Eastern Equine Encephalitis

Eastern Equine Encephalitis (EEE) is a relatively rare zoonotic disease caused by a virus that is transmitted by mosquitoes. Birds are the normal hosts of the virus: when a mosquito bites an infected bird, it can pick up virus particles with the blood meal, then other mammals are bitten and infected  Mammals are considered to be ‘dead end’ host as virus numbers don’t become sufficiently concentrated to infect naive mosquitoes.

This year, there are an increased number of cases of EEE being diagnosed in humans and animals. In humans, there are two types of illness:

  • The ‘systemic’ infection results in a severe flu-like illness that lasts 1-2 weeks, from which patients typically recover completely.
  • The ‘encephalitic’ form has a rapid onset of severe nervous system disease and approximately one third of people with EEE die from the infection.  Individuals with neurologic disease that survive may have long-lasting neurological problems.

Cases of disease in animals and humans have been confirmed in a number of states in the Gulf, Atlantic, and Great Lakes regions. To date there have been 8 human fatalities from EEE and a number of fatalities in horses. Core vaccination protocols in horses include EEE vaccine, many of the horses who have died had incomplete vaccination histories. There is currently not an EEE vaccine for humans.

For more information on EEE, see the CDC web page and the Infectious Disease Manual: Infectious Diseases of Concern to Captive and Free Ranging Wildlife, an official publication of the American Association of Zoo Veterinarians.