Amoebiasis

Amoebiasis is a parasitic infection of the human intestines. It is caused by a single-celled organism called Entamoeba histolytica. This parasite can cause a wide range of health issues. Some people experience no symptoms at all. Others suffer from severe illness known as amoebic dysentery. The infection is significant because it affects millions of people globally. It is especially common in regions with limited modern sanitation systems.

The infection begins when a person swallows a cyst. A cyst is a hardy, semi-dormant structure used by the parasite to survive. These cysts can live in soil for up to one month. They can even survive under fingernails for 45 minutes. Once inside the gastrointestinal tract, the parasite can exist in two forms. The cyst form is used for survival and transmission. The other form is the trophozoite, which is the active, moving stage. In asymptomatic cases, the amoeba lives by digesting bacteria and food particles. It usually stays behind a protective layer of mucus in the gut.

Disease occurs when the parasite invades the intestinal lining. This process involves three main events: direct host cell killing, inflammation, and parasite invasion. The amoeba uses specific molecules to complete this attack. For example, lectins help the parasite attach to the mucosal layer. It also uses amoebapores to destroy bacteria in the colonic environment. To break down human tissue, the parasite secretes cysteine proteases. This destruction often results in flask-shaped ulcerations in the intestine. The parasite then feeds on the destroyed cells through a process called phagocytosis. During this, it may ingest red blood cells, a process called erythrophagocytosis.

In some cases, the infection moves beyond the digestive system. This is known as an extra-intestinal infection. In about 10% of invasive cases, the amoebae enter the bloodstream. The blood carries the parasites to other organs. Most commonly, they travel to the liver. This happens because the blood from the intestine reaches the liver first. Once there, they can cause amoebic liver abscesses. These abscesses can develop even if the person never had diarrhea. In rare instances, the infection can reach the lungs or the brain.

Medical history shows how our understanding of this disease has grown. The first documented case was recorded in 1875. In 1891, the disease was described in much greater detail. This led to the specific terms amoebic dysentery and amoebic liver abscess. In 1913, researchers in the Philippines provided further evidence. They discovered that volunteers developed the disease after swallowing cysts. This helped confirm how the parasite is transmitted between people.

The scale of amoebiasis is quite large. It is estimated that 50 million people are infected with Entamoeba histolytica every year. About 40,000 to 100,000 people die from the infection annually. This represents approximately two deaths for every thousand cases. Most cases occur in the developing world. Symptoms can appear within days or even years after infection. About 90% of people remain asymptomatic, meaning they show no signs of illness. However, for those with severe colitis, the mortality rate can exceed 50%.

Diagnosing the infection requires careful laboratory work. Doctors often use microscopy to examine stool samples for cysts or trophozoites. However, it is difficult to distinguish E. histolytica from harmless species like Entamoeba coli. For example, E. coli cysts can have up to 8 nuclei, while E. histolytica has a maximum of 4. Doctors also use serological tests to find specific antibodies in the blood. While highly accurate for detecting liver abscesses, these tests may stay positive long after a person is cured. More advanced methods include PCR, which is considered the gold standard for diagnosis.

Prevention relies heavily on improved sanitation and hygiene. People can reduce risk by washing hands with soap and hot water for at least 10 seconds. It is also important to separate food and water from feces. In endemic areas, travelers should avoid raw vegetables and street foods. Boiling water or using iodine tablets can make water safer to drink. Because cysts are resistant to chlorination, water must be filtered or treated through sedimentation. These steps help break the cycle of transmission and protect public health.