Death Called a River
By Jason Socrates
Bardi
"And
the priest shall look upon the plague, and shut up those
who hath the plague seven days."
—Exodus
13:50
Ebola hemorrhagic fever is one of the most virulent diseases
known to humankind. Very few pathogens are more dangerous
than Ebola virus once a person is infected. There is no cure,
and with a case-fatality rate of between 50 and 90 percent,
depending on which strain in involved, it is one of the deadliest
viruses on the planet.
But Ebola virus is also one of the rarest viral infections
in humans. Despite the tremendous attention it has received
in recent years, of all the pathogens that have plagued mankind
throughout history, Ebola virus is little more than a bit
player. It has sustained but nine major outbreaks since it
was first recognized some 25 years ago, claiming at most a
few hundred lives each time. By comparison, five times as
many people die in workplace accidents in the United States
each year than all those who have ever died of Ebola hemorrhagic
fever.
"People say to me, 'Why do you work on Ebola virus when
it has still killed less than 1,000 people that we know of?'"
says Immunology Professor Dennis Burton.
"My answer," he says, "is that we don't know where the virus
is headed—whether sooner or later [it] could become more
dangerous to a wider population."
The scariest thing about Ebola virus is not what it has
done but what it might do.
A Virus Emerges
In the summer of 1976, Ngoy Mushola, a doctor from Bumba,
Zaire, traveled to Yambuku, a town on the shores of the Ebola
river.
There, at a local hospital, Mushola recorded the first clinical
description of a new disease that was killing almost all of
the patients who contracted it. "The illness is characterized
with a high temperature of about 39°C, hematemesis [the
vomiting of blood], diarrhea with blood, retrosternal abdominal
pain, prostration with "heavy" articulations, and rapid evolution
death after a mean of three days," he wrote in his daily log.
The illness, which was later named Ebola hemorrhagic fever
after the nearby river, was successfully contained in Zaire
over the course of a few months, but not before 318 people
contracted the virus. Nearly 90 percent of the victims died
within a few days of becoming infected.
Hundreds of miles away, in Maridi and Nzara, two cities
in the southern tip of Sudan, doctors were witnessing an outbreak,
describing patients with high fevers, aches, nausea, bleeding,
delirium, and what they termed a "mask-like" or "ghost-like"
face. Two hundred and eighty-four were infected and over half
died.
One of the main risk-factors associated with Ebola virus
in the Sudan outbreak was caring for the sick. The disease
was spread within hospitals, and many medical care personnel
were infected. In several of the Ebola hemorrhagic fever outbreaks
that have followed, health care workers have been at risk,
and there have been many documented cases of doctors and nurses
contracting Ebola virus from the patients they were tending.
Scientists and laboratory personnel working with the live
virus are also at risk, and a few months after the Sudan outbreak,
a scientist working with the virus in England became infected
after he accidentally stuck himself with an infected needle.
Virulent and Rare
Burton, who does not work with live virus, began to study
Ebola virus in the mid-1990s, expanding his successful studies
on the interplay of viruses and antibodies in humans. In particular,
he had been looking at several "slow" viruses—including
human immunodeficiency virus and herpes simplex virus—and
wanted to raise antibodies against a virus that was very different.
He chose Ebola.
"The virus is intriguing because it acts so quickly," says
Burton. "It kills people in two weeks or less."
As deadly as Ebola virus is, it has never sustained a large
outbreak, probably due to its speed of action and how powerfully
sick it makes people. Even as case-fatality can approach 90
percent, infected patients become bed-ridden while they are
most infectious, and infection is spread only through direct
contact with bodily fluids. Thus, patients are easily quarantined
and outbreaks contained.
"Humans are the unlikely target," says Neuropharmacology
Professor Michael Buchmeier, who has studied Ebola virus and
related viruses for a number of years. Humans are not the
natural reservoir for Ebola virus, but merely incidental or
accidental hosts.
Until recently, Buchmeier and Burton were co-investigators
on a National Institutes of Health project to research immune
therapies against Lassa virus and Ebola virus. Now Buchmeier
is concentrating his research on the virus that causes Lassa
Fever, which is believed to infect over 100,000 people a year,
cause 3,000 to 5,000 deaths, and be the leading cause of fetal
death in some West African countries.
Ebola and Lassa are both non-human viruses. They are persistent
in animal populations in the wild, and remain in this animal
"reservoir" population because they are not deadly enough
to kill the infected animals—an evolutionary advantage
for a virus to remain endemic in its host species population.
In the case of Lassa fever virus, the animal host is the
multimammate rat, a rodent common to many parts of Africa.
Humans become infected when they come into direct contact
with virus particles in rat waste. Scientists suspect a similar
host for the Ebola virus.
"There has to be something out there that harbors Ebola
virus," says Buchmeier.
Though much work has gone into identifying the source of
this virus, none has yet been found. Ebola virus and the closely
related Marburg virus have both been found to infect humans
and monkeys—some strains infect one or the other, and
some strains infect both—but neither human nor monkey
populations harbor the virus in between outbreaks.
Some believe that the natural source of the Ebola and Marburg
viruses might be bats, because of the association of some
outbreaks with people who had visited caves and mines containing
many bats. Given the source of Lassa virus, rodents are another
good candidate. However, despite repeated attempts to culture
Ebola virus from animals in the wild, the source of the virus
has never been found.
Burton thinks an antibody he has made might provide a technology
that would help.
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