Attenuated Phenotype of a Recent House Finch-Associated Mycoplasma gallisepticum Isolate in Domestic Poultry

Abstract

Mycoplasma gallisepticum, known primarily as a respiratory pathogen of domestic poultry, has emerged since 1994 as a significant pathogen of the house finch (Haemorhousmexicanus) causing severe conjunctivitis and mortality. House finch-associated M. gallisepticum (HFMG) spread rapidly and increased in virulence for the finch host in the eastern United States. In the current study, we assessed virulence in domestic poultry with two temporally distant, and yet geographically consistent, HFMG isolates which differ in virulence for house finches-Virginia 1994 (VA1994), the index isolate of the epidemic, and Virginia 2013 (VA2013), a recent isolate of increased house finch virulence. Here we report a significant difference between VA1994 and VA2013 in their levels of virulence for chickens; notably, this difference correlated inversely to the difference in their levels of virulence for house finches. VA1994, while moderately virulent in house finches, displayed significant virulence in the chicken respiratory tract. VA2013, while highly virulent in the house finch, was significantly attenuated in chickens relative to VA1994, displaying less-severe pathological lesions in, and reduced bacterial recovery from, the respiratory tract. Overall, these data indicate that a recent isolate of HFMG is greatly attenuated in the chicken host relative to the index isolate, notably demonstrating a virulence phenotype in chickens inversely related to that in the finch host.

Keywords: Mycoplasma gallisepticum; chicken; house finch; pathology; virulence.

FIG 1

Lesion scores from (A) tracheas or (B) lungs of M. gallisepticum-infected or medium control chickens at 14 dpi. n = 20 total animals per group (n = 10 per group per experiment). Error bars indicate standard errors of the means (SEM), and asterisks (*) and brackets indicate groups significantly different (P < 0.05) in pairwise multiple comparisons.

FIG 2

Tracheal thickness of M. gallisepticum-infected or medium control chickens at 14 dpi. n = 20 total animals per group (n = 10 per group per experiment). Error bars show SEM, and asterisks (*) and brackets indicate groups significantly different (P < 0.05) in pairwise multiple comparisons.

FIG 3

Average percentages of chickens in which M. gallisepticum was recovered from the (A) trachea or (B) lung. n = 20 total animals per group (n = 10 per group per experiment). Error bars indicate SEM in comparisons between two experiments.

FIG 4

Virulence of HFMG strains for house finches. (A) Mean total (left plus right) eye lesion scores in house finches directly inoculated with VA2013 (filled squares) and VA1995 (open circles), an isolate more virulent than VA1994 (18) (n = 15 total animals per group). (B) Mean cumulative eye lesion scores in sentinel house finches in contact with index birds directly inoculated with VA2013 (filled squares, 2014 experiment) and with VA1994 (open squares, 2010 experiment), starting at first appearance of lesions (n = 10 animals per group). Error bars indicate SEM.