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THE WEST NILE VIRUS

West Nile Virus (WNV) is commonly found in Africa, Eastern Europe, West and Central Asia, and the Middle East. It first appeared in North America with an outbreak in the New York City metropolitan area in late summer 1999. It is not known how WNV was introduced to the United States. In succeeding years WNV moved to the west and south and eventually reached Ohio in 2001, causing the deaths of several hundred birds. The first human illness in Ohio due to WNV occurred in 2002. WNV can now be found throughout the continental US and in much of Canada.

People get WNV from the bite of a mosquito that is infected with the disease. West Nile virus is not transmitted from person to person. In Ohio, the northern house mosquito, Culex pipiens, is believed to be the primary vector to humans. Only a small proportion of Culex spp. and other mosquito species are infected with WNV. Mosquitoes become infected after biting infected wild birds that serve as the primary host of the virus. Members of the Corvidae bird family, especially crows and blue jays, are very susceptible to WNV and frequently die from the disease. Many other kinds of birds may also become sick and die from the disease and scientists are now investigating the role of common backyard birds, such as cardinals and robins, in the disease cycle. Horses may receive a specific vaccination to protect them against possible illness and death. WNV is extremely rare in other animals, such as dogs.

Most people infected with WNV have no symptoms of illness, but some may become ill 3 to 15 days after the bite of an infected mosquito. Mild symptoms of the disease may include a fever, headache, and muscle aches. About 1 out of 150 people develop more severe symptoms, such as high fever, severe headaches, stiff neck, confusion, or muscle weakness, which can result in hospitalization and even death. Those inflicted with severe cases of WNV often experience lifelong complications and side effects from the illness. Most people with severe illness due to WNV are over 50 years old.

The District maintains an active surveillance program for West Nile virus and mosquitoes are routinely tested for the presence of disease. The suspected primary vector of WNV, Culex pipiens, is commonly found in Toledo and the Midwest. After a blood meal, Culex spp. mosquitoes seek stagnant water and backyard debris capable of holding water for deposition of their eggs. Portable gravid traps containing smelly, organic water are used as an attractant for these mosquitoes. After capture, the mosquitoes are frozen, sorted, and undergo PCR laboratory testing to confirm the presence of WNV. The results of WNV mosquito testing help the TASD shape control decisions designed to help reduce the risk, to residents, of contracting the virus.