Do manatees hold the key to understanding papillomaviruses?

Viral papilloma on the lip of an endangered manatee

Emergent papillomaviruses in manatees may provide important clues to preventing and curing papillomavirus infections in humans and other animal species, according to a team of veterinarians and physicians studying the viruses.

In 1997, Dr. Gregory Bossart, a veterinarian and the director of marine mammal research and conservation at the Harbor Branch Oceanographic Institution in Fort Pierce, Fla., identified a manatee-specific papillomavirus after seven captive manatees at the Homosassa Springs State Wildlife Park in Florida developed wartlike growths on their skin. The diagnosis marked the first time a viral infection had been discovered in a manatee and surprised many scientists because manatees have a "super" immune system and rarely develop infectious diseases.

"These creatures are amazingly resilient," said Dr. Bossart, explaining that manatees, which frequently suffer from trauma caused by boat propellers and boat hulls, are able to fight off infection and survive injury far better than other marine species.

A second papillomavirus outbreak occurred three years later when four of the previously afflicted manatees developed distinct new growths. Both outbreaks seem to be contained to the Homosassa Springs population of manatees. Similar papillomas have not been described in free-ranging manatees, despite an intensive manatee carcass salvage and necropsy program that has been in place for more than 25 years.

Dr. Bossart and the other researchers suspect, however, that the viruses may exist in other manatees in a latent form and may emerge only when an animal's immune system is compromised—similar to the way human papillomaviruses behave.

This similarity, coupled with the mystery of how the virus is circumventing the manatees' highly developed immune system, leads researchers to believe studying the Homosassa manatees may provide useful information about the behavior of all papillomaviruses.

"The way this virus produces papillomas in manatees is similar to the way (human papillomaviruses) produce papillomas that turn into cervical cancer in humans," said Alfred Bennett Jenson, MD, a papillomavirus expert from the Brown Cancer Center at the University of Louisville, in a statement.

A manatee with papillomas with Art Yerian, curator of Homosassa Springs State Wildlife Park; Dr. Gregory Bossart; Dr. Mark Lowe, veterinarian at Homosassa Springs State Wildlife Park; and Dr. Alfred Bennett Jenson.

"It's a fascinating opportunity to learn more not only about the pathenogenesis of this virus in manatees but also an opportunity to develop an approach to fighting the viral infections and the lesions they cause, which I think is eventually going to benefit humans as well."

Joining Dr. Bossart and Dr. Jenson in the study is Dr. Mark Lowe, the staff veterinarian at Homosassa Springs State Park in Florida; and Dr. Partha Basu, the head of gynecologic oncology at the National Cancer Institute of India, who sees four or five new cases of cervical cancer in India each day. The team published an article on the manatee papillomaviruses in the February 2002 issue of Experimental and Molecular Pathology.

For the researchers, the study of the Homosassa manatees is unique because it promises to advance human medicine and help an endangered species simultaneously.

"It's a very synergistic study," Dr. Bossart said.

Dr. Jenson, who has also studied papillomaviruses in snow leopards and is currently waiting for FDA approval of a human papillomavirus vaccine he helped develop, said he enjoys participating in research that can help ensure the survival of an endangered species.

"I think applied research is absolutely the best," he said. "I think there is a possibility of this research being applied to the management of the species."

Dr. Bossart said he hopes the study will promote more interdisciplinary research on marine mammals; in fact, the Harbor Branch Oceanographic Institution is planning to build a marine mammal teaching hospital that would facilitate the manatee research and other studies on the health and management of marine species.

The $20 million facility will include a 600,000-gallon manatee rehabilitation facility that would house the Homosassa Springs manatees while they are being studied. Other facilities would include a cetacean care center and marine mammal teaching hospital that would work in conjunction with veterinary colleges to train veterinarians.

The institution has raised about $1 million of the $20 million needed to build the facility, according to Dr. Bossart.