Minamata Bay disease

Alternative names
Methylmercury poisoning

Methylmercury poisoning is neurological damage caused by methylmercury.

Causes, incidence, and risk factors

Mercury (“quicksilver”) 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, meat from animals fed treated seedgrain, or fish from waters contaminated with methylmercury, such as Minamata Bay in Japan.

Fetuses and young infants are very sensitive to methylmercury’s effects. Methylmercury causes central nervous system (brain and spinal cord) damage and the severity of the damage depends on the extent of the exposure. Many of the CNS effects of mercury poisoning 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 that 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 large, longer-lived fish, such as swordfish, king mackerel, shark, or tilefish. The FDA especially warns against noncommercial 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, noncommercial fish.

Some physicians have raised concerns about ethyl mercury (thimerosal), a preservative used in some vaccines. Though individual vaccines do not contain high levels of thimerosal, the fear was that multiple childhood vaccines might cause mercury levels in children to rise to dangerous levels. Research indicates that this does NOT, in fact, happen. The highest levels of ethyl mercury found in vaccinated children did not reach a level deemed to be toxic. Research also shows that thimerosal-containing vaccines have NOT been shown to cause Autism or ADHD. Currently in the U.S., routine pediatric vaccines that contain thimerosal have only trace amounts. Further, all of the routine vaccines are also available in thimerosal-free formulas.


  • history of exposure to methylmercury (possibly in the womb)  
  • Cerebral palsy  
  • growth deficiency  
  • microcephaly (small head)  
  • deafness  
  • Blindness

Signs and tests
Tests will vary depending on the symptoms that occur.

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 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.

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.

Johns Hopkins patient information

Last revised: December 6, 2012
by Simon D. Mitin, M.D.

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All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.