What canaries once did for coal miners, dogs could someday do for everyone. That is the hope of a small group of researchers who are fond of stories about animals as early-warning sentinels for human health hazards, including cancer.
In Dickensian London, dogs purportedly keeled over from deadly smogs, signalling residents to cover their faces and scurry indoors. And more recently, cops raiding the Aulm Shinrikyo cult in Japan which attacked Tokyo's subway with nerve gas in 1995 wore gas masks and carried caged canaries.
These are striking images but so far, they haven't been enough to attract a critical mass of researchers to the field. For the past 30 years, studies of cancer in pet dogs have periodically appeared in medical journals, reporting that, among other hazards, nearby industrial activity, weed killer, and second-hand smoke appear to increase tumor incidence. Despite such promising leads, this research has never received much attention from funding organizations.
"The overall enthusiasm [for this work] is moderate, and it's hard to say why," said John Reif, D.V.M., who studies both human and animal epidemiology as head of the department of environmental health at Colorado State University, Fort Collins.
As one of perhaps a half-dozen researchers worldwide who work in pet epidemiology, Reif
can quickly list its advantages. Dogs develop many of the same cancers as people. They share
their environment with people, so are exposed to the same carcinogens. They do not suffer the
vices of humankind no drinking or smoking nor do they suffer the stress of
working. And they eat pretty much the same food day in, day out. Consistency is the word with a
dog's life, and it eliminates many of the factors that entangle human epidemiology.
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Compressed Latency Period
But the biggest advantage lies not with how, but how long, dogs live. Their shortened life span compresses cancer's latency period to a few years.
"One of the main benefits [of pet epidemiology] is, if an animal is going to develop cancer, you don't have to wait 20 years," said Aaron Blair, Ph.D., chief of the occupational epidemiology branch at the National Cancer Institute.
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And as purely observational research, Glickman and others say pet epidemiology is a humane alternative to dosing lab animals with chemicals. Even the People for the Ethical Treatment of Animals, which vocally opposes all animal research, supports pet epidemiology if conducted "in the process of trying to help them [pets] with their disease."
Ideally, that's what Reif and Glickman would like a network of participating community veterinarians who report dog cancers. Keeping tabs on such information could point to cancer trends in dogs long before similar shifts in human cancer appear. One attempt at such a registry, which NCI set up and ran for a few years in Northern California in the 1960s, died for lack of funding after producing what Reif calls "ballpark figures" for prevalence and incidence rates of dog cancer.
The possibilities of building such a system are slim. Proposals for pet epidemiology research routinely get rejected, for reasons that Reif, Glickman, and others in the field do not understand.
Despite this lack of acceptance by the wider medical research community, a few pet epidemiology studies are ongoing. Glickman holds $600,000 in grants from the American Cancer Society and the Department of the Army to study prostate cancer in pet dogs. And at the Armed Forces Institute of Pathology, part of the Walter Reed Hospital complex in Washington, a group of military dogs is serving medical science while serving Uncle Sam.
During a typical year, 2,000 dogs work for the U.S. military. They secure checkpoints and sniff for explosives, their keen senses performing the surveillance work of a small platoon of soldiers.
"The health status of military dogs is extremely well-tracked," said Colonel William Inskeep, D.V.M., chairman of the department of veterinary pathology at AFIP. Like any soldier, each military dog receives a twice-yearly physical and blood work-up. After dying natural deaths, the animals are necropsied. The resulting tissue samples get sent to Inskeep's office, which has warehoused slides from 10,000 dogs. Inskeep says this cache of organ slices "has huge potential" for adding to our understanding of environmentally caused diseases, including cancer.
But with only a small staff, Inskeep and AFIP are working on the more manageable, more tangible task of studying the 118 dogs who served in Iraq and Kuwait during the Gulf War. While eyeballing the dogs' tissues, Inskeep notes any signs of disease, including cancer. If the Gulf War dogs show an increase in tumors over the control population of dogs that didn't travel to the war, it could signal that Gulf War veterans were exposed to carcinogens. That warning, in turn, could trigger human studies.
Inskeep expects results in "2 or 3 years," emphasizing that many of the dogs are living and a few are still on active duty. He would like to hire more staff, particularly another veterinary epidemiologist with a pathology background, but says such a person is "a rare, rare commodity." On top of that, Inskeep received only half the funding, or $150,000, he requested for the study.
Scant Funding
Unlike Inskeep, who plugs away with a tiny staff and a tinier budget, "a lot of the veterinary scientists have given up" trying to get pet epidemiology funded, said Purdue's Glickman. Glickman added that he published one of his studies in a human (not veterinary) journal to stimulate interest. It didn't.
"If it was a lab animal study, there would have been all kinds of follow-up," he said.
Dan Wartenberg, Ph.D., a human epidemiologist at the University of Medicine and Denistry of New Jersey, Piscataway, experienced similar frustration when he served on an Environmental Protection Agency panel. The panel, which was evaluating the health effects of a common weed killer called 2,4-D, reviewed a study showing dogs whose owners used the weed killer developed more lymphomas than control dogs. Wartenberg thought the study, conducted by Howard Hayes, D.V.M., a retired NCI scientist, was compelling. Not only did Wartenberg vote to classify 2,4-D as a possible carcinogen, he later added some pet epidemiology to his own resume.
But other members of the panel objected to the dog research. In its final report, EPA concluded that though Hayes' study showed an increase in tumors in dogs, there was not enough evidence to classify 2,4-D as a potential human carcinogen. (The International Agency for Research on Cancer, part of the World Health Organization, does consider 2,4-D a possible carcinogen.) Wartenberg said he "couldn't identify" reasons why the other panel members rejected the Hayes study.
One possible reason for the lack of enthusiasm is the background of the scientists who serve on funding boards. "When you look at review panels, they are lab scientists cool to these studies, and human epidemiologists who are also cool to animal studies," said Glickman. His math is right: of the 105 scientists who sit on NCI's initial review boards, only one is a veterinarian. And NCI has not yet replaced Hayes, considered a top pet epidemiologist.
"Clearly not much is going on," said NCI's Blair. "But I think there is promise in doing it. And I think the main one is to try to tackle general environmental exposures. This seems to me to be something useful . . . to see if it will help us understand what is going on in humans."
Meanwhile, the emphasis in the cancer funding world is on molecular genetics, sequencing genomes, and pinpointing mutations. There appears to be little room for the less precise, less high-tech work of sorting out environmental exposures and cancer incidence in pets.
"I would like to see us move toward the gene-environment relationships for some of these cancers [in dogs]," said Reif. "That's exactly where we are with humans. And I think the dog could be used precisely the same way, to identify specific genetic patterns . . . and then look to see what additional risk is imposed by environmental exposure. That to me should be fundable."
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