Mosquito fight targets more than West Nile

Published 5:00 am Monday, August 19, 2002

The West Nile Virus threat has captured the public’s and healthdepartment’s attention this year, but health officials say mosquitocontrol techniques also lessen the impact of other potentiallyfatal mosquito-borne diseases.

The state has long been plagued by mosquito-borne viruses andlearned to live with them, said Dr. Brigid Elchos, a public healthveterinarian for the Mississippi State Department of Health.

In addition to the recent emergence of West Nile, the state mustcontend with St. Louis Encephalitis (SLE), Eastern EquineEncephalitis (EEE), Western Equine Encephalitis (WEE) and LaCrosseEncephalitis (LAC), she said. All are transmitted by the bite of aninfected mosquito.

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“Mosquito-borne diseases have been in Mississippi for a verylong time,” she said.

All five of the viruses display similar symptoms, Elchos said,but their severity and rate of progression differ. All of theviruses, except LAC, are transmitted when a mosquito bites aninfected bird and becomes infected itself. When it next bites avictim, such as a human or horse, it injects the virus into itsvictim and may cause illness.

The only difference, Elchos said, with LAC is that it’s host aresmall mammals and not birds.

None of the viruses can be transmitted by direct contact with ahost, she said. They all require a mosquito transmission.

Receiving the virus does not necessarily mean a victim will getthe disease, said Dr. Sally Slavinski, a public veterinarian withMSDH. It exposes the victim to the virus and the victim may becomeill, but, in most cases, the victim’s immune system will developthe anti-bodies to fight off the infection. People with anti-bodiesfor the virus will test positive for the virus but may not have thedisease.

West Nile is in the same family of viruses as SLE, Elchos said,and one will test positive for the other, meaning more exhaustivetests are necessary once a positive result is obtained.

In fact, she said, when West Nile was first discovered in NewYork in 1999, health officials initially believed it was SLE, “butit just didn’t seem to fit the picture,” Slavinski said.

St. Louis Encephalitis was first diagnosed here in 1966 and isresponsible for one of the largest outbreaks of disease in statehistory, Elchos said.

From 1964-1998 there have been nearly 4,500 cases of SLEnationwide with the largest outbreak occurring here in 1975 when210 cases were diagnosed.

“We’ve found people who have been infected a long time, possiblysince the outbreak in 1975, who have never had the disease,” Elchossaid.

From 1974-1982 there were 335 cases in Mississippi, includingthe 210 in 1975. The state has a total case count of 337. Therehave been no human cases of SLE since 1994.

More deadly than either West Nile or SLE are cases of EEE andWEE, which have a 50-60 percent mortality rate in humans.

“It’s very severe,” Elchos said. “Luckily, we don’t see manycases of it.”

Most of these infections occur in the eastern half of the stateand on the Gulf Coast, she said. There have been four human casesof EEE since 1989.

The most common mosquito-borne disease reported each year inchildren found here is LAC.

It was first diagnosed here in 1967 and 11 cases have beendiagnosed from 1967-2001.

All of the tests conducted by the MSDH for West Nile are alsotesting for the other primary diseases, Elchos said.