Anatomy-Lexicon

Amoeba

Synonyms

amoibos (alternating in Gr.), change animals

definition

Under the term "Amoeba“One understands animal protozoa (so-called Protozoa) that do not have a fixed body shape. Amoebas can change their body structure through the formation of vaginal pods (Pseudopodia) are constantly changing and moving in this way.

Read more on the topic: Intestinal parasites

introduction

As unicellular organisms that belong to the group of protozoa, amoeba are counted among the so-called ancient animals. They are approximately 0.1 to 0.8 mm in size. In most cases, amoeba are naked single-cell organisms. However, there are also genera that have a kind of shell (so-called Thecamoeben). Amoebas are further divided into different genera based on different categories. While most of these amoeba genera are completely harmless to humans, amoeba of the genus Entamöba histolytica cause serious illness.

Above all, gastrointestinal diseases, which can be accompanied by severe diarrhea, are caused by this genus of amoeba. In addition, amoebas can form symptom-free cysts or the so-called amoebic liver abscess in the human body.

Read more on the topic: diarrhea

In the case of amoeba, a basic distinction must be made between two life forms. The so-called trophozoites settle mainly in the gastrointestinal tract of humans. The second form of life, the amoeba, is contagious cysts, which the infected person excretes with the stool and can thus be transmitted to other living beings. Entamöba histolytica, which is dangerous for humans, is particularly widespread in the tropics and subtropics. In these regions, it can be assumed that around 70 percent of the population is the carrier of the pathogen. In Central Europe, diseases caused by amoebas are rare. However, if corresponding symptoms develop after a stay in the tropics or subtropics, the attending physician should be advised of the stay abroad.

Pathogenicity - damage to amoeba health

Most amoeba genera are completely harmless to humans.Only a few amoebas are considered to be facultatively pathogenic to humans (potentially harmful to humans) designated. Among the most dangerous amoebas for the human organism are those unicellular organisms that belong to the Entamoeba histolytica genus. They are the cause of what is known as amoebic dysentery, a serious disease that leads to very watery diarrhea in those affected.

In addition, it must be noted that many amoeba genera carry pathogenic germs such as Legionella. The absorption of infected, actually harmless amoebas into the human body can cause Legionella-specific diseases. In addition, the amoeba genera Naegleria, Balamuthia and Sappina severe meningoencephalitis (Inflammation of the brain and meninges, see also meningitis).

Read more on the topic: meningitis

Amoebic dysentery

Amoebic dysentery is a serious diarrheal disease that occurs mainly in tropical and subtropical regions. The only cause of this disease is the amoeba genus Entamoeba histolytica. From a purely statistical point of view, it can be assumed that around one in ten of the critical regions is infected with the amoeba which is the cause of amoebic dysentery. An estimated 100,000 deaths annually can be associated with this diarrheal disease. Due to the increasing number of tourists in these areas, the pathogen is now found worldwide.

Up to 200 cases of amoebic dysentery have been recorded in Germany in recent years. In the case of amoebic dysentery, different forms, which differ in their symptoms and severity, have to be differentiated. With asymptomatic intestinal involvement (so-called Intestinal lumen infection) the causative amoeba only settle in the interior of the intestinal tube. This form of infection does not usually cause any symptoms. In the invasive intestinal amoebic dysentery on the other hand, the intestinal tissue is also infiltrated by amoeba. Affected people develop pronounced symptoms in the course of this. The so-called extraintestinal amoebic dysentery represents the most serious form of the disease. Amoeba can also be found outside the tissue in those affected. In this way, in addition to the typical diarrhea, liver or brain abscesses can develop.

Symptoms of amoeba carriers

Depending on the type of amoebic dysentery, the affected person may develop more or less severe symptoms. While amoeba carriers with a pure intestinal lumen infection do not develop any symptoms in most cases, other patients typically suffer from severe, watery diarrhea. The asymptomatic intestinal lumen variant occurs in approximately 80 to 90 percent of all amoebic infections. Variants of amoebic dysentery that lead to severe diarrhea, on the other hand, are comparatively rare among all amoebic infections.

In the case of invasive intestinal amoebic dysentery, amoebas can also be detected in the intestinal tissue. Because of this, the affected patients experience pronounced symptoms. Typically, the majority of those affected develop bloody, slimy, raspberry jelly-like diarrhea at an early stage. In addition, cramping abdominal pain and pain during bowel movements are among the most common symptoms of this variant of amoebic dysentery.

Due to the amoeba infestation of the intestinal tissue, nutrients can only be insufficiently absorbed. A large part of the energy sources necessary for normal organ processes is excreted unused with the diarrhea. Patients who suffer from intestinal amoebic dysentery therefore usually lose weight quite quickly. About 30 to 40 percent of patients with intestinal amoebic dysentery and severe diarrhea also develop a high fever.

One speaks of extraintestinal amoebic dysentery when the causative amoeba not only attack the intestinal tissue, but are also detectable in other organs. In most cases, the causative amoeba spread from the intestinal tissue to the liver, brain and / or spleen. In this context, however, the amoebic infection of the liver is the most common variant. People with extraintestinal amoebic dysentery do not necessarily have to suffer from diarrhea. However, the occurrence of diarrhea does not rule out an extraintestinal infection. If the liver tissue is affected, a fist-sized, usually single abscess (so-called Amebic liver abscess). It is a cavity in the liver tissue filled with purulent secretion.

The presence of such an amoebic liver abscess is usually noticeable through the following symptoms:

high fever
to cough
Tenderness or pain in the upper right abdomen
Enlargement of the liver
General symptoms (e.g. tiredness, feeling weak, fatigue)

infection

During the amoebic infection, the amoebic cysts excreted in the stool are transmitted. Infection mainly occurs when little or no importance is attached to hygiene. Amoebic cysts can be transmitted through contaminated food as well as contaminated drinking water. A direct infection via the mouth cannot be ruled out if there is appropriate contact. Immediately after the actual infection, the amoebic cysts arise again in the human body Trophozoites. These can then settle in the intestine and / or in other organs and lead to amoebic dysentery. In addition, it must be noted that an amoebic infection does not have to lead to disease in every person. So-called "symptomless Carriers “show no complaints, but can pass on the causative unicellular organisms.

How infectious are amoebas?

The most important amoeba that affects humans, Entamoeba histolytica, reproduces in the human intestine and usually does not affect animals. In the case of an active infection, the host excretes many millions of contagious cysts in the stool which, if ingested orally, can trigger a new infection. The pathogen is therefore dependent on faecal-oral transmission and is therefore particularly widespread in areas with poor wastewater infrastructure and drinking water hygiene.

When traveling to the tropics, certain precautionary measures should be taken, so if in doubt you should boil tap water and not consume unwashed fruit. Not every infection leads to the pathogen spreading in the intestine. In some cases, the pathogens survive in the intestine for a few weeks without causing symptoms and then die again. It can also lead to permanent infestation, which may only lead to disease after months or years. In such unclear cases it is particularly important to inform the attending physician about previous trips to tropical regions.

diagnosis

The method of choice in the diagnosis of amoebic dysentery is the stool examination. This must be carried out at least three times on three consecutive days for the correct detection of amoeba. Both amoebic cysts, as well Trophozoites can be detected in the stool using a microscope. With this method of investigation, however, it must be taken into account that the trophozoites are very short-lived. For this reason, they can only be detected within a time window of approximately 10 to 15 minutes. In addition, if an amoebic infection is suspected, a blood test should be carried out

. However, this examination method is rather unsuitable for detecting the actual infection. Only the effects of amoeba infestation, for example dehydration due to severe diarrhea or changes in liver values in amoebic liver cysts, can be shown in this way. A liver abscess can also be shown with the help of various imaging methods (ultrasound examination, computed tomography, magnetic resonance tomography).

therapy

The treatment of the amoebic infection depends on both the form and the severity of the disease. So-called contact amebicides (for example Diloxanide furoate) only remain in the intestine. They are mainly used to treat asymptomatic amoeba carriers. In addition, these drugs can be used to treat intestinal amoebic dysentery. Tissue amoebicides (for example Dehydroemetine), however, also enter the bloodstream and can therefore be used for therapy of the extraintestinal amoebic dysentery can be used. Because of the possible serious side effects of these drugs, they are now only used in cases of severe disease.

Alternatively you can Contact and tissue amoebicides administered. These drugs used to treat amoebic dysentery remain in the intestine and can also enter the blood. For this reason, both the intestinal and the extraintestinal forms of amoebic dysentery can be treated in this way. In addition, a patient suffering from amoebic dysentery must be kept hydrated. Otherwise, the severe, watery diarrhea can quickly lead to dehydration.

Prevention

When staying in the tropical or subtropical regions, it is advisable to take certain safety measures. In this way, the risk of an amoebic infection can be reduced as far as possible. Drinking water should always be boiled or sterilized by filtration before consumption. The consumption of salads should be completely avoided in the affected regions. In addition, fruit must never be eaten unpeeled. For this reason, only peelable fruit should be consumed. In general, when changing food, it should be noted that this should always be done slowly and carefully.

Amoebic infection in the eye

An amoeba infection may not only affect the gastrointestinal tract, but also the eye. In most cases, corneal inflammation is caused by bacterial pathogens. Infection by viral pathogens or fungi is less common, but it can still occur. According to the latest findings, however, amoebas can also cause inflammatory processes in the eye, more precisely in the corneal area.

Just one by amoeba (so-called Acanthamoeba) caused inflammation in the eye can be very dangerous. The reason for this is the fact that the causative amoeba penetrate the cornea and in this way also cause inflammation in the entire eye. As a result, those affected can even go completely blind.

The symptoms of an amoebic infection in the eye are quite unspecific, especially at the beginning. Affected people usually notice pronounced redness and increased tearing first. In addition, the eyesight can be severely restricted right from the start. Affected patients usually report that their vision is no longer sharp, but more and more blurred. Only in the course of the disease does severe pain typically arise.

At this point it can be assumed that the nerve cells in the eye have already been damaged by the causative parasites. It is precisely this delayed occurrence of pain symptoms that allows a distinction to be drawn between bacterial corneal inflammation and amoebic infection. If the inflammatory processes are caused by bacterial pathogens, the pain usually occurs much earlier. Since the inflammation in the eye caused by amoeba is a serious clinical picture, extensive diagnostics must be initiated at the first suspicion. Permanent impairment of visual performance can only be avoided by promptly identifying the causative parasites and promptly initiating a suitable treatment.

What are "brain-eating" amoebas

Amoeba-like, unicellular organisms with the name Naegleria fowleri are not quite appropriately referred to as brain-eating amoebas. They are about 30 micrometers in size and can move using pseudopodia (pseudopods). Naegleria fowleri occurs mainly in bodies of water or in moist soil and is widespread worldwide. It also occurs in lakes, swimming pools and sewers.

It usually lives on bacteria and dead plant material. If water infected with Naegleria fowleri gets into the nose, the pathogen can penetrate the olfactory nerves into the brain. Symptomatic infections are almost always fatal. The amoebas are not able to eat the brain, but they spread in the cerebrospinal fluid and cause severe purulent meningitis (meningitis).

It takes about a week between infection and the first symptoms such as nausea, vomiting, fever, headache and stiff neck, and death usually occurs after another week. Even early treatment rarely leads to survival. However, not every infection may actually lead to disease. All that remains is to prevent possible infection. Suitable measures are disinfection of swimming pool water and avoidance of natural, especially warm, stagnant water. The disease is very rare, in 50 years there will be hardly more than 100 people in the USA, although young people are often affected.