An 8-year-old North Carolina girl died this week from encephalitis, after she was bitten by a mosquito likely carrying LaCrosse virus. Her death and the hospitalization of her younger brother are the latest evidence that a wet spring and a hot, wet summer have boosted the insects' population and power to imperil public health.
Health officials on Friday awaited results of lab tests to confirm the underlying cause of the brain inflammation that proved fatal to the Henderson County, N.C., child. The youngster, whose name was being withheld, died Wednesday at Mission Hospital in Asheville, in the mountains of western North Carolina. The LaCrosse virus, which travels from the bloodstream into the brain, can cause headaches, fever, nausea, vomiting and weakness. It can only be spread to people through the bite of an infected mosquito. It cannot be spread from person to person.
"North Carolina is one of the areas where LaCrosse virus is endemic, so having them report cases is not uncommon," J. Erin Staples, a medical epidemiologist at a branch of the Centers for Disease Control and Prevention in Fort Collins, Colo., said Friday. "LaCrosse disease is described more often in children, likely due to the interaction between children and the tree-hole breeding mosquitoes that carry the virus."
As of Aug. 30, there were 22 confirmed and probable LaCrosse illnesses reported to the CDC. The CDC tally consisted of four cases from North Carolina, along with others from Georgia, Indiana, Ohio, South Carolina, Tennessee, West Virginia and Wisconsin.
Mosquito surveillance that began in late spring in such states as Connecticut has shown an explosion in the numbers of mosquitoes caught in traps. As a result of this banner year for the buzzing biters, entomologists and health agencies have repeatedly reminded Americans to use insect repellants and avoid being outside at dawn and dusk, when mosquitoes are likeliest to turn to people for their blood meals. They also advise emptying standing water that mosquitoes use as breeding grounds, a particular risk in many states following the flooding from Hurricane Irene. Screened windows and doors can put more distance between mosquitoes and vulnerable skin.
Melting of the heavy winter snowfall, Mississippi River flooding and high waters from Hurricane Irene can be blamed for some of this year's profusion of "nuisance mosquitoes," although they're not the culprits in potentially fatal mosquito-linked diseases, Staples said. She and her colleagues worry more about the high heat of summer, which boosts the population of mosquitoes carrying West Nile virus. Cases peak in late August and early September, Staples said. The virus first appeared in this country in 1999.
As of Aug. 30, 21 states had reported a total of 104 human West Nile cases to the CDC; four of those cases were fatal. The tally included 65 cases that spread to the nervous system. Patients became ill between March and August.
West Nile symptoms include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis. When the virus invades the nervous system, it can produce one of three conditions: meningitis, which is an inflammation of the membrane surrounding the brain and spinal cord; encephalitis, which killed the North Carolina girl; or a type of spinal cord paralysis that can suddenly strike breathing muscles or muscles of the arms and legs.
Reported West Nile infections represent just a fraction of cases because many never get confirmed, said Roger Nasci, a research entomologist at the CDC's Arboviral Diseases Branch in Fort Collins. "For every person diagnosed with meningitis or encephalitis with West Nile, there's approximately 140 people infected. The vast majority will be asymptomatic," he said.
West Nile, carried by Culex pipiens and Culex restuans mosquitoes, can produce fever and neurological problems without causing brain inflammation. Often, the symptoms are so vague that doctors will just prescribe fever reducers like acetaminophen, without seeing the need to perform blood tests that could detect the virus. Nasci estimated that doctors diagnose only 3 percent to 5 percent of the West Nile cases that cause symptoms short of meningitis, encephalitis and muscle weakness.
The most devastating of the mosquito-linked illnesses is Eastern equine encephalitis, which is rare, but fatal in about a third of cases. There is no treatment. Survivors often have brain damage. EEE is carried by Culiseta melanura mosquitoes, which live in marshes, swamps and other bodies of still water. So far, New York has reported the only human case for 2011. Seven other states have detected the disease in mosquitoes, birds and other animals.
As of Aug. 30, Arkansas reported a probable human case of St. Louis encephalitis, typically found in Eastern and Central states, and most dangerous to older patients. Florida and Nevada have detected it in insects and animals, the CDC's latest tally showed.