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Amebic dysentery

By: Tewodros Kidane

Definition

Dysentery is a variant type of gastroenteritis that causes bloody diarrhea.

It is a parasitic infection of the colon which is caused by the infestation of an amoeba and is also known as Amoebiasis or entamoebiasis.

History

• Amoebiasis was first described by Fedor A. Lösch in 1875, in northern Russia. An incident occurred at the Chicago World's Fair in 1933 which caused by contaminated drinking water with more than a thousand cases and 98 deaths. It was observed in 1897 that at least one non-disease-causing species of Entamoeba existed (Entamoeba coli), but was formally recognized by the WHO in 1997 that E. histolytica has two species, eventhough this had initially been proposed in 1925.

• Joel Connolly of the Chicago Bureau of Sanitary Engineering ended the outbreak when he discovered that broken down plumbing had permitted sewage to contaminate drinking water. In 1998 there was another outbreak of amoebiasis in Georgia and between May and September 1998. 177 cases were reported of which 71 cases had intestinal amoebiasis and 106 had probable cases of liver abscess.

• The Nicobarese people have claimed that medicinal properties are in the bark and seeds of Glochidion calocarpum, a plant native to India is effective in curing abdominal disorders caused by amoebiasis.

Causes

The causative organism is Entamoeba histolytica , which is mostly seen in warm geographical climates and are spread by contaminated food and water.

Signs and symptoms

Symptoms can present as none, mild, or severe.

Symptoms can develop within a few days to a few weeks. 

In asymptomatic infections, the amoeba thrives by eating and digesting bacteria and food particles in the gut.

• Abdominal pain

• Melena

• Diarrhea

• Flatulence

• Fatigue

• Fever

• Loss of appetite

• Weight loss

• Liver abscess may be present in severe cases.

Epidemiology

• Amoebiasis is present all over the world, although most cases are endemic in the developing countries.” About 480 million people are currently infected with about 40 million new cases per year with significant symptoms. This results in the death of between 40,000–110,000 people a year.” Peter et al. 2013.

• Most infections are now believed to be caused by E. dispar. E. dispar is more common in certain areas and symptomatic cases may not be previously reported. The first case of amoebiasis was documented in 1875 and in 1891 the disease was described in detail and this resulted in the terms “amoebic dysentery” and “amoebic liver abscess”. Peter et al. 2013.

• Further evidence from the Philippines in 1913 found that upon swallowing cysts of E. histolytica volunteers developed the disease.

Pathophysiology

• Virulence is strain related, and associated with certain isoenzyme patterns and surface antigens.

• The microorganism that causes amebic dysentery is found in the intestine of infected individuals where it forms cysts that passed in feces. When food or water containing the cysts enters the digestive tract of a person, the amoebas is released from the cysts and infects the host.

• Without the cyst, that protects the organism and allows it to live in a dormant state in an unfavorable environment , E. histolytica could be much more easily controlled. The cyst can help it survive for weeks. Even though they are not particularly resistant to drying, the cysts of E. histolytica can withstand temperatures of up to 68 °C (154 °F) for five minutes but are resistant to certain chemicals.

• In asymptomatic infections, the amoeba survives by eating and digesting bacteria and food particles in the intestine. It usually doesn’t come in contact with the intestine itself because of the protective layer of mucus that lines the intestines.

• Symptomatic infection occurs when E. histolytica comes in contact with the cells lining the walls of the intestine. It secretes the same enzymes it uses to digest bacteria, that destroy cell membranes and proteins. Destruction of the colon’s epithelial cells produces mucosal ulcerations which causes edema and hyperemia, but minimal inflammatory response. The inflammatory cells are also lysed, thus explaining the paucity of leukocytes

• This process can lead to penetration, perforation and digestion of human tissues, resulting first in flask-shaped ulcerations in the intestine. E. histolytica ingests the destroyed cells by phagocytosis and is often seen with red blood cells (a process known as erythrophagocytosis) inside when viewed in stool samples. A granulomatous mass (known as an  amoeboma ) may form in the walls of the ascending colon and or rectum as a result of a long-lasting immunological cellular response, and is sometimes confused with cancer.

Mode of Transmission

• Amoebiasis is usually transmitted by the fecal-oral route. It spreads through drinking or eating uncooked food or fruit that was washed in contaminated water.

• It is often endemic in regions with limited modern sanitation systems.

• Human to human transmission occurs by ingestion of cysts.

• Transmission has occasionally been associated with contaminated enema equipment.

• Infected patients excrete cysts intermittently and can continue for years if untreated.

• Venereal transmission is associates with homosexuals or people that practice anal sex.

Diagnosis

• Microscopy is the most common method of diagnosis around the world but is not as sensitive or accurate in diagnosis as the other tests available.

• It is essential to distinguish between the cyst of E. histolytica from the cysts of nonpathogenic intestinal protozoa such as Entamoeba coli by its appearance.

• E. histolytica cysts have a maximum of four nuclei, while the commensal Entamoeba coli cyst has up to 8 nuclei.

• Colonoscopy is used to detect small ulcers but diagnosis may be difficult as the mucous membrane between these areas can appear healthy or inflamed.

• Trophozoites may be identified at the edge of the ulcer or within the tissue, using immunohistochemical staining with specific anti-E. histolytica antibodies.

• Asymptomatic human infections are usually diagnosed by finding cysts in the stool.

• Flotation or sedimentation procedures recover the cysts from fecal matter and stains help to visualize the isolated cysts for microscopic examination. Due to the fact that cysts are not shed constantly, a minimum of three stools are examined.

• In symptomatic infections, the trophozoite can be visually observed in fresh feces.

• Serological tests are used to test for the presence of antibodies. The levels of antibody are much higher in individuals with liver abscesses. Serology only becomes positive two weeks after infection.

• More recent developments include a kit that detects the presence of amoeba proteins in the feces, and another that detects ameba DNA in feces

Treatment

• Amoebic dysentery usually resolves on its own after 3 to 7 days and treatment may not be necessary.

• Drinking copious fluids and use oral rehydration solutions as necessary to prevent dehydration.

• Pain relievers like acetaminophen can help relieve pain and fever.

• E. histolytica infections occur in both the intestine and or liver. Those with symptoms will require treatment with two medications, an amoebicidal tissue-active agent and a luminal cysticidal agent Individuals that are asymptomatic will only need a luminal cysticidal agent.

• Treatment includes antibiotics which stops the growth or kills bacteria.

• Common drugs include Tinidazole.

Prevention

To help prevent the spread of amoebiasis :

• Wash hands thoroughly with soap and hot running water for at least 10 seconds after using the toilet or changing a baby's diaper before handling food.

• Clean bathrooms and toilets often and pay particular attention to toilet seats and taps.

• Avoid as much as possible sharing towels or napkins.

To help prevent infection:

• Avoid eating raw vegetables when in endemic areas, as they may have been fertilized using human feces.

• Filter and boil water. E.histolytica cysts is usually resistant to chlorination, therefore sedimentation and filtration of water is necessary to reduce the incidence of infection

• Avoid eating street foods especially in public dirty places.

• Good sanitary practice, as well as responsible sewage disposal or treatment, are necessary for the prevention of E. histolytica infection on an endemic level .You should stay at home until at least 48 hours after the last episode of diarrhea, to reduce the risk of passing the infection on to others.

• Recovery procedures are not very accurate; cysts are easily lost or damaged beyond recognition, which leads to many falsely negative results in recovery tests

Complications

Complications can include

• Inflammation and ulceration of the colon with tissue death which may result in peritonitis

• Anaemia due to prolonged gastric bleeding

• Amoebomas can lead to intestinal obstruction and can be mistaken for cancer of the caecum or an appendicular mass.

• Bloody diarrhea

• Abscess

Complications of hepatic amoebiasis includes

• Perforation (amoebic peritonitis)

• Subdiaphragmatic abscess

• Perforation of the diaphragm to the pericardium and pleural cavity

• Perforation of skin (amoebiasis cutis).

• Urogenital tract amoebiasis derived from intestinal lesion can lead to amoebic vulvovaginitis (may's disease), rectovesicla fistula and rectovaginal fistula.

• Malnutrition and stunted growth.

Reference

• Beeching, Nick; Gill, Geoff (2014-04-17). "19". Lecture Notes: Tropical Medicine. John Wiley & Sons. pp. 177–182. ISBN 9781118734568.

• Berger SA, Marr JS. Human Parasitic Diseases Sourcebook. Jones and Bartlett Publishers: Sudbury, Massachusetts, 2006.

• "Dysentery". who.int. Archived from the original on 5 December 2014. Retrieved 28 November 2014.

• Farrar, Jeremy; Hotez, Peter; Junghanss, Thomas; Kang, Gagandeep; Lalloo, David; White, Nicholas J. (2013-10-26). Manson's Tropical Diseases. Elsevier Health Sciences. pp. 664–671. ISBN 9780702053061.

• FDA Bacteriological Analytical Manual". Archived from the original on 2008-04-06. Retrieved 2008-03-26.

• Hammer, K (1990). "Barilla (Salsola soda, Chenopodiaceae)". Economic Botany. 44 (3): 410–412. doi:10.1007/bf03183925. JSTOR 4255259. S2CID 32113455.

• Kreidl P, Imnadze P, Baidoshvili L, Greco D (October 1999). "Investigation of an outbreak of amoebiasis in Georgia". Euro Surveillance. 4 (10): 103–104. doi:10.2807/esm.04.10.00040-en. PMID 12631887.

• Mondal D, Petri WA, Sack RB, Kirkpatrick BD, Haque R, et al. (November 2006). "Entamoeba histolytica-associated diarrheal illness is negatively associated with the growth of preschool children: evidence from a prospective study". Transactions of the Royal Society of Tropical Medicine and Hygiene. 100 (11): 1032–8. doi:10.1016/j.trstmh.2005.12.012. PMID 16730764.

• Markell EK (June 1986). "The 1933 Chicago outbreak of amebiasis". The Western Journal of Medicine. 144 (6): 750. PMC 1306777. PMID 3524005.