Trying to Trap a Killer : Health: Scientists test rodents near San Clemente to see if they’re carrying the deadly hantavirus.

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The deer mouse pulled from Trap No. 30 on Wednesday had probably spent most of the night trying to escape from the small metal box in which it was ensnared.

The next time the small, brownish rodent with snow-white paws saw daylight, a group of county scientists in decontamination “space suits” were tossing it into a chest of dry ice. Stunned by the low temperature, the mouse was still and stiff when the needle of a syringe that was plunged into its heart drew most of the blood from its body.

“Quite a way to die for these little guys, isn’t it?” said county biologist Jim Webb, who spent Wednesday morning pulling small rodents from traps near the TRW Capistrano Test Site in the foothills east of San Clemente.


Webb’s quarry was more than just the meek deer mouse and its fresh blood: He was searching for the mysterious hantavirus, a killer of humans that may or may not be lurking in the county’s rural rodents.

Webb and his colleagues reported last month that stored blood samples from five deer mice caught in the same trap area in September, 1992, had tested positive for the hantavirus, although federal lab technicians have not been able to discern if it is the strain responsible for at least 33 deaths nationwide.

“This may all fizzle--we may be out here for nothing,” Webb said, sweating beneath the clinging plastic of his decontamination suit. The trapping done Wednesday, the first since state health officials lifted a ban on field surveys that was imposed in August for safety reasons, will determine if the virus is still turning up among the area rodents.

“We could come out of here with nothing, and that would be great,” Webb said. “A lot of people, including me, would be happy if we turned up zero.”

Indeed, the speed with which the virus kills, and the lack of a cure for the ailments it triggers, make the hantavirus a particularly vexing public health threat. While the virus poses no threat to its deer mice carriers, it brings on flu-like symptoms in humans that quickly worsen, in many cases causing the lungs to fill with fluid, drowning the infected person.

The airborne virus is transmitted via a fine dust created by dried deer mice feces, and Webb said there have been cases in which victims have inhaled the dust without ever seeing the mouse or its droppings.


But those chilling aspects of the hantavirus are tempered by the relative rarity of actual cases. The deer mouse is a rural species that eschews most buildings and other developed areas, and most cases of infection recorded since the virus flared up in the Southwest last summer have been among people who had almost daily contact with rodents, state health officials said.

There were only two documented California deaths, in Santa Barbara County and the Mammoth Lakes area in the eastern Sierra. One victim was a field biology student, the other a ranch hand who had skinned mice to feed his cat. Also, although the Orange County positive test results turned up in stored blood taken during a Lyme disease survey in September, 1992, there have been no hantavirus illnesses reported locally.

Still, the three county biologists who pulled rodents from the traps spread throughout ridges and a canyon near the TRW test site were careful to make sure their plastic cloaks, suits, boots and gloves covered them completely. A pump the size of a loaf of bread was strapped to the back of their belts, feeding them oxygen through a full face mask.

“It may be overkill, but you don’t want to gamble with something like this,” biologist Fred Beams said as he watched his suited colleagues from a distance. “If you gamble, you can die.”

In all, three deer mice were pulled from the 31 traps set out this week by county vector control staff. Two very close relatives, a wood rat (also known a pack rat) and a cactus mouse, were also trapped and tested because they too might be carriers of the virus, Webb said. A kangaroo rat, a species never linked to the virus, was caught and freed.

The blood from the tested rodents will be processed by county technicians and, pending a state paperwork process now under way, should be shipped to the federal Centers for Disease Control and Prevention in Atlanta in a few weeks. Those labs, already overtaxed by the country’s tuberculosis situation and other public health problems with higher priority, have a backlog that will further delay the results, county veterinary services director Richard H. Evans said.


“On a list of the top 100 health problems out there, hantavirus is not going to be very high on the list,” Evans said. “They’re busy with a lot of other things in Atlanta. TB, for example, is a far greater problem than this.”

In the meantime, Webb said, more field surveys will be scheduled across Orange County’s rural areas. Beyond that, all Webb said he and his staff can do is sit tight and wait to hear whether the September, 1992, samples or the blood collected Wednesday indeed show that the deadly strain of the hantavirus is lurking somewhere in Orange County.

For the time being, he said, the information is frustratingly sketchy. A fitting comparison, Webb said, would be identifying an animal as a dog, but not knowing whether it is a rabid Doberman or an affectionate poodle, or whether it is still even in the area.

“One is innocuous and the other is deadly,” he said. “We don’t know which it is, but I hope we can find out soon.”