Minamata disease

Minamata disease
The hand of Tomoko Kamimura, who had Minamata disease
Specialty	Toxicology, neurology, psychiatry
Symptoms	Ataxia, numbness and muscle weakness
Complications	Loss of peripheral vision, and damage to hearing and speech; in extreme cases: insanity, paralysis, coma; can also affect fetuses; see Mercury poisoning for more details
Usual onset	Soon after consuming affected seafood
Duration	Chronic
Causes	Severe mercury poisoning
Risk factors	Affected those who consumed fish and shellfish from Minamata Bay
Diagnostic method	See mercury poisoning
Differential diagnosis	See mercury poisoning
Prevention	Proper handling of industrial waste
Treatment	See mercury poisoning
Medication	See mercury poisoning
Prognosis	35% case fatality rate; for more details see mercury poisoning

Minamata disease is a neurological disease caused by severe mercury poisoning. Signs and symptoms include ataxia, numbness in the hands and feet, general muscle weakness, loss of peripheral vision, and damage to hearing and speech. In extreme cases, insanity, paralysis, coma, and death follow within weeks of the onset of symptoms. A congenital form of the disease affects fetuses in the womb, causing microcephaly, extensive cerebral damage, and symptoms similar to those seen in cerebral palsy.

Minamata disease was first discovered in the city of Minamata, Kumamoto Prefecture, Japan, in 1956, hence its name. It was caused by the release of methylmercury in the industrial wastewater from a chemical factory owned by the Chisso Corporation, which continued from 1932 to 1968. It has also been suggested that some of the mercury sulfate in the wastewater was also metabolized to methylmercury by bacteria in the sediment.^[1] This highly toxic chemical bioaccumulated and biomagnified in shellfish and fish in Minamata Bay and the Shiranui Sea, which, when eaten by the local population, resulted in mercury poisoning. The poisoning and resulting deaths of both humans and animals continued for 36 years, while Chisso and the Kumamoto prefectural government did little to prevent the epidemic. The animal effects were severe enough in cats that they came to be named as having "dancing cat fever".^[2]

As of March 2001, 2,265 victims had been officially recognized as having Minamata disease^[3] and over 10,000 had received financial compensation from Chisso.^[4] By 2004, Chisso had paid $86 million in compensation, and in the same year was ordered to clean up its contamination.^[5] On March 29, 2010, a settlement was reached to compensate as-yet uncertified victims.^[6]

A second outbreak of Minamata disease occurred in Niigata Prefecture in 1965. The original Minamata disease and Niigata Minamata disease are considered two of the Four Big Pollution Diseases of Japan.