|  | Conditions Treatments | Diseases

Signs and Symptoms of Minamata Disease

Minamata is a Japanese fishing town that was home to a chemical plant owned by the Chisso Corporation. The plant opened in 1908 and began dumping waste water into the Minamata River by in the early 1930s. By 1956 residents noticed strange animal behavior--cats "dancing" in the street, then falling over dead. That same year, human residents also began exhibiting troubling symptoms. Doctors soon realized that the residents were suffering from severe mercury poisoning--a result of contaminated water and fish from the bay. In the 1960s another outbreak occurred in the Niiga Prefecture along the banks of the Agano River. Minamata disease is considered one of the Four Big Pollution Diseases of Japan.

  1. Early Symptoms

    • The first documented human case was a 5-year-old girl who had difficulty walking and speaking, and then had convulsions. Her sister was discovered to have the same symptoms and, ultimately, eight other initial cases were uncovered among their friends and neighbors. Over time it became apparent that the disease was widespread throughout the town. Some patients experienced muscle tremors, vision and hearing loss, and trouble controlling their eye movements. Other patients had numbness in their hands and feet or slurred speech. Some patients only exhibited mild symptoms such as headaches, fatigue, and loss of taste and smell. Mercury poisoning is often called "Mad Hatter's Disease," after the effect of prolonged mercury exposure on early hat makers. In severe cases, patients exhibited hallucinations and delusions, aggression, and other forms of "madness," as well as loss of consciousness and even death.

    Congenital Symptoms

    • Mercury not only attacks the nervous system, it also affects fetal development. The disease did not end with the initial outbreak. In the years after, Minamata experienced an abnormally high number of children born with cerebral palsy, birth defects, and neurological problems. Even babies of women who had no visible Minamata symptoms were not immune.

    Later Symptoms

    • Not all the afflicted displayed symptoms at once. Some people had high levels of mercury in their systems and remained asymptomatic for years, and even decades, then suddenly developed severe symptoms later. There were also those who experienced mild symptoms that got progressively worse over a long period of time. In many cases, these people were not considered to be Minamata victims, because their symptoms did not match the rigid criteria set forth by the Japanese government.

Diseases - Related Articles