A cross-protection experiment in pigs vaccinated with Haemophilus parasuisserovars 2 and 5 bacterins, and evaluation of a bivalent vaccine under laboratory and field conditions

Cross-protection between Haemophilus parasuis serovars 2 and 5 was examined in pigs using a bacterin based vaccine, and subsequently the safety and ef ficacy of a bivalent vaccine were evaluated. Upon intratracheal challenge o f a serovar 2 or 5 strain, pigs immunized with a monovalent vaccine were pr otected against challenge with a homologous serovar strain, but not with a heterologous serovar strain. Immunization with a bivalent vaccine containin g both serovars 2 and 5 bacterins conferred protection in pigs against leth al challenge with each of the serovar strains. A total of 86 pigs from two SPF herds were injected with the bivalent vaccine intramuscularly twice at a four-week interval. No adverse reactions following the vaccination were o bserved. On day 7 after the second vaccination, vaccinated and non-vaccinat ed control pigs from herd A were transferred to herd B, where Glasser's dis ease had broken out. Pigs in the control group developed clinical signs of the disease, and 6 of 8 (75%) pigs died until slaughter, in contrast with o nly 4 of 46 (9%) pigs in the vaccinated group. In herd C, where there was n o outbreak of Glasser' s disease, complement fixation antibody titer was ra ised only in the vaccinated group. A challenge experiment on days 20 and 79 after the second vaccination showed that only the vaccinated pigs were pro tected. From these findings, the safety and efficacy of the bivalent vaccin e were confirmed under laboratory and field conditions.