West Nile virus is a seasonal disease that results in many flu-like symptoms but can occasionally result in severe neurological disease. According to the WHO, the virus was first recognized in 1937 in a woman in Uganda. It was identified in birds in Nile delta region in 1953. West Nile virus in humans has been reported around the world for half a century, in a region including Africa, parts of Europe, Middle East, West Asia, and Australia, but it was the importation of the disease to New York in 1999 and ensuring outbreak that caused considerable panic. "The WNV outbreak in USA (1999-2010) highlighted that importation and establishment of vector-borne pathogens outside their current habitat represent a serious danger to the world," says the WHO. The virus also spread to Canada and Latin America.
Humans, horses and other mammals can be infected by bites from mosquitoes that feed on infected birds. Mortality for birds infected with the disease is also much higher in the Americas than the regions in which the disease originated. In a very small number of cases, the CDC reports, the virus also has been spread through blood transfusions, organ transplants, breastfeeding and even during pregnancy from mother to baby -- but not through casual contact like a flu would spread. There have not been any reported cases of healthcare workers contracting West Nile from caring for patients, though lab workers have been reported to contract the virus.
The incubation period between contracting the virus and showing symptoms is 3 to 14 days. About 80 percent of people infected will not show any symptoms at all. About 20 percent develop West Nile fever, which includes symptoms of fever, headache, tiredness, and body aches, nausea, vomiting, occasionally with a skin rash (on the trunk of the body) and swollen lymph glands. These can last anywhere from a few days to a few weeks. But about 1 in 150 of those infected will become severely ill: people over the age of 50 and immunocompromised persons are at higher risk. Severe symptoms can include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis. These symptoms may last several weeks, and neurological effects may be permanent, according to the CDC. There is no vaccine, and treatment consists of supporting the patient through IV fluids, breathing assistance, etc. The more common mild cases may not have to seek medical treatment.
Here are prevention tips from the WHO:
Mosquitoes can breed anywhere from bird baths to pet dishes to kiddie pools to tire swings. The CDC advises draining these areas and keeping good screens on windows and doors to keep mosquitoes out of the house.