Chimpanzees share almost all their gene sequences with humans, and this closeness has made them ideal animal models for many human diseases. But similarities between humans and nonhuman primates go beyond genetics. Nonhuman primates are very social animals, travel long distances to find food, sometimes live on the fringes of the wild, and often become afflicted with diseases closely resembling those of humans.
| PREP FOR FLIGHT: Handlers prepare chimpanzee Ham, one of the NASA "astrochimps," for his Jan. 31, 1961 flight aboard the Mercury-Redstone 2.|| AN APPLE FOR HAM: Ham, still strapped into his special flight couch, reaches for an apple after his flight and recovery from the Atlantic Ocean.|
Observing these similarities, some researchers now believe that wild primate populations could serve as virtual distant early warning systems for emerging infectious diseases in humans. In a recent issue of the journal Emerging Infectious Diseases, researchers say wild primate populations could be considered "sentinels" (N.D. Wolfe et al., Emerg. Infect. Dis., 4:149-58, 1998). In the article, Nathan D. Wolfe, a doctoral candidate in the department of immunology and infectious disease at the Harvard School of Public Health, William B. Karesh, a field veterinarian at the Wildlife Conservation Society in the Bronx, N.Y., and Altaf A. Lal, an investigator in the parasitology division of the Center for Infectious Diseases of the Centers for Disease Control and Prevention, argue that improved collaboration between clinical and basic researchers and field biologists could yield important insights into the history, origin, and future course of some infectious diseases.
Lal says that the idea behind using wild primate populations as sentinels for infectious disease is a natural extension of the widespread use of these animals as models in basic research. For example, nonhuman primates have played a vital role in the development of numerous vaccines and have recently been touted as models for research on HIV and AIDS. "The threat of infectious disease is very real and many scientists already recognize the important role that individual primates play in laboratory-based science." Lal says. "Our proposal takes this idea a step further to include whole populations. In attempting to understand the evolution and course of many diseases, we stand to learn a lot by looking at groups of wild primates."
Research on emerging infectious disease has become a high priority for many investigators around the world. More than 200 articles on emerging and reemerging infectious diseases were published in 1995 in 36 journals and in 21 languages (M.A. Winker, Emerg. Infect. Dis., 2:365-72, 1996). Scientists also note that the majority of emerging diseases have involved zoonotic, or species-jumping, pathogens (F.A. Murphy, Emerg. Infect. Dis.,4: in press, July-September 1998).
The benefits from monitoring wild primate populations could be numerous for clinical and basic researchers, Lal says. For example, surveillance of nonhuman primates could help researchers determine the origin of some pathogens. By constructing molecular phylogenies, or evolutionary charts, researchers also could gain insight on classifying emerging infectious diseases and determine how selective pressure affects the evolution of a disease. Moreover, such charts could help to determine the antigenic diversity of pathogens, a much-needed step in the development of vaccines.
"By looking at proteins and genes comprising some diseases in wild populations, scientists can make a reasonable prediction about how the disease will evolve," Lal explains. "We can also go back in time and see where infectious diseases have been. It will not be easy to gather this information, but this kind of knowledge would be a powerful weapon in the fight against human disease."
The idea for using wild primate populations as sentinels for infectious disease is promising, but could face a number of obstacles when put into practice, according to S.S. Kalter, a virologist at the Virus Reference Laboratoy Inc. in San Antonio, Texas. "There is a general lack of specificity of infectious organisms," Kalter explains. "Many primates, human and nonhuman, have related diseases, and the natural interchange of infectious organisms between species is enormous. Most of the time, there will be thousands and thousands of interchanges of pathogens before a single infection in a human occurs. So, in using primates as sentinels, you can become embroiled in a chicken-and-egg debate over which infectious pathogen came first and which animals served as a host or vector for the disease."
"We stand to learn a lot by looking at groups of wild primates."
-- Altaf A. Lal
"So, there also is a certain level of nervousness in reaction to our proposal," Karesh says. "Conservation biologists also are concerned that any natural connection between human disease and nonhuman primates could serve as an excuse to clear forests and eradicate wildlife that is thought of as a health threat."
But Karesh notes that monitoring infectious diseases in wild primate populations could benefit conservationists and basic researchers. While cases of disease transmitted from primates to humans are well documented, human disease is an increasing threat to primates, especially those endangered. For example, tuberculosis (TB) often is fatal to primates and represents a serious threat to laboratory populations. Studies also have shown that TB probably from bovine sources can infect wild olive baboon populations (R. Tarara et al., Journal of Wildlife Disease , 21:137-40, 1985).
"Hunting, ecotourism, and forest encroachment combine to increase the possibility of human-to-primate pathogen exchange," Karesh says. "But there have been very few formal studies to assess the scope of this threat. As a conservationist or primatologist, you can wave your arms up and down and say, 'Look what's happening to these animals.' But any scientist will rightly demand evidence of this. This can only happen when researchers across disciplines decide to work together and share their resources."
In the past. some primatologists have been reluctant to work with basic researchers and have had minimal interest in infectious disease, according to Kalter. For example, he notes that at a current meeting of the American Primatological Society, there was not one presentation or report on infectious disease in primates. Kalter, for example, attempted to acquire laboratory specimens from wild chimps that showed signs of polio infection. However, the researcher, who is a well-known primatologist, denied Kalter access to the animals. "These kinds of situations are frustrating and all too common," he says. "Some primatologists become overly protective of the animals without realizing it is likely that they have contributed to illness in the animals."
Kalter sums up: "There are a few people out there who have attempted to look at the broader picture of infectious disease in human and nonhuman primates. Of course, better collaboration is the key to gaining better understanding of infectious disease."
An ongoing custody dispute over the fate of a colony of chimpanzees who were invaluable in NASA's effort to put a man on the moon is a prime example of how a host of considerations clash when the subject of primate research comes up.
After a 40-year stint with the U.S. Air Force, 32 surviving chimpanzees trained for aerospace research and 110 of their descendants will no longer be under the care of Uncle Sam. The oldest chimp is 40, and many are descendants of Ham and Enos , who rocketed into space three months before the late Alan Shepard . Over three years ago, the Air Force decided to give up care of the "astrochimps" and began accepting applications from organizations willing to adopt them. The deadline for filing for custody passed in June, and a decision from the Air Force is due some time this month.
Two organizations--the Coulston Foundation, a research laboratory based in Alamogordo, N.M., and the Center for Captive Chimpanzee Care (CCCC) in Boynton Beach, Fla.--have been locked in a bitter custody battle over the astrochimps. The Coulston Foundation, which has cared for the chimps for several decades at their home at Holloman Air Force Base, N.M., would continue to make the animals available for biomedical research if awarded custody.
Frederick Coulston, founder of the research organization, has been studying primates for more than 50 years. Chimps under his care have been used in a variety of studies, including trials for a hepatitis vaccine. In 1997, they also were enlisted in early trials for an AIDS vaccine developed by University of Pennsylvania researchers. Most recently, the foundation was awarded a $1.9 million grant from the National Institutes of Health to use the chimps in prostate cancer studies.
If CCCC can raise $14 million, that organization, founded by well-known primatologist Jane Goodall , will build a sanctuary and let the chimps live out their years in "freedom and peace." As of July, CCCC had raised over $1.4 million and had won the support of notables such as U.S. Sen. John Glenn (D-Ohio), U.S. Rep. Newt Gingrich (R-Ga.), and Roger Fouts , a primatologist most famous for teaching chimps sign language. "Many people have the same view that we have," says Carole Noon , director of CCCC. "These animals have served our nation and really deserve a peaceful retirement."
In a campaign to win custody of the chimps, CCCC has used its Web site (www.savethechimps.org) as one way to cast doubt on the ability of the Coulston Foundation to properly care for the chimps. But, according to David McKinney , director of communications for the Coulston Foundation. "Our reputation in the research community speaks for itself. Anyone who is familiar with us knows that we are not here to abuse or mistreat animals. Chimpanzees are our allies in research and the battle against disease. So, we cannot even begin to think of abusing them."
But the battle over the astrochimps has brought unwanted attention to the Coulston organization. Following a recent NBC Dateline television program on the custody battle, the foundation received numerous "hate calls" and even an unmarked package that appeared to be a bomb, which forced an evacuation of the research center. "We've really been given a black eye by the media and animal activists in this issue over who gets the chimpanzees," McKinney says.
While McKinney is confident that the Coulston Foundation will continue to care for the chimps and make them available to researchers, he is not so sure that the public's perception of the use of animals in research will change. "People have no idea how necessary animals are to experimental science," he says. "I lay blame squarely on the media. They have made no attempt to show the important role chimpanzees play in biomedical research and what animal models in general mean to scientific discovery."