Two more South Dakotans have died from West Nile virus.

The disease has killed five people this summer and sickened at least 161 in the state.

The state Health Department said the most recent victims are a Todd County resident in the 50-59 age group and a Lake County resident in the 80-89 age group.

The previous three victims were from Pennington, Hand and Brown counties, and all were in the 80-89 age group.

Lon Kightlinger, state epidemiologist for the department of health, says even though there may have been frost overnight, the threat of West Nile remains.

"The threat or risk is diminishing, but it has not gone away," he said.

Only a hard frost, of 28 degrees or less, will eliminate the threat, he said. Overnight lows today were expected to be near 34 degrees.

"That (cold temperatures) will orient them in the right direction," he said. "It won't kill them or stop them, but it will give them a biological cue that they need to look to hibernation."

And instead of biting for blood, the mosquitoes will be looking more to plant juices to fatten up for hibernation.

"The threat is decreasing, but it is not going away," Kighlinger said. "We have had people come down with West Nile in October in South Dakota."

Human West Nile virus cases have been reported in 48 of South Dakota's 66 counties. Fifty-four percent of the victims have been men, and 46 percent are women. The majority of all cases - 76 percent - have had West Nile virus fever, and 24 percent have had the more serious West Nile virus meningitis/encephalitis.

"The elderly are at very high risk for West Nile," Kightlinger said. "I can't emphasize enough how important it is for them to take precautions to protect themselves."

The department recommends the following precautions to prevent mosquito bites and reduce the risk of West Nile virus:

* Use mosquito repellents containing deet, picaridin or oil of lemon eucalyptus, and cover as much skin as possible with loose-fitting clothing.

* Limit time outdoors at dusk and dawn, when mosquitoes are most active.

* Eliminate standing water that gives mosquitoes a place to breed.

* Support local mosquito-control efforts.

Elderly people, pregnant women, diabetics, transplant patients, individuals with high blood pressure and those with a history of alcohol abuse should be especially mindful to take precautions. People with a severe or unusual headache should see their physician.