House Finch eye disease continues to spread

Understanding how pathogens, such as disease-causing bacteria, spread and change over time is critical to management of infectious diseases. Implementing effective vaccination strategies and successful disease prevention methods depends upon such research.

House finches are providing a unique window into disease dynamics. Scientists have tracked the spread of Mycoplasma gallisepticum (a bacterial pathogen) in house finches since it emerged in the Washington D.C. area in 1994. Now, nearly 20 years later, this bacteria has spread throughout eastern populations of house finches and has been spreading in western populations since 2003. Click on the map to see how the disease has spread.

The jump to western North America was accompanied by lower virulence (disease severity) in the west. However, that virulence appears to have increased since 2003; now virulence in the west is as high as in the east. This suggests that in order to spread across large geographic distances, virulence (i.e. severity) must be low, but in order to become more common, virulence must increase. Click the picture below to see a figure illustrating this idea.

“We want to understand how this disease is spreading, if cases are more or less severe than they used to be, and how the birds’ immune systems are adapting to fight this threat,” says Wesley Hochachka, Assistant Director of Bird Populations Studies at the Cornell Lab of Ornithology. The question now is: as the disease spreads and becomes more virulent, are house finch defenses increasing as well?

We are asking participants of Project FeederWatch across North America, and especially in the west, to watch their feeders, look for signs of the disease, and report what they find in their FeederWatch counts. The disease manifests as swelling around the eyes, and is often accompanied by sticky head/face feathers. See photos here by FeederWatcher Errol Taskin, and more here.

It is especially important for people to report if they look for the disease but don’t see house finches with apparent infection. For FeederWatchers, this means checking the “yes” box when asked if you looked for the infection, and typing in a “0” when asked how many finches were infected: You may think zeros are boring, but they are not! In order to track the spread of any disease, we need to know where is occurs, but also where it does not yet occur.

Reports from locations in western states such as Utah, Colorado, and Nevada are especially important because these locations likely have newly arriving infected birds. There aren’t as many FeederWatch participants in those states compared to many eastern states, so we need lots of help in those areas! Learn more about the disease here.