Brain & Nervous System Health Center

Mosquito-Borne Brain Infection More Severe Than Thought

From the WebMD Archives

Mar. 14, 2001 -- You may never have heard of La Crosse encephalitis, even though it's the most common mosquito-spread brain infection in the U.S. Now it looks like the disease -- and its long-term effects on children -- are more serious than once believed.

Connie Johnson of Charleston, W.Va., had never heard of it when her son Ronnie Mitchell, then 7 years old, came down with what her pediatrician said was a bad case of the flu. That was on a Thursday.

"Sunday morning, we were getting ready to go to church and I put him in the tub and he didn't seem to know what to do with the washcloth or anything," Johnson tells WebMD. "I called his name, and it was like he was trying to tell me something but his speech was garbled. We took him straight to the hospital and he had a seizure just as we went in. That Monday, he still was still not responding, and by that Wednesday it became so serious they called in a neurologist. They told me that it was a matter of life or death. One day he was OK, and two days later they are telling me he might die. Finally they realized it was La Crosse encephalitis. When you grow up you hear of snake bites, but never that a mosquito could bite you and you could die."

La Crosse encephalitis now is firmly established in 28 U.S. states, mainly those in the Midwest and central Atlantic. Spread by a type of mosquito called the treehole mosquito, it nearly always affects children -- and some of these children have long-lasting thinking and behavioral deficits.

James E. McJunkin, MD, and co-workers at the Health Sciences Center of West Virginia University in Charleston have treated 127 children hospitalized with La Crosse encephalitis from 1987 through 1996. Their report on these children appears in the current issue of TheNew England Journal of Medicine.

"Some children deteriorate after hospital admission," McJunkin tells WebMD. "Fifty percent [show up] with seizure and 10-15% deteriorate with recurrent seizure or [brain swelling], usually within the first 72 hours of admission."

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The children ranged in age from 6 months to 15 years. None died, although several survived only because of aggressive intensive care.

Nearly as frightening is the finding from follow-up studies of 28 children who had the most severe symptoms. Many of these children had long-lasting changes in their behavior and ability to do their schoolwork. A normal IQ score is 100, but more than a third of these children had a full-scale IQ score of 79 or less.

"We found in following children over the long term that in about a third of children old enough to be tested, those children did seem to have suggestion of developmental problems, such as increase in hyperactivity measures in more than half of the kids," McJunkin says. "There was also a suggestion of a decrease in average IQ compared to the norm."

These changes aren't always obvious at first.

"The problems were not there immediately," Johnson says. "One year went by and then one day Ronnie was playing in the living room with his brother and fell on the couch. I thought he was joking, but then I saw he was out of it. The doctors realized he would start having more seizures at that point.

"I've cried about it -- Ronnie seemed totally different from the son I had before," she continues. "His whole attitude had changed. He seemed more defiant; he had learning impairments that we are still working on. He always had done really well in school, and it seemed after the encephalitis, he had no drive. It seemed he was always tired and always moody, not wanting to cooperate. But he's starting to improve now."

John R. Schreiber, MD, MPH, is chief of pediatric infectious diseases at Case Western Reserve University's children's hospital in Cleveland. He praises the McJunkin team for providing sorely needed information. He notes that while La Crosse encephalitis is a serious disease, other mosquito-borne encephalitic diseases firmly established in the U.S. can be far worse.

"The [aftereffects] of La Crosse encephalitis are worse than we thought but not devastating," Schreiber tells WebMD. "In the scheme of things, these are mild deficits. For example, eastern equine encephalitis virus can destroy your brain -- now that is very disturbing. In the fear ratio, La Crosse is considered relatively mild.

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"I don't keep my kids indoors when there is a report of La Crosse in the community," he says. "But when it's in the neighborhood, I make sure the kids are covered and wear insect repellant."

For those most severely affected, however, the relative mildness of La Crosse encephalitis is small consolation.

Debbie Arrington's son Josh, now 13, also came down with the disease when he was 7, just like Ronnie. The similarities didn't stop there. "It was very, very scary," Arrington tells WebMD. "The day [Josh] went into a seizure he was crying, 'My head hurts so bad, please make it go away.' I was rubbing his head and then he started just staring at the wall -- it was a seizure, so we rushed him to the hospital. But when we got him home, that is when the struggle began. We did not get the same child back. He always forgot things, his schoolwork was very poor. A few months later he started having seizures again, and this continued every three months until last year.

"Now we know that God has blessed us," she says, "and we have never had any more trouble. Now his memory is great, and he is 100% there. But it took us four years of hard work and positive reinforcement. It was a struggle to keep him going."

Both McJunkin and Schreiber say it's very important to keep mosquitoes from breeding around one's home. The treehole mosquito loves to lay its eggs in old tires, but also likes small cups and flower pots. These should be removed. During mosquito season, insect repellent should be used -- but make sure that the type and amount of repellent is appropriate for children.

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