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House Finch Eye Disease


The following article is taken from the The Great Backyeard Bird Count website.


What does conjunctivitis look like?


Infected birds have red, swollen, watery, or crusty eyes; in extreme cases the eyes become swollen shut or crusted over, and the birds become essentially blind. If the infected birds die, it is usually not directly from the conjunctivitis, but rather from starvation, exposure, or predation as a result of not being able to see. Some infected birds do recover.


What causes the conjunctivitis?


Although infected birds have swollen eyes, the disease is primarily a respiratory infection. It is caused by a unique strain of the bacterium Mycoplasma gallisepticum, which is a common pathogen in domestic turkeys and chickens. The infection poses no known health threat to humans and had not been reported in songbirds prior to this outbreak.


Where did the disease start?


Conjunctivitis was first noticed in house finches during the winter of 1993-94 in Virginia and Maryland. The disease later spread to states along the East Coast, and has now been reported throughout most of eastern North America, as far north as Quebec, Canada, and as far south as Florida.


Have other bird species been diagnosed with mycoplasmal


So far, the disease is most prominent in the eastern population of house finches. However, a few reports of the disease have been confirmed in American goldfinches, purple finches, evening grosbeaks, and pine grosbeaks, all members of the family Fringillidae.


Why might eastern house finches have been the earliest victims
of the disease?


House finches are not native to eastern North America. Until the 1940s, house finches were found only in western North America. Some birds were released to the wild in the East after pet stores stopped illegal sales of "Hollywood Finches," as they were commonly known to the pet bird trade. The released birds successfully bred in the wild and spread rapidly throughout eastern North America. Because today’s eastern house finch populations originated entirely from a small number of released birds, they are
highly inbred, exhibit low genetic diversity and may therefore be more susceptible to disease than other bird species native to the East.


Why has the disease spread so rapidly among house finches?


The house finch population is large, and the birds tend to move together in highly mobile foraging flocks. Therefore, diseased individuals are constantly entering new areas, increasing the chance of infecting other birds in that area. Also, some infected birds do not die from the disease, which increases the probability of its transmission to other individuals. Lastly, current evidence suggests that infected birds do not acquire immunity to future


Do bird feeders encourage the spread of conjunctivitis?


Whenever birds are concentrated in a small area, the risk of a disease spreading within that population increases. Even so, feeding birds may not necessarily increase the rate of disease spread, and should not have a net negative impact on the house finch population. House Finch Disease Survey data tell us that the disease has decreased from epidemic proportions and is now restricted to a smaller percentage of the population. We estimate that 5% to 10% of the eastern house finch population has this
disease and that the dramatic spread that occurred a few years ago has leveled out. This means that it is still an important and harmful disease, but that house finch populations are not currently at extreme risk of widespread population declines. The best preventive measure is to clean your feeders on a regular basis even when there are no signs of disease.



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