Update:April 1, 2010

(2) Outset of Minamata Disease

1.Establishment of Chisso Co., Ltd. and Outbreak of Minamata Disease

On April 21,1956, an infant with ill-defined nervous disorder such as speech defect and gait impairment was sent to Shin Nihon Chisso Hospital (already abolished). The hospital has subsequently accepted other patients with similar symptoms and reported to Minamata Public Health center of Kumamoto Prefecture on May 1 in the same year that they had so far accepted 4 patients showing cerebral symptoms with unknown causes.
Minamata Disease was regarded to be officially identified on the above day, May 1, 1956. At the beginning, when the cause of the disease had not yet been discovered, people were scared suspecting that it was an epidemic or arare disease without any clinical background .
In May 1956, the Minamata Rare Disease Research Committee was established for remedial measures and etiologic investigation with the contribution of Minamata Public Health Center and other organizations.
The committee made a survey and discovered a large number of patients with similar symptoms, 52 of which were officially recognized in 1956.
Such nervous symptoms were first frequently observed in the vicinity of Minamata Bay, and then spread over an extensive area including the south coast of Shiranui Sea, Amakusa Islands, and the northern part of Kagoshima prefecture (See Figure 3-2 and Table 3-1) .
The Minamata Disease Medical Study Group of Kumamoto University Medical School (hereinafter referred to as "the Medical Study Group") took the initiative of starting the etiological investigation. They disclosed their interim report in November 1956, describing "the disease is free from infectiousness and probably a sort of heavy-metal poisoning.
All they knew was that seafood from Minamata Bay induced the disease if taken in large quantities, and the exact substance polluting marine products had not yet been specified. In 1957, the Science Research Group of the Ministry of Health and Welfare proposed a theory attributing the disease to manganese, selenium, and thallium, which however was not sufficiently convincing.
In those days, since analytical techniques for trace chemical substances were not satisfactorily developed as well as scientific knowledges and experiences concerning environmental pollution problems, considerable time was spent before the discovery of the cause of the disease.
Meanwhile, in 1965, similar symptoms to those of Minamata's were reported in the the basin of the Agano River in Niigata Prefecture and called Niigata Minamata-Disease.