November 21, 2019
Eastern Equine Encephalitis sparked concern among health officials last summer as the deadly mosquito-borne illness experienced a relative resurgence in humans.
In a typical year, about seven EEE cases are reported across the United States.
The risk of contracting EEE should drop with the arrival of winter – and the disappearance of the mosquitoes that carry it. But health officials fear the virus could become more common in the years to come.
Scientists from the National Institute of Allergy and Infectious Diseases have deemed EEE as "an emergent threat." Though EEE has not yet risen to "a disease of major national importance," they have called for a national strategy to address the threat of EEE and other arboviral diseases transmitted by mosquitoes.
They outlined their concerns in a commentary published Thursday in The New England Journal of Medicine:
"In recent years, the Americas have witnessed a steady stream of other emerging or reemerging arboviruses, such as dengue, West Nile, chikungunya, Zika, and Powassan, as well as increasing numbers of travel-related cases of various other arboviral infections. This year's EEE outbreaks may thus be a harbinger of a new era of arboviral emergencies."
EEE is hardly new. Between 1831 and 1959, twelve EEE epidemics were documented in the United States. But the virus mostly has spread between mosquitoes and tree-perching birds found in forested wetlands.
Even when EEE infects humans, an estimated 96% never develop symptoms, the scientists say. But among those that do, one-third die. The other victims generally sustain permanent – and sometimes severe – neurologic damage.
The virus has remained rare in humans partly because the species of mosquito that carries it – Culiseta melanura – primarily feasts on birds, including the American robin, for its blood meals.
But scientists fear EEE could evolve to infect Aedes aegypti mosquitoes, which feed almost entirely on humans. Four well-known arboviruses – Dengue, Yellow Fever, Zika and Chikungunya – have already done so.
The NIAID scientists elaborate on their fears:
"Any virus that can efficiently infect A. aegypti also has potential access to billions of humans, which explains why the four viruses that have done so have spread pandemically. We cannot discount the possibility that other arboviruses will adapt to A. Aegypti in the future – a sobering thought, given the high case-fatality rate of diseases such as EEE."
No vaccine exists to prevent EEE, though several are being developed, and there are no antiviral drugs available to treat it.
With those defenses lacking, NIAID officials urged state and local health departments to "provide early warning of imminent human infections by surveilling equids, birds and mosquitoes." And they backed public health experts who have called for a national defense strategy against arborviruses.
"Arbovirus threats are not easily thwarted by piecemeal efforts," the NIAID wrote. "Given the near certainty of future emergences, arborviruses constitute a real and present danger."
Among humans, EEE takes about 3 to 10 days to cause symptoms. Initial symptoms include fever, malaise, intense headache, muscle aches, nausea and vomiting.