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West Nile virus (WNV) is a virus that is transmitted by mosquitoes that affects thenervous system. It has been found in humans, birds, horses, and other animals, in Africa, Eastern Europe, and the Middle East. In 1999, WNV was detected in the United States for the first time, and since then it has spread across the country. In 2002, WNV caused the largest outbreak of mosquito-borne neurological disease recognized in the Western Hemisphere.
West Nile virus exists in nature through a transmission cycle involvingmosquitoes and birds. Mosquitoes become infected with West Nile virus when they feed on infected birds, which may carry the virus in their blood for a few days. Infected mosquitoes can then transmit West Nile virus to humans and animals when biting to take a blood meal. In rare instances, West Nile virus may be transmitted from human to human through organ donation, blood transfusion, breastfeeding, or from pregnant mother to fetus. These new modes of transmission account for only a small number of cases. WNV is NOT spread by casual contact such as kissing or touching a person infected with the virus.
Most individuals infected with West Nile virus will not have any symptoms or signs of illness. People who do develop illness may experience mild symptoms such as fever, headache, and body aches; occasionally a skin rash and swollen lymph glands maybe noticed. These symptoms typically appear 3 to 15 days after the bite of an infected mosquito. Less than 1% of persons infected with the virus may develop more severe disease with symptoms such as high fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, paralysis, and, rarely, death. People > 50 years of age have the highest risk of developing severe illness. Although most people are at low risk for disease, those who spend a lot of time outdoors have a greater risk of being bitten by an infected mosquito.
No specific treatment for WNV infection exists at present. In severe cases, peoplemay require hospitalization, which might include treatment with IV fluids, breathing support, and nursing care.
Maryland citizens can reduce their risk of becoming infected with West Nile virus by taking the following steps to avoid mosquitoes:
Mosquitoes can breed in as little as 1/4 inch of water. In addition to the personal protective measures listed above, Maryland citizens should take the following precautions to reduce mosquito-breeding sites around their homes and businesses.
Call the nearest Mosquito Control Office if you find, or suspect that mosquito larvae are present. The Maryland Department of Health and Mental Hygiene is collaborating with the Maryland Department of Agriculture and the Maryland Department of Natural Resources to monitor mosquito, horse, and human populations for evidence of West Nile virus and other arboviruses of public health concern.
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