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Learning from Animals: Evolutionary Medicine with a Twist

In 2005, cardiologist Barbara Natterson-Horowitz was called to the zoo to examine a non-human patient, an emperor tamarin with heart failure.  She was surprised when the veterinarian told her not to look her patient in the eyes because eye contact could cause capture myopathy. In this condition, when an animal is captured, restrained, and feels threatened, there is a catastrophic surge of adrenaline that damages muscle tissues and can kill. It was described decades ago, but medical doctors don’t read the veterinary literature. It wasn’t until the early 2000s that American doctors began to recognize a similar phenomenon in human patients, takotsubo or stress-induced cardiomyopathy.

She began to wonder whether animals got other human diseases. She quickly learned that they did. Jaguars get breast cancer and may carry the same BRCA1 gene that plagues Ashkenazi Jewish women, rhinos get leukemia, penguins get melanoma, gorillas die from ruptured aortas, and koalas are in the midst of an epidemic of sexually transmitted chlamydia.  Wild dragonflies infected with parasites become obese and develop a form of metabolic syndrome. Pretty much every human disorder occurs in animals too.

With the help of writer Kathryn Bowers, she distilled her findings into a book: Zoobiquity: What Animals Can Teach Us About Health and the Science of Healing.  It’s a good read: informative, well argued, spiced with intriguing trivia, and more entertaining than a trip to the zoo.

If veterinarians and human doctors collaborated on a routine basis, what might they learn from each other? A doctor working on a novel therapy for melanoma asked a veterinarian “Do dogs get melanoma?” He had promising results in a mouse model with induced cancers, but needed to study the treatment in animals with spontaneously occurring tumors, intact immune systems, and a longer life span. Dogs do indeed get melanoma, and in the ensuing collaboration a vaccine was developed that dramatically prolonged their survival rates.  Human applications are being investigated.

What about sex? The oldest penis on record belonged to a crustacean that lived 425 millions years ago. Animal studies shed light on human erectile dysfunction and premature ejaculation. Animals routinely engage in homosexual couplings, oral and anal sex, interspecies sex, and masturbation.

Human drug addicts are not alone: animals seek and respond to chemical rewards in the lab and in the wild. Human emotions evolved to influence behavior and fitness. Everything from gambling to compulsive shopping can be viewed in terms of beneficial animal activities like foraging and hunting. SIDS might be related to a response in young animals called “fear” or “alarm” bradycardia. Lessons learned from reducing the weight of obese pets and zoo animals might inform human dieting efforts. Humans engage in self-mutilating behaviors like cutting; self-injury also occurs in animals and probably represents grooming gone awry.  Humans develop anorexia nervosa; eating disorders also occur in animals when stress and fear inhibit feeding.

The pathogens from animal diseases can adapt to humans, as in the case of HIV. A sexually transmitted disease in animals can become a human disease where infection is by ingestion, like brucellosis. Pathogens can affect host behavior. Advanced syphilis may promote the spread of spirochetes by compromising judgment and increasing sexual appetites along with egomania, impulsiveness and disinhibition; Al Capone, Napoleon and Idi Amin were syphilitics and the author speculates that their disease may have facilitated their power grabs.

Teenage risk-taking behavior is paralleled in young animals undergoing the transition to adult life. Bullying, gangs, peer oppression, and self-destructive behavior are not limited to humans. Understanding animal behavior could shed light on possible ways to influence human behavior.

An epidemic of dead crows in New York City coincided with the human outbreak of a mosquito-borne disease identified by the CDC as St. Louis encephalitis. An astute veterinarian realized that the bird deaths were not compatible with that diagnosis. He was ignored at first, but eventually the CDC admitted that it was wrong, and the true diagnosis was a virus not previously recognized in the US: West Nile virus. In the wake of this misdiagnosis, agencies are calling for the routine involvement of veterinarians in evaluating public health crises.

Although Carl Zimmer has pointed out some misconceptions  about evolution in her book, Dr. Natterson-Horowitz makes a good argument for evolutionary medicine with a twist. Rather than speculating about our ancestors, we can study our living animal relatives for clues about human diseases and behaviors. Rather than speculating about how traits like homosexuality evolved, we can study how they affect survival in animals today.

There is only one medicine and one biology. Terms like “alternative medicine” or “veterinary medicine” create  false dichotomies.  There is much to be gained from a regular collaboration between people doctors and animal doctors.

 

 

 

Posted in: Book & movie reviews, Evolution, Veterinary medicine

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