Amoebic dysentery is a disease characterized by the experience of a bloody diarrhea. It is caused by the protozoan parasite Entamoeba histolytica, which is found in stool. The parasite exists either as a cyst or as an invasive trophozoite. The cyst is infective and comprises of a group of amoeba which is protected by a gastric acid resistant shell. Consequently, the cyst can survive in the moist environment over a period of several weeks during which it is inactive. The cyst is also resistant to desiccation by stomach enzymes. This implies that the cyst can survive both within and without the gastro intestinal system as long as the environment is moist. On the other hand, the trophozoite is labile and cannot survive for long outside the gastro intestinal system. They therefore invade the intestinal epithelium and can consequently result in infection and through destruction of the host tissues (Dhawan and others 1).
Amoebic dysentery is also referred to as amoebiasis and can advance to amoeboma, fulminant colitis, periceacal abscess or gastrointestinal perforation if not effectively managed. This means that management of the disease should focus on prevention of initiation as well as prevention of advancement to the more fatal conditions that succeed the infection. The disease has been reported to be the second most prevalent disease after malaria, with the natural hosts being humans and primates. In most cases, the disease is experienced in areas where there is poor sanitation (Petri and Singh 1118). In describing the disease, the present report focuses on people with symptomatic amoebiasis without concern for those with the advanced infections such as colitis and gastrointestinal perforations as well as those with asymptomatic amoebiasis infections. The disease is most prevalent in the tropical regions.
Who is affected?
According to Dans and Martinez (3) amoebic dysentery affects about 1 – 40% of persons living in the tropical regions including Central and South America, Asia and Africa and approximately 0.2 t0 10.8% of people in the developed countries e.g. the United States of America. The information provided according to Dans and Martinez is highly volatile since the infection can stay for long periods of time in the asymptomatic state and may not be reported, particularly by the elderly members of the society. In addition to this, it is also difficult to distinguish between the Entamoeba histolytica species and the Entamoeba dispar species which is morphologically identical to the parasite. In developing countries, it is reported that more than 38 percent of the population that reports experiencing diarrhea are usually infected with the Entamoeba histolytica parasite. To accurately diagnose this disease and to distinguish it from infections with Entamoeba dispar, advanced clinical testing techniques such as Enzyme Linked Immunosorbent Assay (ELISA) are recommended.
Amoebic Dysentery is most common in tropical climate especially in areas with low levels of sanitation and poor hygiene. Low hygiene levels that are often associated with the tropical climate, overcrowding, food contamination with feces, ineffective/ unhygienic fecal disposition, and water contamination all contribute to the high rates of infection that are often experienced in the developing countries. In the developing countries, the risk factors associated with Amoebic dysentery include engagement in anal and oral sex, communal living, poor immune systems, and travel and/ or migration from endemic regions. From the study carried out by Dans and Martinez, it is reported that even though it has not been scientifically proven, there is a probability that some animals such as monkeys, pigs and dogs act as hosts for the Entamoeba histolytica protozoa, and can transmit it to humans.
According to a report by Hedley and Panesar (4), transmission of the Entamoeba parasite occurs in most cases through oral and fecal means but can also occur when there is contact with infected objects as well as hands. Ingestion of the cyst which occurs in a semi-dominant phase in feces results in infection with the protozoa. This can occur through the ingestion of fecal contaminated water and food which transmits the cyst into the body. Besides this, indirect contamination of hands by contaminated surfaces also results in the transmission of the cyst. This explains why outbreaks usually occur following contamination of water supply sources. It is important to note that the cyst is resistant to chlorine hence treatment of water does not impact its existence in the water.
Another mode in which transmission occurs is through contact with fecal matter during oral – anal sex which often occurs in gay men. The prevalence rates observed in developed countries indicate that the disease is also endemic among men who have sex with other men. Oral – anal contact with either an asymptomatically ill person or a chronically ill person causes infection with the disease. After infection, the cyst may stay in the human body for periods of 2 – 4 weeks prior to manifestation, but the incubation can go for up to years before manifestation. During the incubation period, cyst excretion can continue for years as long as the cysts are still in the body. The immunity of the body plays an important role in susceptibility to Amoebiasis. All non-immune people are susceptible to the disease as well as those who are already infected although re-infection is rare. Moreover, those who are already infected with Entamoeba dispar may also be re-infected with Entamoeba histolytica but the symptoms do not show in this case (Dans and Martinez 1).
The key primary concern for Aomebiasis is the risk of dehydration and transmission to others. Infection with Entamoeba histolytica is characterized by severe diarrhea, which is sometimes bloody. The possibility and rate of complications also raises concerns about health. According to Dans and Martinez, the rate of diarrhea also determines whether the infection is escalating or not (3). The dysentery itself is characterized by fever, chills, abdominal discomfort and mucous or bloody diarrhea. These interchange with periods of constipation among the patients of dysentery. Following infection, there is the risk of escalation through complications such as amoeboma, chronic cyst carriage and the possibility of extending to the pleural cavity; all these raise concerns to varying levels. Moreover, Hedley and Panesar assert that escalation to amoeboma may be mistaken for pyogenic abscess or colon cancer which further complicates the health concerns associated with the disease (4).
Besides the outlined complications, other more common health concerns regarding amoebiasis include the potential for escalation to the formation of liver abscess, which can occur whether there is infection with the entamoeba protozoa or not. This can be due to the existence of the trophozoites which have the capacity to breach the mucous of the colon and subsequently enter the circulation infecting the liver. Because of these health concerns, amoebiasis is feared for clinical outcomes such as reduced quality of life, increase in the duration of hospital stay, failure of treatment due to the persistence of the parasites or as a result of the persistence of symptoms and adverse treatment effects. In each of the circumstances, addressing the challenges of amoebiasis proves to be more demanding in chronic infections. Relief from the symptoms of amoebic dysentery is therefore an important health step to achieve after infection.
Infections with the Entamoeba histolytica parasite can lead to several health concerns as already highlighted. Consequently it results in high levels of morbidity and is the second most prevalent cause of protozoa initiated mortality after malaria. From the work done by Dhawan and others (11), the severity associated with amoebiasis increases in children particularly neonates, pregnant as well as postpartum mothers, individuals who are under corticosteroids, patients with malignancies, and individuals who are malnourished. Amoebic dysentery can result in chronic carriage as well as chronic passage of the diseases. Moreover, it has a mortality rate of 55- 80%.
Despite the identified escalation conditions associated with amoebic dysentery, it is reported that sever ulceration of the colon and other intestinal issues occurs only in 16% of the cases. The amoebas most commonly remain in the host gastro intestinal tracts and only masses of amoeba which lead to intestinal obstruction are only formed in rare cases. Besides the common exacerbation processes which involve the formation of abscesses in the liver, other local infections may occur in the gastrointestinal tract of the host such as toxic mega colon and gastro-intestinal bleeding. In more than 90% of the cases, the infection is asymptomatic. The negative health impacts associated with the disease makes it necessary to employ preventive tactics due tothe potential for fatality. This occurs especially where intraperitoneal rupture occurs suddenly in a patient with a liver abscess.
Dhawan and other describe the life cycle of the protozoan parasite effectively (8). Entamoeba histolytica is a non-flagellated protozoan parasite which forms pseudopods. It causes proteolysis and lysis of tissues and can also induce the host cells to carry out apoptosis. The first stage in infection with Entamoeba histolytica involves the ingestion of the cyst from fecal matter in the environment. This can occur either through ingestion of contaminated food or drinks. This is followed by ex-cystation in the colon or terminal ileum to form the labile and highly motile trophozoites which can then colonize the colonic mucous. The trophozoites spread throughout the colon, colonizing the mucous and may invade the mucous barrier in the intestine and enter the blood stream. Entrance of the trophozoites into the blood stream can cause more adverse effects, such as the formation of liver abscess. Penetration of the mucous barrier in the colon results in tissue destruction by the trophozoites which eventually leads to the secretion of a bloody diarrhea and colitis, which resembles the inflammatory bowel disease. The ability of the trophozoites to spread through the blood stream makes it possible to result in a broad spectrum of diseases. Alternatively, the trophozoites may encyst again and be excreted in the feces. Once the cysts are excreted, they return to the environment to complete the life cycle of the protozoan parasite. The life cycle of the protozoa is shown in the figure 1 below (Dhawan and others 6).
The treatment of Amoebic dysentery depends on whether the infection is invasive or non-invasive. Invasive infection can also be described as symptomatic and is effectively managed through the administration of nitro-imidazole. The nitro-imidazole used for mainstay therapy in curbing invasive amoebic dysentery comprise of a high dosage of metronidazole and is used to treat amoebic dysentery, especially when it goes beyond the gastro-intestinal system. When nitro-imidazole having a shorter half-lifeis used, the patient takes shorter time for the symptoms to disappear and the drugs are also better tolerated by the body (Hedley and Panesar 4).
From the report by Hedley and Panesar (5), Tinidazole, which has a shorter half-life is more effective in comparison to metrodizole and also has fewer side effects compared to metronidazole. However, the outcome in terms of parasitological failure shows that both tinidazole and metronidazole are effective to varying degrees. Due to the high rate of parasitical resistance (40 – 60%) in patients treated with metronidazole, this treatment should be followed by the administration of a luminal agent such as iodoquinol and paromomycin. The treatment effectiveness when paromomycin is used is however higher than when iodoquinol is used. On the other hand, paromomycin should not be used together with metronidazole due to the potential for adverse effects. Another key disadvantage of using paromomycin is that it results in diarrhea as a side effect which makes it difficult to monitor the effectiveness of the administered treatment (Hedley and Panesar 6). At times, it becomes necessary to administer broad range antibiotics in addition to the medication given to enhance the treatment of contamination by intestinal bacteria. In addition to this, aspiration may also be needed where there are liver abscesses and should be considered where the patients register low response rates to antibiotics. For gastro-intestinal bleeding and/ or toxic mega colon cases, surgical procedures may be necessary although it is reported that such procedures have low post-operative success rates.
When the infection is non-invasive, the treatment involves administration of a luminal agent to reduce the potential for fecal shedding of Entamoeba histolytica cysts as well as infection with the invasive disease (Hedley and Panesar 6).
In addressing the health concerns associated with amoebic dysentery, the communicable disease control unit (par. 11) highlights the need for adopting various preventive measures for the disease. The key issues in preventing infection with Entamoeba histolytica are identified as educating the public about the importance of personal hygiene; creating public awareness about the essence of hand hygiene post defecation and prior to food preparation and/ or consumption; the need for travelers to avoid consuming uncooked fruits and vegetables and drinking water that is potentially contaminated; educating the public on the possibility of sexual transmission; water purification through boiling prior to consumption and monitoring food preparation practices in local food outlets. All these suggested measures focus on improving sanitation and hygiene since the disease infection is linked to poor sanitation levels and low levels of personal hygiene.
In handling patients, clinicians and other health care givers should be made aware of the possibility of infection with the Entamoeba protozoa in cases reported involving gastro intestinal issues. As such, measures are needed to distinguish between conventional gastro intestinal concerns from the concerns that arise due to infection with the disease. Moreover, pharmacists and other care givers should also be trained on effective antimicrobial stewardship to help them take better care of their patients through provision of protective information and requirements (Hedley and Panesar 5). Those who provide travel advisories are also tasked on the need to stress the importance of hygiene and avoidance of potentially contaminated food and drinks. From this view point, it can be concluded that the prevention of Entamoeba histolytica is dependent on proper hygiene, both at a personal level and at the communal level.
Although the evolutionary process in Entamoeba histolytica is only mildly understood, it is clear that the protozoa has effectively adapted to the disease causing mechanism through the ability to encyst, the existence of ameba pores, possession of trans membrane kinases which are putative and availability of epithelial cells which produce inflammatory mediators of various types (Dhawan and others 8). The cysts formed are enclosed in resistant shells that cannot be desiccated by gastro-intestinal chemicals which give them the ability to survive for extended periods of time in warm and moist environments regardless of the chemical conditions of the environment. The ameba pores on the other hand can induce apoptosis and also form pores in bilayers of lipids. To further enhance the parasitic capabilities of the protozoa, the Trans membrane kinases play an essential role as virulence factors and also result in phagocytosis, while the epithelial cells produce inflammatory mediators which attract macrophages and neutrophils. The combined participation of all these different characteristics makes the parasite adapted to its pathogenic role as well as to its environment (Dhawan and others 8).
From the research carried out on Amoebic Dysentery, one of the facts that have been found to be fascinating is the probability of confusion between Entamoeba dispar and entamoeba Histolytica. While this could be expected since the two microorganisms belong to the same genus, the degree of similarity which makes it difficult to distinguish between the two even through microscopic means was not expected. It is fascinating to realize that two microorganisms within the same genus and of different species could require advanced analytical techniques to distinguish. Moreover, this poses a challenge in that there is the question of how many people die due to Entamoeba h. infection in the belief that they are infected with Entamoeba dispar.
Another piece of information that appears fascinating is the finding that the protozoan cyst is resistant to desiccation by stomach acids as well as by the chlorine used in water treatment. This brings out the idea that most of the people in the developing countries where the disease is most prevalent may not be aware of this fact. With advancement in water treatment techniques, the population may be consuming contaminated water without awareness as well as with the presumption that water treatment is sufficient for the elimination of every contaminant.
A final fascination was brought about with the contradictions in the treatment processes. While metronidazole is the primary therapy for invasive infections, the combination of metronidazole with paromomycin which is also an effective complementary drug is not recommended. How is it expected that the treatment will accomplish the most desirable intervention outcome if the most suitable drugs cannot be combined. This still poses a challenge to theconscience.
Pictures and Diagrams
Figure 1: Life Cycle of Entamoeba histolytica (Dhawan and others 6)
Figure 2: Entamoeba histolytica trophozoite (Dhawan and others 7)
Figure 3: Entamoeba histolytica Cyst (Dhawan and others 6)
Communicable Disease Prevention Unit. Amoebiasis. [Web] Department of Health and Human Services, Victoria 2015. Retrieved 14 June 2016.
Dans, Leonila and Elizabeth Martinez. ‘Amoebic Dysentery.’ Journal of Clinical Evidence, 2007.
Dhawan, Vinod, Kerry Cleveland and Robert Cantey. ‘Amoebiasis: background, pathophysiology, etiology.’ Drugs and Diseases, 2016.
Hedley, Lucy and Preet Panesar. ‘Amoebic Dysentery in an Elderly Patient.’ The Pharmaceutical Journal, 2014.
Petri, William and Upinder Singh. ‘Diagnosis and Management of Amoebiasis.’ Clinical Infectious Diseases 29, 5(1999): 1117- 1125.