The Sarcodina’s group of protozoan parasites are represented by amoeba able to move using shape-shifting temporary structures called pseudopodia. Here are some of the most commonly known amoeba able to infect humans.
Entamoeba histolytica is present worldwide, but is more prevalent in developing countries. It infects up to 50 million people worldwide. This parasite is transmitted by the ingestion of cysts present in water, food or soils contaminated with faeces from infected individuals. A wide range of symptoms can be caused by this parasite. The infection can remain asymptomatic or present symptoms of invasive intestinal amoebiasis, such as dysentery with bloody diarrhoea, or of invasive extra-intestinal amoebiasis, such as cutaneous, genital, liver, kidney, peritonea, brain, heart or lungs abscesses. Diagnosis can be tricky as many other non-pathogenic species of the genus Entamoeba are present in humans, meaning that they colonize the human intestine without causing an actual disease. This can lead to false positive identification of Entamoeba histolytica by creating confusion with these other non-pathogenic species. Direct identification of cysts or parasite in faeces is possible, but this method cannot distinguish between Entamoeba histolytica and other non-pathogenic species. Other methods, such as detection of specific antibodies against the parasite, proteins from the parasite or specific DNA sequences, can then be used to distinguish between the different species. Finally, this disease is usually treatable using a cocktail of anti-parasitic drugs.
Acanthameoba species are one of the most frequent protozoan parasites genus found in soils and frequently contaminate fresh water. They are present worldwide and cause rare but severe infections. Actually, it is thought that most people come in contact with one of these parasites at one point in their life, but resulting illnesses are quite rare. These parasites can cause three main disease forms. Acanthamoeba keratitis is a rare infection of the eye’s cornea affecting healthy individuals and that can ultimately result in visual impairment or blindness. In developed countries, this infection is mainly related to improper use of contact lens. Granulomatous amoebic encephalitis is a very severe infection of the brain and the spinal cord that usually results in death in more than 97% of the cases. This disease is more frequent in people with compromised immune system, such as people suffering from AIDS. This infection is extremely rare and approximately 400 cases of granulomatous amoebic encephalitis caused by Acanthamoeba have been reported so far worldwide. It is noteworthy that another amoeba, Balamuthia mandrillaris, can also cause this extremely rare deadly central nervous system disease. Approximately 200 cases linked to Balamuthia mandrillaris have been reported worldwide with only a few surviving patients. However, people surviving granulomatous amoebic encephalitis usually suffer from different sequels, such as permanent brain damages. Acanthameoba species can also provoke a rare disseminated infection affecting many organs independently or concurrently. This disease form is also more frequent in people with compromise immune system and can also be observed with or without granulomatous amoebic encephalitis. Diagnosis of Acanthamoeba keratitis is relatively easy based on the symptoms and on the visualisation of the parasite using a confocal microscope. However, treatment of this disease form can be difficult and early diagnosis is essential to treat efficiently the patient and preserve the vision. Granulomatous amoebic encephalitis and disseminated infection are difficult to diagnose and are usually detected at an advanced stage. Diagnosis methods usually include brain scan and/or biopsy of the infected sites. Disseminated infections of the skin are usually treated successfully. However, there is no effective treatment against the deadly granulomatous amoebic encephalitis.
Naegleria fowleri is also commonly known as the brain-eating amoeba. It causes an extremely rare disease called primary amoebic meningoencephalitis that is fatal in 97% of the cases within 14 days of the exposure to this parasite. For instance, the United States reported 133 infections with Naegleria fowleri in the past 50 years, but only 3 people survived the infection. Survivors usually suffer form different sequels of the disease. Few cases have been reported in other countries, such as Czechoslovakia, India, New Zealand, Pakistan and Venezuela. Actually, a total of more than 300 cases worldwide have been reported so far. It is thought that the occurrence of this disease will increase partly due to better detection methods and climate changes. It is present in warm fresh water, such as lake, rivers and geothermal sources. It can also be present, but extremely rarely, in not sufficiently chlorinated pools or tap water. It is noteworthy that this parasite cannot infect human by drinking contaminated water, but has to penetrate its host through the nose in order to migrate to the brain. Different methods are used to diagnose this infection, such as direct visualisation of the parasite in the cerebrospinal fluid, parasite culture or detection of specific proteins from the parasite. However, because of its very rare occurrence and its rapid evolution, more than 75% of the diagnosis is obtained after death. Moreover, even if there are actually some promising drugs, no effective treatment is yet available.
Source: Centers for Disease Control and Prevention
