Another Reason to Hate Mosquitoes

From the WebMD Archives

May 24, 2000 (Los Angeles) -- Each year, 36,000 people in the U.S. contract the deadly hepatitis C virus, which infects the liver and is the leading cause of damage requiring a liver transplant. The virus goes on to kill up to 10,000 Americans each year. Now researchers in France have evidence suggesting that mosquitoes may spread hepatitis C and other viruses, such as West Nile virus. The scientists discussed their work at a microbiology meeting here this week.

The people at highest risk of getting hepatitis C are drug abusers, people who receive blood transfusions, patients who require kidney dialysis, and health care workers. However, approximately 20% of people with the disease have no risk factors for it at all.

Hepatitis C belongs to a family of viruses, such as the Dengue and yellow fever viruses, that are known to be spread by mosquitoes, says co-author Dominique Debriel, MD, PhD. But, he tells WebMD, "to my knowledge, no one has yet shown [that mosquitoes transmit hepatitis C]."

To determine whether hepatitis C could grow in mosquito cells, Debriel and his colleagues grew the virus in monkey cells, human cells, and mosquito cells. They found that the mosquito cells were uniquely designed to connect with hepatitis C, suggesting that these insects could indeed carry and transmit the virus.

Debriel, a staff physician at the Hôpital Pasteur in Colmar, France, warns that much more research must be done before it can be definitely concluded that mosquitoes actually spread the disease.

However, this is no mere laboratory experiment. The havoc wreaked by a mosquito-borne virus hit close to home last summer, when New York City was swept by an outbreak of West Nile virus, another relative of hepatitis C. Sixty-two cases of encephalitis, or inflammation of the brain, and seven deaths occurred during that outbreak -- all thanks to the West Nile virus carried by mosquitoes.

According to the CDC, this was the first report of a West Nile virus outbreak in the U.S. As its name implies, the virus is most commonly found in Africa, West Asia, and the Middle East. Its fatality rate can range from 3% to 15% and is highest in the elderly.

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Unfortunately, says Debriel, the symptoms are similar to another form of encephalitis caused by herpes and other viruses, so doctors needed a way to make an accurate diagnosis -- fast.

During the New York City outbreak, Debriel and his colleagues developed a test for identifying viruses in the family that includes hepatitis C and the West Nile virus. "By analyzing samples of a patient's blood and [brain and spinal fluid], we can diagnose encephalitis due to [a virus from this family] within just a few hours. Rapid diagnosis of these patients is important because they must be isolated and treated quickly."

Birds serve as carriers of the West Nile virus. Mosquitoes become infected when they bite an infected bird, and they then spread that infection by biting humans. Concerned that birds may be spreading the disease throughout the East Coast, the CDC has allocated $2.7 million to survey 17 states and two cities thought to be at highest risk of another outbreak.

CDC officials recommend that people help stop mosquitoes from breeding through steps such as emptying stagnant water from flower pots and other containers, treating private swimming pools with appropriate chemicals, and removing other standing water that allows mosquitoes to grow to adulthood.

Vital Information:

  • It's estimated that almost four million people are infected with the hepatitis C virus, which infects the liver, killing up to 10,000 people each year.
  • New laboratory research shows that hepatitis C can grow in mosquito cells, leading scientists to believe that the virus could possibly be spread by mosquitoes.
  • People at highest risk for getting hepatitis C are drug abusers, people who receive transfusions, patients who require kidney dialysis, and health care workers.
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