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The Virus, the Manatee, and the Biologist

For once, saving an endangered species could save us too

By Jennifer Tzar and Jack McClintock
Aug 1, 2003 5:00 AMApr 19, 2023 2:06 PM


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Early on a summer morning in northern Florida, four of the world's most endangered mammals, looking a lot like gigantic gray Idaho potatoes, crowd together at the bottom of a concrete pool, gently bumping into one another as the green ocean water drains away beneath them. Two veterinarians and a physician peer down at white spots on the animals' skin. Then they descend concrete stairs into the eight-foot-deep pool and start to work, surrounded by a dozen assistants and chattering spectators. The 1,500-pound manatees lie still. Gregory Bossart, tanned, blond, and barefoot, rubs disinfectant on the manatees' lesions, sprays them with alcohol, and carefully slices them away with a scalpel. He is a vet, a wildlife pathologist, and the director of marine mammal research and conservation at the Harbor Branch Oceanographic Institution in Fort Pierce, on the other side of the state. Alfred Bennett Jenson, a white-haired M.D. from the Brown Cancer Center in Louisville, Kentucky, whisks tissue samples into an open bottle. Meanwhile, Mark Lowe, the consulting vet here at Homosassa Springs Wildlife State Park, bends over the pectoral fin of a manatee named Holly to take a blood sample. When he jabs her with a needle, she flips her flat, powerful tail, tossing a wet-suited keeper into the air. He lands back on top of her and grabs hold again. By the time the three doctors have finished their work, the sun is high and the pool is as hot as a sauna. Jenson, with sweat running down his face, packs up his box of tissue specimens. Lowe leans back and lights a pipe. He was the first to notice the lesions, back in 1997. He sent the samples to Bossart, who was quite surprised when they turned out to be Papillomavirus, which had never been detected in a manatee. The virus causes warts and benign tumors, which are communicable. More than 100 types of the virus have been found in people. In women the virus can transmute into cervical cancer, a disease very much on the mind of Partha Basu, who has come all the way from Calcutta to observe. He is head of gynecological oncology at the National Cancer Institute of India, where he sees four or five new cases of cervical cancer each day. Two years ago, when he saw what he had, Bossart called Jenson, an immunopathologist. Although Jenson had studied Papillomavirus in snow leopards, he had never heard of a manatee carrying the virus. When he examined the tissue samples Bossart sent him, he was stunned. "I thought I'd seen everything," he says, removing his red baseball cap and rubbing his hair. "This is important, really a harbinger of bad news. Something bad is going on." Jenson says that if he can learn how the virus works in manatees, that knowledge might lead to improved treatment for humans. Cervical cancer is the second leading cause of death from cancer among women. Three vaccines for human Papillomavirus have been developed, one by Jenson and Richard Schlegel of Georgetown University. But vaccines are helpful only to people who have never been exposed to the virus, and it will be 20 years before the vaccine has a significant impact on death rates. Many of those exposed to the virus remain carriers for life. "If we can determine why manatees can't clear the virus," Jenson says, "then that is probably the same reason why humans can't clear the virus."

In recent years scientists have gained extraordinary knowledge about manatee intelligence, anatomy, behavior, and adaptability. They have discovered, for example, that although manatees have limited vision and are unable to echolocate like dolphins and whales, they can navigate murky waters by using their long, thin body hairs. At the Mote Marine Laboratory in Sarasota, researchers have easily taught manatees to assist their studies by obediently lifting a pectoral fin to give a blood sample or by rolling over and urinating into a specimen cup. Two years ago, the number of manatees in the wild appeared to be on the upswing, and some scientists were arguing to remove them from the endangered species list. Bossart thought that would be a mistake. Although aerial surveys suggest that Florida manatees have more than doubled their numbers in the past 12 years—in 1991 there were 1,300; this past January there were 3,000—their mortality rate also appears to be rising. Thirty percent of the manatees that die each year are killed by boats, entangled in fishing lines, or crushed in flood-control gates. Another 20 percent are calves, many of which expire after their mothers die. Last year, 325 manatees died in the United States—more than 10 percent of the population. "If we tried to do to dolphins what we're doing to manatees, there'd be an enormous outcry," Bossart says. Manatees, which evolved as tropical animals, follow warm water, swimming as far north as Rhode Island in summertime and heading south again in winter. Over the past half century, however, many of them have learned to congregate around the warm-water outfalls near paper mills and electric power plants in northern Florida—far north of their usual winter range. Studies show that 60 percent of surviving manatees now do this instead of migrating. Nine manatees, radio-tracked as they migrated along the coast, were known to winter by a paper mill in Fernandina Beach near Jacksonville, says Jim Valade, a biologist with the U.S. Fish and Wildlife Service. When the mill shut down in 1997, five of them died. "We were shocked to find that some just hung out there waiting for the warm water to come," Valade says. "Obviously, with 60 percent wintering at these sites, we're very concerned. You're looking at hundreds of animals." As older power plants shut down or shut down temporarily, manatees may be at increased risk. "It pulls their electric blanket away," Bossart says. Their immune systems are weakened and exposed to potentially fatal maladies, from fungal infections to red tide and lung disease, and probably, Jenson says, Papillomavirus. Bossart first began investigating Papillomavirus in 1996, when the disease was found in Keiko, an orca at Sea World in Orlando, who was made famous by the film Free Willy. Since then, papillomas have also been found in dolphins in Florida, Hawaii, and Portugal. The lesions that often accompany Papillomavirus appear on the mouth and can be extremely dangerous. One lesion Bossart examined turned into squamous-cell carcinoma in three months, and four months later the dolphin was profoundly anemic. "Squamous-cell cancer metastasizes in the bone marrow," he says. "I transfused her—that's unheard of—but she died." Since then, a dozen dolphins and orcas have developed papillomas. "This is very worrisome, not only for the species but for the state of animal health in Florida," Bossart says.Papillomavirus in manatees is also worrisome because manatees are famously resistant to infection. The manatee has "a superbly equipped immune system—so powerful they don't ordinarily die of natural causes; it's usually old age or some human-related cause," Bossart says. "You can almost cut them in two with a motorboat and they'll survive."

Early one October morning, field biologist Bob Bonde lets his 17-foot Mako research boat drift to a stop on the Crystal River in northern Florida. "We share habitat with them," he says, looking down at the dozens of idling manatees. "We try to get into their heads, see what makes them tick." Bonde, who worked for the U.S. Geological Survey's Sirenia Project conducting long-term manatee studies, is not alone. Pontoon boats bring 70,000 wet-suited tourists a year here to swim with manatees. Tourists watch as they surface every five to 10 minutes and open their quarter-size nostrils to take a polite sip of air. Bonde gestures at the snorkeling horde. "There are people out here having the most wonderful day of their life because that animal came up to them and wanted to be scratched or petted," he says. "Where else can you interact with an animal the size of an elephant in the wild and never worry about it stepping on your foot? And the little ones just spark with curiosity—you're a novelty in their world. People cherish that." The manatee's nearest living relative is, as it happens, the elephant, a connection easily seen in rough skin, sparse hairs, and a bristly, prehensile snout. A big manatee can weigh 3,000 pounds and eat 200 pounds of sea grass a day. Each has heavy, solid bones that not only support bulk but also act as dive weights, overcoming the natural buoyancy of abundant fat. Slow to mature and slow to gestate—it takes them a full year—female manatees have just one calf at a time. A calf depends on its mother for at least two years. Add high mortality to a lengthy upbringing and it's a recipe for extinction. Pile on stress from the cold and a new, contagious infection, and the picture looks bleaker. But perhaps it is not terminal. In research projects all over Florida, scientists have been learning enough about manatees to help close the charisma gap with dolphins that Bossart laments. At the Mote laboratory, Hugh and Buffett, born in captivity and unlikely to be released, are comfortable around people. The boys, as they're called by Brandie Littlefield, one of a handful of manatee trainers in the world, each get 45 heads of romaine lettuce a day, plus apples, beets, carrots, and monkey biscuits as rewards for learning. "We also give them lots of tactile and verbal reinforcement to keep them focused," she says. The boys have already helped avert one potentially deadly threat: the mysterious rise of creatinine—a substance produced during muscle contractions that can indicate kidney failure—in the blood of released manatees. By manipulating their diet and taking frequent blood and urine samples, Mote researchers learned how to prepare animals for release from captivity by adapting them to salt water early and feeding them wild plants instead of romaine. Gordon Bauer, a comparative psychologist at the New College of Florida, is studying Hugh's and Buffett's eyesight. He's interested in memory and information processing. "But first," he says, "we have to determine what information a manatee actually detects in the outside world." Previous researchers have found that manatees have some color vision, which is unusual for marine mammals, perhaps because color vanishes with water depth. But manatees live mostly in shallows or near the surface. With a trainer's help, Bauer taught Hugh and Buffett to choose between pairs of black-and-white-striped targets placed underwater a yard away. He wanted to find out how wide the stripes had to be before the manatees could distinguish them. Eyesight can be measured in terms of minutes of visual arc. "Humans are really spoiled, with about a minute of visual arc," Bauer says. "A dog or cat is a 4 to 9, a dolphin probably 8 or 10. But Buffett's best-ever performance is 21, about the same as a cow. And Hugh is 60, basically blind. "If manatees don't have a particularly strong need for good eyesight, it might not be selected for in evolution," Bauer says. "If not, though, what do they rely on? Touch? Learning? Chemical reception? And they have these hairs . . . " Bauer reaches into the tank and runs a finger over the bristly hairs on Buffett's body. "No other animal is known to have tactile hairs all over its body," says Roger Reep, an animal physiologist at the University of Florida in Gainesville. Tactile hairs are whiskers with the capacity for touch—like those cats have on their faces. Reep has discovered that manatees have two kinds of tactile hairs, those on their faces and another type on their bodies. A tactile hair has a special structure: Its follicle has an elaborate blood capsule around it with a thin inner wall and a thick outer wall. If the hair shaft moves, it collides with the thin wall, which contains sensory receptors that convert sensation into electrical energy. That information is relayed to the central nervous system and on to the brain's cortex, which has a cell group to process each hair's signals. Cats use whiskers to feel their way in the dark and detect prey; pinnipeds like walruses use them to locate underwater prey and to communicate. A manatee's face is 30 times hairier than the rest of its body. The broad, fleshy expanse between its mouth and nose, called the oral disk, has some 600 stout hairs deployed across it. Researcher Chris Marshall, a colleague of Reep's, found that in searching for food, manatees flare this oral disk, shut their eyes, and grope. "If they like what they feel, they try to chew on it, like a baby," Reep says. The larger bristles on either side of their upper and lower lips "reach out and grab, as if there were little pairs of hands beside the mouth." A German researcher found that a manatee's snout has about the same acuity as the tip of an Asian elephant's trunk. Moreover, every manatee's body sprouts about 3,000 more sparsely distributed hairs, Reep and his colleagues have found. Each hair follicle, spaced an inch or two apart, has 20 to 50 nerve fibers, compared with 5 to 10 in ordinary mammalian hair. Why? Manatees—otherwise nearly blind—use them to "see." "We suspect it's a distributed tactile array that detects underwater pressure waves—movement," Reep says. "It's like a mammalian version of a fish's lateral line." In a scaly fish, this line, visible as a dark stripe of specialized cells down the creature's side, is stimulated when water moves over it. Connecting nerves communicate information to the brain. That's why, Reep says, "you can sneak up behind fish but cannot grab them." Why would a mammal evolve this feature? Consider that manatees are large, slow-moving herbivores with no predators; they have poor vision and no echolocating capability. They spend a lot of time in turbid habitats. How else could they navigate and find feeding grounds? The development of tactile hairs allowed the animals to sense currents and tides as well as approaching animals and fixed objects like rocks and riverbanks.

One winter morning, at Blue Spring State Park, a few miles inland from Daytona Beach, a moving van stopped and people started unloading a manatee called Stormy on a giant litter. They checked the animal, then carried it into the water and let it go. Scientists at the Mote lab rehabilitate and release at least a few injured manatees each year; the U.S. Fish and Wildlife department, which oversees the program, has released about 600 since 1976. More than half have survived. "We're rescuing 40 or 50 a year, and most will eventually be released," Valade says. A few—like Phoenix, her tail lopped off by a boat propeller and living at the Miami Seaquarium—can never be freed. Others are tagged and released in springs like this, where manatees have perennially spent their winters. The pure water bubbling up from deep underground is always 72 degrees, and many manatees congregate here. Valade hopes Stormy will learn their ways and return to this safe haven in the winter. In a recent study, Bossart examined the tissues of 12 manatees found dead. More than 80 percent had severe immune dysfunction, changes in the lymphoid system, infections in lungs and intestines, bizarre skin lesions, degenerative changes of the heart and pancreas, and severe emaciation. "They look similar to AIDS patients," he says, attributing the symptoms to cold stress. Cold may also be a factor in the Papillomavirus outbreak. That's what worries Jenson, who believes the virus coevolved with manatees and has always been latent in them. "It was probably passed on for hundreds of thousands of years, from manatee to manatee," he says—and cold stress weakened the animals enough to let it emerge. Bossart hopes the virus is confined to seven of the nine manatees at Homosassa Springs, where the temperature is also 72 degrees and where manatees have always congregated to avoid the cold. He thinks the virus could have manifested itself only among these seven because they lived their lives in captivity in water of 72 degrees, barely above their cold-stress threshold of 68 degrees. "They've been thermally challenged all their lives," he says. In the wild, migrating manatees spend many months of the year at higher temperatures. Jenson agrees but thinks the activated virus already exists in free-swimming manatees. One manatee rubbing against another can pass the virus on through a cut or an abrasion. Jenson thinks a fish nibbling on one manatee's lesion and then moving on to another animal might be enough. If he is correct, a worst-case scenario might not be far off. Sixty percent of the manatee population—those depending on warm-water outfalls—could be at risk when power plants are switched off. "It could be devastating if it got into the wild population and turned malignant," Bossart says. "My concern is that these animals might get into a catastrophically life-threatened mode."

The three doctors have returned to work. Veterinarian Mark Lowe remains at Homosassa Springs, watching Holly, Ariel, Willoughby, and six other manatees. Sometimes their lesions go away, but they always come back. Jenson went back to his lab with tissue samples and is working to clone them for further study. If he succeeds, and finds a way to clear the virus and prevent lesions from reappearing, he is optimistic he can find a way to do the same in humans, thus preventing or curing the similar virus that causes cervical cancer in women. Greg Bossart hopes to move some of the affected manatees to Harbor Branch for study, in the hope of learning precisely what mechanisms caused the outbreak. In Crystal River, wildlife biologist Bob Bonde watches with mixed feelings. "In general, there are more manatees with less scars now, so maybe our increasing sanctuaries and better boat regulations are helping," he says. "But the real threat is deregulation of the power industry—manatees conditioned to wait for the warm water to come on. If you turn off a plant during a cold front, it could kill 500 or 600 manatees. That's a concern I share with Greg—and I'm the optimist."

For all things manatee, from scientific classification to behavior, see the Seaworld Web site at www.seaworld.org/infobooks/Manatee/indexman.html.

If you like your manatee info with an activist sensibility, go to www.savethemanatee.org/default.html.

For more on biology, ecology, and the current status of manatees on the East Coast, see the U.S. Geological Survey/Florida Integrated Science Centers manatee site: cars.er.usgs.gov/Manatees/manatees.html.

Link to the Sirenia Project for a list of current research efforts: cars.er.usgs.gov/Manatees/Manatee_Sirenia_Project/manatee_sirenia_project.html.

Read more about Papillomavirus from the Harbor Branch Oceanographic Institution, including photomicrographs of the virus and video footage of affected animals: www.hboi.edu/news/features/manateevirus.html.

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