DENVER -- The West Nile virus has claimed a seventh victim in Colorado, which accounts for two-thirds of this year's deaths from the mosquito-borne virus,

local officials said on Friday.

A 69-year-old woman, who lived in a rural area, succumbed to meningitis, one of the serious diseases that West Nile can cause, according to Cindy Parmenter, spokeswoman for the Colorado Department of Health and Environment.

All the fatal cases in Colorado have involved people in their 60s, 70s and 80s.

The U.S. Centers for Disease Control and Prevention reports 2 deaths each in Alabama and Texas.

West Nile, seen commonly in Africa, was imported into the United States in 1999. Carried by birds and mosquitoes, it has spread to most of the country and parts of Canada.

The disease arrived in Colorado last year in August, but this year it is taking a hard toll in the Rocky Mountain state.

Two types of Colorado mosquito, the culex tarsalis and culex papens, are successful at transmitting the disease, according to John Pape, a Colorado Department of Public Health and Environment epidemiologist.

Also, the second year of the disease tends to be much tougher because birds have not developed an immunity.

After the second year, the picture changes. "A large percentage are immune so you don't get a build up. Then the old immune birds die and the virus gets reintroduced and then goes away again," Pape, said.

Colorado has 299 human cases, up from 195 earlier in the week, but Parmenter said Colorado is counting all cases, including West Nile fever, a flu-like affliction. The CDC counts 247 infections in Colorado and 446 nationwide. Only the most vulnerable people suffer serious symptoms and many would not even know they were bitten by a mosquito that carried West Nile. Spraying has begun in Colorado.

North of Denver in Larimer County, two deaths and more than 60 cases of the infection have been reported.

In Houston, where mosquitoes thrive in the moist, hot climate, aerial pesticide spraying began early after officials confirmed the presence of West Nile an infected dove in May.

Since then, the Houston area has been sprayed repeatedly and 17 human cases have been confirmed, according to the Houston Department of Health and Human Services.