WASHINGTON _ A Navajo was the first to die. One day FlorenaWoody, 21, was healthy, the next day she could no longer breathe.Her abrupt death, on May 9, 1993, was not alarming. After all,Woody had a history of asthma.
But five days later, her fiance, Navajo long-distance runner MerrillBahe, 20, died too. Bahe began gasping for air during the 55-miledrive from the couple's trailer in Little Water, N.M., to Woody'sfuneral in Gallup. His horrified sister sister-in-law stopped at ageneral store and dialed 911. Bahe paced, agitated, his skin tingedwith yellow, his lips and fingertips turned blue. Then he collapsed.
Autopsies showed that both had essentially drowned, their lungssoaked in serum from their own blood.
And no one knew why.
The inexplicable deaths of Woody and Bahe, quickly followed bymore cases, ignited a nationwide alert over the mysterious newillness, which is now known to be caused by a rodent-borneorganism known as a hantavirus. The most recent case was reportedthis month in an Australian who was hiking the Appalachian trail inVirginia. The hiker, who was in his mid-sixties, survived. Othershaven't been as lucky. Of the 99 victims diagnosed in the U.S. sinceMay 1993, just 48 have survived.
The search for the cause of the illness _ known as the Four CornersOutbreak because it cropped up in the region of the Southwest whereNew Mexico, Arizona, Colorado and Utah meet _ is a textbookexample of how disease detectives go about their work. It alsorepresents a major advance in the way epidemiologic investigationsare conducted.
In most prior epidemic investigations, field epidemiologists playedthe key roles, gathering clues and analyzing statistical associationswith lab workers providing technical support. In this case, theepidemic was quietly solved by bench scientists working overtime atbuilding 15 at the Centers for Disease Control and Prevention (CDC)headquarters in Atlanta.
Building 15 houses the Maximum Containment Laboratory, wheresome of the world's most dangerous germs are stored.
C.J. Peters, chief of the CDC's special pathogen's branch presidesover this warren of air locks, safety showers and moon suits. Peters,an infectious disease expert, had his own pet picks for the cause ofthe mysterious illness: Two classes of rodent-borne agents known ashantaviruses, named for the Han River in South Korea where thevirus was first isolated, and arenavirus, a speckled organism whosename derives from the Latin word for sand.
"Originally we suspected these families because the victims wererural people you might expect to have had an exposure to rodents,"Peters says.
A Clue: Victims' High White Blood Cell Counts
A simple lab test provided another clue. Patient serum flown in fromthe field had an abnormally high white-blood-cell count "which ismore likely linked to a hantavirus infection than any virus I knowof," he said.
Yet virologists rarely trust their intuition. Peters and his team pulled25 vials of disease causing organisms out of laboratory freezers.Then, using tests developed by Thomas Ksiazek in the lab, theresearchers exposed them to antibodies taken from nine patients withthe illness.
In the test, the patients' antibodies zeroed in on a panel of threehemorrhagic fever viruses, from the hantavirus family. The reactionswere weak, and raised the possibility that the results were merely across-reaction or a laboratory artifact.
But the antibodies did not react with any other organism. And toKsiazek's practiced eye, the results did not look like cross reactions_ it appeared that victims of the outbreak had indeed been exposedto a hantavirus _ and that the virus might be related to the mysteryillness.
"That was a big surprise," said Stuart Nichol, chief of themicrobiology section of CDC's special pathogen's branch. Theimmunological data was strongly suggestive of a hantavirus, but itwasn't definitive and it didn't tell us what we were looking at.Because of the weak reactivity, it suggested that this wasn't one ofthe known hantaviruses. But it wasn't a very definitive test forlooking at that question."
Researcher Tapped Into GenBank
Nichol went to the computer. He logged on to the GenBank database of DNA sequences in Los Alamos. Until 4 a.m., he worked atthe keyboard, looking for multiple sequence alignments trying tofind conserved regions that he could use as priming sites. "When youare fishing for an unknown [organism] you don't want to use areasof the genome that are very variable because then maybe the primerswill work well with one specific type of hantavirus," and perhapsmiss the sought-after strain, Nichol said.
Armed with those sequences, which would be used as primers toinitiate reverse transcriptase polymerase chain reactions, Nicholcould generate nucleic acids that would pinpoint the new virus byhybridizing with any virus hidden in autopsy tissues taken fromvictims of the Four Corners outbreak.
The method worked. Using a sequence that was 139 bases long, theCDC researchers had found a newly emergent hantavirus that wasabout 10,000 bases long. It was June 4; the CDC researchers hadbeen working on the outbreak for less than a week. But a key testremained: To use the same techniques to prove that the virus hadcome from mice captured at the epicenter of the outbreak.
Enter microbiologist Jamie Childs, one of the few U.S. experts inhantaviruses.
For the CDC "rat trapper" that's not a simple task. Childs said hisfour-person team brought five trunks containing "everything weneed for the safe processing of animals and transporting them." Oncein the Four Corners, the team also trained health workers from theIndian Health Service and the state health departments of NewMexico and Arizona to do their own trapping.
Wearing sophisticated gas masks and surgical garb, the rat trappersvisited patients' homes, trapping mice, killing them and processingblood and tissue specimens so that lab scientists in Atlanta couldattempt to determine whether the outbreak was caused by a rodent-borne disease.
The rat trappers specimens arrived in Atlanta by June 12. Within aweek, the lab team had teased out the genetic sequence of the virustaken from the mice.
"It was exactly the same virus that was found in the initial patient,"said Ksiazek. "That closed the circle."
Thirty-four days after Florena Woody's death, her killer had beenidentified. All that remained was to isolate the virus itself, and thattask fell to LuAnn Elliot, who has spent the last 17 years in CDC'sspecial pathogens lab, much of the time working with the mostdangerous organisms known to man. To tackle the isolation of thehantavirus, Elliot had to postpone her efforts at designing a vaccinefor Lassa fever.
Elliot was working under conditions that were difficult, at best. Toisolate the virus, she had to manipulate the third most lethal virusever found in the U.S. And she had to accomplish this wearing thickgloves in a sealed suit weighing 25 pounds.
The breakthrough came when she found a source of lab-bred deermice. Elliot inoculated them with a 10 percent suspension of lungtissue in phosphate buffered saline, with bovine albumin as astabilizer.
It worked. The virus grew, and Elliot was able to isolate it.
The Four Corners outbreak was solved, but that doesn't meanhumankind's brush with the hantavirus is over. "We don't want to bealarmists about this" Ksiazek said. "But eventually it's likely that wewill get cases of the disease in all the states." n
-- Steve Sternberg Special To BioWorld Today
(c) 1997 American Health Consultants. All rights reserved.