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27-08-2012 | Article

CDC: West Nile virus outbreak among worst in memory

Abstract

Fact sheet

medwireNews: The current West Nile virus (WNV) outbreak is one of the largest ever seen in the USA, according to the Centers for Disease Control and Prevention (CDC).

WNV has been detected in birds, mosquitoes, or people in 47 states (only Alaska, Hawaii, and Vermont have reported no viral activity), and human cases have been reported in 38 states as of August 21, Lyle Petersen, director of the CDC's division of vector-borne infectious diseases, said in a briefing.

Of the reported 1118 human cases of WNV, 629 (56%) led to neuroinvasive infections such as meningitis or encephalitis, with the remainder classified as non-neuroinvasive disease. There have been 41 human deaths attributable to WNV infections at the most recent report.

"These 1118 cases and 41 deaths identified thus far in 2012 are the highest numbers of West Nile virus disease cases reported to CDC through the third week in August since West Nile virus was first detected in the United States in 1999. In comparison, one month ago, there were only 25 people with West Nile virus disease reported to the CDC," Petersen said.

Approximately half of all cases occurred in Texas, and Texas, Mississippi, Louisiana, Oklahoma, and South Dakota together account for about 75% of all cases reported to the CDC.

The Dallas-Fort Worth area of Texas has been hardest hit, with 270 cases reported, 142 of which were classified as neuroinvasive disease, and 128 were marked by fever. As of the third week in August there were 11 deaths in Dallas County alone, said Texas Health Commissioner David Lakey.

The CDC also reports that 242 potentially viremic blood donors were reported in 26 states, however; the US blood supply is screened for WNV, so the risk for infection from donated blood is low, Petersen noted.

Approximately 80% of people who are infected with WNV are asymptomatic, the CDC says, but around one in five infected individuals may have mild disease, manifested by fever, headache, body aches, nausea, vomiting, and, occasionally swollen lymph nodes or rash on the chest, stomach, and back.

"About one in 150 people infected with WNV will develop severe illness. The severe symptoms can include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis. These symptoms may last several weeks, and neurological effects may be permanent," according to a CDC fact sheet.

There is no specific treatment apart from supportive care, the CDC adds.

By Neil Osterweil, medwireNews reporter