An amoeba is a parasite that circulates freely in the environment and in particular in dirty water. Some of them proliferate in the human digestive tract. If the majority of amoebae are harmless, some are the cause of sometimes serious diseases. We take stock.

An amoeba is a single-celled eukaryotic living being belonging to the group of rhizopods. As a reminder, eukaryotic cells are characterized by the presence of a nucleus and organelles containing genetic material and separated from the rest of the cell by a phospholidic membrane.

Amoeba have pseudopodia, i.e. temporary cytoplasmic extensions for locomotion and capture of prey. Indeed, amoeba are heterotrophic protozoa: they capture other organisms to feed by phagocytosis.

Most amoeba are free organisms: they can be present in all compartments of the environment. They appreciate humid environments, especially warm fresh water whose temperature ranges from 25 ° C to 40 ° C. However, there are a number of amoebae that parasitize the human digestive tract. Most of the amoeba are not pathogenic.

Some amoebae are lodged in the digestive tract of humans while others are found in our environment. Only a small number of amoeba are pathogenic.

These amoebae are frequently found in parasitology examinations of the stool. Their presence indicates contamination linked to the faecal hazard, but they are generally non-pathogenic. Among the latter, we find amoeba of the genus:

• Entamoeba (hartmanni, coli, polecki, dispar);
• Endolimax nana;
• Iadamoeba (pseudolimax) bütschlii ;
• Dientamoeba fragilis;
• etc.

Amebiasis, meningitis, encephalitis, keratitis, pneumo-bronchitis, etc., these pathologies can be caused by amoeba most often present in water or food soiled by feces. These often serious pathologies remain rare. The best known are intestinal amebiasis, meningoencephalitis by Naegleria Fowleri and Acanthamoeba keratitis.

Intestinal amibiase (amœbose)

Amebiasis is a serious digestive and liver disease caused by Entamoeba histolytica, the only intestinal amoeba of the genus Entamoeba capable of invading tissues and considered pathogenic.

Amebiasis is one of the three main parasitic diseases responsible for morbidity in the world (after malaria and bilharzia). Amebiasis is common in tropical and intertropical zone. The most symptomatic forms are found mainly in India, Southeast Asia, Africa and tropical America.

Infection is more common in children and mainly in countries with a low level of equipment for collective hygiene (less industrialized countries). In industrialized countries, it mainly affects travelers from an area with a high prevalence of the disease.

Contamination occurs orally, by ingestion contaminated food or water (fruits and vegetables) or by inintermediary of contaminated hands. The dissemination is carried out by resistant cysts contained in the stools which contaminate the external environment.

The severity of the disease is caused by the specific pathogenicity of the parasite and its ability to diffuse into tissues, especially the liver.

Meningoencephalitis caused by Naegleria Fowleri

La meningoencephalitis due to Naegleria Fowleriis rare: since 1967, in total, only 196 cases of meningoencephalitis have been identified in the world, not all of them being linked to this amoeba.

Contamination occurs by inhalation of contaminated water (during swimming for example).

Hot water discharged downstream from industrial installations, in particular power stations, is particularly at risk. Note that children are the preferred targets of amoeba.

The amoeba penetrates through the nasal mucosa to reach the brain and then develops there. The disease caused by Naegleria Fowleri results in inflammation of the brain (meningoencephalitis). The most common symptoms are:

• headaches ;
• discomfort;
• convulsions;
• drowsiness;
• sometimes abnormal restlessness.

The disease can be fatal if left undiagnosed.

Acanthamoeba keratitis

It is an inflammation of the cornea caused by the amoeba Acanthamoeba, frequently found in soil, soil and water (both sea water and tap water or that of swimming pools, etc.). An Acanthamoeba presents itself in two states: in the trophozoite state and in the cystic state, the latter resists extreme environments in order to guarantee its survival.

In 80% of cases, the disease affects contact lens wearers. Indeed, the latter cause irritation and delimit a cavity where amoebae can multiply. The remaining 20% ​​concern inhabitants of regions with a dry climate.

Inoculation is done by depositing on the cornea cysts brought into contact by a dirty finger, an insufficiently cleaned or rinsed contact lens, water, a blunt object (blade of grass, splint of wood, etc.) , dusty wind, etc.

The onset of this keratitis is characterized by a painful sensation of a foreign body with tearing, and sometimes by photophobia. Eye redness, reduced visual acuity, and eyelid edema are common. When the treatment is not started in time and / or proves ineffective, the in-depth progression of the amoebae continues with damage to the anterior chamber, then the posterior chamber, the retina and finally we observe in severe cases cerebral metastases either by hematogenous route or by nervous route (along the optic nerve).

The clinical examination must always be supplemented by samples in case of suspicion of amoeba.

Intestinal amibiase (amœbose)

First of all, the clinical examination puts the doctor on the right track. The method used to confirm the diagnosis depends on the location of the infection:

Intestinal infection

• Stool microscopic examination and enzyme immunoassay in stool;
• Search for parasite DNA in stool and / or serological tests.

Extra-intestinal infection

• Imaging and serological tests or therapeutic trial of an amebicide.

Meningoencephalitis in Naegleria Fowleri

• Physical examination ;
• Imaging tests, such as computed tomography (CT) and magnetic resonance imaging (MRI), are done to rule out other possible causes of the brain infection, but they cannot confirm that amoeba is responsible;
• Lumbar puncture and cerebrospinal fluid analysis confirm the diagnosis;
• Other techniques can be performed in specialized laboratories and are more likely to detect amoebae. This is the case, for example, with a biopsy of brain tissue.

Acanthamoeba keratitis

• Examination and culture of corneal scrapings;
• The diagnosis is confirmed by examining the surface biopsy of the cornea, stained with Giemsa or trichrome, and by culturing it in special media.

Pathologies caused by amoeba generally require rapid treatment in order to avoid complications. The treatments are generally medicinal (antiamibiens, antifungals, antibiotics, etc.) and sometimes surgical.

Intestinal amibiase

Treatment consists of the administration of a diffusible antiamoebic and a “contact” antiamoebic. Prevention against amebiasis is essentially based on the implementation of individual and collective hygiene rules. In the absence of support, the prognosis remains bleak.

Amebic meningoencephalitis in Naegleria Fowleri

This condition is most often fatal. Doctors usually use a combination of several drugs, including: Miltefosine and one or more of the following drugs: amphotericin B, rifampicin, fluconazole or related drugs such as voriconazole, ketoconazole, itraconazole, azithromycin, etc.

Acanthamoeba keratitis

The treatment has several possibilities:

• medicinal products such as propamidine isethionate (in eye drops), hexomedine, itraconazole;
• surgical procedures such as keratoplasty or cryotherapy.