During the winter of 1993-94, house finches (Carpodacus mexicanus ) with severe conjunctivitis (swollen, crusty eyes) and impaired vision were reported at bird feeders in Virginia and Maryland. Birds with these symptoms were diagnosed as infected by the microorganism Mycoplasma gallisepticum (MG). Reports of infected house finches have become more frequent and widespread. The disease has been documented in Ohio and states east of the Mississippi River as well as in some states west of the Mississippi River. Finches with symptoms of MG infections were observed in Ohio in the fall of 1994; reports to the Division of Wildlife, nature centers, wildlife rehabilitators, and Cornell Laboratory of Ornithology (organizer of Project FeederWatch) have increased. MG has been cultured from several goldfinches with swollen eyes. Prior to infecting house finches, this bacterium was only known to attack poultry.
This disease has been mostly confined to the eastern populations of house finches, although it has begun to show up in the northwestern U.S. This songbird is native to the western states, mostly west of the Rocky Mountains, and this mountain range still serves as a barrier between eastern and western populations. In 1940, a small number of house finches were liberated in New York City, and they rapidly spread throughout eastern North America. House finches were first detected in Ohio in 1964, and had colonized the entire state by the mid-1980s. They are common throughout Ohio today.
Infected birds typically show various degrees of crusty thickened growths around the eyes. In extreme cases, these growths can completely cover the eye. Eyes are often reddish, watery as well. Avian pox is another disease that can affect house finches; this condition causes growths on featherless areas of the bird’s body, such as the legs and feet. Sometimes, avian pox will affect the skin around the eyes and may resemble mycoplasmal conjunctivitis. However, avian pox typically results in obvious growths – a symptom not caused by conjunctivitis.
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