ATLANTA — West Nile virus has been found in mosquitos, birds and other animals in 32 states this year, up from about 20 states at this time last year, health officials said.
Four people in the United States have contracted the disease, the same as a year ago, the Atlanta-based Centers for Disease Control and Prevention said this week. Three cases have been confirmed in Texas and one in South Carolina.
In Georgia this year, the virus has infected mosquitos, birds and horses but not humans.
"Overall, the national activity level is increased," said Dr. Julie Gerberding, CDC director. "There is reason to anticipate a problem."
West Nile — first discovered in the United States in 1999, in New York — left only a few Western states untouched last summer, infecting more than 4,100 people and killing 284. Authorities expect it to reach the West Coast this year.
Meanwhile, researchers continue to work on possible vaccines and treatments for the mosquito-borne disease.
A vaccine that mixes West Nile proteins with a yellow fever vaccine will be tested in volunteers late this summer, said Dr. James Meegan, virology program officer at the National Institute of Allergy and Infectious Diseases.
In addition, immune globulin — pooled antibodies from the blood of people who have recovered from West Nile — will be given experimentally to treat patients with the disease this year, Meegan said.
The blood donation system began using new tests to screen for West Nile last month.
Last week the government approved a diagnostic test that could expand the number of labs able to confirm that patients have the disease.