AMOEBIASIS – DISEASE CAUSED BY ENTAMOEBA HISTOLYTICA

INTRODUCTION :- AMOEBIASIS

Entamoeba histolytica is a protozoan parasite responsible for a disease called amoebiasis. It occurs usually in the large intestine and causes internal inflammation as its name suggests (histo = tissue, lytic = destroying). 50 million people are infected worldwide, mostly in tropical countries in areas of poor sanitation. In industrialized countries most of the infected patients are immigrants, institutionalized people and those who have recently visited developing countries.

Classification of Entamoeba hystolytica

• Phylum – Protozoa
• Subphylum– Sarcomastigophora
• Supesclass– Sarcodina
• Class– Rhizopodea
• Subclass– Lobosia
• Order– Amoebida
• Genus– Entamoeba
• Species– histolytica

General Characters of Entamoeba hystolytica

• It is found mainly in tropics & subtropics in addition to that higher in rural and densely populated urban areas.
• It is a monogenetic parasite which affects mainly children’s and young adults.
• It is a microscopic endoparasite of man that is commonly found in the upper part of the large intestine.
• It occurs in three distinct forms i.e. Trophozite/magna form, precystic/minuta form and cystic form.
• It is holozoic in nature and feed by phagocytosis.
• Encystation i.e. formation of a cyst wall during unfavourable environmental conditions is an adaptation by this parasite to thrive in harsh conditions.
• It reproduces asexually by binary fission.
• Metacyst is the infective stage of parasite.
• It causes Amoebic dysentery disease.

Inside humans Entamoeba histolytica lives and multiplies as a trophozoite. Trophozoites are oblong and about 15–20 µm in length. In order to infect other humans they encyst and exit the body. The life cycle of Entamoeba histolytica does not require any intermediate host. Mature cysts (spherical, 12–15 µm in diameter) are passed in the feces of an infected human. Another human can get infected by ingesting them in fecally contaminated water, food or hands. If the cysts survive the acidic stomach, they transform back into trophozoites in the small intestine. Trophozoites migrate to the large intestine where they live and multiply by binary fission.

Both cysts and trophozoites are sometimes present in the feces. Cysts are usually found in firm stool, whereas trophozoites are found in loose stool. Only cysts can survive longer periods (up to many weeks outside the host) and infect other humans. If trophozoites are ingested, they are killed by the gastric acid of the stomach. Occasionally trophozoites might be transmitted during sexual intercourse.

Life cycle of Entamoeba hystolytica

It is a monogenetic parasite. Its life cycle concludes within a primary host i.e. man. Inside humans Entamoeba histolytica lives and multiplies as a trophozoite. Trophozoites are oblong and about 15–20 µm in length. Trophozoites multiply asexually by binary fission inside the wall of large intestine, which grow rapidly in size feeding upon bacteria and host tissue. In order to infect other humans they encyst and exit the body. Mature cysts (spherical, 12–15 µm in diameter) are passed in the feces of an infected human. Transmission of the parasite takes place by the intake of contaminated food & water with faecal matter containing tetra nucleate cyst.

The cystic or minuta form is excreted out with faeces which infect new host when ingested and pass down the alimentary canal & reach small intestine. After 5-6 hours excystation takes place thereby releasing tetra nucleate amoeba, called the excystic amoeba or metacyst. These metacyst immediately start dividing to produce 8 small uninucleate amoebulae or metacystic trophozoites, which invade intestine mucous linining & grow into mature trophozoites. Both cysts and trophozoites are sometimes present in the feces.

Cysts are usually found in firm stool, whereas trophozoites are found in loose stool. Only cysts can survive longer periods (up to many weeks outside the host) and infect other humans. If trophozoites are ingested, they are killed by the gastric acid of the stomach. Occasionally trophozoites might be transmitted during sexual intercourse.

Pathogenecity

Several protozoan species in the genus Entamoeba colonize humans, but not all of them are associated with disease. Entamoeba histolytica is well recognized as pathogenic amoeba, associated with intestinal and extraintestinal infections. The other species are important because they may be confused with E.hystolytica in diagnostic investigations.

Entamoeba hystolytica causes Amaoebiasis or Amoebiotic dysentry. It Causes ulcers which are flask shaped containing lymphocyctes, blood corpuscles, cellular debris and bacteria which lead to information of cavity filled with pus. The blood and ulcer content pass outside with stool . Infected person’s stool is usually acidic and consists of swarms of entamoeba which causes the new infection. Sometimes trophozoites make their way through blood circulation into brain, liver, spleen, lungs and gonads where they destroy tissues.

Symptoms of Amoebiasis

Symptoms of these more severe infections include:

• anemia
• appendicitis (inflammation of the appendix)
• bloody diarrhea
• fatigue
• fever
• gas (flatulence)
• genital and skin lesions
• intermittent constipation
• liver abscesses (can lead to death, if not treated)
• malnutrition
• painful defecation (passage of the stool)
• peritonitis (inflammation of the peritoneum which is the thin membrane that lines the abdominal wall)
• pleuropulmonary abscesses
• stomach ache
• stomach cramping
• toxic megacolon (dilatted colon)
• weight loss.

Prevention from amoebiasis

To prevent spreading the infection to others, one should take care of personal hygiene. Always wash your hands with soap and water after using the toilet and before eating or preparing food. Amoebiasis is common in developing countries. Some good practices, when visiting areas of poor sanitation:

• Wash your hands often.
• Avoid eating raw food.
• Avoid eating raw vegetables or fruit that you did not wash and peel yourself.
• Avoid consuming milk or other dairy products that have not been pasteurized.
• Drink only bottled or boiled water or carbonated (bubbly) drinks in cans or bottles. Natural water can be made safe by filtering it through an “absolute 1 micron or less” filter and dissolving iodine tablets in the filtered water. “Absolute 1 micron” filters are found in outdoor/camping supply stores.

 Diagnosis

Amoebiasis is diagnosed by your health care provider under a microscope by finding cysts and (rarely trophozoites) from a stool sample. The results are usually said to be negative, if Entamoeba histolytica is not found in three different stool samples. But it still does not necessarily mean that you are not infected because the microscopic parasite is hard to find and it might not be present the particular samples.

A blood test might also be available but is only recommended, if your health care provider believes that the infection could have spread to other parts of the body. Trophozoites can be identified under a microscope from biopsy samples taken during colonoscopy or surgery.

Entamoeba histolytica should be differentiated from the non-pathogenic Entamoeba dispar. The two are morphologically identical and differentiation must be based on immunologic or isoenzymatic analysis or molecular methods. They can be distinguished under a microscope, if Entamoeba histolytica has ingested red blood cells. Entamoeba dispar is about 10 times more common. If either one is found, then you are usually treated.

Treatment

If you are experiencing amoebiasis symptoms, you are treated with two antibiotics. The preferred drugs are metronidazole or tinidazole immediately followed with paromomycin, diloxanide furoate or iodoquinol. Asymptomatic intestinal amoebiasis is treated with paromomycin, diloxanide furoate or iodoquinol.