Last spring’s plague movie, Outbreak, had to compete with a real- life cliff-hanger: an appearance, in Zaire, of the dread Ebola virus. It came to the attention of health authorities in early May, after a sick laboratory technician died in a 350-bed hospital in Kikwit, a city of just over half a million people 186 miles east of Kinshasa. Before he died, the technician had gone through two abdominal operations, infecting the medical staff who took care of him. His symptoms--high temperature, headache, vomiting, and a rash that announced massive internal bleeding--were characteristic of the viral hemorrhagic fever group, which includes yellow fever, dengue, and hantavirus as well as Ebola. In its worst previous human visitation (also in Zaire, in 1976), Ebola virus achieved a death rate near 90 percent. There’s no vaccine, no cure. So when the Kikwit pathogen was identified as Ebola virus, health authorities and the media shifted into adrenaline overdrive.
Reports began appearing in the U.S. press in May, and--doubtless recalling the 1976 outbreak’s intimations of doomsday--they inclined heavily toward the sensational and gruesome. But the panic also surely owed something to a slowly dawning awareness among us that modern medicine hasn’t, as it once blithely appeared to promise, delivered us forever from contagious plagues. No sooner do we defeat one than a new one pops up: AIDS, Legionnaires’ disease, Lyme disease, hantavirus. Richard Preston’s grisly best-seller, The Hot Zone--which recounts a 1989 flare-up of Ebola sickness among a population of macaques at a quarantine facility in Reston, Virginia, and abounds in graphic descriptions--fanned the flames of terror. You couldn’t help wondering: Were we now facing a real-world Andromeda strain?
Not just yet, it seems. On August 24 the World Health Organization announced the apparent end of the 1995 epidemic, noting that two full three-week incubation periods had passed without the appearance of a new case. There’d been 315 known victims, of whom 244 (or 77 percent) had died. A horrendous toll, surely, but far short of the uncontrolled worldwide spread some pessimists feared. (In the 1918 influenza epidemic, for instance, 20 million people died and more than a billion were sick.) Luckily, the Zaire strain of Ebola virus, while devastating to those it attacks, is fairly easy to contain. The incubation period is short, the symptoms too catastrophic to be ignored, and the virus itself hard to transmit, apparently requiring either exposure to infected blood products or very close contact with a sick individual.
That, however, proved of small comfort to epidemiologists. In the monkey epidemic in Reston, it appeared possible that the deadly virus spread through the air, like a common-cold virus. Four of the five workers at the facility were infected with Ebola virus, yet only one, who’d cut himself while dissecting an infected macaque, had any intimate exposure to it. Fortunately, the Reston strain appears not to cause disease in humans, and none of the infected workers became ill. But viruses are notorious for their genetic instability, and it’s easy to imagine a strain, either yet to evolve or lurking undetected, as lethal as the Zaire variant and as easily spread as the Reston one.
Before they emerge, viruses may plod along for millennia, cycling quietly through animals or isolated human populations, unknown to the world at large, perhaps not even causing serious illness in their hosts. But some change in the biome--new roads, an airstrip, or overbuilding and a concomitant influx of mice or rats able to harbor the virus--can expose a vulnerable new population.
Ebola, like AIDS, seems to be released by the encroachment of new populations on once-remote country. Just as the Zaire epidemic was hitting the papers, French researchers reported that another Ebola outbreak had struck chimpanzees in the Ivory Coast’s Tai Forest in November 1994. Observers recognized it only when a primatologist who’d been studying the chimps fell ill with what turned out to be a hitherto unknown strain of Ebola (she survived). The team recalled that two years before, the chimps had undergone a similarly devastating epidemic, with eight animals dying in two weeks. Both outbreaks had occurred at the end of the rainy season, suggesting that the chimps may have been infected by a population of animals that moved into the region to hunt or forage among the lush growth nurtured by the rain.
Some such animal must be out there somewhere. But thus far it’s remained elusive. By late fall, according to Anthony Sanchez of the Centers for Disease Control’s Special Pathogens Branch, epidemiologists had traced the 1995 Zaire outbreak back past the unfortunate lab technician to an earlier patient at Kikwit’s hospital--a charcoal maker, who probably picked up the disease in the jungle where he worked. Yet, Sanchez concedes, that still leaves a wide range of crannies where the virus might be hiding. The worker would typically head into the jungle, cut down a tall tree, then burn it in a pit he’d dug. So the source might be anywhere from the top of the forest canopy down to some subterranean animal, Sanchez points out.
There’s another conundrum as well--the virus itself, which belongs to the filovirus family. Filoviruses were utterly unknown before 1967, when the first member of the family, Marburg virus, arrived in Germany in a shipment of African green monkeys. While Marburg appears less dangerous to humans than the worst forms of Ebola, it shares a number of peculiarities with its more lethal cousin, including a puzzling mode of interaction with the immune system. For reasons not yet clear, animals infected with a filovirus typically seem not to become immune to it for long, which makes it hard to imagine an effective vaccine or a cure.
Research on filoviruses is still in its infancy and receives very little funding. In a sense, that’s reasonable. So far, at least, the filoviruses have affected only a relatively small number of people and don’t yet loom as a major cause of human disease. What has researchers worried is their potential and our state of blithe unpreparedness for what, given the right mutations and circumstances, they might do.
People don’t realize until their house is on fire that the town hasn’t bought enough fire trucks, Sanchez warns. We’ll be seeing more Ebola. Population is increasing in Africa; so are incursions into the virus’s habitat. Sooner or later somebody’s going to haul it back out of the jungle.
