A Wild Rotation; “Between animal and human medicine, there is no dividing line — nor should there be"
I would never have predicted that I would spend my final month of medical school performing fetal ultra-sounds on a pregnant gorilla, phlebotomizing a 500-pound tapir with hemochromatosis, caring for a meerkat in heart failure, and investigating medical mysteries across the animal kingdom. Yet spending the final month of my MD-PhD program working at the veterinary hospital of a zoo was one of the more remarkable and humbling experiences I had during medical school — a unique capstone to my education as a physician-scientist.
Early during medical school, I became fascinated by the diversity of anatomy and physiology across the animal kingdom. After lectures on cardiology, I read the scant literature on whale heart physiology, in near disbelief that the aorta of a sperm whale has a 2-foot circumference and a staggering cardiac output of 450 liters per minute.1 It was breathtaking trying to imagine the dynamics of blood flow in such a massive cardiovascular system. During neurology courses, I was amazed to learn that marsupials do not have a corpus callosum connecting the hemispheres of their brain (they are connected via a different tract). The differences between “us” and “them” across the myriad dimensions of function seemed to probe basic assumptions about human pathophysiology. What mechanisms protect giraffes from hypertensive organ damage when their systolic blood pressures are twice that of humans?2 How do hibernating bears avoid uremia despite months of minimal urine output?3 The human animal, I came to appreciate, is but a single point among a cloud of points revealing otherwise invisible physiologic trends and questioning principles often taken for granted. This perspective also seemed an inexhaustible source of research ideas with potential to affect both human and animal health.
Later in medical school, I read about the remarkable ways in which diseases can be prevalent in specific species but not others. I helped diagnose my family’s cocker spaniel with Evans syndrome — the co-occurrence of autoimmune hemolytic anemia and thrombocytopenia — and was intrigued to learn that Evans syndrome and immune thrombocytopenia more commonly afflict cocker spaniels, suggesting a genetic susceptibility for this breed and an opportunity to reveal some of the mystery of its cause. One of the first patients I saw on the wards in medical school had Evans syndrome. The look on the clinical team’s faces when I blurted out, “My dog has that!” was priceless. Yet it spurred me to share with my colleagues the bridges I was finding between human and animal medicine.
These experiences led me to reach out to the Franklin Park Zoo’s veterinary hospital in Boston, whose veterinarians bravely agreed to host a medical student for an admittedly unorthodox, perhaps unprecedented rotation. And for both the gorillas and myself, this experiment changed how we view and understand medicine.
For nearly every disease I saw at the zoo, the simple question of why certain species, human or nonhuman, are susceptible to it, while others are not, raised immediate possibilities for research into their etiology. Chimpanzees have an ostensibly more atherogenic lipid profile than humans, yet they do not appear to get atherosclerosis; instead, they and other great apes (gorillas, orangutans, and bonobos) are susceptible to a different disease —fibrosing cardiomyopathy — that is uncommon in humans.4
At the zoo, I helped perform cardiac ultrasounds of the gorillas as part of the Great Ape Heart Project to understand how heart disease manifests in our closest cousins. When I cared for a cotton-top tamarin with colitis and a bowel obstruction secondary to colon cancer, I learned that tamarins (a small New World monkey) have high rates of chronic colitis and subsequent colon cancer. Remarkably, this appears to preferentially occur to tamarins in captivity,5 suggesting an environmental etiology and an opportunity to study the underlying causes of inflammatory bowel disease.
At the zoo, I realized that natural veterinary disease models present unique opportunities for elucidating disease etiology beyond induced disease models often used in research since they manifest spontaneously and in more natural contexts. They may also provide an animal model where one does not otherwise exist. For example, hepatitis B virus research was greatly advanced when a related virus was discovered in woodchucks at the Philadelphia Zoo,6 and in 1909, a tumor in a chicken from a Long Island farm led to the seminal discovery of the Rous sarcoma virus, which was later pivotal to revealing the first oncogene and the genetic origins of cancer.7
*Editor's Note: Our daughter recently visited the Peaceable Primate Sanctuary; A Home for Retired and Rescued Baboons in Winamac, Indiana (a 501(c)(3) tax-exempt nonprofit organization). The sanctuary was designed with experts in baboon housing, management and care, and upholds all local, state and federal regulations. They accepted their first baboons in May 2016 and their goal is to care for 60 baboons by 2020. There's a newsletter signup as well as ways to donate to the Peaceable Primate Sanctuary, such as Amazon.
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