There have been more cases of West Nile virus reported so far this year than any year since the disease was first detected in the United States in 1999, the Centers for Disease Control said on its website.

Nearly half of the 693 human cases of the mosquito-borne West Nile virus infections reported this year to the CDC have been in Texas, along with 14 of the 26 deaths confirmed by the federal agency as of Tuesday.

The Texas health department said the number of cases of West Nile in the state had reached 465 and there had been 17 deaths. There is a lag in the CDC confirming cases and deaths.

The emergency declaration by Mayor Mike Rawlings followed a similar action last week by Dallas County officials and paves the way for aerial pesticide spraying to begin this week.

Aerial spraying also is being used elsewhere, including in neighborhoods in New York City and Sacramento, California, to combat the spread of West Nile virus. Officials say such spraying is the most effective way to fight the mosquitoes that carry the disease despite safety concerns about exposing people to chemical pesticides.

"We are on track to have the worst year ever for West Nile virus in Texas," said Christine Mann, a spokeswoman for the Texas health department, adding that the number of cases was triple the previous high year of 2003.

It is not clear why the number of West Nile cases in Texas is so high. It could be related to a warmer winter and rainy spring that has contributed to an increased mosquito population, Mann said.

West Nile virus usually flares up in the summer because it is most often transmitted by mosquito bites. People infected can suffer fever and aches that can become severe or even cause death, especially of the elderly, children and other at risk groups. There is no specific treatment for the West Nile infection.

(Editing by Colleen Jenkins and Greg McCune. Editing by Andre Grenon)

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