Pasteurella multocida infections in mice with reference to haemorrhagic septicaemia in cattle and buffalo.

Haemorrhagic septicaemia (HS) is an infectious disease of cattle and buffalo caused by particular serotypes of Pasteurella multocida and is one of the most economically important livestock diseases in South-East Asia. While HS has been recognized for many years, very little is understood about the disease, primarily because of the expense of cattle and a lack of suitable animal models. The suitability of using mice to study HS was assessed using parameters such as the critical pathogenic dose, kinetics of infection, pathology of disease and resistance to reinfection. Pasteurella multocida M1404, the type strain for Carter group B, the serotype responsible for Asian HS, was injected intraperitoneally into BALB/c mice. As few as 20 colony forming units produced an overwhelming septicaemia in mice in less than 30 h. The kinetics of infection demonstrated a very rapid in vivo multiplication rate. There was no evidence of inhibition of bacterial cell growth by natural host defence mechanisms, even with the very small inocula used. The gross pathology of the disease in mice was characterized by splenomegaly, lymphadenopathy and petechial haemorrhages similar to that observed in cattle and buffalo with HS. Mice were found to develop a short-lived resistance to reinfection following a primary infection which had been successfully treated with antibiotics. The mouse would seem to provide an ideal tool by which to study HS, but warrant further studies in order to be able to critically assess it as a model for this economically important disease.