Neurological damage caused by methylmercury.

Alternative Names

Minamata Bay disease

Causes, incidence, and risk factors

Mercury is a metal that is liquid at room temperature. Most compounds containing mercury are poisonous. Methylmercury is an organic form of mercury that has been used to preserve seed grain. Methylmercury can also be produced from metallic mercury or mercury compounds in bodies of water by the action of bacteria. Outbreaks of methylmercury poisoning have occurred following ingestion of treated seed grain, from meat from animals fed treated seedgrain, or from fish in waters contaminated with methylmercury, such as Minamata Bay in Japan. The fetus and young infants are very sensitive to methylmercury's effects. Methylmercury causes central nervous system (CNS -- i.e., the brain and spinal cord) damage and the severity of the damage depends on the extent of the exposure. Many of the CNS effects are similar to those seen in cerebral palsy , and methylmercury is thought to cause a form of cerebral palsy. In January, 2001, the FDA issued a warning to pregnant women, women who may become pregnant, nursing mothers, and small infants to avoid fish that may contain unsafe levels of methylmercury. These fish include larger, longer-lived fish, such as swordfish, king mackerel, shark, or tilefish. The FDA especially warns against non-commercial fish, or fish caught by friends and family, and the Agency recommends that consumers check their local or state health departments for warnings against locally-caught, non-commercial fish.

Signs and tests

Treatment

Methylmercury damage is irreversible. Treatment is determined by the severity of the condition and is similar to that given for cerebral palsy .

Expectations (prognosis)

The symptoms are irreversible; however, they do not usually worsen unless there is a new exposure to methylmercury.

Complications

Complications depend on the severity of the condition, and the specific symptoms manifested (such as blindness or deafness ).

Calling your health care provider

Call your health care provider if symptoms of this disorder are present. If you know about a possibly suspicious exposure (eating foods that may have been contaminated with methylmercury) and you develop symptoms, mention this exposure to your health care provider.

Prevention

Strict avoidance of any foods contaminated with methylmercury will prevent poisoning. Because of manufacturing, mercury has become so common in the environment that trace amounts of methylmercury are present in many foods derived from the ocean, including deep-sea tuna. Fortunately, the levels are low enough that most of these foods remain safe. Contact Poison Control if you believe you may have been exposed.