Which mosquito-borne viral infection is raising alarm in the United States?

At the end of August, news broke that residents of the state of Massachusetts (United States) were being advised to stay home at night.

The cause, the risk of being infected with a disease that can be fatal.

It was earlier that month that Massachusetts health officials confirmed that a man over 80 had contracted the state’s first case of eastern equine encephalitis this year.

An outbreak had not been reported in Massachusetts for four years, alarming authorities that it could spread across the region.

Eastern equine encephalitis is a rare viral disease that can be fatal in up to one-third of casesIt is transmitted by the bite of infected mosquitoes and, as its name suggests, can affect horses, but also birds such as pheasants, emus, ostriches, quail and ducks.

The New York State Department of Health notes that infection and resulting illnesses can also occur in various types of livestock, deer, dogs and other mammals, reptiles and amphibians.

In the United States, there are 5 to 10 cases annually, and of the five cases reported by the state since 1971, all have been fatal.

The Department itself warns that people over 50 and under 15 years of age are at risk of developing a serious illness.

Symptoms of equine encephalitis

The effects of mosquito infection take 4 to 10 days to appear and while most people do not develop any symptoms, severe cases result in encephalitis, which begins with the sudden onset of headache, high fever, chills and vomiting.

This may be followed by disorientation, seizures, and coma.

People who become infected and survive may end up with mild to severe brain damage.

There is no treatment for the disease, as no effective antiviral has been discovered against the virus. Nor is there a way to prevent infection, only measures to avoid mosquito bites.

Severe cases may receive medical support limited to hospitalization, respiratory assistance, intravenous fluids, and prevention of further infections.

Types of Equine Encephalitis

The National Producer of Veterinary Biologicals (Pronabive) indicates that there are four types of this disease.

The first is eastern equine encephalitis, which occurs in the far east of the United States, with a greater presence in Florida due to its accumulation of swamps, ponds and wetlands.

Western equine encephalitis presents varying degrees of morbidity and lethality. It is generally mild in humans, while it is more virulent in equines.

West Nile virus encephalitis has other ways of being infected besides mosquito bites, such as through blood transmission, breastfeeding, transplants or contact with livestock.

Finally, Venezuelan equine encephalitis (VEE) occurs in jungle areas, including Mexico. Its transmission and symptoms are the same as those of the eastern type.

The first cases of EEV were discovered in 1962 in Campeche. This disease caused a serious epizoodemic between 1969 and 1972 that affected the entire American continent.

An epizoodemic occurs when an event in animal health exceeds the normal incidence at a given time and place.

In an article from May 2021, Pronabive stated that Venezuelan equine encephalitis has been eradicated in Mexico following a vaccination campaign that began in 1971.