The outbreak of the West Nile virus this year has been "one of the largest" since the virus first appeared in the country in 1999, with three times the usual number of  cases being reported for this time of year, U.S. health officials say.  

So far, 1,118 illnesses have been reported, about half of them in Texas, according to the Centers for Disease Control and Prevention. In an average year, fewer than 300 cases are reported by mid-August. There have also been 41 deaths this year.

"We're in the midst of one of the largest West Nile outbreaks ever seen in the United States," said Dr. Lyle Petersen, a CDC official.

We're in the midst of one of the largest West Nile outbreaks ever seen in the United States

- Dr. Lyle Petersen, a CDC official

Never before have so many illnesses been reported this early, said Petersen, who oversees the CDC's mosquito-borne illness programs.

Most infections are usually reported in August and September, so it's too early to say how bad this year will end up, CDC officials said.

They think the mild winter, early spring and very hot summer have fostered breeding of mosquitoes that pick up the virus from birds they bite and then spread it to people.

West Nile virus was first reported in the U.S. in 1999 in New York, and gradually spread across the country over the years. It peaked in 2002 and 2003, when severe illnesses reached nearly 3,000 and deaths surpassed 260. Last year was mild with fewer than 700 cases.

Only about one in five infected people get sick. One in 150 infected people will develop severe symptoms including neck stiffness, disorientation, coma and paralysis.

In recent years, cases have been scattered across the country. Hot spots are usually in southeast Louisiana, central and southern California, and areas around Dallas, Houston, Chicago and Phoenix.

Those areas seem to have a combination of factors that include the right kinds of virus-carrying mosquitoes and birds, along with large numbers of people who can be infected, health officials say.

The best way to prevent West Nile disease is to avoid mosquito bites. Insect repellents, screens on doors and windows and wearing long sleeves and pants are some of the recommended strategies. Also, empty standing water from buckets, kiddie pools and other places to discourage breeding.

Based on reporting by the Associated Press.

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