Stern strain was obtained from Central Disease Investigation Laboratory (CDIL), Dhaka and used in immunization trial. A virulent field isolate was grown on PLET agar medium was used in protective efficacy trails. Group C (n=05) and D (n=05) female mice were immunized subcutaneously with 0.1ml of anthrax vaccine. Group A (n=05) and B (n=05) mice were served as non-immunized control. Following 6 months of immunization the Group B (n=05) and Group D (n=05) mice were challenged intraperitoneally with 2x105 colony forming unit (CFU) of virulent field isolate of B. anthracis. Polymerase chain reaction (PCR) technique was carried out to detect pX01 (210bp) and pX02 gene (1035bp) specific PA and Cap genes of B. anthracis from the challenged mice and field isolates. The vaccine efficacy was evaluated in terms of anti-anthrax IgG antibodies responses in ELISA (A450±SD) and protection to challenge in vivo. The early anti-anthrax IgG antibody response was detected in Group C and D mice (0.501±0.167) following week 2 of immunization and reached its peak in study week 4 (1.237±0.257). A steadily higher level of anti-anthrax IgG antibody response was detected until the end of study (06 months, 1.269±0.217, group average±SD). In vivo challenge to vaccinated mice with the virulent B. anthracis found to confer solid protection up to six months of immunization. Non-immunized mice challenged with field isolate of B. anthracis were died within 18-24hours of infection, showed characteristics lesions of anthrax including black berry jam spleen, wide spread congestion and hemorrhages and bleeding through natural opening after death. B. anthracis bacteria was re-isolated from the visceral organs of infected mice. This study provide evidence that the Sterne strain F-34 Anthrax vaccine is protective in mice model and generated higher level of anti-anthrax IgG antibody response that was detected until 06 months of immunization. It needs to study whether the vaccine response persisted higher and longer in mice model and replicate the experiment in ruminants.

Key words: B. anthracis, vaccine efficacy, immunity, Sterne strain, experimental mice