West Nile virus is a disease spread by mosquitoes. Researchers believe West Nile Virus is spread when a mosquito bites an infected bird and then bites a person.
Mosquitoes carry the highest amounts of virus in the early fall, which is why the rate of the disease increases in late August to early September. The risk of disease decreases as the weather becomes colder and mosquitoes die off. Although many people are bitten by mosquitoes that carry West Nile virus, most do not know they've been infected.
Risk factors for developing a more severe form of West Nile virus include conditions that weaken the immune system, such as HIV, organ transplants and recent chemotherapy. The elderly, very young and pregnant women also are at a higher risk to contract the virus.
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