West Nile Virus

If you would like to report a possible case, contact:

Disease Investigation Branch: 808-586-4586

If you have questions or concerns about mosquitoes, contact Vector Control:
On the Big Island:
  East Hawaii: 808-974-6001 or
  West Hawaii: 808-322-4880
Oahu: 808-586-8021
Maui: 808-873-3560
Kauai: 808-241-3306

About West Nile Virus

West Nile virus (WNV) is a viral illness spread by mosquitoes. It mainly affects birds, but humans, horses, cattle, reptiles and other animals can also become ill. It was first discovered in Africa in 1937, and first appeared in the US in 1999 in New York. It quickly spread westward across the continental US and by 2004, all states had detected WNV with the exception of Alaska and Hawaii. Health and wildlife agencies in Hawaii are working to prevent the spread of the virus to the state.

Back to top


WNV is a bird virus that is spread from bird to bird by infected mosquitoes. When an infected mosquito bites a human, that person can be infected with WNV. It is also very rarely spread through blood transfusion, organ transplants, and through breastfeeding. WNV is not spread through casual contact such as touching or kissing a person infected with the virus.

Back to top

Signs and Symptoms

Most people who are infected with WNV will have No symptoms. A small number of those infected will have symptoms such as fever, headache, body aches, nausea, vomiting and, a rash on the chest and back. Even fewer people infected with WNV will develop severe illness, which may include encephalitis (brain inflammation). People with WNV encephalitis require hospitalization and may die or be left with permanent brain damage.

Symptoms usually begin between 3 and 14 days after being bitten by an infected mosquito.

Back to top


There is no specific treatment for WNV. In mild cases of illness, the fever and aches will go away by themselves. Bed rest and medications for reducing fever and pain are usually all that are necessary. Severe cases may require hospitalization for supportive care.

Back to top


People over the age of 50 are more likely to have severe illness from WNV infections. The more bites one has from infected mosquitoes, the higher their chances are of becoming ill. The risk of getting WNV through medical procedures is very small. All donated blood is tested for WNV before it is given to patients.

Back to top


Mosquito proof your home and yard by keeping them free of standing water that could provide breeding sites for mosquitoes. Keep mosquitoes out of your home by making sure you have well-fitting screens on doors and windows. Be involved in community efforts to clean up mosquito breeding sites in vacant lots, parks, and other areas in your neighborhood. When traveling to areas that have WNV, try to avoid exposure to mosquitoes by using mosquito repellents and wearing appropriate clothing such as long-sleeved shirts and long pants.

Back to top

Back to top