Comparative infectiousness of three passerine bird species after experimental inoculation with Mycoplasma gallisepticum.

Mycoplasma gallisepticum has been isolated from various species of free-living birds, and we therefore tested the hypothesis that bird species other than the main host, the house finch (Carpodacus mexicanus), could play a role in the epidemiology of the infection. We compared the disease course in the house finch, American goldfinch (Carduelis tristis) and house sparrow (Passer domesticus) after inoculation into the conjunctival sac with M. gallisepticum, and also the degree to which the three species were infectious to other naive house finches. Severity of clinical signs was least in house sparrows, intermediate in American goldfinch and the highest in house finch. House sparrows were only mildly infectious to naive house finches for a short time, whereas American goldfinches remained infectious for up to 49 days post inoculation, although by then there were no physical signs of disease. We conclude that since American goldfinches can be infectious without showing any conjunctivitis, and since they often make long-distance movements, they might play an as yet unsuspected but important role in M. gallisepticum dynamics in house finches.