Entamoeba Histolytica & Amoebic Dysentery, NURSING WORLD

 

Entamoeba Histolytica & Amoebic Dysentery

 

Introduction:

 Entamoeba histolytica is an anaerobic parasitic amoebozoan, part of the genus Entamoeba. Predominantly infecting humans and other primates causing amoebiasis, E. histolytica is estimated to infect about 35-50 million people worldwide. E. histolytica infection is estimated to kill more than 55,000 people each year. Previously, it was thought that 10% of the world population was infected, but these figures predate the recognition that at least 90% of these infections were due to a second species, E. dispar. Mammals such as dogs and cats can become infected transiently, but are not thought to contribute significantly to transmission.

 

The word histolysis literally means disintegration and dissolution of organic tissues.

 

 

 

Transmission:

The active (trophozoite) stage exists only in the host and in fresh loose feces; cysts survive outside the host in water, in soils, and on foods, especially under moist conditions on the latter. The infection can occur when a person puts anything into their mouth that has touched the feces of a person who is infected with E. histolytica, swallows something, such as water or food, that is contaminated with E. histolytica, or swallows E. histolytica cysts (eggs) picked up from contaminated surfaces or fingers.

 

The cysts are readily killed by heat and by freezing temperatures, and survive for only a few months outside of the host. When cysts are swallowed they cause infections by excysting (releasing the trophozoite stage) in the digestive tract.

 

The pathogenic nature of E. histolytica was first reported by Fedor A. Lösch in 1875,but it was not given its Latin name until Fritz Schaudinn described it in 1903. E. histolytica, as its name suggests (histo–lytic = tissue destroying), is pathogenic; infection can be asymptomatic or can lead to amoebic dysentery or amoebic liver abscess.[6][7] Symptoms can include fulminating dysentery, bloody diarrhea, weight loss, fatigue, abdominal pain, and amoeboma.

 

 

Pathogen interaction:

E. histolytica may modulate the virulence of certain human viruses and is itself a host for its own viruses.

 

For example, AIDS accentuates the damage and pathogenicity of E. histolytica. On the other hand, cells infected with HIV are often consumed by E. histolytica. Infective HIV remains viable within the amoeba, although there has been no proof of human reinfection from amoeba carrying this virus.

 

A burst of research on viruses of E. histolytica stems from a series of papers published by Diamond et al. from 1972 to 1979. In 1972, they hypothesized two separate polyhedral and filamentous viral strains within E. histolytica that caused cell lysis. Perhaps the most novel observation was that two kinds of viral strains existed, and that within one type of amoeba (strain HB-301) the polyhedral strain had no detrimental effect but led to cell lysis in another (strain HK-9). Although Mattern et al. attempted to explore the possibility that these protozoal viruses could function like bacteriophages, they found no significant changes in Entamoeba histolytica virulence when infected by viruses.

 

 

 

Laboratory Diagnosis:

 Diagnosis is confirmed by microscopic examination for trophozoites or cysts in fresh or suitably preserved faecal specimens, smears of aspirates or scrapings obtained by proctoscopy, and aspirates of abscesses or other tissue specimen.

 

A blood test is also available but is only recommended when a healthcare provider believes the infection may have spread beyond the intestine (gut) to some other organ of the body, such as the liver.

 

 

 

However, this blood test may not be helpful in diagnosing current illness because the test can be positive if the patient has had amebiasis in the past, even if they are not infected at present.Stool antigen detection and PCR are available for diagnosis, and are more sensitive and specific than microscopy.

 

 

Risk Factors:

Poor sanitary conditions are known to increase the risk of contracting amebiasis E. histolytica.In the United States, there is a much higher rate of amebiasis-related mortality in California and Texas, which might be caused by the proximity of those states to E. histolytica-endemic areas, such as Mexico.

 

Other parts of Latin America, and Asia. E. histolytica is also recognized as an emerging sexually transmissible pathogen, especially in male homosexual relations, causing outbreaks in non-endemic regions.As such, high-risk sex behaviour is also a potential source of infection.

Although it is unclear whether there is a causal link, studies indicate a higher chance of being infected with E. histolytica if one is also infected with HIV.

 

 

 

Treatment:

There are a number of effective medications. Generally several antibiotics are available to treat Entamoeba histolytica. The infected individual will be treated with only one antibiotic if the E. histolytica infection has not made the person sick and most likely be prescribed with two antibiotics if the person has been feeling sick.Otherwise, below are other options for treatments.

 

Intestinal infection: Usually nitroimidazole derivatives (such as metronidazole) are used because they are highly effective against the trophozoite form of the amoeba. Since they have little effect on amoeba cysts, usually this treatment is followed by an agent (such as paromomycin or diloxanide furoate) that acts on the organism in the lumen.

 

Liver abscess: In addition to targeting organisms in solid tissue, primarily with drugs like metronidazole and chloroquine, treatment of liver abscess must include agents that act in the lumen of the intestine (as in the preceding paragraph) to avoid re-invasion. Surgical drainage is usually not necessary except when rupture is imminent.

 

People without symptoms: For people without symptoms (otherwise known as carriers, with no symptoms), non endemic areas should be treated by paromomycin, and other treatments include diloxanide furoate and iodoquinol.[citation needed] There have been problems with the use of iodoquinol and iodochlorhydroxyquin, so their use is not recommended. Diloxanide furoate can also be used by mildly symptomatic persons who are just passing cysts.

 

 

 

 

 

Amoebiasis (amoebic dysentery)

 

Introduction:

Amoebiasis is an infectious disease caused by a one-celled parasite called Entamoeba histolytica, which causes both intestinal and extraintestinal infections. Two species of Entamoeba are morphologically indistinguishable: Entamoeba histolytica is pathogenic and Entamoeba dispar harmlessly colonizes the colon.

Amoebas adhere to and kill the cells of the colon and cause dysentery with blood and mucus in the stool. Amoebas also secrete substances called proteases that degrade lining of the colon and permit invasion into the bowel wall and beyond. Amoebas can spread via the circulation to the liver and cause liver abscesses. The infection may spread further by direct extension from the liver or through the bloodstream to the lungs, brain, and other organs.

 

 

Transmission:

Amoebiasis is usually transmitted by the fecal-oral route,[7] but it can also be transmitted indirectly through contact with dirty hands or objects as well as by anal-oral contact. Infection is spread through ingestion of the cyst form of the parasite, a semi-dormant and hardy structure found in feces. Any non-encysted amoebae, or trophozoites, die quickly after leaving the body but may also be present in stool: these are rarely the source of new infections.[7] Since amoebiasis is transmitted through contaminated food and water, it is often endemic in regions of the world with limited modern sanitation systems, including México, Central America, western South America, South Asia, and western and southern Africa.[18]

 

Amoebic dysentery is one form of traveler's diarrhea[19], although most traveler's diarrhea is bacterial or viral in origin.

 

 

Statistics on Amoebiasis (Amoebic Dysentery)

Amoebiases occurs worldwide, although much higher rates of incidence are found in the tropics and subtropics. About 5,000 to 10,000 cases are diagnosed each year in the US, leading to about 20 deaths annually.

 

 

Cause:

Amoebiasis is an infection caused by the amoeba Entamoeba histolytica. Likewise amoebiasis is sometimes incorrectly used to refer to infection with other amoebae, but strictly speaking it should be reserved for Entamoeba histolytica infection.[citation needed] Other amoebae infecting humans include:[13]

 

Parasites

1.  Dientamoeba fragilis, which causes Dientamoebiasis

2.  Entamoeba dispar

3.  Entamoeba hartmanni

4.  Entamoeba coli

5.  Entamoeba polecki

6.  Entamoeba bangladeshi

7.  Entamoeba moshkovskii

8.  Endolimax nana and

9.  Iodamoeba butschlii.

 

 

Risk Factors for Amoebiasis (Amoebic Dysentery)

Although anyone can have this disease, it is most common in people who live in developing countries that have poor sanitary conditions. In the United States, amoebiasis is most often found in immigrants from developing countries. It also is found in people who have traveled to developing countries and in people who live in institutions that have poor sanitary conditions. It also commonly affects active homosexual men.

 

 

Signs and symptoms

Most infected people, about 90%, are asymptomatic,[7] but this disease has the potential to become serious. It is estimated that about 40,000 to 100,000 people worldwide die annually due to amoebiasis.[8]

 

Infections can sometimes last for years if there is no treatment. Symptoms take from a few days to a few weeks to develop and manifest themselves, but usually it is about two to four weeks. Symptoms can range from mild diarrhea to dysentery with blood, coupled with intense abdominal pains. Extra-intestinal complications might also arise as a result of invasive infection which includes colitis, liver, lung, or brain abscesses.[7] The blood comes from bleeding lesions created by the amoebae invading the lining of the colon. In about 10% of invasive cases the amoebae enter the bloodstream and may travel to other organs in the body. Most commonly this means the liver,[9] as this is where blood from the intestine reaches first, but they can end up almost anywhere in the body.

 

Onset time is highly variable and the average asymptomatic infection persists for over a year. It is theorized that the absence of symptoms or their intensity may vary with such factors as strain of amoeba, immune response of the host, and perhaps associated bacteria and viruses.

 

 

 

 

How is Amoebiasis (Amoebic Dysentery) Diagnosed?

Stool examination is the commonest examination done for diagnosis. The finding of trophozoites are diagnostic. White blood cells and pus are also often present. Since trophozoites are killed rapidly by water or drying, at least three fresh stool specimens have to be examined for a positive diagnosis. Fresh stool or concentrated stool examination is positive in 75 to 95 percent of patients.

A blood test can also be performed, and is positive in more than 90 percent of patients with invasive amoebiasis.

Barium studies are contraindicated in acute amoebic colitis for fear of perforation.

An ultrasound, CT and MRI scans of the abdomen can be useful in diagnosing hepatic amoebiasis. Since abscesses resolve slowly or may even increase in size during treatment, clinical response is more important in the follow-up rather than repeated scans.

Acute intestinal amoebiasis should be differentiated from organisms causing traveller’s diarrhoea (due to Escherischia Coli) and also inflammatory bowel disease.

Amoebic liver abscess has to be differentiated from pyogenic abscess which are seen in older patients with underlying bowel disease or after surgery.

 

 

How is Amoebiasis (Amoebic Dysentery) Treated?

General therapy relieves symptoms, replaces blood, and corrects fluid and electrolyte losses. Antibiotics, such as Metronidazole are necessary, and are given for 5 days for amoebic dysentery and for 10-14 days if there is a liver abcess or extraintestinal spread. Large abcesses in the liver may require drainage, using an ultrasound scan to localise the abcess accurately and position the drainage needle.

 

 

 

 

 

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References:

1.    "Entamoebiasis - MeSH - NCBI". www.ncbi.nlm.nih.gov. Archived from the original on 2016-05-15. Retrieved 2015-07-21.

2.   ^ "Entamoebiasis". mesh.kib.ki.se. Archived from the original on 2015-07-22. Retrieved 2015-07-21.

3.   ^ Jump up to:^{a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag ah ai aj ak al am an} 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.

4. Kumar P, Clark M (eds). Clinical Medicine (4th edition). Edinburgh: WB Saunders Company; 1999. [Book]
5. Longmore M, Wilkinson I, Torok E. Oxford Handbook of Clinical Medicine (5th edition). Oxford: Oxford University Press; 2001. [Book]
6. Amebiasis [online]. Whitehouse Station, NJ: Merck Manual of Diagnosis and Therapy; 2004
7.  "Entamoeba histolytica". cdc.govPrevention. Center for Disease Control & Prevention. Retrieved 24 October 2017.
8. ^ American Water Works Association (June 2006). Waterborne Pathogens. American Water Works Association. ISBN 978-1-58321-403-9.