The #1 source for news about monkeys and apes

[Josh Greenman <joshg1973 AT yahoo.com>]

http://news.nationalgeographic.com/news/2003/06/0612_030612_hivvirusjump.html#main

HIV Originated With Monkeys, Not Chimps, Study Finds

Stefan Lovgren
for National Geographic News
June 12, 2003

Scientists now say that the simian immunodeficiency virus (SIV) in 
chimpanzees (Pan
troglodytes), which is believed to have been transmitted to humans to become 
HIV-1—the
virus that causes AIDS—didn't start its life in chimps. 
Instead, it was a product of separate viruses jumping from different monkey 
species into
chimps, where they recombined to form a hybrid virus, according to a new 
study. 

Researchers believe the chimpanzee virus is a hybrid of the SIVs naturally 
infecting two
different monkeys, the red-capped mangabey (Cercocebus torquatus) and the 
greater
spot-nosed monkey (Cercopithecus nictitans). Chimps eat monkeys, which is 
likely how they
acquired the monkey viruses. The hybrid virus then spread through the 
chimpanzee species,
and was later transmitted to humans to become HIV-1. 

The study suggests striking parallels between SIV infection of chimps and HIV 
infection
of humans. Just as chimps acquired viruses from two different sources, humans 
are
infected by two distinct AIDS viruses: HIV-1 and the less virulent HIV-2, 
which humans
acquired from sooty mangabey monkeys. 

"Because of the similarity between chimpanzees and humans, any virus that 
successfully
adapts to spreading among chimps would be a candidate for a further jump to 
humans—a
potential HIV-3," said Paul Sharp of the Institute of Genetics at University 
of
Nottingham in England, who led the study. 

The discovery also spotlights how many of our most virulent viruses were 
transmitted
across species. The jumping of viruses from animals to humans occurs all the 
time.
Diseases like SARS and monkeypox, which recently hit the northern United 
States, likely
originated by cross-species transmissions. 

"It seems this is happening more frequently because of two reasons," said 
Michael Lai, a
virus expert at the University of Southern California, Los Angeles. "First, 
the detection
of the virus is easier today because of advances in medical science. Second,
international travel brings animals from far-away places to a new place." 

>From SIV to HIV 

In 1999, the same team of scientists identified the origin of HIV-1 as being 
the
transmission of a virus known as SIVcpz from chimpanzees to humans, but they 
didn't know
how chimps acquired the virus in the first place. 

SIVs are carried by many species of monkeys in Africa, but chimps are the 
only apes known
to be naturally infected. While monkeys have been infected with SIVs for a 
long time,
chimps apparently acquired the virus more recently. 

The study shows that the SIVcpz strain arose in chimps through repeated 
transmission and
recombination of SIVs from the red-capped mangabeys and greater spot-nosed 
monkeys.
Chimps prey on both of these species and their ranges overlap in West and 
central Africa.


It is now widely accepted that humans contracted HIV from chimpanzees, 
probably by
butchering them for bush meat. The new findings thus show that humans are not 
the only
primate species to acquire two different immunodeficiency viruses by 
cross-species
transmission. 

The complexity of the HIV virus has increased through constant recombination. 
There are
already many subtypes of the HIV-1 strain, and the diversity is growing. Even 
strains of
the same subtype may now differ by up to 20 percent. 

This knowledge is imperative in the quest for an AIDS vaccine. If a vaccine 
can be
created, it's still unclear how much diversity it will be able to cope with. 

Scientists say it will be important to examine whether chimpanzee predation 
on smaller
monkeys has led to additional SIV acquisitions, and possibly coinfection and
recombination with SIVcpz, and whether the resulting chimpanzee-adapted SIVs 
are more
likely to infect humans. 

"The major difference between SIV infection of chimpanzees and HIV infection 
of humans is
that chimpanzees are not known to develop any disease symptoms," said Sharp. 
"Given the
very close genetic relationship between chimpanzees and humans, this prompts 
the question
whether chimpanzees have co-evolved with their virus to reach this 
non-pathogenic
association." 

Jumping and Recombining 

Many, though not all, human viruses originated by cross-species transmission. 
On the list
of viruses that have jumped from animals to humans are measles, influenza A, 
Ebola, HIV,
SARS, dengue, and many others. 

Some appeared in the last century; others emerged thousands of years ago and 
stayed. A
few have always been with us, infecting our ancestors before they evolved to 
become
humans. 

"Almost all the human viruses have this kind of counterparts in animals, so 
they must
have a common origin," said Lai. 

The influenza A virus jumped into humans from birds, perhaps using pigs as a 
"mixing
vessel," to create devastating pandemics in 1918, 1957, and 1968. Ebola hides 
in an (as
yet unidentified) animal from where it jumps to humans. SIVcpz jumped from 
chimpanzees to
humans at least three times. 

"Advances in the ease of finding and characterizing viral genome sequences 
are having a
major impact on our understanding of the diversity of human viruses and of 
their
relatives infecting other species," said Sharp. 

After jumping species, viruses can recombine with other viruses that have 
made the same
jump, or with divergent strains already existing in the host, sometimes 
creating new
hybrid viruses that may in some cases increase virulence. 

Measles is one virus where recombination probably did not happen. Measles 
infections only
last about two weeks, and generally there is only one strain common in a 
geographic area.
So the opportunity for two viruses to meet may be limited. 

Exotic Pets 

Another virus that jumped species is monkeypox. Health officials in 
Wisconsin, Illinois,
and Indiana recently reported the first outbreak of monkeypox in the Western 
Hemisphere.
This is a rare viral disease that occurs primarily in the rain forests of 
central Africa.


The disease is called monkeypox because it was discovered in laboratory 
monkeys in 1958.
Studies later showed evidence of infection in ground squirrels, which may be 
a natural
host for the virus. 

Infection with the virus results in a rash similar to smallpox, but less 
infectious. It's
usually not fatal. Symptoms include fever, headache, muscle aches, backache, 
and swollen
lymph nodes. 

The people who became ill in northern United States reported close contact 
with ill
prairie dogs. Health officials believe the prairie dogs contracted the 
monkeypox virus
from infected Gambian giant rats, which were imported from Africa and housed 
in the same
animal-holding facility as the prairie dogs. 

"When we expose ourselves to exotic animals, there is always a risk of being 
exposed to
something unknown," said Lai. 

Scientists believe the encroachment by humans on nature also increases the 
spread of
infectious diseases. The SIVcpz strain jumping from chimpanzees to humans 
likely occurred
when humans hunted and butchered chimps for "bush meat," something humans 
have done for
centuries. 

Increased human populations have increased the chances of a virus successfully
propagating among humans once it has made the jump. The SIVcpz strain was 
probably
transmitted to humans in previous centuries, but never established a 
substantial enough
transmission chain among humans to cause a large outbreak. 

"When we perturb the existing peace between human beings and nature, we are 
opening a
Pandora box, which may contain many surprises," said Lai.