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West Nile still worries health officials
Health advice
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Mosquito season is here and public health officials are reminding residents that mosquitoes can transmit a number of diseases, including West Nile virus.
Vector-borne diseases are made up of organisms that spend part of their life inside a mosquito, flea, tick or other arthropod, and the other part inside a vertebrate. The vector picks up the disease when it bites an infected host, and then carries it to new hosts during its next blood meals.
The normal vertebrate hosts of most vector diseases of man (malaria is almost an exception) are wild or domestic animals. Humans become infected usually only when they step into an already existing natural cycle.
The life cycle of all mosquitoes consists of four stages: egg, larva, pupa and adult. And regardless of the type of mosquito species, water is essential for breeding. Eggs are laid in batches of 50 to 200 and one female may lay several batches. In warm water, the eggs of most species hatch in two or three days although some eggs require a drying period.
Contrary to popular opinion, mosquitoes do not breed in the heavy undergrowth of weeds, bushes or shrubs. Although these places provide excellent refuge for adults, they do not provide a suitable habitat for mosquito larvae. Common breeding sites for mosquitoes are drainage ditches, ponds, tin cans, old tires and tree holes.
There are 2,700 different species of mosquitoes throughout the world and the United States is home to 150 varieties. These different types show considerable variation in their preferred hosts. Some species feed on cattle, horses, or other domestic animals while others prefer man. A few species feed only on cold-blooded animals and some live entirely on nectar or plant juices. Some are active at night and others only during the day.
Mosquitoes can be extremely annoying and can cause serious problems. In addition to interfering with work and leisure time, their attacks on farm animals can cause loss of weight and decreased milk production. Some mosquitoes are capable of transmitting diseases such as West Nile virus, yellow fever and dengue, encephalitis to man and horses, and heartworms to dogs.
The spread of WNV has been unpredictable in the United States but trends throughout the country have shown an increase of cases. Carried by infected mosquitoes, WNV can cause serious illness in some people and horses. Mosquitoes become infected when they feed on infected birds. The virus has been reported in more than 70 bird species in the U.S. You cannot get the virus from another person or animal.
Most people who become infected do not become ill but about 20 percent will develop West Nile fever, which features fever, headache, body aches, and occasionally a rash as well as swollen lymph glands. Symptoms begin three-14 days after the bite and when there is a mild disease, last only a few days.
One out of 150 infected people, however, will develop a severe infection known as West Nile encephalitis or meningitis. Symptoms can include headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, weakness and paralysis. Symptoms may last several weeks, although some brain and nerve damage may be permanent. There is no effective treatment for WNV other than supportive medical care.
To date, there are no vaccinations for humans, but vaccinations are available for horses.
There are two basic prevention strategies for mosquitoes; reducing the mosquito population where you are and avoiding mosquito bites.

Ratcliffe works with the Coastal Health District.
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