Delaware Turns to Chickens Amid Early West Nile Virus Transmission

The transmission of West Nile virus has begun unusually early in some states, with the highest case counts in early summer since 2004, according to the US Centers for Disease Control and Prevention (CDC) in July. This prompted Delaware to look to chickens for help.

Tom Moran, who leads the mosquito control section at the Delaware Department of Natural Resources and Environmental Control, described these birds as the “proverbial canary in the coal mine.”

These so-called sentinel chickens act as an early warning system for mosquito-borne diseases, particularly Eastern equine encephalitis (EEE) and West Nile. They can often indicate when virus activity starts to increase, which enables officials to focus their mosquito control measures and inform the public about necessary precautions. Doctors are alerted to watch for flu-like symptoms, especially when it’s not flu season, which can aid in quicker diagnoses. Similarly, veterinarians can ensure that horses receive vaccinations.

Interestingly, the chickens are considered “dead-end hosts.” They might test positive for the viruses, but they don’t transmit them, making them perfect sentinels for this kind of monitoring.

In Delaware, flocks of four chickens are maintained at 20 different sites across the state, a program that started in the early 1980s. It’s a rather straightforward method for tracking and preparing for potentially deadly viruses.

“It is kind of the old-school gold standard,” Moran noted. While some states have shifted to testing mosquito pools for a quicker detection of viruses—because it typically takes about a week for the chickens to develop antibodies after being bitten—Delaware has opted to stick with the chickens. “The chickens sometimes pick up virus activity in an area that the mosquito pools did not,” Moran explained. Unlike mosquitoes, the chickens don’t fly away, which allows officials to pinpoint infected mosquito activity in a specific locale.

“It gives you a little more surgical information,” he added. Collecting this data helps mitigate the risks of human transmission.

Cases of the virus generally spread from north to south as migratory birds carry the viruses to mosquitoes, with Delaware’s season typically kicking off in early August.

These chickens can also be tested for other mosquito-borne illnesses that might arise. This was the case when West Nile started showing up in Delaware in 2000. Initially, officials would test dead wild birds for the virus but soon shifted their focus to the sentinel chickens in their program.

Other areas might test for local diseases like St. Louis encephalitis. If a neighboring state detects such a pathogen, Moran believes they could rapidly adapt and begin testing in Delaware as well.

The extensive data gathered from sentinel chickens over the years can be incredibly useful in developing models to predict seasonal severity. Lindsay Campbell, an associate professor in entomology and nematology at the University of Florida, has concentrated on this in her research. She’s digitized numerous paper records from Florida’s health and mosquito control departments and analyzed environmental conditions like temperature and precipitation alongside community science data to monitor bird migration.

The insight gained from this data, and the models derived from it, helps address what causes variations in West Nile and EEE activity.

According to Robert Guralnick, curator of biodiversity informatics at the Florida Museum of Natural History and a co-author with Campbell, the sentinel chickens provide crucial information about past virus patterns while also suggesting potential future developments.

“It allows us to observe the ebbs and flows of these viruses over time, and try to correlate them with various environmental factors,” Campbell added.

Predicting how diseases spread is complex due to numerous factors, such as different hosts and environmental conditions. However, these models investigate how previous weather patterns might influence future viral seasons.

“For certain viruses like EEE, there’s a strong link to specific landscapes that are related to the mosquito vector,” Campbell stated. For West Nile, some precipitation and temperature patterns from months prior have been linked to when chickens begin testing positive.

“The information from these programs is incredibly valuable,” Campbell noted regarding the sentinel chickens, while Guralnick remarked, “It’s a clever way to collect quality information on current events.”

Over time, officials have experimented with various methods and learned what proves effective. In the initial years of the Delaware program, they utilized white leghorn chickens, but they were quite restless, often trying to run away into bushes and forests.

“Chasing them around felt like a scene from Rocky—you really couldn’t catch them,” Moran recalled, highlighting how it sometimes took an hour to locate them. Once they switched to Rhode Island red chickens, things improved significantly.

Officials have also explored other approaches for tracking mosquito-borne illnesses, including one study that suggested using honey traps to capture mosquitoes. “We’re always examining: is there a faster, more efficient, or more economical method?” Moran said. “People are constantly making progress.”

But for the time being, it seems that chickens remain the go-to for monitoring these viruses.