A pathogen for bird pink eye remains viable on bird feeders in winter conditions much longer than in summer conditions without losing any of its severity, according to a recent study.
"In colder temperatures, birds essentially have a much longer window of time — up to seven days — to encounter this pathogen on a bird feeder," said Sara Teemer, who will receive a Ph.D. in biological sciences in May. "However, that window appears to be much shorter — only up to two days — on feeders in warmer temperatures."
Teemer was the lead author of the recently published study in Ecosphere detailing the findings that the pathogen Mycoplasma gallisepticum, which causes a type of bird pink eye, remains pathogenic on feeder surfaces at cold ambient temperatures for up to one week, much longer than previously documented. The findings have strong implications for house finches, which require more food in colder months as they expend more energy to maintain their body temperature, just when their natural food sources become scarce.
Another finding in the study revealed the pathogen incubated on feeders at colder ambient temperatures caused more severe disease in birds compared with the pathogen incubated on feeders at warmer temperatures.
"I was definitely surprised when the pathogen, which we swabbed off of a bird feeder after a full week of surviving outside the host, caused disease in birds that was just as severe as if the pathogen hadn't spent any time on a bird feeder," said Dana Hawley, professor of biological sciences and co-author of the study.
To get these new findings, researchers assigned feeders to two ambient environments in the lab to represent average winter temperatures and summer temperatures in Southwest Virginia. They inoculated the bird feeders with the pink eye pathogen, and any remaining pathogen from feeders on specific days was used to quantify the amount of viable cells in culture or to measure the resulting disease severity and pathogen loads in birds.
"In house finches, outbreaks of mycoplasmal conjunctivitis tend to occur around the same time of year that birds rely heavily on bird feeders for energy to stay warm during cold outside conditions," said Teemer, an affiliate with the Global Change Center . "Given that previous studies have shown that the pink eye pathogen can be spread from bird feeders, I was particularly interested in whether colder temperatures might be influencing its survival and facilitating its transmission from surfaces."
The pathogen that causes pink eye in songbirds spreads through direct contact or when the infected bird sheds pathogenic cells at feeding ports, where other birds come to feed and become infected. In the wild, some birds recover, but others die from predation as a consequence of impaired vision. All captive birds in the study recovered.
Fall and winter outbreaks of the pathogen have been documented in the Eastern house finches since 1994, decreasing the population by over half, and they have not recovered since. However, house finches are still one of the most common backyard birds, which makes them a good study system.
"The pathogen is definitely influencing bird survival and population growth potential, but this is certainly not a bird that we have conservation concerns about," said Hawley, also an affiliate with the Fralin Life Sciences Institute Global Change Center.
Understanding the effects of ambient, or environmental, temperature on pathogen viability outside of the host can give insight into the role of abiotic factors, which are non-living parts of the ecosystem, on the transmission dynamics and potential management strategies to reduce disease spread.
Hawley said this is where bird lovers who maintain feeders in their yards can contribute to mitigating the spread of this pathogen among house finches.
"Our results suggest that cleaning will have the most bang for the buck when it's cold outside," said Hawley, an affiliate with the Center for Emerging, Zoonotic, and Arthropod-borne Pathogens . "At least once a week, we suggest a simple wipe down of the feeder surfaces that birds contact, such as the perches and the holes around the feeding ports, with a bleach wipe to clear away the bacteria."
Potential next steps for the researchers are to look at other abiotic factors that could affect the pathogen's persistence and pathogenicity on the feeders, such as humidity and ultraviolet exposure from sunlight. Better understanding of the pathogen's survival outside the host will help with determining how to mitigate the pathogen's spread.
In the meantime, the researchers don't recommend taking down their feeders anytime soon.
"I maintain a bird feeder in my backyard year-round because I think feeders offer important benefits to both the birds that rely on them and the people who provide them to connect with nature." Teemer said. "Both birds and humans win when it's done responsibly."
Other researchers involved in the study funded by the National Science Foundation included Alicia Arneson, a Ph.D. student in the Hawley Lab, and Edan Tulman and Steven Geary in the Department of Pathobiology at the University of Connecticut, Storrs.
Original Study DOI: 10.1002/ecs2.70139
