By Suzanne Rostler

NEW YORK, Mar 14 (Reuters Health) - A sometimes serious mosquito-borne virus may be more common and more severe in children than previously believed, new study findings suggest. The infection can leave some children with lingering problems, according to researchers in West Virginia.

The ailment, known as La Crosse encephalitis, can cause headache, fever and disorientation. In extreme cases, it can lead to seizures, brain swelling and death. Many cases of the disease may be mistakenly diagnosed as meningitis (an inflammation of the membranes covering the brain or spinal cord) or other types of encephalitis (inflammation of the brain), according to a report in the March 15th issue of The New England Journal of Medicine.

The disease was first identified in 1965 in a 4-year-old from La Crosse County, Wisconsin, and has since been found in 28 states. The virus is transmitted via a "tree-hole" mosquito and is largely found in states with hardwood forests east of the Mississippi.

"Our experience suggests that La Crosse encephalitis may be underrecognized not only in terms of its prevalence but also in terms of its severity," Dr. James E. McJunkin, from West Virginia University in Charleston, and colleagues write.

The researchers closely examined 127 children aged 6 months to 15 years who were hospitalized with the virus around Charleston, West Virginia during a 10-year period.

The investigators found that 15 children (12%) left the hospital with some neurological problems, such as poor balance, memory difficulties or speech problems.

When the researchers looked at a subset of children over 5 with a severe case of the illness, they found that 15 out of 25 had signs of attention-deficit/hyperactivity disorder a year after they left the hospital. Ten of 28 children had IQ scores indicating borderline or mental retardation.

The authors estimate that the virus infects 20 to 30 children per 100,000 youngsters under 15 years of age in West Virginia, an incidence similar to states in the Midwest.

Dr. James Meegan from the National Institutes for Allergy and Infectious Diseases of the National Institutes of Health suggests that changing environments may end up causing more people to be at risk for mosquito-borne ailments. This may be due to urban environments that provide the stagnant water in containers or tires that mosquitoes need to breed.

"We have been, as a culture, increasing the number of sites where the mosquito can breed," Meegan said.

While La Crosse encephalitis is not always serious, children should avoid areas where mosquitos live, wear insect repellent and long sleeves, and avoid walking in the early morning and early evening when mosquitos are most active, Dr. John LaMontagne, also with the NIH, told Reuters Health.

"(This disease) is probably unrecognized and people should be more on the lookout," he said.

Related MEDLINEplus Pages:

• Encephalitis