Abstract
Mice and rats, free from Pasteurellaceae, were exposed to Haemophilus spp. (V-factor dependent pasteurellaceae) by housing in proximity to infected rats or guineapigs, and monitored by culture and enzyme-linked immunosorbent assay (ELISA) for cross infection. A minority of mice became infected when exposed to Haemophilus-infected rats but none when exposed to guineapigs. Rats were readily infected when exposed to Haemophilus-infected guineapigs or rats. Although Pasteurellaceae infections are commonly considered as host specific, our data show that Haemophilus spp. can cross the species barrier from rats to mice and from guineapigs to rats.