Are Purple Finches () the Next Host for a Mycoplasmal Conjunctivitis Epidemic?

Abstract

Ever since 1994, when the bacterial pathogenjumped from poultry to wild birds, it has been assumed that the primary host species of this pathogen in wild North American birds was the house finch (), in which disease prevalence was higher than in any other bird species. Here we tested two hypotheses to explain a recent increase in disease prevalence in purple finches () around Ithaca, New York. Hypothesis 1 is that, asevolved and became more virulent, it has also become better adapted to other finches. If this is correct, early isolates ofshould cause less-severe eye lesions in purple finches than in house finches, while more-recent isolates should cause eye lesions of similar severity in the two species. Hypothesis 2 is that, as house finch abundance declined following theepidemic, purple finches around Ithaca increased in abundance relative to house finches and purple finches are thus more frequently exposed to-infected house finches. This would then lead to an increase inprevalence in purple finches. Following an experimental infection with an early and a more-recentisolate, eye lesions in purple finches were more severe than in house finches. This did not a support Hypothesis 1; similarly, an analysis of Project Feeder Watch data collected around Ithaca did not show differences in changes in purple and house finches' abundance since 2006, a result which does not support Hypothesis 2. We conclude that purple finch populations will, unlike those of house finches, not suffer a severe decline because of aepidemic.