Two more people have died of West Nile virus in the United States - both of them in Illinois, state health officials said on Tuesday.

If confirmed by the Centers for Disease Control and Prevention, the latest deaths would indicate that the mosquito-borne virus, once focused on the South, is increasingly infecting people farther north.

The Illinois deaths would bring the national death toll to 22.

The two latest victims were an 83-year-old man from Chicago, who died on 21 August, and a 92-year-old woman from the city's suburbs who died on Saturday.

Insect repellents can help prevent the disease

The pair suffered from West Nile encephalitis - an inflammation of the brain.

The male victim also suffered from cancer and diabetes, the Illinois Department of Public Health said.

A private laboratory determined that the cause of death was the West Nile virus, but the finding has yet to be confirmed by state health officials.

"At this point in time it's a presumable or probable West Nile case," said George Miller, manager of the Oakland County Health Division.

There have been 425 reported cases of West Nile virus in the US so far this year, making it the worst outbreak since it was first detected in 1999.

That year, the disease was reported to have caused seven fatalities, all of them in New York.

Since then, people have been diagnosed with West Nile in 20 states and the District of Columbia.

Northern cases

In the latest outbreak of the virus, cases have been reported from the Gulf of Mexico to the Great Lakes, but the greatest damage has been done in the South.

Louisiana is the hardest hit, with 171 cases and eight deaths.

Louisiana officials said last week it appeared the number of new cases there was decreasing, but northern states have seen a surge in reports of infection.

On 16 August, the CDC reported only about 4% of West Nile infections, and none of the deaths, were outside the South.

The latest Illinois deaths, and 29 new cases announced on Monday and Tuesday, bring the figure to almost 30%.