House Finch Eye Disease (HFED), also known as mycoplasmal conjunctivitis, is a widespread illness affecting numerous songbirds, particularly those visiting backyard feeders. Highly contagious among avian species, HFED caused substantial population declines in the House Finch starting in the mid-1990s. This disease is not known to be transmissible to people; you cannot contract it from an infected bird or contaminated feeder.
Identifying House Finch Eye Disease
The disease often begins by causing noticeable changes around the bird’s eyes. Affected birds exhibit eyes that are swollen, red, or have a watery discharge that can become crusty. This conjunctivitis can cause the eyelids to swell completely shut, severely limiting the bird’s vision and giving it a ragged appearance.
The infection leads to significant impairment, making it difficult for the bird to find food or avoid predators. Sick finches may act lethargic, sit fluffed up at the feeder, or struggle to fly straight. Birds suffering from severe vision loss are often easily approached and may spend time on the ground near feeders pecking at fallen seeds. While common in House Finches, the disease also affects other species like American Goldfinches and Purple Finches.
The Cause: Understanding Mycoplasma gallisepticum
House Finch Eye Disease is caused by the bacteria Mycoplasma gallisepticum (MG), which is responsible for the ocular and respiratory symptoms. This organism lacks a rigid cell wall, making it resistant to many common antibiotics that target cell wall formation. MG is an established pathogen in domestic poultry, causing chronic respiratory disease in chickens and turkeys. The finch-specific strain emerged in the wild bird population in the 1990s.
The bacterium primarily targets the respiratory and ocular systems of birds. It spreads through direct contact with secretions from an infected bird’s eyes or nose. Transmission is also facilitated by contaminated surfaces, such as bird feeders, where the pathogen can survive for a short period. An infected bird can become a long-term asymptomatic carrier, continuing to shed the bacteria and infect other birds even after recovering from visible symptoms.
Addressing Zoonotic Risk
Mycoplasma gallisepticum is not considered a zoonotic pathogen, meaning there is no known risk of transmission from birds to humans. Extensive surveillance and studies by wildlife health organizations have found no documented cases of the finch-specific strain infecting people. This lack of transmissibility is due to host specificity, where the bacterium is highly adapted to the unique physiology of avian species.
While other species within the Mycoplasma genus can cause illness in humans, the MG strain found in finches has evolved to colonize and thrive only within the avian host environment. The bacterium’s structure is specifically tailored to bird cells, preventing it from successfully establishing an infection in a human host. Interacting with a backyard bird feeder or observing a sick finch poses no direct health risk.
Preventing Spread and Maintaining Bird Feeder Safety
Maintaining clean feeders is important to protect the health of the bird population, even though the disease does not spread to humans. Feeders and bird baths act as points of disease concentration, where sick and healthy birds come into close contact and contaminate surfaces. Routine cleaning involves scrubbing the feeder to remove debris and then disinfecting it with a bleach solution.
A recommended disinfectant solution is one part household bleach mixed with nine parts water; soak the feeder for at least ten minutes. Allow the feeder to air-dry completely before refilling with fresh seed to ensure the bleach residue is gone. If multiple sick birds are noticed, temporarily removing all feeders for a week or more encourages the birds to disperse, reducing concentrated contact and slowing the spread of the disease. Washing your hands thoroughly after handling feeders or bird seed is always recommended.