Blog post

Eastern Equine Encephalitis Virus (EEEV) making you EEEk this Halloween?

Eastern equine encephalitis virus, often termed EEEV or Triple-E, has been making headlines lately in the United States. This mosquito-borne virus can cause a sometimes-fatal brain infection. With 31 cases and 9 deaths this year to date, this is the worst outbreak of EEEV disease since the US began monitoring the disease 15 years ago. While those numbers sound scary, EEEV disease is relatively rare.  An average of 7 human cases of EEEV disease are diagnosed in the United States annually. Mosquitoes can pick-up the virus from birds, humans, and other mammals including horses – which is how the disease was originally named. A vaccine has been developed for horses but no human vaccine is available.

Infection can only be caused by the bite of a virus-carrying mosquito, and cannot be passed person-to-person. Four to five percent (4-5%) of people infected will develop symptoms.  These symptoms may include chills, fever, malaise, arthritis, and muscle pains, and will last 1-2 weeks.  A subset of these patients will develop the encephalitic form of the disease (involving brain inflammation, referred to as EEE).  Patients with EEE will also experience headache, irritability, vomiting, convulsions, or other neurologic signs. Approximately a third of all patients with EEE die from the disease.

Fortunately, there is no cause for alarm in California. According to the CDC, most cases of EEEV disease are reported from Florida, Massachusetts, New York, and North Carolina.  One reason for this is that the primary mosquito responsible for spreading the virus, Culiseta melanura, is not found in California. The San Mateo County Mosquito and Vector Control District is working hard to detect invasive mosquitoes early and prevent them from establishing a home here.