By Charlene
Laino
MSNBC
CHICAGO
– As humans go further and further into the wilds of Africa in search of
new resources, potentially fatal HIV-like viruses could be unleashed. So suggests
new research that finds for the first time that chimps and other primates often
hunted for human consumption harbor a variety of previously unknown microbes.
THERE IS no evidence yet of a novel AIDS-like disease in humans, stressed researchers
at the Eighth Annual Retrovirus Conference here. But the possibility exists and
steps should be taken to head off another pandemic, they said Tuesday.
The
finding of new HIV-like viruses in 13 species of primates often hunted for "bush
meat" or kept as pets also lends weight to theories that AIDS originated
from animal contact, the researchers said.
"If
another simian [ape or monkey] virus crosses over to people, we could see another
type of HIV... another AIDS-like disease," said Mario Santiago of the University
of Alabama at Birmingham.
"Cross-species
transmissions of which we are not yet aware are continually going on, I believe,"
he said.
Many
human activities such as going deeper into the forests to cut down trees for firewood
actually foster this process, he added. As people penetrate the rainforest, they
can be exposed to animals carrying unknown viruses, which might otherwise have
been relatively contained.
New
pathogens don't come in on a tail of a comet, said Dr. David Heymann, executive
director of the World Health Organization's Program on Communicable Diseases in
Geneva. "They're lurking in animals. But by disrupting nature, we unleash
them onto ourselves."
And
once a new microbe is unleashed onto humans, it can spread from continent to continent,
hitching a ride, along with the passenger who carries it, on any plane, experts
pointed out.
STUDY DETAILS
In
one new study, Santiago and colleagues collected urine and fecal samples from
several chimpanzee families in East Africa. Antibody testing showed that one animal
had been infected with simian immunodeficiency virus (SIV) – and subsequent
genetic analysis showed it to be a previously unseen strain.
In
a separate study, Dr. Eric Delaporte of the University of Montpellier in France
analyzed blood samples from 384 wild primates, representing 17 species, in Cameroon.
Many of the species are hunted for bush meat or kept as pets, he said.
About
18 percent of the samples from 13 different species harbored simian immunodeficiency
viruses – four strains of which were previously unknown, Delaporte found.
The best known strain of simian immunodeficiency virus, SIV-1, was also detected.
"These data
document for the first time that humans are continuously exposed to an unprecedented
variety of SIVs through the consumption of bush meat," Delacorte said.
Current theory
on the origin of AIDS holds that SIV-1 jumped from chimps to humans, mutated slightly
and caused the human infection, HIV-1, Santiago said. DNA analysis of an SIV-1
sample from Delacorte's study showed it was genetically similar to human HIV-1,
further supporting the hypothesis that SIV caused human AIDS, he added.
Scientists
think that the virus infected humans either through cuts in preparing the meat
or bites or scratches from pets.
"There's
no reason the same type of thing can't happen with one of these novel SIV strains,
causing a new HIV-type disease," Santiago said.
So
what should be done to head off another pandemic?
"Although
all the circumstances, frequencies and routes of transmission of viruses from
primate to humans remain to be determined," Delacorte said, "surveillance
programs using specific tests for the various SIVs may be warranted."
Then, when novel
SIVs are detected, humans living in those areas could be warned not to consume
infected primates or keep them as pets, Santiago said.
OTHER RESEARCH
In another study
presented at the retrovirus meeting Tuesday, U.S. and Ugandan researchers reported
that HIV-infected women are one-and-one-half times more likely to transmit HIV
to uninfected male partners than the other way around.
Overall,
the chance of an HIV-positive woman transmitting the AIDS virus to her uninfected
partner was 1 in 450, compared with a 1 in 700 probability for male-to-female
transmission, said researchers at Johns Hopkins University in Baltimore.
Surprisingly,
infected partners who also had other sexually transmitted diseases were no more
likely to transmit the virus, the researchers said. But uninfected men who were
circumcised were less likely to catch the virus, they said.
The
findings held true regardless of the subtype of HIV the infected partners harbored,
the study showed. While some scientists have theorized that a greater infectivity
of the HIV subtypes prevalent in Africa could explain the explosive growth of
the epidemic there, the lack of difference in transmission rates by subtype argues
against this, the researchers said.
The
investigators studied 174 couples in Rakai, Uganda, in which one partner was infected
and reported having intercourse an average of nine times per month. While condoms
were offered to the couples, less than 10 percent opted to use them, primarily
due to their married status, the researchers said.
While
the study was done in Uganda, the rates are similar in the United States and Europe,
the researchers said.
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