The types of Ebola and hantavirus
worrying officials are very different from the species identified decades ago,
raising new questions about how to respond.
·
Recent
outbreaks involving hantavirus and Ebola-like viruses have raised global
concern because the viruses are behaving differently from what scientists
traditionally understand.
·
Experts
say the outbreaks highlight major gaps in scientific understanding of the
“virosphere” — the vast diversity of viruses existing in nature.
·
A
hantavirus outbreak aboard the cruise ship M.V.
Hondius reportedly caused:
o 13 infections,
o including 3 deaths.
·
Scientists
were surprised because the virus appeared to spread from person to person,
which is extremely rare for hantaviruses.
·
Hantaviruses
are usually transmitted through exposure to infected rodent urine, saliva, or
droppings.
·
The
outbreak was linked to Andes virus, a strain of Hantavirus infection found in
South America.
·
Unlike
most hantaviruses, Andes virus is capable of direct human-to-human
transmission.
·
Virologist
Jens Kuhn said scientists still do not know which mutations allow this
transmission.
·
A new
Ebola outbreak in Africa has caused:
o more than 900 infections,
o and over 220 deaths.
·
However,
scientists say this outbreak is not caused by the classic Ebola virus strain
for which vaccines and antiviral drugs were developed.
·
The
current outbreak is linked to Bundibugyo virus, scientifically known as Orthoebolavirus bundibugyoense.
·
Scientists
say existing Ebola vaccines and treatments developed for the Zaire strain are
likely to be weak or ineffective against this species.
·
The
virus was first identified in Uganda in 2007 and is genetically over 30%
different from earlier Ebola strains discovered in Zaire and Sudan.
·
Researchers
emphasized that many viruses grouped under a common name can actually behave
very differently.
·
Jens
Kuhn stressed that accurate virus taxonomy is essential because treatments
effective for one species may fail against another.
·
Scientists
currently recognize:
o 38 species in the Orthohantavirus genus,
o compared with only 6 species in the Ebola
virus genus.
·
Experts
believe many more undiscovered Ebola-like viruses may exist in African
wildlife.
·
Researchers
warned that additional dangerous virus species could emerge unexpectedly due to
limited surveillance and incomplete scientific understanding.
·
Scientists
are now expected to intensify genetic sequencing and virus monitoring efforts,
especially in South America and Africa.
·
Experts
say clearer naming of virus species is important to avoid confusion and false
assumptions about available treatments.
This
month, a pair of viruses seized the headlines. First came a hantavirus outbreak
aboard a cruise ship, which caused as many as 13 infections, three of which were
fatal. Then an Ebola outbreak flared in Africa, so far leading to more than 900
infections and 220 deaths.
In
both cases, the news has been not only frightening but also confusing, even to scientists.
The hantaviruses didn’t seem to be acting like hantaviruses, and the Ebola viruses
weren’t behaving like Ebola viruses.
Hantaviruses
are carried by rodents and other animals, and typically infect people who inhale
dried animal urine and saliva. But aboard the cruise ship M.V. Hondius, hantaviruses
were moving from person to person.
As
for the African outbreak, scientists have made huge strides in fighting Ebola in
recent years. They’ve created vaccines that can slow the spread of the disease and
antiviral drugs that can cure infections.
But
these treatments are probably going to be weak or useless. This is a very different
Ebola virus.
What
gives? There is a vast diversity of viruses, but we employ a limited vocabulary
to talk about them. It would be just as confusing to treat blue whales like fruit
bats and Siberian tigers, simply on the grounds that they’re all mammals.
Jens
Kuhn, a virologist who serves on the International Committee on Taxonomy of Viruses,
said that the recent outbreaks point to yawning gaps in our understanding of the
so-called virosphere, the millions — perhaps even trillions — of virus species thriving
around us.
“These
are case-use examples of why taxonomy is important,” he said. “Is something the
same, or is it different? Well, if it’s different, then stuff we know about the
other thing will not work on it.”
Ebola
viruses got their names from the site of one of the first documented outbreaks in
1976: the Ebola River, in what was then Zaire, now the Democratic Republic of Congo.
When scientists examined blood from the victims, they isolated long, snakelike viruses
distinct from any previously known.
But
1976 saw another outbreak that also caused deadly, bloody fevers — this one hundreds of miles to the east, in what was then Sudan,
now South Sudan. The infected also harbored snakelike
viruses.
When
scientists compared the viral genes, however, they found a striking number of differences.
In later years, Ebola outbreaks occurred dozens of times, and in most cases the
viruses resembled either the type first seen in Zaire or the type seen in Sudan.
Eventually,
Dr. Kuhn and his colleagues formally recognized the two kinds of viruses as two
distinct species. And, as taxonomists do in such cases, they gave each species a
Latin name: Orthoebolavirus zairense
and Orthoebolavirus sudanense.
But
in the 50 years since the first Ebola outbreak, scientists have found other relatives
of these viruses. In 2007, for example, 149 people in the Bundibugyo District of
Uganda came down with hemorrhagic fevers, and 37 died.
The
virus they harbored was, genetically speaking, over
30 percent different from the viruses isolated in Zaire and Sudan — a new species,
known now as Orthoebolavirus bundibugyoense.
The
Bundibugyo virus caused a second small outbreak in 2012 before exploding back on
the scene this month. The vaccines and the drugs that were developed for the Zaire
species don’t work against the Bundibugyo virus, which belongs to a different evolutionary
lineage. That’s one reason the new outbreak has public health experts so worried.
Hantaviruses
also got their names from a river: the Hantan River, which flows through North and
South Korea. It’s in a region where a mysterious kidney disease struck people every
year. In 1978, researchers isolated the cause: a virus carried by striped field
mice.
Since
then, scientists have discovered hantaviruses lurking in rodents and other mammals
around the world. Some of them also cause kidney damage, while others strike the
heart and the lungs.
The
actor Gene Hackman’s wife, Betsy Arakawa, died at their New Mexico home last year
after being infected with a type of hantavirus called Sin Nombre. Diagnosed earlier
with Alzheimer’s, Mr. Hackman died days afterward.
As
hantaviruses have adapted to rodents and other mammals across much of the world,
they have evolved an enormous diversity — Dr. Kuhn and his colleagues recognize
38 species in the genus Orthohantavirus. (The Ebola genus, by contrast, includes
only six species.)
Each
species in turn may harbor a lot of diversity. As viruses
replicate, strains can pick up new mutations that can drastically change their biology.
The
outbreak on M.V. Hondius this spring was caused by a species
called Orthohantavirus andesense, carried by a number
of rodents in South America. But there are four strains of this species; the outbreak
was caused by one called Andes virus.
Unlike
the other three strains — and unlike the 37 other species of hantaviruses — Andes
virus can spread directly from one person to another.
“It seems like there are some mutations that under
certain circumstances can make Andes virus person-to-person transmissible,” Dr.
Kuhn said. No one knows what those mutations are.
Dr.
Kuhn suspects that the other strains related to Andes virus are lurking in rodents
and share this ability to spread among people. After the M.V. Hondius outbreak, he predicts, scientists in Argentina and Chile
will “go into their freezers with all the samples and sequence the crap out of everything
and figure out — what are all these things?”
As
for Ebola, Dr. Kuhn expects more unpleasant surprises. He points to Orthoebolavirus taiense, also known
as Taï Forest virus.
The
first and last time anyone saw this species was in 1994, when it infected a scientist
dissecting a dead chimpanzee. She developed Ebola symptoms but eventually recovered.
“I’m
sure it’s still out there, but nobody focuses on it because it caused only one case,”
Dr. Kuhn said. “I think that’s a big mistake.”
Other
Ebola-like species that have yet to be discovered and named may be lurking in African
animals. The classification system that Dr. Kuhn has helped create will hopefully
make it an easier process.
He
doesn’t expect people to learn to rattle off Orthohantavirus andesense and other Latin names in casual conversation. But
instead of referring to the cause of the outbreak in Africa as the Ebola virus,
he suggests calling it Bundibugyo virus. (It’s pronounced boon-dee-boo-joh.)
“The
moment you mix up Bundibugyo virus and Ebola virus, the impression will be, ‘Oh,
we’ve got something for that,’” Dr. Kuhn said. “But we don’t.”