Last week, the Florida Department of Health in Orange County issued an advisory that there had recently been an increased presence of eastern equine encephalitis virus (EEEV), a rare mosquito-borne virus that has a high mortality rate when transmitted to humans, in the area. No case in people has been associated with this advisory so far.
According to the advisory, the virus was detected in several of their sentinel chickens, which are just regular chickens that health departments raise in areas endemic to mosquito-borne viruses. (EEEV doesn’t bother the birds, which carry out normal lives aside from getting some bug bites.) With the presence of EEEV found in the chickens, it signals to health department officials that the risk for transmission to humans has increased and should be monitored closely.
The virus is considered rare and is certiainly nothing new. According to the Center for Disease Control, about seven cases pop up every year—and not just in Florida. In the past, the disease has been found in 21 states, with the most infections found in Florida, Massachusetts, New York, North Carolina and Michigan. Out of 73 people infected in the United States between 2009 and 2018, 30 died of the virus, which equates to a 40 percent mortality rate. Last year, six people were infected with the virus, with one recorded death. Survivors of the infection often have ongoing neurological problems.
There is no treatment for the virus, so getting the word out that the virus is afoot is the best way to stop its spread, reports Bruce Y. Lee at Forbes. The disease is usually confined to birds and the mosquito species Culiseta melanura, which only targets avian hosts. Occasionally, however, mosquitos in the genus Aedes or Culex will sip on an infected bird and then bite a person, passing the virus into the human population.
The incubation period for EEEV is four to ten days and symptoms can vary. In some cases, people have no idea they’ve been infected and carry on as normal. Others develop flu-like symptoms for a couple of weeks. But for the unlucky few, the virus becomes “neuroinvasive,” attacking the brain and nervous system and sometimes leading to encephalitis, or swelling of the brain, which can be fatal—especially in EEEV cases. There is no way to stop the virus once it takes hold, so doctors can only try to limit the swelling and keep patients alive until the infection subsides.
It’s possible that infection rates are higher than those officially recorded by the CDC, since people with no symptoms and others who are misdiagnosed with a cold or the flu are not tested for EEEV antibodies.
Michelle Marchante at the Miami Herald reports that the only real way to combat the disease is to follow recommendations for controlling mosquito populations. That includes finding and draining any standing water, such as buckets, bird baths, old tires and anything else that can hold a small puddle where mosquitoes could lay their eggs. Plastic swimming pools should be drained when not in use and big pools should be properly chlorinated so they don’t turn into mosquito nurseries. People spending time outdoors are advised to cover up exposed skin and use CDC-approved mosquito repellent to prevent bites in the first place.
Preventing the spread of the virus also means listening to the chickens. Amanda Carrozza at American Veterinarian reports that Florida began deploying sentinel chickens in the battle against viruses beginning in 1978 to get early warnings of diseases like EEEV and West Nile Virus. Chicken coops are strategically deployed throughout counties and each week, blood samples are drawn from several chickens in each coop, then sent to a central lab where they are examined for viruses. The diseases don’t affect the chickens, but they do let officials know when an outbreak is occurring in the bird world and has the potential to jump to humans.
Aimee Cunningham at Science News reports that Florida operates 268 coops in about one third of its counties. Last year, 833 chickens tested positive for West Nile and 154 showed antibodies for EEEV. The chickens have also proved useful to researchers. A recent study in the American Journal of Tropical Medicine and Hygiene found that EEEV is active year-round in the Florida panhandle, and that the virus moves from there to other parts of the state and the East coast during outbreaks.
“Without the sentinel program, it would be a total guess as to the level of virus activity happening,” Glen-Paul Edson, who works on mosquito control in Pinellas County, Florida, tells Carrozza. “We would be effectively flying blind until human cases started popping up.”
Ed Cara at Gizmodo reports that the chickens will become even more important since climate change is expected to make outbreaks of mosquito-borne diseases, like EEEV, even more common.