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West Nile fever is a disease spread mainly by mosquitoes. Although it usually doesn't cause any complications, in some cases, the illnes can take a severe form and, potentially, cause death.

The West Nile fever is a viral disease that affects a large number of different species — including humans, a number of other mammals, birds, reptiles, amphibians, as well as insects. The disease is caused by a virus from the family Flaviviridae. It was first discovered in humans in 1937 in Uganda, but has spread around the world since then. There have been many outbreaks of this disease in the past century (in Greece, Israel, Romania, and Russia), but the outbreak in the US that lasted from 1999 to 2010 was the most dramatic one, mainly because this was the first time that this disease appeared in the Western hemisphere. 

About 80 percent of people infected do not show any symptoms. In 20 percent of cases, the symptoms include:

  • Headache
  • Tiredness
  • Nausea
  • Fever
  • Vomiting
  • Body ache
  • Swollen lymph nodes
About one in 150 patients develops the most severe form of the disease. This form affects the brain, and is accompanied by symptoms such as a high fever, tremor, convulsions, headache, neck stiffness, muscle weakness, stupor, and coma. Although this form of the disease can affect anybody, people over the age of 50 have the highest risk of developing it.

How is the West Nile virus spread?

To understand what we can do to prevent this disease, we must first discuss the ways in which the virus is spread. The virus cannot be transmitted directly via human to human contact. The virus can be spread through blood transfusions, organ transplants, via breast ilk or from mother to child during pregnancy, but these ways of transmission are very rare.

The most important way in which the disease is transmitted is via mosquito bites. Mosquitoes get infected by feeding on infected bird blood. A few days after the ingestion of this infected blood, the virus moves to the salivary glands of the mosquito. When the insect bites the the next host, it injects the virus into the bloodstream of the host, possibly causing infection. Humans and horses are so-called "dead-end hosts". This means that the infected individuals can't be the source od infection for the new mosquitoes, and cannot spread the disease in that way. One of the ways the virus is spread around the globe is through migrating birds. When an infected bird migrates, the mosquitoes in that area can become infected by feeding on their blood and then spread the disease.

How can we prevent West Nile fever?

Unfortunately, there is no vaccine for humans to prevent this disease. Reducing the number of mosquitoes and the risk of the disease being transmitted this way is the best way to protect ourselves against West Nile virus. 

Reducing the number of mosquitoes

There are a number of ways to recuce the number of mosquitoes. Many countries have means to regulate the number of these insects. Chemicals, such as pesticides, are often used to kill both larvae and adults, but there are other ways, too. Draining puddles, swampy areas, or removing old tires and plastic waste eliminates mosquito breeding grounds. 

Biocontrol can also be used to manage the number of mosquitoes. Many species of fish feed on mosquito larvae, and can be used to reduce the number of larvae, but introducing a new species into an ecosystem can have devastating consequences. Dragonflies feed on mosquitoes, as well as several species of lizards, birds, and bats.

Microorganisms can be used as a way of control too, as there are several species of bacteria and fungi that can infect and kill mosquito larvae. The use of GMO mosquito males is a way in which the mosquito population can be controlled and their numbers lowered, without messing with the rest of the ecosystem. Releasing a bunch of sterile males into the population lowers the numbers of impregnated females, and thereby the number of larvae. There is also a strain of male mosquitoes whose offspring need tetracycline to develop in the larval stage. Since there is no tetracycline in nature, the larvae are not able to develop.

Traps can also be set, for both larvae and adult mosquitoes. 

Reducing the risk of being bitten by a mosquito

A number of means can be used to reduce the risk of being bitten by a mosquito. Insect repellents are the most popular, and the most widespread method. It is also recommended to wear long sleeves, trousers, hats, and generally speaking, any clothing that protects your skin. Although fabric usually doesn't completely protect against mosquito bites, it does make it harder for the insect to bite you, and a repellent can be applied on the clothing too. Most mosquitoes are primarily active during dawn and dusk, so it is recommended to stay inside at these times. Mosquito netting can be used on a bed, to protect yourself from being bitten during sleep. 

You can also do your share to reduce the number of mosquitoes by eliminating old tires, barrels, plastic bottles, or any types of vessels that can hold a body of water, where the insects could breed. Covering garbage cans, cleaning the gutter and maintaining your pool, if you have one, are also effective ways of eliminating the larvae. Some plants, like marigold, lavender or basil, are known to repel mosquitoes, so planting them in your garden can be a way of reducing the risk of being bitten.

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