House Finch Conjunctivitis
Cause and Origins
Currently House Finch Conjunctivitis (HFC) remains largely a disease of House Finches and has been confirmed in most if not all of the species' eastern range. This eastern population originated from a small release of birds on Long Island in 1940. Therefore, it has been speculated that lack of genetic diversity may have contributed to the vulnerability of this population to disease. Recently, however, HFC has been detected in House Finches in the Northwestern United States and its spread will be closely monitored. HFC poses no threat to human health or non-avian pets.
HFC is an extremely important cause of morbidity (illness) in House Finches. It is caused by the bacterium Mycoplasma gallisepticum, well-known for causing chronic respiratory tract disease in domestic poultry and gamebirds. It was not recognized as a potentially important pathogen of wild birds until it began to decimate House Finch populations in the eastern United States in the mid-1990s. HFC has also been confirmed infrequently in other finches and allies, particularly goldfinches.
Symptoms and Diagnosis
The chief symptoms in House Finches are swollen reddened eyelids, usually accompanied by a clear discharge that often mats the feathers around the eye. One or both eyes may be involved. Sick birds may linger around bird feeders for extended periods, not following the comings and goings of other House Finches. Mortality has been shown to be low in experimental infection of captive birds. However, mortality of free-living birds is apparently high, no doubt in part due to predation and added stress of exposure to challenging weather.
The observed ocular (eye) symptoms are caused by infection of the conjunctiva by M. gallisepticum. The conjunctiva is the transparent membrane comprising the inner lining of the eyelid and adjoining surfaces of the eyeball. Infection of the nasal sinuses is also common in House Finches. M. gallisepticum is spread by direct contact with infected birds at feeding stations and roosts. Transmission also probably occurs by contact with contaminated surfaces. Tube-type bird feeders are suspected as likely to facilitate this latter means of infection.
A tentative diagnosis of HFC can be readily made from the gross appearance of the eyes in most cases. Should more definitive confirmation be desired, M. gallisepticum DNA can be detected by polymerase chain reaction testing. Culture attempts, even from fresh specimens, are frequently unsuccessful.
Sick birds are easily captured once vision is seriously impaired. They can potentially be treated with ocular antibiotic ointments and tetracycline in drinking water. The value of such treatment is controversial as treated birds may still harbor the organism after overt disease is no longer apparent. Treated birds may therefore continue to be a source of infection on release.
The recommended course of action once an outbreak is detected is to suspend bird feeding operations for a minimum of two weeks. All feeders should be cleaned with a 10% solution of household bleach (1 part bleach: 9 parts water). Clean-up of seed hulls and spilled seed under feeders is also recommended.