The start of West Nile virus transmission began unusually early in some US states, with the most cases in early summer since 2004, the US Centers for Disease Control and Prevention (CDC) warned in July – so Delaware turned to chickens. Sentinel chickens, as they’re called, serve as an early warning for mosquito-borne diseases, especially Eastern equine encephalitis (EEE) and West Nile. They can often predict when virus activity begins ramping up, allowing officials to target mosquito control efforts and warn the public about taking precautions.
Doctors know to be on the lookout when patients have flu-like symptoms – especially when it’s not flu season – and that can help reach diagnosis faster. Veterinarians can make sure horses are vaccinated. The chicken itself is a “dead-end host”, Moran said.
They can test positive for the viruses, but they can’t spread the diseases, which is why they’re ideal sentinels, he said. Delaware keeps flocks of four chickens each at 20 locations throughout the state, a program that began in the early 1980s. It’s a relatively lo-tech way to monitor and prepare for the viruses, which can be deadly.
Some states have transitioned to testing mosquito pools, which can be a faster way to detect viruses, because it takes about a week for the chickens to develop antibodies after being bitten. They tried both in Delaware, but decided to go with the chickens only. Unlike the insects, they don’t fly away – which means officials can be certain that infected mosquitoes are active in that exact area.
Delaware’s season usually begins in early August. The chickens could also be tested for other mosquito-borne illnesses if they emerge. That’s what happened when West Nile appeared in Delaware starting in 2000.
At first, officials would test wild birds found dead to see if they had the virus, but they soon began testing the sentinel chickens they already had. Some places test for other local mosquito-borne illnesses, suchas St Louis encephalitis. If a neighboring state were to detect a pathogen like that, “we could probably pretty quickly get up to speed and start testing for that here too”, Moran said.
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