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Chimps and HIV: The story behind the study

This chimpanzee from Gombe National Park was the first in the wild known to be infected with the SIV virus.
Photo by Michael L. Wilson
This chimpanzee from Gombe National Park was the first in the wild known to be infected with the SIV virus.

When Vincent's enemies dumped his battered corpse into a Tanzanian creek bed, University of Minnesota Professor Michael L. Wilson rushed to the scene of the killing, salvaged the body, stowed it in a freezer and alerted scientists back in the United States.

Though terribly unlucky in life, Vincent had considerable scientific value in death. He was the first wild chimpanzee known to be infected with SIV — the primate version of the HIV/AIDS virus — whose body would be available for research.


Findings from nine years of study on Vincent and other wild chimps came together in breakthrough news published last week in the journal Nature.

Contrary to prevailing wisdom, chimpanzees get an AIDS-like illness and die from it, said the research team — which included Wilson as well as Prof. Anne Pusey and several others with U of M connections. Dr. Beatrice Hahn of the University of Alabama at Birmingham led the team.

Scientists had known for years that African primates are naturally infected with more than 40 different simian immunodeficiency viruses (SIVs). They also knew that two of the viruses had crossed the species barrier to generate HIV-1 and HIV-2, which cause AIDS in humans. But primates were thought to have escaped the devastation AIDS has visited on humans.

'Missing link' in understanding HIV evolution
Many scientists not connected with the study hailed the new findings as a "missing link" in the understanding of the evolution of HIV.

"It is a pretty momentous study," Danny Douek, chief of the human immunology section of the National Institutes of Health vaccine research center in Bethesda, Md. told the Los Angeles Times.

Prof. Anne Pusey
Minnpost photo by Sharon Schmickle
Prof. Anne Pusey

"You can regard the study as one that provides a missing link in the history of the HIV pandemic," said Douek, who is searching for possible AIDS vaccines. "If we identify the evolutionary adaptations, that opens up therapeutic avenues for HIV disease."

The findings also shed new light on causes of deaths of wild chimpanzees, which are an endangered species.

Evolved from SIV
The story behind this study is nearly as interesting as the findings.

Warning: It could shatter romantic notions about the adventurous work of the wildlife researcher. These scientists muck around in chimp droppings.

Before touching that indelicate subject, we need to look back to 1981, when dozens of young gay men in California and New York died from a mysterious pneumonia. We now know the cause was an HIV virus that led to AIDS. Since then, the virus has killed more than 32 million people worldwide and infected at least 65 million.

Beyond the staggering loss of lives, the quest for a cure or a vaccine has cost tens of billions of dollars.

One part of conquering the disease involved learning where it came from. Studies have shown that HIV evolved from SIV, probably in the cells of hunters who had killed infected apes and monkeys for the lucrative "bush meat" trade in Africa.

A logical place to look further for the virus's natural reservoirs was in chimpanzees, the closest relatives to humans. Hahn, the AIDS researcher at the University of Alabama, had established links between HIV-1 and a type of the virus called SIVcpz, which infected chimps.

But her early work was criticized because the studies were done on chimps in captivity. So Hahn set out to find and study infected wild chimps.

A stage already set
This is where the Minnesota role begins.

Wild chimpanzees are very elusive. And there are ever fewer of them to study. During the 20th century their numbers plummeted from 2 million to 150,000 because of diseases, poaching and destruction of the forests where they live.

One place, though, where chimps were accessible was in Tanzania's Gombe National Park. Primatologist Jane Goodall began documenting their behavior there in the 1960s. Pusey, the U of M professor, worked there in the 1970s as Goodall's research assistant.

Later, Pusey discovered that field notes she, Goodall and others had painstakingly recorded were deteriorating in musty trunks in Goodall's house. So in the 1990s, Pusey and colleagues transferred more than 320,000 pages of the records to Minnesota and created the Jane Goodall Institute's Center for Primate Studies on the U's St. Paul Campus.

Prof. Michael L. Wilson observes a chimpanzee in Gombe National Park.
Photo by Jill Griffiths
Prof. Michael L. Wilson observes a chimpanzee in Gombe National Park.

Wilson and many other young scientists came to the center Pusey directs, dividing their time between desk work there and field studies in Gombe. Now, the center houses a rich record of the Gombe chimps, documenting everything from their daily diets to their sexual partners.

Indeed, scientists know more about the chimps than anyone could learn about human HIV subjects because the chimps do everything in the open, from mating to defecating.

"These chimps are completely used to us," Pusey said in an interview. "We see most chimps most days. We keep track of where they go, what they eat, who they interact with.  ... Then sometimes we find bodies when they die, which is hard to do. Nobody studying chimps in other places has had much luck finding bodies."

Every bit of information comes back to St. Paul, where it is computerized.

In other words, the scene already was set for the research Hahn wanted done.

Clues in chimp droppings
One rule at Gombe, though, is that research be non-invasive. Watch but don't touch. Only on rare occasions have field workers darted a chimpanzee to knock it out and check for an illness that might endanger the other animals.

So scientists recruited for Hahn's studies relied initially on urine samples, typically collected under trees where chimps slept at night. That yielded valuable clues, but not the actual virus the researchers wanted. Eventually, Hahn's team developed techniques to extract the virus from chimp feces.

At the time, Wilson was working in Tanzania on a three-year stint as director of field research for Gombe Stream Research Center. He oversaw the collection of feces and other data needed for the SIV study.

It wasn't sufficient to pick up any old piles of chimp droppings. Because a goal of the research was to learn whether SIV-infected chimps got sick, workers watched to see which chimp did which pile and scoop it up right away.

"If somebody pooped and we saw it, I made sure that it got collected, and I kept track of the samples," Wilson said.

A wealth of information
Not that he's complaining. Feces had served up a wealth of scientific information about the Gombe chimps long before the SIV study.

"You can find out what the chimpanzees have been eating, and all of this wonderful molecular stuff," Wilson said. "You can find their own genetic information in there, what they have in terms of parasites, and hormones and also the genetics of whatever is infecting them."

Back in the lab, the payload was treated with a salt solution to prevent RNA and DNA from decomposing. Then it was packed for shipping to the United States.

Few of us have struggled through the bureaucratic demands of shipping feces from an endangered species. It's complicated.

Wilson had to transport the packages across Tanzania to a building in Dar es Salaam called the Ivory Room. Long ago, ivory was cleared for export there. Now, it's the place where trophy hunters and reptile exporters wait for clearance to take away their bounty.

"There I am with a box of poop to weigh and pack and for the inspector to look at and make sure it's poop and not something else," Wilson said.

But Wilson's work on the project went further, and it continued after he returned to Minnesota, where he now is a professor of anthropology as well as of ecology, evolution and behavior.

Enter Vincent
Vincent, the chimp who met a violent end in that stream bed, was of great interest to Wilson — whose main academic focus is studying aggression.

The alpha male had lived a tough 28 years. Among other mishaps, he had fallen from a tall tree while trying to steal a monkey some younger chimps had caught to eat. He survived the broken bones, but his weakened state made him a prime target for other aggressive males. So he spent much of his time alone.

This female chimpanzee also was found to have the SIV virus.
Photo by Michael L. Wilson
This female chimpanzee also was found to have the SIV virus.

On top of everything else, Vincent was SIV positive. No wild chimp known to have the virus ever had been available for the post-mortem examination called a necropsy.

So on the night two young male chimps killed Vincent in December 2004, field workers put in a radio call to Wilson — who got up before dawn and hiked to Gombe's remote northern reaches.

"We had to be very careful because he had to be treated like an AIDS patient," Wilson said. "He had a very high level of the virus in his system. We already knew that from his feces."

Dominic Travis from the Lincoln Park Zoo and Michael Kinsel from the University of Illinois came to Tanzania to join local veterinarians for the necropsy, along with Dr. Titus Mlengeya from Tanzania National Parks and Dr. Ephata Kaaya from Muhimbili University College of Health Sciences.

Ultimately more infected chimps died and their tissue was shipped to American labs for further study and for comparison with non-infected chimps.

Shocking findings
To everyone's surprise, the infected chimps' immune systems were damaged, much as they would be in a human AIDS patient.

"It was a shock," Pusey said. "It is not fun to find out there is another disease in your population."

Among other measures, the infected chimps had unusually low counts of a type of T-cell white blood proteins. The cells are vital to immunity, and their loss is a classic indication of AIDS in humans.

Meanwhile, the team in Minnesota knew, usually to the day, the age of all 94 chimps in the study, so they were able to work with James Holland Jones of Stanford University on sophisticated mortality analysis. 

Putting everything together, the researchers reported that the infected chimps were 10 to 16 times more likely to die than those not infected. They also reported that infected females were less likely to give birth and that all of the infants born to infected mothers died within a year.

Four others with U of M ties were authors on the study. Doctoral candidate Emily Wroblewski sequenced DNA from fecal samples and came up with a genetic bar code to identify each chimp. Research Administrator Joann Schumacher-Stankey matched new findings from Gombe with birth dates and everything else known about each chimp. Elizabeth Lonsdorf, who earned a Ph.D. in the Minnesota studies in 2003 and went to work at Lincoln Park Zoo in Chicago, led a health-monitoring project at Gombe. And Anna Moser, who got her Ph.D. in 2008, directed research at Gombe.

Pusey cautioned that the sample size is small and more study will be needed. One remaining puzzle is why SIV infection is patchy in chimps across Africa. It hasn't been found, for example, in a chimp population in Uganda, which borders Tanzania.

"You can have a population here that has it and a population right next door that doesn't have it," Pusey said.

Where the disease does strike, treating chimps with therapies developed for humans is not an option.  Nor is it possible to contain the spread by educating chimps. No safe-sex campaigns in the wild.

There is reason to hope, though, that the virus isn't as deadly for chimps as it is for humans. Though the study found infected chimps were more likely to die, the risk isn't as high as it is for humans.

There also is hope the findings could help save more chimps from hunters.

"One lesson we can draw from it is that it's a really bad idea to eat chimpanzees," Wilson said.

Sharon Schmickle writes about science, international affairs and other topics.

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Comments (1)

This is a very elementary question but do viruses affect different species differently? For example h1n1 flu pigs/fowl/humans. I know the virus mutates or changes. HIV SIV is there a primate IV? Sorry to sound like ALI G but I am curious and I don't want to do the google research.