Pathogenicity of Haemophilus pleuropneumoniae for laboratory animals and possible role of its hemolysin for production of pleuropneumonia.

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Abstract
Pathogenicity of Haemophilus pleuropneumoniae (Hpn) serotype 2, strain SH-15 was investigated using five different animal species including piglet. Guinea pigs, cotton rats, and Afghan pikas were found to be sensitive to the bacterium depending on the route of inoculation, whereas mice were insensitive via any route of inoculation. The death occurred within two days postinoculation, and gross hemorrhagic lung lesions similar to those induced in piglets were produced only in all the dead animals. The inoculated organism was recovered constantly from all the lung lesions and heart blood samples, and rarely from the upper respiratory tract of the dead animals except for piglets. Various Hpn-hemolysin preparations killed piglets within 12 hr after intratracheal administration, however, most of the guinea pigs given any of the preparations survived for two days post-administration. Severe hemorrhagic lung lesions similar to those induced by the live organism were produced in these piglets and guinea pigs. The ability of crude hemolysin preparation to produce the lung lesions was not abolished after heating at 121°C for 2 hr, and the heat-stable hemolysin seemed to be a virulent factor of Hpn. The present results suggested that guinea pigs were useful for the pathogenicity test of Hpn instead of piglets.