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West Nile virus (WNV) is a mosquito-borne disease that can, in rare instances, cause serious illness and/or death. In Delaware, the virus was first identified in 2000 and the first human case was confirmed in 2002. The chances of becoming ill with WNV are small. You can reduce your risk of WNV by using insect repellent and wearing long-sleeved shirts and long pants to prevent mosquito bites.
No symptoms in most people.
Febrile illness (fever) in some people.
Serious symptoms in few people.
How Does West Nile Virus Spread?
West Nile virus is most commonly spread by the bite of an infected mosquito. In nature, WNV cycles between mosquitoes (commonly Culex species) and birds. Some types of birds are considered amplifier hosts because they generate high levels of the virus in their blood and can infect other mosquitoes.
Sometimes mosquitoes with WNV can bite and infect humans, horses, and other mammals. However, humans, horses, and other mammals are considered “dead end” hosts because they don not develop enough virus in their blood to infect mosquitoes.
In less common cases, WNV can also be spread through blood transfusions, organ transplants, and mother to baby, during pregnancy, delivery, or breast feeding.
Mosquitoes live part of their lives in water. After taking a blood meal, female Culex mosquitoes will lay their eggs on top of water in rafts. Some species of Culex mosquitoes will lay eggs in artificial containers like buckets, while others lay eggs in freshwater habitats with organic matter like roadside ditches and coastal wetlands. Within a few days (temperature dependent), these eggs hatch into larvae.
The larvae feed on organic matter in water and need to come to the surface to breathe with their siphon. After the larval stage, the larvae turn into pupae and stop eating. After a few days to a week, the adult mosquito emerges from the pupal case. The entire life cycle can range from 4 days to as long as a month.
Healthcare providers diagnose WNV infection based on:
Although there is a vaccine available for horses, there is no human vaccine for WNV. Rest, fluids, and over-the-counter pain medications may relieve symptoms. If you have severe symptoms, you may need to be hospitalized to receive supportive treatment.
Avoiding Mosquito Bites
The best way to reduce your risk of WNV is to avoid mosquito bites.
Tires and buckets create ideal habitats for mosquitoes. Photo credit: CDC.
Remember, mosquito larvae can develop in standing water around your home in artificial containers like:
How Many Cases of West Nile Virus are There in Delaware?
See Delaware mosquito-borne disease human cases for specific data.
Office of Infectious Disease Epidemiology
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