Minamata Disease

Minamata disease is a condition that is not well known to most part of the world, but for those who survived and is living in the city of minamata Japan; it is a painfully real disease.

Minamata disease is disease caused by methylmercury (MeHg) poisoning that occurs in humans who ingests fishes and river products contaminated by MeHg waste discharged into these waters from a chemical plant.

The first outbreak of Minamata disease was recorded back in 1956 May at a local Public health Centre. The primary cause and transmission mode was revealed to be contaminated fish and shellfish. In 1961, scientific researchers in Japan correlated evaluated urinary mercury levels with the features of the previously mysterious Minamata disease.

Before the etiologic agent for this poisoning was discovered as methylmercury, a by-product of acetaldehyde production which was known to be discharged from a company- Chisso factory that operated from 1932 till 1968, it plagued the residents around Minamata Bay in Japan with tremors, sensory losses, ataxia and vision impairment.

During this period, the discharges of this waste did not halt, and no proper effective measure or investigation was put in place to combat the menace.

The city lends its name to the condition as it was first identified there. Minamata disease is not actually a disease in the scientific sense of the name; it is more of a neurological syndrome that results from industrial pollution and environmental depredation and contamination.

The poison from the residue MeHg has an adverse effect on the central nervous system and this affect both humans and local wildlife; felines to be more precise and the problem continued to afflict more people through the decades as nothing was done about the contamination.   

Causes of Minamata Disease

With the etiology of Minamata disease to be MeHg, it is caused through the absorption of this chemical into the body. MeHg gets into the body through various environmental sources, the primary source been through seafood.

The level of mercury in the body is tested by using the hair samples and urine samples and medically it is widely agreed that when these mercury levels are higher than 50ppm (parts per million), there is a potential nerve damage threat.

While people living outside of the city of minamata had an average level of 4ppm, residents of minamata had levels even as high as 700ppm! While the main cause been mercury poisoning through environmental pollution, there are also other presumed causes of Minamata disease:

  • There are some cases of mercury poisoning found in New Mexico, USA, which was as a result of consumption of livestock that fed on mercury tainted grains.
  • Mercury poisoning is also a big health risk for pregnant women, as Minamata disease is known to affect the unborn child as well. It enters into the bloodstream of the fetus via the placenta and causes adverse effect on brain development.
  • In Iraq, over 6000 people were affected by exposure because they consumed flour processed from grains treated with methyl mercury.
  • In case of residents in Minamata Bay, Methyl-mercury deposits were observed to be concentrated in neural tissues. This observation also serves as a further explanation for the effect of neotoxicity, mostly in newborns as fetal transfer of the toxin cannot be adverted.

Symptoms of Minamata Disease

The target system of Methylmercury is the nervous system. The symptoms and combination of symptoms can differ in severity; affected patients manifest neurological signs including:

  • Ataxia: The inability to generate a normal or expected voluntary movement trajectory that is attributed to weakness or involuntary muscle activity.
  • Constriction of the visual field
  • Hearing loss
  • Paresthesia- a situation of burning or pickling sensation resulting from lesions in nervous tissue and other structures.
  • Dysarthria- speech disorder/impairment was also observed
  • Affect patients also manifested psychiatric symptoms such as impairment of intelligence, mood and behavioral dysfunction
  • Partial paralysis
  • Severe uncontrolled seizures and tremors
  • Numbness in some part of the body, especially the extremities like the hands and feet

In children and infant who have inherited the Minamata disease from their parents, the symptoms may include:

  • Growth and developmental problems with both physical and mental health
  • Microcephaly- a neuro-developmental disorder characterized by reduced head size with irregular shape in children.
  • Mental retardation
  • Infants will display symptoms that are similar to those afflicted with cerebral palsy, which is not surprising as it is the cause of seizures and neurological development impairment.
  • Blindness and deafness in children

Diagnosis of Minamata Disease

Minamata disease is mostly diagnosed in hospitals using mercury tests levels from hair and urine samples; it is a non-invasive and straightforward procedure. In places of outbreak such as Japan, Minamata disease is not just decisively concluded by a doctor but the national government and local officials because it is legally required with regards to compensation and polluted-related health incidents.

In newer cases with mild symptoms where these symptoms are difficult to identify, when health care providers suspect a Minamata disease, they request for an electro-ophthalmography (EOG) and optokinetic nystagmus pattern (OKP) test in order to obtain referential data.

Treatment for Minamata Disease

Treatment of Minamata disease varies in patients depending on the severity of the condition and the symptoms presented. But there are standard medical procedures used to approach any condition suspected to be Minamata disease.

They include:

  • Identifying the source of exposure and isolation (quarantine) so as to prevent further poisoning due to exposure. This is the first step in every treatment approach; as a prerequisite.
  • The removal of mercury from the body is the most important aspect of treating Minamata poisoning by using chelating agents. Chelating agents are chemicals that react with mercury by binding to it, thereby preventing the mercury from binding with body tissue. However, this comes with some side effect such as risk of redistribution of the mercury in the body which can aid it to travel further into the body and can even get to the brain. This is why medical experts strongly recommend the use of chelating agents with lowest toxicity risk.
  • One of the chemical properties of mercury which is very harmful to the body is that it increases levels of reactive oxygen. This can be combated through the use of antioxidants.   
  • In some cases, patients suffer seizure and convulsion attack. In such cases, doctors prescribe anticonvulsant drugs.
  • Paralysis and loss of muscle function are very common with Minamata disease, but severity may vary. Physical rehabilitation and therapy are always necessary and useful to help patient regain some control over mobility.

Possible Preventive Measures for Minamata Disease

Minamata Disease

One of the obvious preventions of Minamata disease is the reduction or total elimination of the consumption of sea produce especially fishes caught from bodies of water that are contaminated with high concentration of mercury.

Another is raising basic laws and counter-legislations against the use of Methylmercury as production materials by companies. Advance research should be conducted by these companies to find non-toxic substitute chemicals to replace mercury to prevent the occurrence and further pollution of the environment.

Plants manufacturing chemicals such as vinyl chloride monomer and acetaldehyde by the acetylene method which were major sources of mercury pollution should be banned or reformed to non-mercury processors.


Note that Minamata Disease can be contacted by consuming a contaminated seafoods with methylmercury and also pregnant women is advised to take note of what they eat because when they are infected by Minamata Disease, the baby is at a high risk to suffer from a fetal Manamata Disease.