Mosquitoes have plagued humankind throughout history.

Timothy Winegard in his book “The Mosquito: A Human History of Our Deadliest Predator,” shows how mosquitoes influenced human conflicts from those waged by the Romans to World War II. 

He reports, for example, that 35 percent of European crusaders were killed by mosquitoes, and that during the Spanish American War, only 379 American servicemen were killed in combat, but 4,700 died of mosquito-borne diseases.

Development of pesticides and vaccinations have reduced but not ended the scourge.

This week, the state’s agriculture commissioner, Richard Ball, urged horse owners throughout New York to vaccinate their animals against two viruses caused by mosquito bites: eastern equine encephalitis and West Nile virus.

“A simple vaccination can go a long way toward protecting horses against mosquito-borne diseases,” said Ball in a press release. “If you’re a horse owner and your horse is in need of a vaccination, I encourage you to make an appointment with your veterinarian as soon as possible.”

He also urged eliminating standing water where mosquitoes breed; using insect repellent; and removing animals from mosquito-infested areas at dawn and dusk, the peak biting times.

There is no risk to humans catching either of the diseases from horses or other animals; humans contract West Nile virus and eastern equine encephalitis, known as EEE, only directly from mosquito bites. Nor do horses spread it among themselves; again, a mosquito bite is needed to cause the disease.

While there are vaccinations, recommended annually, to protect horses from both eastern equine encephalitis and West Nile viruses there are no vaccinations to protect humans from those diseases.

There is no cure for either virus, which can be fatal in both horses and humans.

“Mosquitoes will be present in our communities until at least the end of September, so it’s important to be mindful of how we can protect ourselves when spending time outdoors,” said the state’s health commissioner, James McDonald in a statement posted on the Department of Health website on Aug. 21.

Like the agriculture commissioner, McDonald cautioned against standing water, but with more specificity: Eliminate all standing water in yards and around the home and property where mosquitoes can breed, including plastic containers, pool covers, wading pools, ceramic pots, clogged drainpipes, and wheelbarrows. Also change water in bird baths twice a week.

McDonald further urged wearing long sleeves and pants tucked into socks at dusk or dawn; using repellents containing DEET; and having screens in all windows and doors.

Only female mosquitoes have the needle-shaped proboscis needed to puncture skin and draw blood, which is necessary for producing eggs. Male mosquitos subsist on nectar.

Out of 112 mosquito genera, just three transmit human diseases. Aedes mosquitoes carry yellow fever, dengue, and encephalitis. Anopheles mosquitoes carry malaria and harbor filariasis and encephalitis. Culex mosquitoes carry encephalitis, filariasis, and the West Nile virus.

EEE

 EEE has been confirmed in horses in Saint Lawrence, Madison, Oneida, Orange, Ulster, Cayuga, Wayne, and Washington counties, according to both the health and agriculture commissioners. There are currently no confirmed human cases in New York state.

In nature, EEE is maintained through a bird-mosquito-bird cycle as mosquitoes feed on the blood of birds.

The Centers for Disease Control and Prevention report just three cases of EEE in humans in 2024: one in Vermont, one in Massachusetts, and one in New Jersey.

On average in the United States, 11 human cases of EEE are reported annually, the CDC says.

“Eastern equine encephalitis virus transmission is most common in and around freshwater hardwood swamps in the Atlantic and Gulf Coast states and the Great Lakes region,” says the CDC. “All residents of and visitors to areas where eastern equine encephalitis virus activity has been identified are at risk of infection.”

People over 50 and under 15 years old are most at risk for developing severe disease, the CDC says, and overall only 4 to 5 percent of human EEE virus infections result in eastern equine encephalitis.

Eastern equine encephalitis virus infection is thought to provide life-long immunity against reinfection, the CDC says, but the immunity does not protect against other alphaviruses such as western equine encephalitis virus, flaviviruses such as West Nile virus, or bunyaviruses such as La Crosse virus.

EEE virus can cause a febrile illness, which lasts a week or two, and causes fever, chills, body aches, and joint pain. Most people recover completely when there is no central nervous system involvement, the  CDC says.

However, the virus can also cause neurologic disease, which can include meningitis, an inflammation of the membranes that surround the brain and spinal cord, or encephalitis, which is a swelling of the brain, the CDC says. Signs and symptoms include fever, headache, vomiting, diarrhea, seizures, behavioral changes, drowsiness, and coma.

For horses, according to the release from the state’s agriculture department, typical symptoms of EEE virus include staggering, circling, depression, loss of appetite and sometimes fever and blindness.

West Nile virus

As with EEE, birds are the primary host of the West Nile virus so it, too, is maintained through a bird-mosquito-bird transmission cycle.

So far in 2024, the CDC reports 289 cases, across 33 states, of West Nile virus in humans. Of those, 195 cases were neuroinvasive.

Historically, from 1999 to 2023, according to the CDC, Albany County has had an incidence of 0.03 per 100,000 of population for West Nile virus human neuroinvasive disease.

Nationwide, the most cases — nearly 10,000 — were reported in 2003. Another spike, of close to 6,000 cases, occurred in 2012; reported cases have been under 3,000 annually since then.

So far this year, New York state, according to the CDC, has had 10 cases of West Nile human disease reported.

Several instances of presumptive viremic blood donors were noted; those are people who had no symptoms at the time of donating blood through a blood collection agency, but whose blood tested positive when screened for the presence of West Nile virus.

“Non-human activity” this year was reported in several counties in western New York, a half-dozen counties in the North Country, and several counties in or close to New York City.

The CDC defines non-human activity as “veterinary disease cases or infections in mosquitoes, birds, or sentinel animals.”

As with EEE virus, West Nile virus can result in febrile illness or neurologic disease, including meningitis or encephalitis — and again, there is no vaccine or no treatment.

Eight out of 10 people infected with West Nile virus do not develop any symptoms, says the CDC.

About one in five people who are infected develop a fever with other symptoms such as headache, body aches, joint pains, vomiting, diarrhea, or rash. Most people with febrile illness due to West Nile virus recover completely, but fatigue and weakness can last for weeks or months.

About one in 150 people who are infected with West Nile virus develop a severe illness affecting the central nervous system such as encephalitis or meningitis.

Symptoms of severe illness include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis. Recovery can take several weeks or months and some effects might be permanent.

About one out of 10 people who develop severe illness affecting the central nervous system die.

If a horse contracts the West Nile virus, it may show signs of lethargy, weakness in the hind quarters, stumbling, lack of awareness, head tilt and head twitching, convulsions, circling, partial paralysis, and coma.

Horses exhibiting symptoms of either the West Nile or EEE virus should be reported to the State Department of Agriculture and Markets’ Division of Animal Industry at 518-457-3502 and the local health department right away, the department urges, adding that horses suffering from neurologic problems must always be handled with extreme caution, since they may be unpredictable.