The Diseases We Share with Our Animals, including Reptiles (2012)

The following is from the latest Herp Digest release (if you don’t subscribe already, please do!) and a collaboration of Barbara Natterson-Horowitz, a cardiology professor at U.C.L.A. and writer Kathryn Bowers. This essay is adapted from their forthcoming book “Zoobiquity: What Animals Can Teach Us About Health and the Science of Healing,” which is told from the doctor’s point of view.

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People often ascribe the prevalence of the disease to modern habits like smoking and tanning, but cancer is common in animals. Cougars are susceptible to breast cancer. Photo by Jeff Vanuga/Corbis.

Melanoma has been diagnosed in the bodies of animals from penguins to buffalo. Koalas in Australia are in the middle of a rampant epidemic of chlamydia. Yes, that kind — sexually transmitted. I wondered about obesity and diabetes — two of the most pressing health concerns of our time. Do wild animals get medically obese? Do they overeat or binge eat? I learned that yes, they do.

I also discovered that geese, gorillas and sea lions grieve and may become depressed. Shelties, Weimaraners and other dog breeds are prone to anxiety disorders.

Suddenly, I began to reconsider my approach to mental illness, a field I had studied during the psychiatric residency I completed before turning to cardiology. Perhaps a human patient compulsively burning himself with cigarettes could improve if his therapist consulted a bird specialist experienced in the treatment of parrots with feather-picking disorder. Significantly for substance abusers and addicts, species from birds to elephants are known to seek out psychotropic berries and plants that change their sensory states — that is, get them high. The more I learned, the more a tantalizing question started creeping into my thoughts: Why don’t we human doctors routinely cooperate with animal experts?

We used to. A century or two ago, in some rural communities, animals and humans were cared for by the same practitioner. And physicians and veterinarians both claim the same 19th-century doctor, William Osler, as a father of their fields. However, animal and human medicine began a decisive split in the late 1800s. Increasing urbanization meant that fewer people relied on animals to make a living. Motorized vehicles began pushing work animals out of daily life.

Most physicians see animals and their illnesses as somehow “different.” Humans have their diseases. Animals have theirs. The human medical establishment has an undeniable, though unspoken, bias against veterinary medicine.

While it rankles when M.D.’s condescend, most vets simply take a resigned approach to their more glamorous counterparts on the human side. Several have even confided to me a veterinarians’ inside joke: What do you call a physician? A veterinarian who treats only one species.

My medical education included stern warnings against the tantalizing pull to anthropomorphize. In those days, noticing pain or sadness on the face of an animal was criticized as projection, fantasy, or sloppy sentimentality. But scientific advancements of the past two decades suggest that we should adopt an updated perspective. Seeing too much of ourselves in other animals might not be the problem we think it is. Underappreciating our own animal natures may be the greater limitation.

Cancer

PEOPLE who didn’t smoke, drink or tan and who avoided microwaving food in plastic and cooking on Teflon can develop cancer. It strikes yoga practitioners, breast-feeders and organic gardeners; infants, 5-year-olds, 15-year-olds, 55-year-olds and 85-year-olds.

Even the briefest survey of cancer in other animals sheds light on a critical but overlooked truth: Where cells divide, where DNA replicates, and where growth occurs, there will be cancer. Cancer is as natural a part of the animal kingdom as birth, reproduction and death. And it’s as old as the dinosaurs.

Osteosarcoma, the cancer that forced Ted Kennedy’s son, Ted Junior, to undergo an amputation in the early 1970s, attacks the bones of wolves, grizzly bears, camels and polar bears. And the neuroendocrine cancer that claimed the life of Apple’s co-founder, Steve Jobs, while rare in humans, is a fairly common tumor of the domestic ferret and has been diagnosed in German shepherds, cocker spaniels, Irish setters and other dog breeds.

Breast cancer strikes mammals from cougars, kangaroos and llamas to sea lions, beluga whales and black-footed ferrets. Some breast cancer in women (and the occasional man) is connected to a mutation of a gene called BRCA1. All humans have a BRCA1 gene. But about one in 800 of us are born with a mutated version, which increases the risk for certain cancers. For Jewish women of Ashkenazi descent, it’s as high as one in 50. And BRCA1-related breast cancer occurs in some animals, too: English springer spaniels, and possibly big cats like jaguars.

But some groups of mammals, intriguingly, may be protected from it.

The latte you sipped this morning contained milk from an animal sorority that very rarely gets breast cancer. Professional lactators — the dairy cows and goats that make milk for a living — have rates of mammary cancer that are so low as to be statistically insignificant. That animals which lactate early and long seem to have some protection against breast cancer is not only fascinating, it parallels human epidemiologic data that tie breast-feeding to reduced mammary cancer risk.

Another thing we can learn from animal cancer is the extent to which it’s caused by outside invaders: viruses. Veterinary oncologists see this all the time. Lymphomas and leukemias among cattle and cats are quite frequently viral. Many of the cancers sweeping sea creatures from turtles to dolphins are rooted in papilloma and herpes viruses. Between 15 and 20 percent of cancers worldwide are caused by infections, many of which are viral.

And noticing where cancer isn’t can be as instructive as noticing where it is. Dogs rarely get colon cancer. Lung cancer is also atypical, although short- and medium-nosed dogs living in homes with smokers are susceptible. Canine breast cancer is rarer in countries that promote spaying but quite common where most female dogs remain reproductively intact. As the veterinary oncologists Melissa Paoloni and Chand Khanna point out, two breeds of dogs seem to get cancer less often than others: beagles and dachshunds. Like the professional lactators who rarely get breast cancer, these extra-healthy dog breeds may point to behaviors or physiology that offer cancer protection.

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Addiction

ANIMALS don’t have access to liquor stores, pharmacies or corner drug dealers. But the intoxicants in those drugs are found in nature — opium in poppies, alcohol in fermented fruit and berries, stimulants in coca leaves and coffee. Given the opportunity, some animals do indulge … and get intoxicated.

Addiction researchers have shown that genetics, vulnerable brain chemistry, and environmental triggers play roles in human substance abuse. But ultimately, on the receiving end of the syringe, joint or martini glass is a person making a choice, at least in the initial stages of drug use. This makes addiction uniquely bewildering to physicians, psychiatrists, sufferers and the people who care for them. Why is it so hard for addicts to “just say no”? It turns out that saying “no” is hard for animals too.

Cedar waxwing birds are known to ingest fermented berries, fly while intoxicated and crash into glass walls. In Tasmania, wallabies have broken into fields where medical opium was growing, eaten the sap and got stoned.

Some animals show chronic drug-seeking behaviors. Bighorn sheep grind their teeth to the gums scraping hallucinogenic lichen off boulders in the Canadian Rockies; some Siberian reindeer seek out magic mushrooms.

 

Cane Toads – Don’t lick them!

A friendly cocker spaniel in Texas once sent her owners’ lives into a tailspin when she turned her attention to toad licking. As described in an NPR story, the spaniel, Lady, had been the perfect pet, until one day she got a taste of the hallucinogenic toxin on the skin of a cane toad. Soon she was obsessed with the back door, always begging to get out. She’d beeline to the pond in the backyard and sniff out the toads. Once she found them, she mouthed them so vigorously she sucked the pigment right out of their skin. According to her owners, after these amphibian benders Lady would be “disoriented and withdrawn, soporific and glassy-eyed.”

In lab settings, rats have been shown to seek out and self-administer doses — sometimes to the point of death — of various drugs, from nicotine and caffeine to cocaine and heroin. Once addicted (researchers say “habituated”) they may forgo food and even water to get their drug of choice. Like us, they also use more when they’re stressed by pain, overcrowding or subordinate social position. Some ignore their offspring.

Taking a species-spanning perspective of drug use reveals something important: The urge to use has stayed in the gene pool for millions of years and for a counter-intuitive reason. Although addiction can destroy, its existence may have promoted survival.

Here’s what I mean: Foraging, stalking prey, hoarding food, searching for and finding a desirable mate, and nest building are all examples of activities that greatly enhance an animal’s chances of survival and reproduction, or what biologists call fitness. Animals are rewarded with pleasurable, positive sensations for these important life-sustaining undertakings. Pleasure rewards behaviors that help us survive.

Conversely, unpleasant feelings like fear and isolation indicate to animals that they are in survival-threatening situations. Anxiety makes them careful. Fear keeps them out of harm’s way.

And one thing creates, controls and shapes these sensations, whether positive or negative: a cacophonous chemical conversation in the brains and nervous systems of animals. Time-melting opioids, reality-revving dopamine, boundary-softening oxytocin, appetite-enhancing cannabinoids and a multitude of other neurohormones reward behavior.

We humans get drug rewards for life-sustaining activities just as animals do. We simply call those activities by different names: Shopping. Accumulating wealth. Dating. House hunting. Interior decorating. Cooking.

When these behaviors have been studied in humans, they are associated with rises in the release of certain natural chemicals, including dopamine and opiates.

The key point is that behaviors are the triggers. Do something that evolution has favored, and you get a hit. Don’t do it, and you don’t get your fix.

And this is precisely why drugs can so brutally derail lives. Ingesting, inhaling or injecting intoxicants — in concentrations far higher than our bodies were designed to reward us with — overwhelms a system carefully calibrated over millions of years. These substances hijack our internal mechanisms. They remove the need for the animal to input a behavior, before receiving a chemical dose. In other words, pharmaceuticals and street drugs offer a false fast track to reward — a shortcut to the sensation that we’re doing something beneficial.

This is a critical nuance for understanding addiction. With access to external drugs, the animal isn’t required to “work” first — to forage, flee, socialize or protect. Instead, he goes straight to reward. The chemicals provide a false signal to the animal’s brain that his fitness has improved, although it has not actually changed at all.

Why go through a half-hour of awkward small talk at an office party when a martini or two can trick your brain into thinking you’ve already done some social bonding? Drugs tell users’ brains that they’ve just done an important, fitness-enhancing task.

Ultimately, however, the powerful urge to use and reuse is provided by brain biology that evolved because it maximized survival. Seen this way, we’re all born addicts. Substance addiction and behavioral addiction are linked. Their common language is in the shared neurocircuitry that rewards fitness-promoting behaviors.

Consider the most common behavioral addictions from an evolutionary perspective. Sex. Binge eating. Exercise. Working. They are exceedingly fitness enhancing.

Connecting brain-rewarding behaviors to increased survival allowed me to rethink technological “addictions” like video gaming, e-mailing and social networking. Our smartphones, Facebook pages and Twitter feeds profoundly combine the things that matter most to animals competing to survive: a social network, access to mates, and information about predatory threats.

Understanding the comparative biology and evolutionary origins of addiction can improve how we understand this disease and its sufferers. First, individual humans vary greatly in their vulnerability to addiction. So do animals, from mammals to worms. In addition, human and animal data both suggest that the younger the animal is at the first exposure to an external drug, the more likely it is to become addicted and responsive to that drug in the future. This is a very important point.

In the United States, we’ve tried Prohibition and “just say no” campaigns. We’ve set the drinking age at 21 and the illegal drug use age at never. None of these interventions has completely stopped teenagers from going after what they want.

But the evidence suggests that it’s wise for parents to try harder to delay their children’s first exposures and, perhaps, to teach them natural ways of achieving those chemical rewards: through exercise, physical and mental competitions, or “safe” risk-taking, like performing.

Substance abusers can learn healthy behaviors that provide the same (albeit less potent) good feelings they used to seek from a bottle, a pill or a needle. In fact, that may be what makes some rehab programs so effective for certain addicts. The behaviors these programs encourage — socializing, seeking companionship, anticipating, planning and finding purpose — are all part of an ancient, calibrated system that rewards survival behaviors with drugs from an animal’s inborn pharmacy.

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Fat Planet

ALTHOUGH I’m a cardiologist, some days I feel more like a nutritionist. Patients, family members and friends frequently ask me, “What should I be eating?” We all know by now that choosing the wrong foods and carrying extra weight on our bodies can make us sick.

But humans aren’t the only animals on our planet who get fat. In the wild, animals as varied as birds, reptiles, fish and even insects regularly gain — and then take off — weight. Closer to home, nearly half of our pet dogs, cats, even horses and birds are now overweight or obese, despite the low-carb, feline “Catkins” diet, canine liposuction and increased exercise for bird “perch potatoes.” With our pets’ excess pounds has come a familiar suite of obesity- related ailments: diabetes, cardiovascular problems, musculoskeletal disorders, glucose intolerance, some cancers and possibly high blood pressure. They’re familiar because we see nearly identical problems in obese human patients.

I’d long assumed that wild animals stayed effortlessly lean and healthy. I’d always thought that wild animals ate until they were full and then prudently stopped. But in fact, given the chance, many wild fish, reptiles, birds and mammals overindulge. Sometimes spectacularly so. Abundance plus access — the twin downfalls of many a human dieter — can challenge wild animals, too.

Although we may think of food in the wild as hard to come by, at certain times of the year and under certain conditions, the supply may be unlimited. Many gorge, stopping only when their digestive tracts literally cannot take any more. Tamarin monkeys have been seen to eat so many berries in one sitting that their intestines are overwhelmed and they soon excrete the same whole fruits they recently gobbled down.

Mark Edwards, an animal nutrition expert, told me, “We’re all hard-wired to consume resources in excess of daily requirements. I can’t think of a species that doesn’t.” Wild animals can get fat with unfettered access to food.

Of course, animals also fatten normally — and healthily — in response to seasonal and life cycles. Remarkably, it is the landscape around an animal that determines whether its weight stays steady or rises.

And nature imposes its own “weight-maintenance plan” on wild animals. Cyclical periods of food scarcity are typical. Threats from predators limit access to food. Weight goes up, but it also comes down. If you want to lose weight the wild animal way, decrease the abundance of food around yourself and interrupt your access to it. And expend lots of energy in the daily hunt for food. In other words: change your environment.

Looking across the species divide and seeing weight gain in a broader context forces us to consider factors beyond the “diet and exercise” dogma. Even without an assist from 32-ounce sodas, the yellow-bellied marmots in the Rockies, blue whales off the coast of California and country rats in Maryland have gotten steadily chubbier in recent years. The explanation might lie in the disruption of circadian rhythms. Of the global dynamics controlling our biological clocks — including temperature, eating, sleeping and even socializing — no “zeitgeber” is more influential than light.

New research suggests that when, and how much, light beams through your eyes may play a quiet and unrecognized role in determining your dress or pants size. And the breaking up of light-dark cycles may be a culprit. Light pollution from suburban sprawl, big-city skyglow, electronic billboards and stadium lights has brightened our planet. A rodent study published in the Proceedings of the National Academy of Sciences showed that mice housed with constant light — whether bright or dim — had higher body mass indexes (B.M.I.’s) and blood sugar levels than mice housed with standard cycles of dark and light.

Another invisible weight driver is housed within our own abdomens: the trillions of microscopic organisms that live in our guts. This world is called the microbiome, and it is colonized by two dominant groups of bacteria: the Firmicutes and the Bacteroidetes. In the mid-2000s, some scientists made an interesting observation. They found that obese humans had a higher proportion of Firmicutes in their intestines. Lean humans had more Bacteroidetes. As the obese humans lost weight over the course of a year, their microbiomes started looking more like those of lean individuals — with Bacteroidetes outnumbering Firmicutes.

When the researchers looked at mice, they found the same thing. Although not all research has replicated those results, if that observation turns out to be true, it means that a booming Firmicute colony might help harvest, say, 100 calories from one person’s apple. That person’s friend may have a dominant Bacteroidete population that would extract only 70 calories from the same apple. This could be one factor in why your co-worker can eat twice as much as everyone else but never seems to gain weight. The power of the microbiome is well known to the veterinarians who oversee the care of animals we make fat on purpose: livestock. Nowadays, it’s common for factory farming operations to administer antibiotics to food animals from 1,500-pound steers to one-ounce baby chicks. The effect of those antibiotics on the living colonies of gut bugs in the animals’ intestines may inform human obesity research.

Antibiotics don’t kill just the bugs that make animals sick. Simply by giving antibiotics, farmers can fatten their animals using less feed. One hypothesis is that by changing the animals’ gut microflora, antibiotics create an intestine dominated by colonies of microbes that are calorie-extraction experts. Anything that alters gut flora, including but not limited to antibiotics, has implications not only for body weight but for other elements of our metabolism, such as glucose intolerance, insulin resistance and abnormal cholesterol.

Modern, affluent humans have created a continuous eating cycle, a kind of “uniseason.” Our food is stripped of microbes, and we remove more while scrubbing off dirt and pesticides. Because we control it, the temperature is always a perfect 74 degrees. Because we’re in charge, we can safely dine at tables aglow in light long after the sun goes down. All year round, our days are lovely and long; our nights are short.

As animals, we find this single season an extremely comfortable place to be. But unless we want to remain in a state of continual fattening, with accompanying metabolic diseases, we will have to pry ourselves out of this delicious ease.

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Cutting

PROBABLY our era’s most iconic form of human self-harm, seemingly tailor-made for suburban-parent hand-wringing and tabloid ogling, is cutting. Its name says it all, but in case you don’t know: it means taking something sharp — maybe a razor blade, scissors, broken glass or a safety-pin — and slicing it across your skin to draw blood and create wounds. Psychiatrists call cutters “self-injurers” to include the whole range of inventive ways people dream up to hurt themselves. Some burn themselves on purpose with cigarettes, lighters or teakettles. Others bruise their skin by banging, punching or pinching themselves. Those with trichotillomania rub and rip out hair on their heads, faces, limbs and genitals. Some are swallowers, ingesting objects like pencils, buttons, shoelaces or silverware. We see this particular method a lot in prisons.

You may think self-injury occurs only in edgy subcultures or the seriously mentally ill. But my psychiatrist colleagues say it’s sweeping through the general population. Why? A 22-year-old woman posting on a university blog put it this way: “I began cutting my arms at the age of 12… I think I could best describe the feeling I get as total bliss. It relaxes me.”

Bliss? Relaxation? Relief? Even after years of psychiatry training and two decades around a hospital, I still think this sounds incredible. But cutters and their therapists say it’s true. And they confirm that most self-injurers are not suicidal. But as to why they do it, the short answer is that we don’t really know.

I decided to see what insights a zoobiquitous approach could add.

A friend of mine once took her cat to the vet assuming it had a skin affliction that was causing all the hair to fall off its legs, revealing red, oozing sores. After some tests to rule out parasites and systemic diseases, her vet said her pet was a “closet licker.” It’s a common diagnosis for house cats, sometimes called psychogenic alopecia. The cat was injuring itself with no clear physical trigger, in a way that was reminiscent of a human cutter alone in her room.

Owners of golden retrievers, Labrador retrievers, German shepherds, Great Danes, and Doberman pinschers will probably recognize a condition that often affects those breeds — in which they obsessively lick and gnaw at their own bodies. The open sores they create can cover the entire surface of a limb or the base of the tail.

“Flank biters” are horses that violently nip at their own bodies, drawing blood and reopening wounds.

The owners of these horses, like parents who discover their teenager is cutting, are often confused and heartbroken by the behavior, which can include bursts of violent spinning, kicking, lunging and bucking.

When owners bring in pets who circle furniture for hours, do back flips to the point of physical exhaustion or rub their skin to the point of breakage and bleeding, veterinarians sometimes describe these behaviors as “stereotypies.” Many of the compulsive behaviors seen in horses, reptiles, birds, dogs and humans share core clinical features, including the potential to cause suffering and profoundly disrupt a patient’s life. But many also share an intriguing connection to cleaning activities.

You’ve probably heard about the repetitive hand washing practiced by many sufferers of obsessive-compulsive disorder. Similarly, a stressed cat may go overboard with a feline’s cleaning tool of choice, its raspy tongue. Veterinarians have come up with a colloquial term that cuts right to the heart of what’s going on here. They call it, simply, “overgrooming.”

Grooming is as basic an activity for many creatures as eating, sleeping and breathing. Evolution probably favored nature’s neat freaks because they were the ones with fewer parasites and infections.

Grooming plays a vital role in the social structure of many animal groups, and it feels good. There’s also a more private form of grooming — small behaviors that all but the most virtuous of us engage in all the time and often unconsciously. In general, they’re innocent enough, but given the choice, we definitely wouldn’t want to show them in public or watch other people do them.

Are your cuticles smooth or are there some rough edges begging to be picked or nibbled off? Are you twirling a lock of hair around your finger, twisting your eyebrows, stroking your own cheek, massaging your own scalp? Studies looking at hair pulling, scab picking and nail-biting all point to a calm, trance like state that typically accompanies these small, automatic, self-soothing activities.

Perhaps the fingers playing with your hair sometimes have the urge to pull a strand out. There’s that slight tension as the root clings to the follicle …you gently tug harder … and a little harder …until finally, there’s that short, sharp sting and the hair releases. Humans rely on this release-relief loop throughout the day. We may rub, pull, nibble or squeeze a little more when we’re stressed, but for most of us the behavior never escalates. But for some people the need for that feeling of release and relief is so strong that they seek extreme levels of it. Self-harm is truly grooming gone wild.

In a way, self-harmers are actually self-medicators. That’s because, paradoxically, both pain and grooming cause the body to release natural opiates, such as endorphins, the same brain chemicals that give marathoners their runner’s high.

The typical middle-class teen is a little like the horse alone in its stall, with most of its needs provided in easy-to-digest chunks. He’s left with lots of extra time and few activities as invigorating as a daily struggle for survival. Zookeepers make animals forage to avoid boredom. Should we explore getting teens involved in growing and preparing their own foods, an activity that can produce feelings of profound calm and purpose?

All of us — from full-blown cutters to secret hair pluckers and nail biters — share our grooming compulsions with animals. Grooming represents a hard-wired drive, one that’s evolved over millions of years with the positive benefits of keeping us clean and binding us socially.

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Our essential connection with animals extends from body to behavior, from psychology to society. This calls for physicians and patients to join veterinarians in thinking beyond the human bedside to barnyards, oceans and skies.