|What is West Nile virus?
West Nile virus is a Flavivirus (in the same group of viruses that cause yellow fever, dengue, and tick-borne encephalitis) spread by certain species of mosquitoes. The presence of the virus is perpetuated year after year as it cycles between mosquitoes and a wide variety of bird species. Humans and other animals such as horses and tree squirrels are also susceptible but do not contribute to the disease cycle.
How did West Nile virus get here?
West Nile virus was first recognized in the West Nile District of Uganda in 1937. It first appeared in the United States in New York in 1999 – most likely carried by an infected stowaway mosquito in a plane or cargo ship. Within four years the virus had swept across the country with the seasonal movement of infected birds and arrived in the Los Angeles area in late 2003.
How is the virus spread locally to humans?
Only certain species of mosquitoes can transmit the virus. Unfortunately the most common and efficient vectors of West Nile virus live in close association with humans. Mosquitoes inject a small amount of saliva into the host when biting and feeding. Female mosquitoes pick up the virus when they feed on infected birds. The virus penetrates the mosquito’s gut where it replicates (makes copies of itself) and moves into the salivary glands of the mosquito. It is during subsequent blood-feeding by female mosquitoes when transmission of the virus can occur.
What happens if I am bitten by a West Nile-infected mosquito?
Approximately 80% of humans infected with West Nile virus never exhibit any symptoms. In those who do, it can take a variety of forms. Some infections resolve without lasting ill effects in several weeks or months, in others complications can result in hospitalization, permanent disability, and even death.
What are the symptoms and prognosis?
West Nile Fever: Symptoms usually appear anywhere from 3 to 15 days following the bite of an infected mosquito. Typical symptoms include high fever, headache, sore throat, backache, muscles aches, joint pain and fatigue. Acute illness can last for one or two weeks with some patients experiencing long term exhaustion and muscle weakness. Most make a full recovery. West Nile Neurologic Disease is a more severe manifestation of the illness and involves swelling of the brain, spinal cord, profound muscle weakness, polio-like paralysis, disorientation, and coma. Permanent paralysis or death can occur in a small percentage of cases.
Who is at risk?
Anyone living in an area where West Nile-infected mosquitoes exist is at risk of infection. Those most susceptible to symptoms and severe illness are the very young, elderly, chronically ill, and those with a suppressed immune system.
How can I protect myself from getting this virus?
No human vaccine exists for West Nile virus and care of those ill with the virus includes supportive care and treatment of symptoms. The best prevention is to wear insect repellent applied directly to all exposed skin. Repellents should contain one of the following active ingredients: DEET (N,N-diethyl-meta-toluamide), IR3535, Oil of Lemon Eucalyptus, or Picaridin/KBR 3023. Remove all standing water of any amount and all potential containers that might catch and hold water (even a bottle cap) from areas around your home. Report standing water that cannot be removed and/or adult mosquitoes to vector control.
Current Status of West Nile:
Human cases occur in Los Angeles every year. West Nile virus is now a permanent part of the ecology of local bird and mosquito populations and will never go away.
California Arbovirus Surveillance Bulletin
For more information on West Nile Virus please visit:
Center for Disease and Control Prevention-West Nile Virus
West Nile California