Cutaneous Lesions in the Gular Region Caused by Feather Follicle Infestation with Harpirhynchidae sp. Mites in Great Crested Flycatchers (Myiarchus crinitus) in New York, USA 2016-23.

Great Crested Flycatchers (Myiarchus crinitus), migratory passerines with a breeding range throughout the northeastern, midwestern, and southern US, are banded annually at the Braddock Bay Bird Observatory located on the southern shore of Lake Ontario, New York, USA. In 2016, a Great Crested Flycatcher was observed with distinct lesions in the gular and ventral neck region, which prompted evaluation for similar lesions in subsequently trapped flycatchers and other passerine species. From 2016 to 2023, 62/102 banded Great Crested Flycatchers had their gular region examined, and seven were found to have lesions (11.3% incidence). Similar lesions were not found in any other species. Lesions were localized to the gular region and included extensive feather loss with thickened, corrugated, pale-yellow skin. Grossly visible 1- to 2-mm-diameter, raised, white-to-yellow foci throughout the affected region corresponded microscopically to feather follicles that were massively dilated with mites. Morphologic analysis of mites obtained from skin scrapes revealed that this mite species belongs to the family Harpirhynchidae. Mites in this family have restricted avian host ranges and cause varying clinical presentations in passerines, though many species remain unidentified. PCR efforts were unsuccessful in yielding a species-level identification. Further monitoring of Great Crested Flycatchers and other avian species is warranted, as the fitness implications of this ectoparasitism at the individual and population levels are not known.

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

Ever since 1994, when the bacterial pathogen Mycoplasma gallisepticum jumped 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 (Haemorhous mexicanus), 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 (Haemorhous purpureus) around Ithaca, New York. Hypothesis 1 is that, as M. gallisepticum evolved and became more virulent, it has also become better adapted to other finches. If this is correct, early isolates of M. gallisepticum should 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 the M. gallisepticum epidemic, purple finches around Ithaca increased in abundance relative to house finches and purple finches are thus more frequently exposed to M. gallisepticum-infected house finches. This would then lead to an increase in M. gallisepticum prevalence in purple finches. Following an experimental infection with an early and a more-recent M. gallisepticum isolate, 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 a M. gallisepticum epidemic.

¿Son los pinzones purpúreos (Haemorhous purpureus) los próximos huéspedes de una epidemia de conjuntivitis por micoplasma? Desde el año 1994, cuando el patógeno bacteriano Mycoplasma gallisepticum saltó de las aves comerciales a las aves silvestres, se ha supuesto que la principal especie huésped de este patógeno en las aves silvestres de América del Norte era el pinzón mexicano (Haemorhous mexicanus), en el que la prevalencia de la enfermedad era mayor que en cualquier otra especie aviar. En este estudio se analizaron dos hipótesis para explicar un aumento reciente en la prevalencia de la enfermedad en los pinzones purpúreos (Haemorhous purpureus) alrededor de Ithaca, en Nueva York. La hipótesis 1 es que, a medida que M. gallisepticum evolucionó y se volvió más virulento, también se adaptó mejor a otros pinzones. Si esto es correcto, los aislamientos tempranos de M. gallisepticum deberían causar lesiones oculares menos graves en los pinzones purpúreos que en los pinzones mexicanos, mientras que los aislamientos más recientes deberían causar lesiones oculares de gravedad similar en las dos especies. La hipótesis 2 es que, a medida que la abundancia de pinzones mexicanos disminuyó después de la epidemia de M. gallisepticum, los pinzones purpúreos alrededor de Ithaca aumentaron en abundancia en relación con los pinzones mexicanos y, por lo tanto, los pinzones morados están expuestos con mayor frecuencia a los pinzones caseros infectados con M. gallisepticum. Esto conduciría a un aumento de la prevalencia de M. gallisepticum en los pinzones purpúreos. Después de una infección experimental con un aislamiento temprano y uno más reciente de M. gallisepticum, las lesiones oculares en los pinzones purpúreos fueron más graves que en los pinzones mexicanos. Esto no apoyó la Hipótesis 1; de manera similar, un análisis de los datos del Proyecto Feeder Watch recopilados alrededor de Ithaca no mostró diferencias en los cambios de la abundancia de pinzones purpúreos y mexicanos desde 2006, un resultado que no respalda la Hipótesis 2. Se concluye que las poblaciones de pinzones purpúreos, a diferencia de las de los pinzones mexicanos, no sufrieron un declive severo a causa de una epidemia de M. gallisepticum.

CHANGES IN TISSUE TROPISM OF MYCOPLASMA GALLISEPTICUM FOLLOWING HOST JUMP.

Mycoplasma gallisepticum, a pathogen of worldwide economic importance in poultry, is recovered in chickens, especially from the respiratory tract. Some strains, however, are specialized to other tissues and because it jumps from poultry to wild birds, the new strains also cause severe conjunctivitis in new hosts. Nevertheless, most studies of M. gallisepticum in wild birds use choanal swabs or combine choanal and conjunctival swabs to quantify bacterial load. Because the clinical signs associated with M. gallisepticum infection differ markedly between poultry and House Finches (Haemorhous mexicanus), we compared the bacterial load in choanal and conjunctival samples following experimental inoculation of House Finches with M. gallisepticum isolates originating from poultry or from House Finches. This allowed us to test two hypotheses: M. gallisepticum changed tissue tropism, or M. gallisepticum simply expanded its within-host niche. By comparing bacterial loads from choanal and conjunctival swabs in birds inoculated with one of a suite of M. gallisepticum isolates, we found support for hypothesis 2. The choanal loads in House Finches did not differ between isolates, while the conjunctival loads of birds inoculated with poultry isolates were lower than in birds inoculated with House Finch isolates. When measuring the bacterial load of M. gallisepticum in birds, it is important to sample and analyze separately choanal and conjunctival swabs, as quantifying bacterial loads in pooled samples may not provide reliable information on differences in virulence.