Q: What is West Nile virus?

A: West Nile virus is a new virus imported accidently into the United States in 1999 in New York. Within three years it has emerged as a recurring mosquito-borne infectious disease across the entire country.

Q: How is it spread?

A: The virus infects black birds, crows and robins. Mosquitoes contract the virus from those birds. The mosquitoes then feed on and consequently infect horses and humans with the virus. The mosquitoes that do so are most prevalent in the late summer and early fall. They typically bite at dusk and dawn. This year is unusual in that the first cases started in June and July, and the total human cases to date in 2012 are the highest number yet in the United States.

Q: What are the symptoms?

A: Most people have only mild, flu-like symptoms, and occasionally a rash on the torso and swollen lymph glands.

Q: How is it treated?

A: There is no specific treatment for human cases of the virus. In milder cases people experience symptoms such as fever and aches that pass on their own, although even healthy people have become sick for several weeks. In more severe cases with infection of the brain, people need to go to the hospital where they can receive supportive treatment including intravenous fluids, help with breathing and nursing care.

Q: What can people do to prevent West Nile virus?

A: The best protection is mosquito avoidance. However, if you are going to be outside at dawn or dusk, then you should wear long sleeves and long trousers; wearing shorts and not wearing a shirt create an invitation to be bitten. You should also cover exposed areas of skin with dabs of deet-containing mosquito repellant. You should eliminate standing pools of water on your property to stop mosquito breeding.

Be aware that the Pennsylvania Department of Health has an active surveillance team that traps mosquitoes year round and looks for West Nile infection in the mosquitoes. They also spray safely to eliminate pools of mosquito eggs. Their activities are easy to follow on the Pennsylvania Department of Health website www.westnile. state.pa.us.

Q: Why is it worse this year?

A: It is not entirely clear why the number of human West Nile cases is so high this year. Some speculate it is related to our warmer winter and rainy spring, which theoretically could have led to an increased mosquito population.

Dr. Rhodes is the chief of infectious diseases at Lehigh Valley Health Network.