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The disease was first recorded in North America in 1999. In 2002, it has been identified in 38 states, including Minnesota, where it has been found in horses and birds, including in Stearns and Kandiyohi counties.

The following information comes from the Center for Disease Control.

Q: What is West Nile encephalitis?
A: Encephalitis is an inflammation of the brain and can be caused by viruses and bacteria, including viruses transmitted by mosquitoes. West Nile encephalitis is an infection of the brain caused by West Nile virus, a flavivirus commonly found in Africa, West Asia, and the Middle East. It is closely related to St. Louis encephalitis virus found in the United States.

Q: Where did the West Nile virus come from?
A: West Nile virus has been commonly found in humans and birds and other vertebrates in Africa, Eastern Europe, West Asia, and the Middle East, but until 1999 had not previously been documented in the Western Hemisphere. It is not known from where the United States virus originated, but it is most closely related genetically to strains found in the Middle East.

Q: How long has West Nile virus been in the United States?
A: It is not known how long it has been in the United States, but CDC scientists believe the virus has probably been in the eastern United States since the early summer of 1999, possibly longer.

Q: How many cases of West Nile encephalitis in humans have occurred in the United States?
A: In 1999, 62 cases of severe disease, including seven deaths, occurred in the New York area. In 2000, 21 cases were reported, including two deaths in the New York City area. In 2001, there were 66 human cases of severe disease and nine deaths. No reliable estimates are available for the number of cases of West Nile encephalitis that occur worldwide.

In 2002, as of Friday, Aug. 23, 371 confirmed and probable cases had been reported to the CDC, including 171 in Louisiana, 91 in Mississippi, 28 in Texas, and 26 in Illinois.

No human cases have been reported in Minnesota so far.

Q: What is the basic transmission cycle?
A: Mosquitoes become infected when they feed on infected birds, which may circulate the virus in their blood for a few days. Infected mosquitoes can then transmit West Nile virus to humans and animals while biting to take blood.

Q: If I live in an area with birds or mosquitoes with West Nile virus and a mosquito bites me, am I likely to get sick?
A: No, even in areas where the virus is circulating, very few mosquitoes are infected with the virus. Even if the mosquito is infected, less than one percent of people who get bitten and become infected will get severely ill. The chance you will become severely ill from any one mosquito bite is extremely small.

Q: Can you get West Nile encephalitis from another person?
A: No, West Nile encephalitis is NOT transmitted from person-to-person. For example, you cannot get the virus from touching or kissing a person who has the disease or from a health care worker who has treated someone with the disease.

Q: What proportion of people with severe illness due to West Nile virus die?
A: Among those with severe illness due to West Nile virus, case-fatality rates range from three to 15 percent and are highest among the elderly. Less than one percent of persons infected with West Nile virus will develop severe illness.

Q: What can be done to prevent outbreaks of West Nile virus?
A: Prevention and control of West Nile virus and other arboviral diseases is most effectively accomplished through integrated vector management programs. These programs should include the surveillance of West Nile virus activity in mosquito vectors, birds, horses, other animals, and humans and the implementation of appropriate mosquito control measures to reduce mosquito populations as necessary.

Q: Is there a vaccine against West Nile encephalitis?
A: No, but several companies are working towards developing one.

Q: What can I do to reduce my risk of becoming infected with West Nile virus?
A: *Stay indoors at dawn, dusk, and in the early evening.

*Wear long-sleeved shirts and long pants whenever you are outdoors. Spray clothing with repellents containing permethrin or DEET since mosquitoes may bite through thin clothing.

*Apply insect repellent sparingly to exposed skin. An effective repellent will contain 35 percent DEET, which in high concentrations (greater than 35 percent) provides no addition protection.

*Repellents may irritate the eyes and mouth, so avoid applying repellent to the hands of children. (Whenever you use an insecticide or insect repellent, be sure to read and follow the manufacturer's DIRECTIONS FOR USE.)

*Install or repair window and door screens so that mosquitoes cannot get indoors.

Q: Who is at risk for getting West Nile encephalitis?
A: All residents of areas where virus activity has been identified are at risk of getting West Nile encephalitis; persons over 50 years of age have the highest risk of severe disease.

Q: What are the symptoms of West Nile encephalitis?
A: Most infections are mild, and symptoms include fever, headache, and body aches, occasionally with skin rash and swollen lymph glands. More severe infection may be marked by headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, paralysis, and, in rare cases, death.

Q: What is the incubation period for West Nile encephalitis?
A: Usually three to 15 days.

Q: What should you do if you have possible symptoms of WNV?
A: Contact your health care provider if you have concerns about your health. If you or your family members develop symptoms such as high fever, confusion, muscle weakness, and severe headaches, you should see your doctor immediately.

Q: How is West Nile treated?
A: There is no specific therapy. In more severe cases, intensive supportive therapy is indicated, often involving hospitalization, intravenous fluids, airway management, respiratory support (ventilator), prevention of secondary infections (pneumonia, urinary tract, etc.), and good nursing care.

Q: How do horses become infected with West Nile virus?
A: The same way that humans become infected - by the bite of infectious mosquitoes.

Q: How does the virus cause severe illness or death in horses?
A: Following a transmission by an infected mosquito, West Nile virus multiplies in the horse's system, crosses the blood brain barrier, and infects the brain. The virus interferes with normal central nervous system functioning and causes inflammation of the brain.

Q: Can a horse infected with West Nile virus infect horses in neighboring stalls?
A: No, there is no documented evidence that West Nile virus is transmitted between horses. However, horses with suspected West Nile virus should be isolated from mosquito bites if at all possible.

Q: Can I vaccinate my horse against the West Nile virus?
A: A West Nile virus vaccine for horses was recently approved, but its effectiveness is unknown.