Is It Safe to Swim in the Chesapeake Bay?
Pathogens in Water, Oysters Pose Risks to Health
Jul 2, 2009
At the Virginia Institute of Marine Science (VIMS), scientists are studying naturally occurring pathogens and others that enter the ecosystem from elsewhere to determine the risks to marine life and human health.
Due to recent beach closings, people are concerned about swimming on the beaches of the Chesapeake Bay and its tributary rivers. Virginia and Maryland tourism is important to the regional economy, so officials are alert to the illnesses and infections experienced in the region. Negative media attention could be disastrous to hotel, restaurant, and other vacation destination businesses in Virginia Beach, Williamsburg, Baltimore, and other locations on the western shore watershed and along the Eastern Shore.
VIMS Professor Howard Kator delivered a lecture as part of the VIMS After Hours series on the topic of risks to human health from these natural and non-native pathogens. Illnesses range from stomach aches and minor infections to life-threatening complications. In a nutshell, he warned that swimming and fishing in the Bay and eating seafood are generally not risky as long as safety procedures are followed. These procedures include showering before and after swimming, cleaning and covering open wounds, keeping water out of bodily “portals of entry” (from eyes and mouth to cuts and scrapes), and handling and cooking seafood with care.
Information about pathogens one may encounter around the Chesapeake Bay waters follows with a brief discussion of sources and illnesses that may develop from exposure to them.
Non-naturally Occurring (Allochthonous) Pathogens
Most non-naturally occurring pathogens enter the Chesapeake Bay from sewage treatment plant spills. Due to the aging infrastructure and population pressure, there are times when the sewage plants simply can’t keep up. In addition, heavy rains tax the system and cause overflows. Another major source of pollution is pet waste. While we can’t pick up after wild animals, humans can pick up after pets to cut down on bacterial inputs to the many creeks, rivers, and bays of Maryland and Virginia as well as Washington D.C.
Bacteria enters the body through portals, when eaten (as in contaminated shellfish) and through puncture wounds received from fish hooks, shells, and barbs. The symptoms of infection by such pathogens are usually a gastrointestinal illness. Norovirus, Hepatitis A, and salmonella are frequently diagnosed.
Methicillin-resistant staphylococcus aureus (MRSA) is an emerging infection of great concern. This infection is transferred from person to person. People with MRSA come in contact with water and sand, so the resistant pathogen can be passed to swimmers by an infected person or from something he has touched while at the beach. Because MRSA is resistant to antibiotics, it is serious. Swimmers should shower before and after contact with Bay waters and seashore.
Naturally Occurring (Autochthonous) Pathogens
Vibrio bacteria are commonly found in brackish saltwater ecosystems and occur naturally in shellfish. They are increasing in occurrence in North American waters especially as water temperatures increase due to global climate change. Vibrios are associated with plankton blooms and the changes in wind and temperatures that signal these events.
Vibrio cholerae is perhaps the most well known and is endemic to South Asia, although global in occurrence. Cholera epidemics have swept the world and outbreaks have been associated with the Chesapeake Bay as recently as the early twentieth century.
Vibrio parahaemolyticus is a more common vibrio related to the eating of contaminated seafood. Bacteria invade the colon. Symptoms of infection include very bad diarrhea. People who enjoy seafood should use care to ensure that the food has been continually refrigerated after being caught and then cooked thoroughly. Older individuals and those with compromised immune systems should avoid seafood, especially raw or undercooked oysters.
Vibrio vulnificus is an extremely dangerous vibrio, and a virulent strain has been associated with oysters from the Gulf of Mexico. Due to the decline of native Chesapeake Bay oysters, Gulf oysters are frequently served in Chesapeake Bay restaurants. This vibrio is associated with 90% of seafood-related deaths, according to Professor Kator of VIMS. Fifty percent of those infected with Vibrio vulnificus die. The bacterium grows in the body until other functions are shut down. Symptoms include vomiting and severe diarrhea. Older individuals and those with compromised immune systems are at high risk.
Mycobacterium strains are related to fresh water (above the Chesapeake Bay watershed's tidal zones) and have been associated with red sores and granular lesions seen on striped bass in the Shenandoah River and other places in the watershed. The symptom of mycobacterial infection in humans is red bumpy lesions. Scientists are not sure yet of the relationship between the mycobacteria strains that infect humans and striped bass.
Read more Suite 101 articles by Sara E. Lewis on the Chesapeake Bay
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