Sentinel Dogs and Cats: Potential Key Players in the Study of Human Environmental Exposures
Roberta Attanasio, Georgia State University
Here is a half-known secret—our cherished pets do for us more than we think. Among other feats, they can serve as sentinels of human exposure to pollutants. It all started with canaries in coal mines. By the late 1890s, these birds were used to detect carbon monoxides and other toxic gases. For coal miners, canaries could make the difference between life and death. Signs of distress in the birds indicated that it was necessary to quickly evacuate miners from the pit in order to avoid lethal consequences. Canaries were used in Britain, Canada and the U.S. They were part of the mining culture—miners whistled to the birds as they worked, treating them as pets.
In Colorado coal mines, the “canary” wasn't an actual canary. Centennial State miners relied mostly on mice to carry out the birds’ functions. As noted in a Denver Public Library article, “Many a miner came to befriend mice and even took to naming and feeding them. At mealtime, the miners frequently shared their lunches with the rodent friends.”
Next in line are the infamous “dancing cats” of Minamata Bay in Japan. In the 1950s, the New York Times described, “Cats began dancing in the streets and fell, dead, writhing in pain. Dogs and pigs went mad. Crows dropped from the sky. Then the mysterious malady struck human beings. It destroyed their control over their arms and legs, made them blind and deaf and killed them. It hit babies in their mothers’ wombs and condemned them to live after birth as mental and physical vegetables.” By the late 1950s, medical researchers had identified the culprit. Victims had been poisoned by eating fish and shellfish contaminated by mercury. The mercury, in turn, was traced to sludge dumped at the bottom of Minamata Bay by a chemical plant.
The next “big” sentinel stint was the one performed in 2007 by tens of thousands of cats and dogs that died of renal failure in China, which was caused by eating food tainted with melamine, a chemical normally used to make plastics and, in some countries, fertilizers. About 1,500 racoon dogs bred for their fur died in 2008. Melamine was identified in their kidney stones, raising the question of how far melamine had penetrated China's food chain. Unsurprisingly, melamine-contaminated baby formula sickened about 300,000 infants and killed at least six of them in 2008.
There are many studies from the last few decades that show the value of companion animals as sentinels of human exposure. For example, pet dogs with spontaneous mesothelioma have been used to identify environmental exposures that could increase their owner’s risk of asbestos-related disease. In 1991, the National Research Council’s Committee on Animals as Monitors of Environmental Hazards stated, “Like humans, domestic animals and fish and other wildlife are exposed to contaminants in air, soil, water, and food, and they can suffer acute and chronic health effects from such exposures. Animal sentinel systems—systems in which data on animals exposed to contaminants in the environment are regularly and systematically collected and analyzed—can be used to identify potential health hazards to other animals or humans.”
What makes pet dogs and cats more useful sentinels of relevant exposures that may affect humans, compared with other animals, including wildlife? They share the same environment with humans—living in the same home, often consuming foods and water from the same sources, breathing the same air, getting into contact with the same household cleaning products, being chronically exposed to pesticide treatments in and around the home and herbicide applications in lawns, and experiencing similar stressors imposed by technologic advances and human conflicts. Notably, pets’ behavioral patterns resemble those of toddlers—for example mouthing and licking. In addition, pets and humans respond to many toxic agents in analogous ways, frequently developing similar environmentally induced diseases by the same pathogenetic mechanisms. Furthermore, because they have shorter lifespans, pets usually develop environmentally induced pathologic conditions more rapidly than humans.
Programs that collect health, environmental and behavioral data are useful tools to explore and exploit the value of sentinel pets. For example, the Golden Retriever Lifetime Study is a prospective longitudinal and observational study that aims to identify the major dietary, genetic and environmental risk factors for cancer and other important diseases in dogs. It gives researchers the opportunity to request data and biological samples from a cohort of more than 3,000 purebred golden retrievers. In December 2021, a planning committee of the National Academies of Sciences, Engineering, and Medicine hosted a workshop that examined the potential role of companion animals as sentinels of exposures that may affect human aging and cancer. The workshop explored opportunities and challenges of this evolving field, identified research gaps, and proposed a research agenda.
Notably, a research article on U.S. domestic cats as sentinels for per- and polyfluoroalkyl substances (PFAS) reaches an interesting conclusion – a “One Health” approach assessing humans, pets and their common environment may improve our understanding of chronic low-level, largely indoor, PFAS exposure and effects in humans and animals alike. This concept could be applied to many other contaminants – it’s a novel and promising approach to exposure science and it deserves to be further developed as it provides opportunities for interdisciplinary collaborations that can accelerate discoveries in environmental health.
Authors’ contact information: [email protected]