No Hantavirus Found in Mice in South County

Federal scientists found no trace of the often fatal, rodent-carried hantavirus among blood samples recently taken from Orange County deer mice, county health officials said Thursday.

The findings counter results from earlier field studies, which identified five deer mice near San Clemente carrying a strain of the air-carried virus that has been tied to at least 33 deaths nationwide.

County vector ecologist James Webb said the new results are encouraging, but it may be too soon to breathe easy. The new study included only 15 rodents, seven of them deer mice.

“It’s not good news and it’s not bad news,” said Webb, who has led the field studies. “It’s not a sign one way or the other because it’s such a small sample size.”

Webb said local field research would continue, while the federal Centers for Disease Control and Prevention in Atlanta continues its effort to isolate the virus, which is carried via a fine dust emitted by deer mice droppings.

The hantavirus strikes with flu-like symptoms that quickly worsen and often lead to a death similar to drowning, in which the victim’s lungs fill with fluid. No cure is known.

There have been two California cases of the illness, both leading to death, but there have been no cases in Orange County. There have been indications locally that the virus may be present.

County vector control officials reported in September that stored blood samples collected from five deer mice in south Orange County a year earlier tested positive for the virus.

But that result was not clear-cut--so little is known about the virus, that federal researchers were unable to say if the strain present in the Orange County rodents was the same that led to deaths across the Southwest.

News that the virus might be in Orange County triggered a wave of anxiety in September. Although only rural rodents, not their house-invading cousins, have been linked to the hantavirus, hundreds of residents flooded county vector control workers with calls. Several high school athletic events were moved from Carbon Canyon Regional Park for fear that athletes and spectators might be in danger, and employees in the county’s rural parks received courses on safety measures.

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Hoping to better pin down the true danger level, Orange County health officials returned to do more tests in the area that yielded the positive results, the rocky foothills surrounding the TRW Capistrano Test Site, just outside San Clemente.

“This time we didn’t get any positive results, but we still need a better picture of the situation,” Webb said.

More extensive follow-up efforts will be needed to accurately gauge the danger, Webb said. Webb said he wants to do a two-year study, with at least 50 trapped animals.

Scientists, who don airtight “space suits” to protect themselves during field work, will return to the TRW test site within the next two weeks to continue their survey, Webb said. Rural rodents also will be caught near the Bolsa Chica wetlands and the foothills of Tonner Canyon near Brea, he said.