Ocean Health / Human Health

Tundi Agardy, Ph.D.

The Myriad Linkages between Ocean Health and Human Well-Being

Waterborne Diseases
Some viruses, bacteria and parasites that occur in ocean waters can be harmful agents for humans. Degraded coastal waters can spur the growth of pathogens, and marine ecosystems with altered biodiversity quickly lose the ability to keep harmful populations of microbes in check. Marine pathogens have been responsible for some large epidemic events, such as the cholera outbreak in South and Central America that resulted in over 1 million cases and over 10,000 deaths between 1991 and
1995⁵. Around the world, it is estimated that marine contamination related diseases from swimming in polluted seawater and eating contaminated seafood are responsible for more than 3 million disability-adjusted years (based on premature death and years of loss of health life) per year, with an estimated economic impact of US$13 billion⁶.

Photo by Y. Beaulieu, IDRC

Warmer oceans associated with a changing global climate increase the potential for humans to be affected by waterborne diseases⁷. The best-documented case is cholera, whose causative agent, Vibrio cholerae, can be transported in seawater. Researchers have found links between pollution-driven algal blooms (population explosions that are enhanced by warmer surface waters) and incidence of cholera outbreaks⁸. Such outbreaks are not only a public health issue but a human well-being issue as well: epidemics extract huge financial costs via lost profits in fisheries and tourism, for instance⁹. Because many other human pathogens can be found in seawater, there is good reason to fear that warmer seas will result in a sicker world, as pathogen development rates and geographic ranges increase¹⁰.

Filter-feeding animals, such as oysters and clams, can concentrate pathogens, such as hepatitis A and Norwalk virus, found in sewage. The pathogens then can be transmitted to people when shellfish, especially if un-cooked, are eaten. Shellfish beds downstream from sewage treatment plants often are closed after storms until pathogens are naturally released from the shellfish. Viruses can be so lethal that ingesting a single virus can cause infection. Rotaviruses, for example, are extremely robust in seawater and cause diarrhea and death, killing an estimated 870,000 children around the world each year¹¹. In a more straightforward route of infection, illness can also occur by direct contact with contaminated water containing viral, bacterial, or protozoan pathogens¹².

Illness Caused by Harmful Algal Blooms
Most marine algae are benign, and all phytoplankton play an irreplaceable role in providing the underpinnings of marine food webs and in globally sequestering carbon. However, algae can become toxic and affect large areas of coastal ocean when they bloom, growing quickly and harming the health of other plants, animals, and humans. Blooms of harmful algae, collectively known as HABs, can deplete the oxygen and block the sunlight that other organisms need to live, and some HAB-causing algae release toxins that are dangerous to animals and humans. HABs can occur in marine, estuarine, and fresh waters, and they appear to be increasing around the world. HAB effects include not only illnesses in affected individuals, but high costs to communities and industry as well. A single red tide producing species, Karenia brevis, causes annual economic losses of roughly $50 million in the Gulf Coast of the U.S., through health care costs of treating ill individuals and depressed earnings in fisheries, recreation, and tourism¹³.

Red Algal Bloom. Photo by Miriam Godfrey

Scientists do not yet understand fully how HABs affect human health, however it is a serious enough concern that authorities in the United States and abroad are monitoring HABs and developing guidelines for HAB-related public health action. The U.S. Environmental Protection Agency (EPA) has added certain algae associated with HABs to its Drinking Water Contaminant Candidate List. This list identifies organisms and toxins that EPA believes are priorities for investigation¹⁴. HABs include blooms of blue-green algae (cyanobacteria), red tides, and population explosions of organisms that are normally non-toxic, but which revert to a toxic form under some as yet undetermined environmental trigger (such as Pfiesteria, described below).

Cyanobacteria can produce toxins that may taint drinking water and recreational water. Humans who drink or swim in water that contains high concentrations of cyanobacteria or cyanobacterial toxins may experience gastroenteritis, skin irritation, allergic responses, or liver damage.

Fish kill following a P. Piscicida outbreak, Neuse River, North Carolina, USA

Harmful marine algae, such as those associated with red tides, occur in the ocean and can produce toxins that may harm or kill fish and marine animals. Toxins may be produced by dinoflagellates, such as those that produce fish poisoning known as ciguatera, or diatoms. Humans who eat shellfish containing toxins produced by these algae may experience neurologic symptoms (such as tingling fingers or toes) and gastrointestinal symptoms. Breathing air that contains toxins from algae associated with red tide may cause susceptible individuals to have asthma attacks.

Pfiesteria piscicida, a single-celled organism that lives in estuaries, has been found near large quantities of dead fish. Scientists do not yet know exactly how severly P. piscicida affects human health. However, reports about symptoms such as headache, confusion, skin rash, and eye irritation in humans exposed to water containing high concentrations of P. piscicida have prompted public concern.

Coastal communities have long had to face the presence of highly dangerous natural marine toxins in their seafood. Yet there is evidence that new toxins have emerged in recent decades, and that toxic blooms are occurring more often across the globe.

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⁵ Statistics from the Food and Drug Administration of the U.S., available at http://vm.cfsan.fda.gov/~mow/chap7.html

⁶ Taken from www.oceansatlas.org/cds_static/en/human_health_ocean__en_2234_all_1.html

⁷ See especially Harvell CD, Mitchell CE, Ward JR, Altizer S, Dobson AP, Ostfeld RS, et al. 2002. “Climate warming and disease risks for terrestrial and marine biota,” Science 296:2158-2162; and Patz, J. A. et al. 1996. “Global climate change and emerging infectious diseases,” Journal of the American Medical Association 275:217–223; also Millennium Ecosystem Assessment (MEA). 2005. “Coastal ecosystems and coastal communities,” Ch 19 in Ecosystems and Human Well-Being. Island Press, Washington, DC

⁸ See Anderson et al, 2001. “Monitoring and management strategies for harmful algal blooms in coastal waters,” APEC#201-MR-01.1 and IOC Technical Series No. 59; also Colwell, R. and W.M. Spira. 1992. “The ecology of Vibrio cholerae,” Cholera: Current Topics on Infectious Disease. D Barua and W.B.I. Greenough (eds.) Plenum Press NY

⁹ Rose et al. 2001. “Climate variability and change in the United States: Potential impacts on water- and food-borne diseases caused by microbiologic agents,” Environmental Health Perspectives 109: 211-221.

¹⁰ Knowlton, N. 2004. Available on http://www.ehponline.org/docs/2004/112-5/editorial.html

¹¹ Statistics from the CDC, reported in National Research Council (U.S.). 1999. From Monsoons to Microbes: Understanding the Ocean’s Role in Human Health. National Academy Press, Washington DC

¹² Taken from http://www.waterencyclopedia.com/Ge-Hy/Human-Health-and-the-Ocean.html

¹³ National Research Council (U.S.). 1999. From Monsoons to Microbes: Understanding the Ocean’s Role in Human Health. National Academy Press, Washington DC

¹⁴ This and the following 3 paragraphs taken from the U.S. Centers for Disease Control (CDC) webpages on oceans and human health: http://www.cdc.gov/hab/about.htm