Newswise — AMES (Iowa) – A study that examined eye disease in common birds shows how behavior and pathology interact in complex ways that can determine the spread of a pathogen.
The study was published in the academic journal Biology Letters. It examined pairs of house finches to determine how easily mycoplasmal conjunctivitis spreads from one bird to the next based on feeding behavior and severity. The researchers identified trends in transmission that were more likely by following the severity of disease in infected birds. Rachel Ruden, an associate professor of veterinary diagnostic animal medicine at Iowa State University, was a co-author. Ruden, who also serves as the state wildlife veterinarian at the Iowa Department of Natural Resources, has a dual appointment in Iowa State.
” This study is about disease transmission and how behavior can mitigate clinical signs that could expose others,” Ruden stated. “We found that the best conditions for infecting others is when you have severe clinical signs, in our case conjunctivitis, but still maintain a high index of activity, in our case feeding.”
Mycoplasmal conjunctivitis commonly infects house finches. Ruden stated that the disease is more common in young birds who are exposed to the environment for the first-time. The disease can cause noticeable lesions around the eyes in severe cases. The researchers studied 24 house finches under laboratory conditions. The birds were split into pairs and shared water and food resources. Researchers recorded the symptoms of conjunctivitis in the birds and the feeding habits of infected individuals. They also tracked how long it took for the disease to spread between pairs.
The experiment revealed that house finches with severe diseases transmitted the disease faster than those with milder disease. It was also shown that birds who ate less while sick transmitted the disease faster than those who maintained normal feeding habits.
The study authors compared conjunctivitis among birds with the spread of seasonal influenza among humans.
” If you feel sick from the flu and are bedridden, you will self-isolate yourself and make contact with fewer vulnerable hosts than if you continue to go about your day as normal. Ruden stated.
It may seem obvious that disease transmission is more likely for those with more severe diseases and more normal activity. The study considered disease severity and behavior separately to assess competence or an individual’s ability to infect others.
The study on house finches highlighted the importance of disease tolerance, noting that conjunctivitis was transmitted as easily by birds with milder diseases than those with severe illness. Researchers concluded that pathology and behavior have equal effects on transmission.
This is similar to the situation for asymptomatic COVID -19, carriers, she explained. High disease tolerance may not be aware they are sick, and could unintentionally expose others by going about their daily routines.
” Often, we only use the pathology pieces, the clinical signs to determine transmission. Ruden stated. Ruden said, “It turns out that there may be other factors at work that complicate this picture. It’s important to consider both behavior and pathology when trying to unravel the transmission dynamics. You don’t need severe clinical signs to be an effective vector of infection.”
James Adelman, an assistant professor of biological sciences at the University of Memphis, is a co-author of the study.
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