Assessing the Landscape of Eastern Equine Encephalitis Prevention and Treatment

Eastern Equine Encephalitis (EEE) has been making news headlines in 2019. The mosquito-borne illness has been existence for centuries, with 12 US-based epidemics recorded between 1831 and 1959. Annual cases have remained low over the past decade, until 2019.

The first case in the 2019 season was confirmed in August in Massachusetts. As of November 12, there have been 36 cases of the illness reported across 8 states. This is a sharp contrast to the 6 cases confirmed in 2018. More worrisome, one-third of the cases confirmed in 2019 have been fatal.

Now, experts from the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health have published a commentary in The New England Journal of Medicine describing the EEE virus along with research and development that is needed to address the growing threat of the virus and other vector-borne conditions.

The virus is typically spread between Culiseta melanura mosquitoes and birds that live in wetlands; however, other mosquito species can transmit the virus to humans and mammals. In the event of human infection, it takes approximately 3 to 10 days for symptoms to present.

Initial signs and symptoms include fever, muscle aches, nausea, and headache. Infection may progress to neurological EEE are “nonspecific” but progress rapidly and can be permanent. However, the authors of the report noted that 96% of individuals infected with EEE virus do not develop symptoms. Furthermore, specific diagnostic testing may not reveal the infection as the virus is difficult to isolate from clinical samples.

“Although point-of-care diagnostics for EEE and many other mosquito-borne causes of encephalitis are not available, currently they would be of limited value in the absence of effective treatment,” the authors of the report write.

Currently, there are no available antiviral drugs or vaccines that are safe and effective against EEE. At this point in time, patients with EEE are treated with supportive care including intensive care and ventilator assistance. Social support and counseling are recommended for the patient and their family members due to the serious, and sometimes long-term, effects of the infection.

According to NIAID’s statement, many compounds and candidates are currently in development. The authors note that monoclonal antibodies have demonstrated efficacy when given prior to infection in an animal model.

While there are several EEE vaccine candidates in development, the authors caution that these candidates may struggle to reach advance development and licensure. Vaccines that are mosquito-saliva based which are in development to protect against multiple mosquito-borne diseases are in early stages.

Moreover, due to the rare nature of the outbreaks which occur sporadically in unpredictable locations for short periods of time it is difficult to identify an appropriate target population for vaccination.

“In the absence of effective EEE vaccines and treatments, state and local health departments can provide an early warning of imminent human infections by surveilling horses, birds and mosquitoes, but these efforts are threatened by insufficient funding,” the authors said in the press release.

Despite the challenges to developing vaccines and treatments for EEE, the authors of the report caution that simply ignoring the virus would be irresponsible. While EEE outbreaks have been infrequent, a number of emerging and re-emerging mosquito-borne diseases such as dengue, West Nile, Zika, and chikungunya have been documented in the Americas in recent years.

“The spike in cases in 2019 and the looming presence of other, potentially deadly arboviruses in the United States and globally demand a national defense strategy for arboviruses and other vector-borne diseases,” the authors conclude.