April 4, 2018

Healthy House Finch (left) by Bob Vuxinic; Diseased House Finch (right) by David Guerra.

Usually, individual birds infected with a disease develop an “immune memory” that is used to help protect them from reinfection. It’s similar to when your body creates antibodies after you get sick or receive a vaccine. The antibodies help prevent reinfection by that same pathogen strain. However, since birds can’t walk into vaccine clinics, their immune memories are not always perfect, and we’re learning about this phenomenon from House Finch eye disease.

Recent findings indicate that the pathogen that causes House Finch eye disease, Mycoplasma gallisepticum, is becoming stronger and more dangerous than earlier versions of the pathogen, according to a study published March 2nd in the journal Science by researchers at Cornell, Virginia Tech, Princeton, San Diego, and North Carolina State universities. The researchers found that lapses in immune memory allow stronger strains of M. gallisepticum to survive and make the next host they infect even sicker.

This study specifically looked at whether these incomplete immunities favor the evolution of pathogen strains that are more virulent and lead to a greater host mortality. The authors found that over time, when M. gallisepticum replicated in the first host, more virulent strains of the pathogen survived to be passed on to the next host, causing a worse case of the disease. The researchers determined that these stronger strains were almost twice as deadly.

So, what can FeederWatch participants do? Continue to wash your feeders regularly with a diluted bleach solution or boiling water, keep an eye out for infected individuals, and continue reporting your sightings in your FeederWatch counts. If you see a sick bird at your feeders, we recommend that you take down the feeders that the sick bird is using for a week or more to let the birds disperse and to assure that no disease is being spread at your feeders. If sick birds return once you put your feeders back up, avoid using feeders with large ports that birds put their heads into and wash your feeders at least weekly. Visit our website to learn more about House Finch eye disease and safe bird feeding.

Reference: Fleming-Davies, A.E., Williams, P.D., Dhondt, A.A., Dobson, A.P., Hochachka, W.M., Leon, A.E., Ley, D.H., Osnas, E.E., Hawley, D.M. 2018. Incomplete host immunity favors the evolution of virulence in an emergent pathogen. Science 359:6379, 1030–1033.