Bethesda / Maryland - In the US, 36 people have already developed Eastern equine encephalomyelitis this year, which was fatal in 14 patients. The CDC is concerned about the rise in the number of illnesses. In the New England Journal of Medicine (2019;) they present the disease, which is unknown in Europe.
"Eastern Equine Encephalitis" or EEE has probably been widespread in North America for centuries. 12 epidemics were recorded between 1831 and 1959. In the past 10 years, with the exception of 2010 (10 cases) and 2012 (15 cases), there have been fewer than 10 diseases in each year: The increase to 36 diseases this year is therefore remarkable.
That EEE virus belongs to the genus Alphavirus from the Togaviridae family. It is transmitted by the mosquito Culiseta melanura. The natural reservoir is forest birds that are common in wetlands in the eastern United States. Horses are infected only occasionally, and even more rarely humans. Transmission among horses or humans has not yet been observed.
After entering the body, the EEE viruses infect the Langerhans cells and the dendritic cells. These immune system outposts transport the viruses to the lymph nodes where they multiply. It is estimated that 96% of infections remain asymptomatic.
However, if an illness does occur, more than third of the cases become fatal. As David Morens and coworkers at the National Institute of Allergy and Infectious Diseases in Bethesda / Maryland report, the disease begins about 3 to 10 days after infection with fever, fatigue, severe headache, muscle pain, nausea and vomiting. At this stage the antibody tests are still negative. Detection of the viruses in the blood or in the cerebrospinal fluid is rarely successful.
Neurological symptoms occur within 5 days of the onset of the disease. They are initially unspecific, but progress quickly. So far there is no specific therapy. According to Morens, no antiviral drug has proven effective.
Treatment with EEE-specific antibodies only protected animals from disease if it occurred before infection. The treatment of the patient is purely symptomatic. The patients are ventilated in the intensive care unit until they gradually recover after the body's own antibodies have formed, which, however, often remains incomplete. Many patients experience permanent disabilities.
Several vaccines are in development, according to Morens. However, it is unclear whether they will ever be used in humans.There is no incentive for manufacturers to develop vaccine for the rare disease that only occurs sporadically in unforeseeable places. It is difficult to identify group of people for whom vaccination would be worthwhile.
One possible approach is the development of vaccines that do not target the viruses, but instead generate antibodies against the insects' salivary proteins. The immune reaction triggered by this is intended to prevent the viruses from entering the immune cells. These vaccines would have the advantage that they could protect against several viral infections at the same time.
For Morens, the increasing number of EEE infections is symptom of the increasing threat from arboviruses, which in addition to EEE also cause dengue fever, West Nile fever, Chikungunya fever, Zika fever, and Powassan fever are responsible. The Powassan virus, like the EEE virus, can cause encephalitis. It is common in the United States and Siberia. Although there is currently no strategy as to how diseases caused by arboviruses can best be combated, according to Morens it would be irresponsible to ignore the (still) rare diseases and not act.