How Zoos Contribute to Disease Transmission Between Humans and Animals

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Black bear, Portland Zoo. Photo: Jeffrey St. Clair.

In recent decades, scientists and public health experts have increasingly examined how human interactions with wildlife and ecosystems can contribute to the emergence of infectious diseases. Two human activities that directly contributed to climate change are extensive deforestation and increased livestock farming, which have had devastating effects on the health of both humans and nonhuman animals.

Deforestation deprives many animals of their native habitats, and the few who can adapt are driven into proximity with human-made environments, which also increases the likelihood that a disease will adapt to a new population (from human to nonhuman animal, or vice versa).

Intensified livestock farming traps animals and their waste in a small area, creating an environment for a virus to spread and mutate. Specifically, bird and pig farming involves a high degree of antibiotic use, which helps pathogens become increasingly resistant to antibiotics. This results in infections becoming “difficult or impossible to treat” in human patients.

Zoos—along with circuses, rodeos, and petting zoos—are other examples of human-dominated ecosystems where disease can increase and spread between species. There are many factors in the care of captive animals that increase the likelihood that they will transmit diseases to humans.

Keeping animals locked up causes them stress and contributes to the deterioration of their overall health, making them more vulnerable to disease. Laws and regulations governing captive animals are often inadequate, and even where citations are issued, they can still fail to resolve matters relating to animal welfare and mismanagement. Animals can pass diseases to zookeepers, and, conversely, humans can infect captive animals with diseases they may not otherwise encounter in their natural habitat. They will not have a natural resistance to these diseases.

Finally, zoos are often willing to bolster the illegal wildlife trade to obtain rare species. Not only do poaching and smuggling contribute to the stress, poor health, and untimely death of countless animals, but these criminal acts also threaten the survival of entire species. Humans are one species among many, and our health outcomes are connected to those of nonhuman animals. Their health is our health. It is in our best interests to treat wild animals well and leave them alone so they can thrive in their native habitats.

One reason zoos can be hotbeds for the transmission of diseases is that captive animals can suffer from compromised immune systems due to the confines of captivity, rendering them more susceptible to illnesses.

Captivity is a stressor and can lead to severe psychological and physiological problems. Many animals become stressed and depressed, just as many humans do when institutionally confined. This kind of stress is such a common phenomenon that there is a term for it: zoo-induced psychosis, or zoochosis, a condition in which animals self-soothe by engaging in monotonous, obsessive, and repetitive behaviors—behaviors that they do not exhibit in the wild. These are reminiscent of obsessive-compulsive disorder symptoms in humans.

Certain species are more susceptible to stress and early death in captivity. This is especially true of animals with a long lifespan, low reproductive rate, and low predation in the wild. While earlier studies flagged this issue, recent science confirms that Asian elephants in Western zoos remain non-self-sustaining and continue to face high infant mortality and severe welfare challenges. A data review by my organization, In Defense of Animals, found that 75 percent of captive-born elephants in North America die before reaching middle age, and 1 in 4 calves die before their fifth birthday. The mortality rate is so high that zoos cannot breed elephants fast enough to replace those who die. Without restocking from the wild, the North American elephant population would go extinct within 50 years.

Animals have evolved to live in the wild, and confining them to an artificial environment is usually not in their best interest. The bottom line is that zoos and aquariums are profit-making enterprises underpinned by the legally enshrined assumption that we can use animals for our entertainment. The concept of a zoological garden rests on the belief that animals are here to serve us and that their needs are less important than our wants.

In most of the world, there are no laws........

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