For more information on all the diseases, visit the U.S. Centers for Disease Control and Prevention at www.cdc.gov.
West Nile virus
What it is: A viral infection that first showed up in the United States 10 years ago and infected thousands each summer but has dropped off dramatically in recent years.
How it spreads: When a mosquito feeds on a bird infected with West Nile, the mosquito can carry the virus and infect a person through a bite. It is not transmitted from person to person.
Symptoms: Most people who are infected never develop symptoms. About 20 percent will develop headache, fever, body aches or rash. In very rare cases, the virus can lead to encephalitis (inflammation in the brain). Last year, 32 people in the United States died of West Nile virus.
Treatment: Doctors can treat the symptoms, but there is no cure. Most patients recover on their own.
Prevention: Spray insect repellent with DEET on exposed skin. Avoid being outdoors at dusk, when mosquitoes are most active. Remove all standing water from flower pots and bird baths.
Incidence: 720 confirmed cases in the United States last year.
What it is: A viral infection.
How it spreads: Dengue is transmitted by infected mosquitoes, not person to person. Dengue is the most common cause of fever in U.S. travelers to the Caribbean, central and South America and Asia. Upon their return, sickened U.S. travelers can infect domestic mosquitoes, who then spread it to other people.
Symptoms: Dengue typically causes mild illness or none at all. Symptoms can include fever, headache, severe joint pain, eye pain, rash and vomiting. Rarely, severe cases can lead to dengue hemorrhagic fever, which can be fatal.
Treatment: There is no specific drug to treat dengue illness, but the symptoms usually can be treated.
Prevention: As with West Nile, the best prevention is avoiding mosquito bites. Researchers at St. Louis University are conducting a human clinical trial of an experimental dengue vaccine. E-mail firstname.lastname@example.org or call 314-977-6333.
Incidence: The most common mosquito-borne virus, dengue infects more than 100 million people worldwide each year, mainly in tropical regions. There were no reports of cases acquired in the United States before 1980. Since then, a few cases have been reported along the Texas-Mexico border. Last month, the CDC confirmed 28 cases of dengue in Key West. Other recent outbreaks have been linked to American relief workers returning from Haiti.