COVID-19 Overshadows Rises in Mosquito Viruses EEE, Dengue, West Nile

In 2019, there were 38 human cases of EEE throughout the U.S., equal in number to the combined total of U.S. EEE cases from the past decade.
By on 09/22/2020 2:00 PM

Source: MedicineNet Health News

Michigan residents in 10 counties should shelter inside this week, especially during the early mornings and evenings, to avoid infection by a deadly disease: not the coronavirus that causes COVID-19, but the mosquito-borne Eastern Equine Encephalitis.

Infection rates have been growing among livestock. Horses are particularly susceptible to the rare-but-deadly brain infection – hence “equine” in the name, according to the Detroit Free Press.

If your horse contracts EEE, the animal appears sleepy and may have fever within five days of the mosquito bite. The symptoms of the brain infection will progress to muscle twitches, staggering gate, and eventual inability to stand. The disease is 90% fatal in horses and kills in about three days after symptoms start. Even the animals that survive tend to have permanent brain damage, according to the Louisiana State University Ag Center.

Michigan reported its first human EEE case in mid-September as aerial pesticide spraying programs commenced throughout the state, according to the Michigan Department of Health and Human Services. EEE appears to be harder to catch if you're a human, but the fatality rate is 33 percent, according to the department.

“Severe cases of EEE infection begin with the sudden onset of headache, high fever, chills, and vomiting,” the department states. “The illness may then progress into disorientation, seizures, and coma. Approximately a third of patients who develop EEE die, and many of those who survive have mild to severe brain damage.”

The shocking and tragic assault of COVID-19 on the U.S. continues, leaving a vast swath of 200,000 Americans dead and counting. Clearly, the coronavirus pandemic is the biggest health story of 2020, but if it weren't for this deadly disease, the rise of mosquito-borne disease outbreaks in the northern latitudes of the country would surely splash headlines across the nation's media outlets.

Warm, wet winters like the recent ones many scientists attribute to climate change lead to bumper crops of summer mosquitoes. All these extra mosquito vectors carry diseases like EEE, West Nile, dengue fever and other, even rarer arboviruses like Jamestown Canyon virus, according to the Michigan Health Department.

In 2019, there were 38 human cases of EEE throughout the U.S. – equal in number to the combined total of U.S. EEE cases from the past decade, the Michigan department states.

“It is unknown exactly why some years are more severe than others, although weather, including temperature and rainfall, is thought to play a role,” states the Michigan Health Department EEE fact sheet.

Even a few ounces of rainwater in an old tire or collected on a tarp can breed thousands of the Aedes aegypti and other mosquito species that carry dengue fever, Zika, West Nile and other nasty viruses once confined to tropical regions, according MedicineNet author Sandra Gonzalez Gompf MD, FACP.

As of Sept. 21, 32 animals across 13 Michigan counties had tested positive for EEE, the health department states.

Michigan residents may have noticed planes in the past weeks scouting residential areas, tracts of forests and wetlands for nightly pesticide spraying. These pilots are using pyrethrin-based pesticides in aerosol form, designed to kill adult mosquitos on contact in the air and leave little to no residue on foliage and outdoor surfaces, according to the Michigan Health Department.

Vector control agencies have used these formulations of pesticides throughout the U.S., and they are common in agriculture. They have no reported effects on humans at the concentrations used for mosquito control, according to the Michigan Department of Health and Human Services.

Dengue Spikes

Other strategies – such as the one used this year in parts of Florida to control mosquito-borne illness – rely on treating standing water and swamplands with a species of bacteria called Bacillus Thuringiensis, which makes a toxin that is deadly to mosquito larvae and many of the other pest insect larvae, but is harmless to humans and other vertebrates.

In July in Key Largo, Florida, a Keys Mosquito Control District helicopter commandeered the quarantine-vacant local high school stadium as a makeshift base to douse the surrounding countryside with the bacterial mosquito larvicide. The twice-a-week program helped stave off the dengue fever outbreak there, according to a district press release.

Locals in Florida and parts of Texas have been battling not only mosquitos carrying dengue fever, a serious, but usually mild flu-like illness, but also efforts by a biotech company to release sterile male mosquitos in endemic areas to drastically cut the population, according to reports by MedicineNet news this summer.

Environmental activists worry the genetically modified mosquitoes could accidentally make the existing mosquito populations more robust, but this assertion is disputed by some scientists. Proponents say though the solution may be imperfect, it is low-risk and could save lives and medical costs by potentially eradicating dengue in Florida altogether, MedicineNet reported.

The Florida Health Department this month issued a public notice to all property owners to drain standing water and cover outdoor items that collect rainwater to avoid further dengue and West Nile spread. This is particularly important in the wake of the flooding caused Hurricane Sally in mid-September, the notice states.

West Nile Virus in 2020

All but 13 states have reported cases of West Nile virus in humans and/or animals this year, according to the U.S. Centers for Disease Control. West Nile is a typically mild infection, but it can cause death and severe neurological damage in some cases.


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The number of reported West Nile Cases in the U.S. spiked at 5,647 in 2012, but has remained at about 2,000 to 2,500 per year since then. In 2018, the last year with complete statistics available, there were 2,647 reported human West Nile cases nationwide.

From 1999 through 2018, almost 60,000 people reported the severe form of the West Nile infection called West Nile virus neuroinvasive disease. Of these, 2,330 succumbed to the illness, a death rate of about five percent, according to the CDC.

Vector control agencies in nearly every state have added West Nile to the list of yearly challenges they have to combat to keep the population safe from infectious diseases.

How to Stay Safe from Mosquitos

You can do a great deal to control disease-carrying mosquitoes simply by inspecting areas around the house where even a bottle cap full of water may collect, and emptying them, Dr. Gompf writes. For example:

  • Pots should be stored upside down to prevent water collection or be stored inside.
  • Rain gutters should be inspected and cleared of debris that can block drainage.
  • Used tires should be disposed of by recycling or at tire disposal centers. Stored outdoors, they make excellent mosquito incubators, offering pockets of stagnant water and shelter from the elements.
  • Stay indoors at dawn, dusk, and in the early evening.
  • Wear long-sleeved shirts and long pants when outdoors.
  • Use an insect repellent containing DEET or a new kind of mosquito killer containing nootkatone, which is government-approved, but not yet on the market as of mid-September.
  • Take preventive measures in and around your home. Repair or install door and window screens, use air conditioning, and reduce breeding sites (eliminate standing water).
  • Note: Vitamin B and "ultrasonic" devices are not effective in preventing mosquito bites.

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