Louisiana Gov. Mike Foster declared a statewide emergency Aug. 1 after West Nile virus was found to have reached almost every corner of the state. Scores of Louisiana residents have been infected and eight of them died in what is the worst West Nile virus outbreak in the United States since it emerged three years ago. Human fatalities have also been reported in Illinois, Mississippi, and Texas.
Given the rapid transmission of West Nile virus across the country, the national Centers for Disease Control and Prevention believes the once exotic virus is now permanently established in this country. At press time in late August, a total of 253 human cases of West Nile infection had been reported this year, compared with 149 cases from 1999-2001.
"[W]e have more cases already this year than we have had in any of the previous three years, so this will be obviously a peak year," said James Hughes, MD, director of the CDC's National Center for Infectious Diseases.
The Louisiana Department of Health and Hospitals has confirmed West Nile encephalitis infections in 147 people. The state Department of Agriculture and Forestry has confirmed 118 equine infections. The governor is requesting federal assistance to offset the costs of spraying for mosquitoes carrying the virus, discovered in Louisiana in 2001.
"It is becoming quite evident that the broad nature of this outbreak is going to quickly deplete both state and local funds dedicated to epidemiological efforts, laboratory testing, surveillance, and mosquito control efforts," said David Hood, secretary of the state Health and Hospitals Department.
The second largest number of infections have occurred in Mississippi, which reported 55 illnesses and two deaths.
Since the virus was first detected in the Western Hemisphere in the northeastern United States in 1999, more than half the states have found the West Nile virus in birds, animals, mosquitoes, or humans. Texas, Oklahoma, Kansas, Nebraska, Wyoming, Colorado, North Dakota, and South Dakota are the newest states this year to report infections.
The Louisiana residents who died from West Nile encephalitis ranged from 53 to 94 years of age. Elderly people and those with compromised immune systems are most at risk from the virus, and 18 human deaths have been attributed to the virus between 1999 and 2001.
Data from this year's outbreak, however, indicate that younger people are becoming ill. In Louisiana, infections were reported in a girl younger than 14, 11 people between 15 and 29 years of age, 11 people between 30 and 44 years of age, and 15 between 45 and 59 years of age. Illinois reported its first human infection in a 22-year-old student from Maryland living in suburban Chicago.
Of those with severe illness from West Nile virus, the CDC says, case fatality rates range from 3 percent to 15 percent. Less than 1 percent of persons infected with West Nile virus will develop severe illness.
Horses appear especially susceptible to West Nile infection, prompting the conditional approval of a West Nile virus vaccine for equines (see JAVMA, Sept. 15, 2001, page 715).
The equine cases in North Dakota, Wyoming, Colorado, and Texas are the first West Nile infections ever detected in those states. For timely reports on West Nile virus, check www.avma.org.