Virus Spreads Outside Four Corners Area : Medicine: Officials report cases of the flu-like illness in Texas and Nevada. Scientists say the mysterious disease, transmitted by deer mice, may increase in fall, when rodents take shelter in houses.

The flu-like mystery illness that has plagued the Four Corners area of the Southwest is spreading outside the region, with new cases reported in Nevada and Texas, the U.S. Centers for Disease Control and Prevention said Thursday.

The disease, which has now been linked to a hantavirus carried by the deer mouse, also continues to show up in new cases in the Four Corners region, according to the agency’s Morbidity and Mortality Weekly Report.

Meanwhile, New Mexico ecologists say that previous epidemics of disease in Europe and Asia caused by other strains of hantavirus have shown dramatic increases in autumn, when rodents invade houses because of the onset of winter and crop harvesting.

A similar scenario may await the Southwest if rodent populations remain high, warned ecologist Robert Parmenter of the Long-Term Ecological Research Center in Sevilleta, N.M.

To date, the Four Corners illness, now officially called hantavirus-associated respiratory distress syndrome, or HARDS, is thought to have killed 29 of the 49 people infected. So far, however, the presence of the virus has been confirmed in only 21 of those patients, 15 of whom have died.

The inability to confirm the presence of the virus in the other suspected cases reflects the fact that scientists have not yet been able to grow the hantavirus in the laboratory. That is not surprising, said Dr. Stephen Ostroff, a medical epidemiologist at the Centers for Disease Control, because similar difficulties were encountered in isolating previous strains of hantaviruses.

One of the hantaviruses, which take their name from the Hanta Valley in Korea where they were first recognized, took 30 years to grow in the lab.

But Ostroff said he is confident that the centers’ researchers will isolate the virus within the next month. When they do, he added, it will be much easier to search for the virus in suspected cases. Now, researchers can only use indirect approaches, such as looking for antibodies against the virus.

All but three of the cases were among residents of the Four Corners region, where New Mexico, Colorado, Arizona and Utah meet. More than half of them were American Indians, primarily from the Navajo reservation, the country’s largest.

One of the victims, an Idaho woman who contracted the disease last year, had traveled to the Four Corners area shortly before developing the disease. But the other two victims from outside the area, one in Nevada and one in eastern Texas, were apparently infected at their homes.

Ostroff noted, however, that none of 55 blood samples from suspected victims in 24 states outside the Four Corners area showed any evidence of the hantavirus, suggesting that the illness is still relatively rare.

The New Mexico researchers said that the ultimate cause of the epidemic was most likely heavy precipitation in the Four Corners region in the winter and spring of 1992-93 caused by El Nino, a large area of warmer-than-normal water in the Pacific Ocean that has affected weather patterns throughout the United States.

As a result of the extra rainfall and plentiful food supply, the population of deer mice in the region increased tenfold this spring, Parmenter and ecologists James Brunt and Douglas Moore of the Long-Term Ecological Research Center have found. The deer mice are hosts for the hantavirus, but do not suffer any ill effects. The virus is spread to humans through mouse urine and droppings, which often become airborne after they dry.

If the large population of mice remains this fall, the researchers cautioned, they are likely to invade homes in search of food, sharply increasing the risk of a new outbreak.

Ostroff downplayed that possibility, however, saying, “I am not in the prediction game. It would be unfair to make those predictions when we don’t know enough about the virus.” In particular, he added, it is not clear whether the disease is caused by encounters with the mice in the home or outside it.

But the Centers for Disease Control and state and Indian agencies are making a concerted effort--supported by $6 million in new funds authorized by Congress--to warn people in the Southwest about the risk of infection. Among other things, they recommend that residents seal all openings by which rodents can enter homes, keep garbage in rodent-proof containers, remove abandoned cars and other junk that rodents use for nesting, and set rodent traps in woodpiles.