An unprecedented survey of seabirds, marine mammals, and sharks on the U.S. East Coast has revealed that marine wildlife contains a wide variety of disease-causing microbes--including many that have developed resistance to antibiotics and several that can be transmitted to humans.
The new study provides no evidence that the widespread presence of these disease agents in marine animals is affecting the health of people. But it raises several provocative questions:
* Are more animals acquiring disease-causing microbes in coastal waters increasingly contaminated by human, agricultural, and medical waste?
* Can marine species act as carriers for infectious diseases, spreading pathogens through the oceans?
* Can marine animals that ingest antibiotic-resistant pathogens from medical waste serve as incubators to maintain, multiply, and spread antibiotic-resistant genes through marine and coastal ecosystems?
Over the past four years, a research team led by Woods Hole Oceanographic Institution (WHOI) collected and analyzed samples from 370 marine animals, encompassing 33 species of whales, dolphins, seals, porpoises, sharks, and seabirds, ranging from Kent Island, Canada, to Virginia. WHOI biologists Andrea Bogomolni, Michael Moore, and Rebecca Gast spearheaded the study and led efforts to collect fecal samples from live seals and seabirds, as well as specimens of dead animals found in the wild. The research team necropsied animals in the new Marine Research Facility at WHOI in search of infectious agents.
To collect more specimens, Bogomolni also forged links with stranding networks and fisheries managers, who sent samples of stranded and bycaught animals (animals unintentionally caught in fishing gear) to the WHOI necropsy facility. She accompanied fishermen to gain access to seals on beaches of local islands. She even took advantage of a unique opportunity to collect samples from mako and thresher sharks caught during a local shark-fishing tournament.
The study, published August 2008 in the journal Diseases of Aquatic Organisms, also included Julie Ellis of the Tufts University Cummings School of Veterinary Medicine; Katie Pugliares of International Fund for Animal Welfare Marine Mammal Rescue & Research; and Betty Lentell of the National Marine Fisheries Service.
Giardia, Brucella, and Cryptosporidium
The researchers focused on testing their specimens for four relatively common microbes known to be zoonotic, or transferable from animals to humans: Brucella, Leptospira, Cryptosporidium, and Giardia, which cause symptoms that include high fever, severe headaches, chills, muscle aches, vomiting, and diarrhea. Thirty-five percent of the animals they examined contained Brucella; 17 percent contained Giardia; 13 percent had Cryptosporidium. To date, initial results indicating the presence of Leptospira in 10 percent of the tested animals have not been confirmed. Altogether, the researchers found nearly 100 types of disease-causing agents in their specimens.
The number of zoonotic agents in the animals surprised the researchers, but they strongly cautioned against interpreting their results as a reason to avoid the beach. Zoonotic microbes are not new, infections usually require a bite or other direct exposure, and people have developed immunities to many such organisms, explained Moore, a WHOI biologist. But it is one of many reasons not to approach beached seals, he said.
Gast, a microbiologist at WHOI, also noted that the presence of Cryptosporidium and Giardia cysts in fecal material does not necessarily mean that the animals were infected; they might be carriers that spread or shed only small amounts of pathogens.
Nevertheless, the presence of Cryptosporidium and Giardia may be an indicator of pollution levels in the ocean, Gast said. The parasites live in the intestines of their warm-blooded hosts and are released to the environment in feces that end up in the ocean. …