West Nile Not the Only Virus Out There

By: Jarrod Aldom
By: Jarrod Aldom

It's not West Nile virus.

But La Crosse Encephalitis has been around longer than West Nile and it's just as deadly. And while you may not know a lot about it, WHSV set out to learn more.

An Augusta County man has contracted La Crosse Encephalitis. The virus is spread by mosquitoes and it can be deadly. But, unlike West Nile, this virus directly attacks the cells in your central nervous system. And, it only occurs in certain parts of Virginia.

"Last year we had several thousand cases of human West Nile virus and 364 deaths," says Dr. Doug Larsen, Health Director for the Central Shenandoah District. "I think nationwide we've had something like 70 cases of La Crosse Encephalitis reported and less than 1 percent died from it."

But there's another problem with La Crosse. While you can get rid of mosquitoes that carry West Nile by pouring out standing water, La Crosse mosquitoes lay their eggs in a different place.

"Often the mosquitoes live in holes in the trees where rainwater comes in, so that's a little different," says Larsen. "And that's a little harder for us to be able to do that throughout a whole forest."

So what are the warning signs of La Crosse Encephalitis?

"The clinical symptoms of the person that has it are severe headaches, problems with balance, problems that eventually go into coma," explains Larsen. "If it destroys enough of the brain cells of course it causes death."

There's currently no vaccine for West Nile or La Crosse Encephalitis, but scientists are working on one.

There have been two reported cases of La Crosse in Virginia, the one in Augusta County and one in Tazewell County. Larsen says it's believed the Augusta County man got the virus while in West Virginia. He says it's unlikely the virus can be transmitted from person to person.

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La Crosse Encephalitis

Introduction

La Crosse encephalitis is a relatively rare viral disease that is spread by infected mosquitoes. The disease affects the central nervous system and can be serious and even lethal in rare instances. It is named for the city of La Crosse, Wisconsin, where it was first identified in 1963. Since then, La Crosse encephalitis has been identified in several Midwestern and Mid-Atlantic states.

An average of 73 cases per year are reported to the Centers for Disease Control (CDC), with the majority being from children under 16 years of age. It is suspected that La Crosse encephalitis has a higher incidence and wider distribution in the eastern United States, but is not reported because the virus is often not identified, and because symptoms are often mild and medical attention is not sought.

Disease Cycle

The La Crosse encephalitis organism is an arbovirus (a virus carried by arthropods such as mosquitoes, flies, and ticks). It is normally cycled between the treehole mosquito Ochlerotatus triseriatus and vertebrate hosts (chipmunks and squirrels) in forest habitats throughout the range of the disease.

A. triseriatus is a daytime biting mosquito that normally inhabits tree holes, but can also breed in other water holding containers such as discarded tires, cans, etc. Recently, eggs of the Asian Tiger Mosquito, Aedes albopictus, infected with the La Crosse encephalitis virus have been collected in North Carolina and Tennessee. The virus can be maintained during the winter by transmission in mosquito eggs (an infected female lays eggs that carry the virus and eventually develop into infected adults).

In a normal cycle, the virus is transmitted to the vertebrate host through the bite of an infected mosquito. In the host, the virus replicates and increases in abundance rapidly (a process known as amplification). When sufficiently abundant, the virus can then be passed on to other mosquitoes that may bite the infected vertebrate host. Infected chipmunks and squirrels do not show signs or symptoms of disease. Although not part of the normal cycle of the disease, humans can also contract the disease by the bite of an infected mosquito. However, humans are "dead end hosts", meaning that an infected human can't transmit the disease because sufficient amplification of the virus does not occur in humans.

Symptoms

As the name implies, the disease can cause inflammation of the brain which interfere with brain and spinal cord functions. Initial symptoms of La Crosse encephalitis infection include fever, headache, nausea, vomiting and lethargy. More severe symptoms usually occur in children under 16 and include seizures, coma, paralysis and neurological aftereffects. The death rate for clinical cases of La Crosse encephalitis is about 1%. Many pediatric cases that present La Crosse encephalitis symptoms are screened for herpes or other viral diseases, but are not specifically tested for presence of the La Crosse encephalitis virus. Many of these cases are reported as "aseptic meningitis" or "unknown viral encephalitis."

Treatment

There is no specific treatment for La Crosse encephalitis. No anti-viral drugs are available at this time, and antibiotics are not effective against viruses. Patients with the disease are given supportive treatment for the symptoms, particularly headaches, fever and seizures.

Risk and Prevention

Risk of contracting La Crosse encephalitis is highest in children younger than 16 years, in people residing in or near woodlands that harbor the treehole mosquito, in people that maintain water holding containers in their residences, and in those involved in outdoor activities where O. triseriatus is present. Prevention of the disease involves mostly protection against the bite of infected mosquitoes. Personal measures include the use of repellents containing DEET, and the use of protective clothing (long sleeved shirts and long pants) when exposed to mosquitoes.

Effective local mosquito control measures can also decrease disease risk by lowering mosquito populations and thus decreasing the probability of mosquito-human encounters, and possibly, the transmission of the disease among wild populations of mosquitoes and vertebrate hosts. Mosquito control includes the use of appropriate pesticides, and also the cleanup of water holding containers that may offer breeding sites for O. triseriatus.

Source: http://edis.ifas.ufl.edu/BODY_IN420 (University of Florida Cooperative Extension Service Web site) contributed to this report.


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