The number of US cases of West Nile virus climbed by nearly a third in the latest week as the spread of mosquito-borne disease accelerated and threatened to make the 2012 outbreak among the most severe on record, government figures showed on Wednesday.

So far this year, 2,636 cases have been reported to federal health officials, up from 1,993 reported the week before, the Centers for Disease Control and Prevention said in its weekly update of outbreak data. A total of 118 people have now died from the disease, compared with 87 reported one week ago.

The disease has been reported in people, birds or mosquitoes in 48 US states, so far absent only in Alaska and Hawaii. About 40 percent half of all human cases are in Texas, the CDC said. Two-thirds of the cases have cropped up in six states.

Of the cases reported to the CDC this year, 1,405, or 53 percent, are of the severe neuroinvasive form of the disease, which can lead to meningitis and encephalitis.

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