West Nile virus (WNV) is a mosquito-borne disease that affects the nervous system. It is one of a group of arboviruses (arthropod-borne viruses) belonging to the Flavivirus genus. Originally identified in Uganda in 1937, West Nile virus 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 steadily across the country. It is a seasonal epidemic that re-emerges every summer and persists throughout the fall season. People over the age of 50 and those who are immunocompromised (such as organ transplant recipients) are at greatest risk of developing severe disease when infected with WNV.
In Maryland, West Nile Virus first appeared in 1999 in a crow in Baltimore City. The first human West Nile cases were reported in 2001 and since that time WNV activity has been found in humans, birds, mosquitoes, horses and/or other mammals throughout all jurisdictions, reaching a peak of 73 human cases and over 230 infected horses in 2003. The Maryland Department of Health and Mental Hygiene collaborates with the Maryland departments of Agriculture and Natural Resources and with the US Department of Defense to monitor WNV and other arboviruses in humans, mosquitoes, and wildlife throughout the state.
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