The threat of emerging ocean diseases

Much attention has been paid to newly emergent diseases that have afflicted humans in recent decades--HIV/AIDS, SARS, avian influenza, etc. Conversely, deadly diseases that have emerged in the world's oceans during the same time period have been largely ignored. While these diseases haven't caused epidemics in humans, they have proved troublesome to marine animal populations and to susceptible humans who have ventured into contaminated waters. Therefore, we should pay closer attention to what's happening in the world's oceans since it could be an important sentinel for global environmental health.

Take for instance, recent epizootics (epidemics in animals) of Atlantic Ocean bottlenose dolphins and endangered Florida manatees. They perished because of the neurotoxins produced by Karenia brevis, a marine plankton that lives year-round in the Gulf of Mexico. (See "Emerging Diseases in Marine Mammals: From Dolphins to Manatees." PDF)

A single-celled organism (called a dinoflagellate), K. brevis has two whip-like appendages, or flagella, it uses to swim through the water. The neurotoxins produced by K. brevis can kill fish and birds, as well as marine animals.

When they become aerosolized in sea spray and inhaled by humans, these organisms can cause people to develop respiratory and eye irritations. The toxins can also accumulate in shellfish such as clams, coquinas, and oysters, causing food poisoning in those who eat them. Symptoms usually begin a few hours after ingestion and include tingling and numbness in the tongue, lips, throat, arms, and legs and dizziness, nausea, and diarrhea. The symptoms usually go away after a few days.

Red tides--gigantic masses of seawater microorganisms such as K. brevis--aren't limited to Florida's coastal waters. For example, in 1995, a massive red tide stretched for 500 miles off the coast of California, and three years later, a red tide killed more than 50 sea lions in Monterey Bay, about 120 miles south of San Francisco. (See "Studies Bring New Data to Mystery of Red Tides.") In addition, there's evidence that other dinoflagellate species are expanding their range off of the Australian and Tasmanian coasts and in the Mediterranean Sea. Severe hurricanes can expand their distribution, and hurricanes and coral bleaching increase the risk of ciguatera fish poisoning, which, once rare, is now reaching epidemic levels--especially in French Polynesia.

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