(Reuters) - The number of U.S. cases of West Nile virus rose 25 percent in the latest week, while the number of deaths jumped 32 percent, placing the 2012 outbreak of the mosquito-borne disease on track to be the most severe on record, health officials said Wednesday.

So far this year 1,993 cases have been reported to federal health officials, up from 1,590 reported the week before, the U.S. Centers for Disease Control and Prevention said in its weekly update of outbreak data. A total of 87 people have now died from the disease compared with 66 reported one week ago.

The disease has been reported in people, birds or mosquitoes in 48 U.S. states, so far absent only in Alaska and Hawaii. Nearly half of all human cases, 888, are in Texas, which has been the epicenter of this year's outbreak, the CDC said. The state accounts for 35 deaths, or 40 percent of those who have perished from the disease this year.

South Dakota has the next-highest number, with 119 cases and two deaths. More than 70 percent of the cases have been reported from Texas, South Dakota and four other states: Mississippi, Oklahoma, Louisiana, and Michigan.

The CDC said the number of cases so far this year is the highest reported to federal health officials through the first week in September since the disease was first detected in the United States in 1999. Even at the current record pace, this year's outbreak amounts to roughly a quarter of the all-time high reached in 2003: 9,862 cases and 264 deaths.

Of the nearly 2,000 cases this year, 1,069, or 54 percent, are of the more severe neuroinvasive form of the disease, which can lead to meningitis and encephalitis.

This year's outbreak is already nearly three times the size of last year's, when 712 cases were reported nationally, with 43 deaths.

(Reporting By Dan Burns; Editing by Vicki Allen)


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