Meeting Abstract
In 1994, an endemic bacterial poultry pathogen, Mycoplasma gallisepticum, underwent a dramatic shift of host range into house finches (Haemorhous mexicanus). The result was a devastating epizootic that killed tens of millions of house finches. The factors that enabled the bacteria to jump to the very distantly related and novel house finch host remain unclear. Transmission of M. gallisepticum requires exposure to moisture droplets with M. gallisepticum and thus a shared environment. Under most circumstances, house finches would not be in such close proximity to poultry. Here we tested whether lack of contact between house finches and poultry was a limiting factor in this host switch. We experimentally infected house finches (N=15) with a high dose of a known virulent chicken strain of M. gallisepticum (Rlow) through an ocular inoculation and then monitored infection development over several weeks. While Rlow colonized and persisted in the house finch mucosal epithelium of the upper respiratory tract (i.e., trachea), it did not cause clinical symptoms; the only exception was one bird that exhibited mild conjunctivitis after 7 days. Given that exposure to Rlow led to colonization of the respiratory epithelium but not infection levels or clinical disease symptoms comparable to what was seen at the start of the epizootic, our results suggest that the emergence of M. gallisepticum in the novel house finch population was unlikely to have been limited by host access. Rather, genetic changes in the bacteria would have been necessary to initiate this epizootic.
