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Study: Dead manatees infected by parasite
By CRAIG PITTMAN, Times Staff Writer Manatees that died in Tampa Bay and the Gulf of Mexico in the past year were infected by a parasite that likely was spread by water pollution, according to a study unveiled this week by a University of South Florida biology professor. Microbiologist My Lien Dao took tissue samples from 10 manatees that died during the winter, searching for why the marine mammals might have been susceptible to Red Tide. Instead she found something she called "scary." Every manatee she examined had high levels of microsporidia in its vital organs, including the lungs, liver, kidneys, spleen and lymph nodes. The fact that every single tissue she examined from every animal had an infection shows that the problem is widespread, she said Thursday. "When you have 10 out of 10, that's a scary thing," Dao said. "This is a big ecological problem." Microsporidia are single-celled parasites that, in healthy humans, can cause diarrhea. Among people whose immune systems are weak -- particularly the very young, the very old or anyone with AIDS -- microsporidia can invade other organs such as the kidneys and lungs. That can lead to other ailments, such as bronchitis and pneumonia, which may not seem directly connected to the original infection. "It's really like a silent killer," Dao said. The infection is often spread from person to person through contact with feces and urine. Because the species of microsporidia Dao found in the manatees is similar to the one that infects humans, she believes the manatees may have picked up their infections from swimming in human sewage. She fears the infected ones may have later spread the disease with their own waterborne excretions. "Are we infecting them? Will they infect us back?" she asked. Worse, she suspects that the way the infection entered the manatees' organs came from another human activity: boating. Many manatees bear scars from being slashed by boat propellers. Those wounds are "just like an open door" for the parasite, Dao said. Dao does not believe the widespread infection killed the manatees outright, but she does believe it contributed to their deaths by weakening their ability to survive cold and other stresses. Last year was the second deadliest year ever for the endangered marine mammals, with a total of 325 turning up dead in 2001. Speeding boaters killed 81, just one less than the record. More than 30 were killed by the severe cold of last winter, the most killed by cold stress in the past decade. Another 108 were listed as dead from undetermined causes. Manatees were not the only ones infected by microsporidia. Dao said she also found microsporidia in the tissues of a baby sperm whale and an infant dolphin that died in Florida waters last year. Dao said the next step should be to begin testing the waterways where manatees are known to congregate in hopes of finding the spores that spread the infection. Dao's study, due to be presented at a conference on marine mammals in Gainesville next week, marks a sharp departure from past findings on manatees' immunity to infection, said Patti Thompson, a biologist with the Save the Manatee Club in Maitland. "Everybody has sort of wondered all along how coastal pollution affects manatees," Thompson said. "We've always heard they have incredibly strong immune systems, with high numbers of T-cells that are known for fighting infection." But the findings make sense, Thompson said. "Manatees have long been known to hang out in some pretty nasty water," she said, noting that they are not averse to drinking from sewer outfalls. In the past no one thought to look for microsporidia, she said, "but now we'll be looking for it."
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