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Maryland State Government Maryland Department of the Environment

Agency Warns Against Eating Shellfish From Private Piers

bullet  Daily Advisory on Conditionally Approved Shellfish Harvesting Areas 

bullet  MDE Opens Kent Narrows For Shellfish Harvesting

The growing proliferation of home based aquaculture projects and oyster gardens has lured some to eat the shellfish grown for water quality improvement initiatives.  Due to the potential presence of pathogens, officials at the Maryland Department of the Environment (MDE) urge oyster growers against doing so.  

Shellfish are filter-feeding organisms; they strain the surrounding water through their gills which trap and transfer food particles to their digestive tract. If the water they are housed in is contaminated with disease-causing organisms, these organisms are also trapped and consumed as food. Because shellfish pump large quantities of water through their gills each day, even low concentrations of harmful organisms from the waters can reach dangerous levels in the shellfish. If shellfish containing these organisms are eaten raw or partially cooked, illness may result.

Shellfish are bivalve mollusks such as clams, oysters, and mussels. [The term shellfish does not include crabs, lobsters, or shrimp.] Therefore, to protect public health, it is mandatory that shellfish be harvested from approved shellfish waters where protective standards have been met. MDE protects and classifies the state’s shellfish harvesting waters.

To protect public health, MDE does not permit the harvest of shellfish from marinas because of the potential for illegally discharged or unintentional discharge of boat waste. This restriction does not include blue crabs, which are crustaceans and do not filter-feed like oysters. MDE further recommends against consuming oysters grown from private piers. The area around a private dock or pier is near the shoreline in quiet waters, rather than out in the river where the oyster’s natural habitat is typically found. Activities such as the unexpected failure of a neighbor’s septic system, drainage of water from yards where pets are kept and other factors can introduce disease-causing organisms, which can be concentrated by oysters, posing a risk to people eating them.

In Maryland, the responsibility for the sanitary control of the shellfish industry is split among three state agencies: MDE, the Department of Health and Mental Hygiene (DHMH), and the Department of Natural Resources (DNR). MDE is responsible for identifying and eliminating pollution sources affecting Maryland’s shellfish harvesting waters, as well as determining whether the shellfish harvested are safe for human consumption. DHMH is responsible for any food control measures necessary to ensure that shellfish are harvested, processed, packaged and transported under sanitary conditions. DHMH also regulates shellfish dealers to assure compliance with the required sanitary standards. DNR is responsible for posting areas restricted to shellfish harvesting and for patrolling these areas to prevent illegal harvesting.

Diseases Associated With Shellfish Consumption

There are a number of diseases that are caused by the transfer of fecal bacteria or viruses from human sanitation sources to raw shellfish. While these diseases do not infect the shellfish, oysters and clams may filter the disease-causing organisms out of the water and can accumulate enough of them to make consumers of raw or partially cooked shellfish ill.

Norwalk and Norwalk-like virus – The main reservoir for this virus is man. Symptoms include nausea, vomiting, diarrhea, abdominal cramps, and fever. The disease is usually self-limiting.

Hepatitis A virus – This virus causes weakness, fever, abdominal pain and yellow jaundice. It may result in damage to the liver. Although death is rare, it may occur among those with underlying diseases.

Salmonella – Several species of Salmonella are naturally found in the intestines of mammals, birds, amphibians, and reptiles. Salmonella can be transferred to shellfish by sewage pollution of coastal waters. Salmonella infections cause nausea, vomiting, abdominal cramps, and fever. One species causes typhoid fever.

Shigella –This bacterium causes symptoms very similar to Salmonella. Shigella is found only in the human intestinal tract and is not a result of contamination by animal species.

Escherichia coli – Also known as E. coli, this bacterium is one of the fecal coliforms. Most types of E. coli are essential inhabitants of the human intestinal tract and are needed for proper digestion and processing of foods. Pathogenic forms can cause abdominal cramps, diarrhea, fever, nausea and vomiting. Death may occur among the very young, the elderly, or immuno-compromised individuals.

Campylobacter jejuni – This bacterium is widely distributed in the intestinal tract of poultry, livestock, and warm-blooded domestic animals. In humans, it causes diarrhea, abdominal pain, headache, weakness, and fever.

Potential Risk to Some Individuals

Consumption of raw or partially cooked oysters creates a risk of illness to certain individuals with predisposed medical conditions.  People at “high risk” include those who have liver disease, excessive alcohol intake, diabetes, AIDS or HIV infection, stomach disorders, inflammatory bowel disease, cancer, abnormal iron metabolism, steroid dependency or any illness or medical treatment which results in a compromised immune system. Older adults are more likely to have these health conditions and should be aware of their health status. Anyone at high risk needs to be especially careful to avoid eating raw shellfish.

In addition to diseases associated with pollution sources, different kinds of Vibrio bacteria are found naturally in coastal waters and are not a result of pollution. Vibrio bacteria can be found in waters approved for oyster and clam harvesting. Symptoms of illness from Vibrio bacteria include vomiting, diarrhea, stomach pains, severe weakness, skin rashes, blisters, shaking chills and high fever. If you have any of these symptoms after eating raw shellfish, see your doctor for medical treatment.

Shellfish harvested from Maryland waters have never been implicated in a Vibrio illness. During the warm weather months more of the Vibrio bacteria can be found in shellfish and the risk to consumers is higher.  Everyone should enjoy fresh seafood but should also be aware that eating raw molluscan shellfish can cause illness. For people with the medical conditions described above, eating raw shellfish may be a risk they need to consider and determine if they want to eat cooked shellfish instead.

Enjoy Maryland Oysters from Approved Areas

Oysters harvested from approved waters, packed under sanitary conditions, and properly refrigerated are usually safe for raw consumption by healthy individuals. Cooking oysters to an internal temperature of 140° F or greater for 4 to 6 minutes destroys the common microorganisms of public health concern. The nutritional value of oysters is very good. Raw oysters have a protein content of about 9 percent, and a fat content of less than 2 percent. One-half pound of raw oysters contains about 150 calories. The cholesterol content of oysters is 50 milligrams/100 grams of meat, and the sodium content is 109 milligrams/100 grams. Oysters are also very high in iron content.

Oysters can be enjoyed in a variety of cooked preparations including steamed, stewed, roasted, baked, broiled, sauteed, poached, and fried.

Shellfish Links

     Shellfish Harvesting Area Notices of Openings and Closures

     Clean Water - Safe Shellfish

     Shellfish Safety Guidelines for Boaters and Commercial Harvesters

     Growing Oysters for Commercial Sale in Floats off of Private Piers

     Application Procedures for On-Bottom Private Lease Holders, for the Relaying of Shellstock from Polluted Waters for the Purpose of Natural Cleansing

     Procedure for the Relaying of Off-Bottom Cultured Eastern Oysters, Crassostrea virginica, for the Purpose of Natural Cleansing Prior to Commercial Harvest

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