At Cornell University’s Baker Institute for Animal Health, groundbreaking horse health research is not surprising but standard. Such is the tone with which Prof. Doug Antczak ’69, animal science, refers to various scientific feats that have emerged from the 66-year-old facility, although the professor mentions the endeavors of his predecessors before his own work.
Regardless, Antczak, in collaboration with colleagues from Cornell University, the University of Glasgow, Iowa State University and the University of Florida, recently published findings from a research project of their own. The team proposed that genetic differences in horse species could allow for papillomavirus-induced sarcoid (skin) tumors to grow in some horses and not others.
This papillomavirus is similar to one found in humans, known as Human Papillomavirus (HPV), and the group’s findings could shed light on whether certain people are more susceptible to the virus and subsequently the cervical cancer it causes.
Sarcoid skin tumors are the “most common tumor of any kind described in the horse,” Antczak said, with tumors coming in various shapes and sizes and potentially occurring anywhere on a horse’s body.
Although these tumors are often not fatal – they are categorized as non-malignant – the placement of a tumor could interfere with the functionality of the horse, for example if the tumor lies in the same location as where the saddle sits. Horses get sarcoid tumors if they are exposed to papillomavirus, but the way certain horses became exposed to the virus was misunderstood prior to this study.
photo courtesy of Doug Antczak
Sarcoid tumor on a horse’s ear
Now, Antczak believes that histocompatibility genes, responsible for ensuring that tissues are compatible in different horses, are the root of why not all horses are equally susceptible to these tumors. The team came to this conclusion based on a genomewide association study in which they compared the genomes of horses suffering from sarcoid tumors to those that were not.
“We determined that horses of certain breeds got sarcoid [skin tumors] more often than other breeds,” Antczak said.
He first noticed a difference in horse susceptibility after combing through decades of veterinary hospital admission records. From this, Antczak proposed that Standardbred horses are missing a specific gene that would otherwise allow for sarcoid tumors to grow.
Antczak compared the presence of this specific histocompatibility gene to differences in eye color.
“If a disease-free population is made up of people with exclusively brown eyes, and a disease is known to be associated with people who have blue eyes, then the gene for blue eyes most likely allows for you to get that disease,” Antczak said. “Here, it’s exactly the same thing, except instead of having brown and blue eyes, you’ve got 10 different colors.”
In this way, sarcoid tumors are considered a complex disease, impacted by both a genetic and an environmental component. The genetic component is the histocompatibility gene that allows the horse to acquire the papillomavirus, while the environmental component is the exposure to the virus itself.
Cervical cancer in humans is also a complex disease, except the virus of importance is HPV, a type of papillomavirus which is specific to humans. Despite the difference in species, however, the general mechanism of obtaining the disease is the same.
“There are genetic variations in the same genetic region in women with cervical carcinoma caused by Human Papillomavirus,” Antczak said, referring to where the genes for papillomavirus susceptibility was discovered in horses.
Thus, just as animal scientists can now identify which horse breeds are more likely to become infected by the papillomavirus, doctors may one day be able to identify which humans are more susceptible to HPV.
It is important to note that while papillomavirus may be linked to certain histocompatibility genes in horses, humans and many other mammalian species, the exact mechanism behind why this is the case is still a mystery. Additionally, while animal scientists may now be able to determine which horse breeds are more likely to get exposed to the papillomavirus, the range of susceptibility in horses of the same breed is yet to be quantified.
Despite these unknowns, Antczak considers this project one of his favorites because of these very complexities.
“It’s got everything,” Antczak said. “It’s a tumor, it’s an infection which causes a tumor, there’s a genetic basis, there’s lots of variation that we don’t understand and it’s an important disease in humans, of course.”