Amoebae are members of the protozoa family. Many amoebae are pathogenic and can cause severe disease in humans.
What are amoebae?
Amoebae, contrary to what is often claimed, are not a kin group, but rather a life form. All amoebae are single-celled organisms. Their body shape is not solid. They can form false feet, called pseudopodia, and thus change their body shape rapidly. The organisms are between 0.1 and 0.8 millimeters in size. Most amoebae are naked and feed by phagocytosis. However, some amoebae are also coated and can photosynthesize. The small protozoa are usually transparent. The granular cell interior is visible through the transparent outer skin. This endoplasm pulsates and contains many small bubbles. The nucleus, on the other hand, is rather difficult to see. The small feet serve the amoebae for locomotion and food intake. They catch bacteria and other unicellular organisms with their feet, enclose them within so-called food vacuoles and finally digest them. This process is called phagocytosis. Reproduction of amoebae occurs asexually by division. Many amoebae are potential pathogens for humans. The best known diseases caused by amoebae are amoebic dysentery and meningoencephalitis. Furthermore, many amoebae contain bacteria that can cause infectious diseases in humans. One such disease is legionellosis, which is caused by legionella.
Occurrence, distribution, and characteristics
Amoebae are common throughout the world. They are found from Antarctica to the Arctic and are particularly comfortable in moist soils. Many species of amoeba live in water. The unicellular organisms use both freshwater and seawater as their habitat. The amoeba species Entamoeba histolytica, the causative agent of amoebic dysentery, is also widespread worldwide. The protozoa are found particularly in countries and areas with inadequate hygienic conditions. People become infected through contact with contaminated sewage or drinking water. The number of infections with amoebic dysentery increases especially after disasters and when there is a lack of pure drinking water. However, unpeeled fruits and vegetables, ice and ice cubes are also frequently contaminated with amoebae in subtropical and tropical areas such as Bangladesh, Indonesia, Thailand and India. It should be noted in this context that conventional drinking water disinfection with chlorine does not kill the protozoa. Only water that has been boiled for at least five minutes is free of amoebae. Amoebic encephalitis, on the other hand, is caused by other amoeba species. These include, for example, Acanthamoeba, Balamuthia or Naegleria fowleri. These are grouped under the term free-living amoebae or aquatic amoebae. While acanthamoebae are mainly present in mud, at the edges of water bodies and in biofilms, Balamuthia amoebae also live in dust and soil. Acanthamoebae also commonly colonize the nasopharynx of humans. Naegleria fowleri prefers freshwaters as its habitat. However, the pathogen is also increasingly found in temperate climates. The amoebae enter the human body via the olfactory epithelium during bathing and then enter the central nervous system and thus the brain via the olfactory nerve (nervus olfactorius).
Diseases and ailments
Amoebic dysentery characteristically presents via bloody and mucous diarrhea. This is also described as raspberry jelly-like. Settling of the diarrhea is associated with abdominal pain and cramps. In some cases, those affected suffer from very high fever. Depending on the severity of the infection, 40 to 50 defecations per day may be observed. During this phase, however, the patients hardly defecate at all. The excretions consist to a large extent of pure mucus. An inflammation with ulceration in the colon is responsible for these symptoms, which appear after an incubation period of one to seven days. The pathogen Entamoeba histolytica can pass through the damaged intestinal mucosa into the blood. From the blood, the amoeba then travels to the liver and other internal organs. There, the protozoa can destroy the resident tissue, causing severe ulceration. The result is internal bleeding. If amoebic dysentery is not detected in time, it can be fatal. It is treated with various antibiotics. If taken in time, the disease heals quickly.However, surgery may also be required for abscesses in internal organs. Primary amebic meningoencephalitis predominantly affects children. It starts suddenly and violently out of full health. Patients suffer from high fever, nausea, vomiting and neck pain. The stiffness of the neck is striking. Rapidly, there are perceptual changes and limitation of body control. Primary amebic meningoencephalitis is fatal within a week. To date, there are few patients who have survived the disease with early therapy. Granulomatous amoencephalitis occurs almost exclusively in patients with immunodeficiencies. For example, the disease is more commonly found in AIDS patients. The pathogen Balamuthia mandrillaris is an exception. It also infects people with a healthy immune system. The granulomatous form of amoebic dysentery begins insidiously with fever, vomiting, headache, and mild neck stiffness. Patients become lethargic, complain of memory problems, and their consciousness is clouded. Later, they develop symptoms such as seizures and hemiplegia or fall into a coma. Granulomatous amebic encephalitis progresses over a few days to several months and, like primary amebic meningoencephalitis, is usually fatal. However, some patients have been successfully treated with a combination of different antibiotics. Treatment must be given over several years.
