Rabbits with Horns

Human Papillomavirus

The stories about rabbits with horns circulated for centuries. Eventually they crystallized into the
myth of the jackalope. If you go to Wyoming and twirl a rack of postcards, chances are you’ll find a
picture of a jackalope bounding across the prairie. It looks like a rabbit sprouting a pair of antlers.
You may even see jackalopes in the flesh—or at least the head of one mounted on a diner wall.

On one level, it’s all bunk. Most jackalopes are nothing but taxidermic trickery—rabbits with
pieces of antelope antler glued to their heads. But like many myths, the tale of the jackalope has a
grain of truth buried at its core. Some real rabbits do indeed sprout horn-shaped growths from their
heads.

In the early 1930s, Richard Shope, a scientist at Rockefeller University, heard about horned rabbits
while on a hunting trip. He had a friend catch one and send him some of the tissue so that he could
figure out what it was made of. Shope’s colleague, Francis Rous, had done experiments with chickens
that suggested viruses could cause tumors. Many scientists at the time were skeptical, but Shope
wondered if rabbit “horns” were also tumors, somehow triggered by an unknown virus. To test his
hypothesis, Shope ground up the horns, mixed them in a solution, and then filtered the liquid through
porcelain. The fine pores of the porcelain would only let viruses through. Shope then rubbed the
filtered solution onto the heads of healthy rabbits. They grew horns as well.

Shope’s experiment did more than show that the horns contained viruses. He also demonstrated that
the viruses created the horns, crafting them out of infected cells. After this discovery, Shope passed
on his rabbit tissue collection to Rous, who continued to work on it for decades. Rous injected virus-
loaded liquid deep inside rabbits and found that it didn’t produce harmless horns. Instead, the rabbits
developed aggressive cancers that killed them. For his research linking viruses and cancer, Rous won
the Nobel Prize in Medicine in 1966.

The discoveries of Shope and Rous led scientists to look at growths on other animals. Cows
sometimes develop monstrous lumps of deformed skin as big as grapefruits. Warts grow on mammals,
from dolphins to tigers to humans. And on rare occasions, warts can turn people into human
jackalopes. In the 1980s, a teenage boy in Indonesia named Dede began to develop warts on his body,
and soon they had completely overgrown his hands and feet. Eventually he could no longer work at a
regular job and ended up as an exhibit in a freak show, earning the nickname “Tree Man.” Reports of
Dede began to appear in the news, and in 2007 doctors removed thirteen pounds of warts from
Dede’s body. They’ve had to continue to perform surgeries to remove new growths from his body
since then. Dede’s growths, along with all the others on humans and mammals, turned out to be caused
by a single virus—the same one that puts horns on rabbits. It’s known as the papillomavirus, named
for the papilla (buds in Latin) that cells form when they become infected.

In the 1970s, the German researcher Harald zur Hausen speculated that papillomaviruses might be
a far bigger threat to human health than the occasional wart. He wondered whether they might also
cause tumors in the cervixes of women. Previous studies on cases of cervical cancer revealed