Hesperian Health Guides

West Nile Virus

In this chapter:

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This mosquito breeds in swamps or other stagnant or dirty water.

West Nile virus is spread by the Culex mosquito. These mosquitoes are medium-sized, brown, and have whitish markings on the abdomen. By day, they rest in and around homes and other structures and near plants and vegetation. Crows, other birds, and horses carry West Nile virus. The mosquito bites an infected animal and then bites a person, passing the virus and the illness.

Signs of West Nile virus

Most people infected with West Nile virus do not get signs of illness and may not know they had it. But about 1 in every 5 people infected will feel sick and may have some of these signs:

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  • Fever
  • Headache
  • Feeling tired all the time (fatigue)
  • Body aches
  • Vomiting
  • Rash on the body
  • Swollen lymph nodes

Treatment can help you feel better.

West Nile virus can become severe, although this is not common. The severe form of the virus affects the brain. Older people are more likely to develop severe West Nile virus than younger people. Get medical help quickly for any danger signs.

Danger signs of severe West Nile virus
  • Neck stiffness
  • Tremors (trembling)
  • Paralysis (being unable to move)
  • Mental confusion or loss of consciousness

Dead birds and sick horses in a region with West Nile virus are a warning that the illness may start in people. There is a vaccine for horses that prevents West Nile virus; so vaccinating horses protects people too. Also avoid mosquito bites and prevent mosquitoes from breeding.

This page was updated:14 Sep 2020