Dynamics of conjunctivitis and Mycoplasma gallisepticum infections in house finches

Conjunctivitis, an infectious disease caused by Mycoplasma gallisepticum (M G), has produced a significant decline in eastern House Finches (Carpodacus Mexicanus) of North America. In this paper, we present findings from two c omplementary studies designed to clarify annual and seasonal trends of MG i nfections in House Finches from the northeastern United States. The first w as a field study of House Finches common to urban and residential habitat f rom Mercer County, New Jersey. We documented conjunctivitis in 11% (188/1,6 51) of the birds examined. Conjunctivitis prevalence in House Finches range d from 0 to 43% per month, and exhibited marked seasonal fluctuation (eleva tions during fail and winter months and lower disease prevalence during the breeding season). There was excellent intermethod agreement on disease pre valence when measured by either presence of physical signs (conjunctivitis) or MG infection (kappa = 0.75). During the peak of the breeding season (Ap ril through June), conjunctivitis was present in a greater proportion of ma les lacking a cloacal protuberance than males with a cloacal protuberance ( P < 0.01), but was similar between breeding and nonbreeding females. The se cond study, a volunteer survey, revealed the proportion of northeastern U.S . monitoring sires with at least one diseased House Finch each month ranged from a peak of 59% (August 1995) to a minimum of 12% (July 1999). Subseque nt to the epidemic peak of disease in 1995, a series of recurring cycles oc curred, with elevations in those proportions noted in late fall and winter and minima during the breeding season. Mycoplasmal conjunctivitis now appea rs endemic among House Finches of that region and demonstrates dynamics con sistent with annual Variation in host density.