- The protozoan Entamoeba histolytica is responsible for intestinal amebiasis as well as extraintestinal symptoms.
- Despite the fact that 90% of E. histolytica infections are asymptomatic, about 50,000,000 people become symptomatic each year, and around 100,000 people each year pass away as a direct result of their illness.
- In this exercise, you will learn about the examination and treatment of amebiasis caused by Entamoeba histolytica, with an emphasis on the function of the interdisciplinary team.
- Intestinal amebiasis is caused by the protozoan Entamoeba histolytica, which can also appear in other parts of the body.
- In spite of the fact that 90% of E. histolytica infections are asymptomatic, almost 50,000,000 people develop symptoms and about 100,000 die every year as a direct result of this bacteria.
- In countries with weaker economic infrastructure, amebic diseases are more common.
- Amebic cysts of Entamoeba histolytica are ingested via fecal-oral contact, most commonly through tainted food or water.
What is Gastrointestinal Amebiasis?
- Microscopic, single-celled parasites called amoebas are responsible for the infection of the large intestine known as gastrointestinal amebiasis (Entamoeba histolytica).
- These parasites, which thrive in the human colon, are spread by human waste and can poison water supplies in areas with inadequate sanitation.
- Produced in regions where human waste is used as fertiliser is at risk of contamination by the parasite.
- Infected people who don’t regularly and properly wash their hands can spread the germs on their hands.
- The large intestine is where amoebas eventually settle after entering the body through the mouth.
- There, harmless parasites (Entamoeba dispar) thrive. Even though E. histolytica might be asymptomatically resident in the colon, it also poses a significant health risk if it invades other organs.
- Amoebic dysentery is an infection caused by these amoebas that can penetrate the gut and result in diarrhoea, abdominal pain, and even ulcers and bleeding.
- Occasionally, these amoebas can even make it into the bloodstream and establish infection in isolated areas of the brain or liver (abscesses).
- Amoebas infect over 10% of the world’s population, mostly those who reside in tropical regions such as Mexico, India, Central America, South America, Africa, and Asia.
- Amebiasis is most commonly seen among recent immigrants and tourists from countries where amoebas are common to developed nations.
- Secreted E. histolytica macrophage migration inhibitory factor (EhMIF) causes mucosal inflammation.
- Matrix metalloproteinases (MMPs) are upregulated in response to inflammation caused by E. histolytica. MMPs degrade the extracellular matrix (ECM) in the intestine, paving the way for cell migration.
- Infiltrating inflammatory cells generate oxygen free radicals (ROS) which are capable of destroying parasites. Collateral tissue damage during an inflammatory period is also caused by oxygen free radicals.
- E. histolytica invades the intestinal mucosa by evading and manipulating the human immune system.
- E. histolytica causes cell death upon contact.
- Elevated amounts of P. copri raises the risk of colitis
Characteristics of Entamoeba histolytica
- parasitic pseudopod-forming anaerobic protozoan.
- capable of moving about by means other than flying or swimming.
- are found in three distinct stages—the Trophozoite, the Precyst, and the Cyst.
- a single nucleus creates cysts with a diameter of 10–16 m in the juvenile stage; this increases to four nuclei in the mature stage.
- Cysts are able to endure in damp environments, such as dirt, water, and foods.
- binary fission split it in two.
- intolerant of being dried out, heated, or chemically sterilised.
- Both pseudopodia development and motility are stifled by the low temperatures.
- Trophozoites have a diameter of 10-50 m with a solitary nucleus.
Life Cycle of E. histolytica
- Both a cystic form and a trophozoite form are involved in the infectious life cycle of E. histolytica. The nuclei count in the cyst is four or less, and its diameter is 10-15 m.
- Cysts from fecally contaminated food or water are the most prevalent route of infection with Escherichia histolytica.
- Transmission via oral-anal sexual practises has also been observed. The trophozoites are excysted in the intestinal tract.
- The invasive trophozoite form, about 10-60 m in diameter, has a single nucleus with a central karyosome.
- The intestinal mucin layer is a possible site for cyst formation by trophozoites. The parasite cell surface Gal/GalNAc lectin appears to have a role in quorum sensing during cyst formation.
- Beta-adrenergic receptor 18 signalling and autophagy are two more pathways involved in cyst development (a method of degrading damaged or unnecessary proteins and organelles).
- There are a total of 672 genes that are unique to cysts and 767 genes that are unique to trophozoites.
Gene Structure and Organization
- Genomic organisation and promoter elements of E. histolytica appear to be unique from those of both metazoans and better-characterized protozoa.
- The genome of E. histolytica is projected to have 14 chromosomes and 10,000 genes, with a current estimate placing its size at 24 million base pairs.
- Roughly 20% of the DNA in a cell is ribosomal RNA, and a whopping 10% is made up of tRNA genes arranged in repeated linear arrays.
- Predictions indicate that 30% of genes have introns33 and that 6% of genes have two or more introns. Relatively recently, an expressed sequence tag library was used to study about 7 percent of the putative amebic genes.
- U2, U4, and U5 snRNAs were shown to have molecular evidence supporting their role in splicing, and 60% of introns were shown to have splicing evidence.
- Heterologous gene expression in Escherichia coli via DNA-mediated transfection has been achieved both transiently and persistently. The promoter of the E. histolytica gene producing the heavy subunit of the N-acetyl—Dgalactosamine-specific adhesin has been analysed by deletion and replacement (hgl5).
- Upstream of the transcription start site, a total of 200 bases were analysed, and within that space, four positive upstream regulatory elements and one negative upstream regulatory element were found.
- In two instances, the transcription factors that are responsible for the regulation of genes by these upstream regulatory elements have been isolated.
- There are two novel transcription factors; one has RNA-binding motifs and the other has EF-hand motifs.
- Notably, calcium regulates the ability of the EF-hand containing transcription factor to bind to its homologous DNA motif.
- There are a few core promoter elements that have been shown to regulate gene expression and control the site of transcription initiation. These elements include a TATA element 30 base pairs upstream of the transcription start site, the novel conserved sequence GAAC between the TATA and initiator elements, and the conserved sequence at the transcription start site (putative initiator).
Cell Biology and Biochemistry
- There are no organelles in E. histolytica that resemble the rough endoplasmic reticulum, the Golgi apparatus, or the mitochondria, despite the fact that this organism is a eukaryote.
- It is likely that mitochondria were once present in E. histolytica due to the existence of nuclear-encoded mitochondrial genes such as pyridine nucleotide transhydrogenase and heat shock protein 60 (hsp60).
- The leftover organelles of defunct mitochondria, called mitosomes, have also been discovered.
- Signal sequences are present in cell surface and secreted proteins despite the absence of the rough endoplasmic reticulum and Golgi apparatus, and tunicamycin blocks protein glycosylation.
- In the trophozoite’s cytoplasm, the ribosomes have crystallised into aggregated arrays. The E. histolytica genome remarkably contains over a hundred transmembrane kinases.
- These kinases belong to the family of Gal/GalNAc lectin-related proteins, which all share the lectin intermediate (igl) subunit’s CXXC and CXC extracellular patterns.
- To my knowledge, E. histolytica is the only protist that has both the phosphorylated and nonphosphorylated serine metabolic pathways.
- For E. histolytica, the cysteine biosynthesis route is also crucial. Amino acids may play a role in ATP creation in E. histolytica, even though the glycolytic route is the primary source of ATP in this organism.
Sources of contamination of Amebiasis
- Human faeces are the most common source of contamination in the food and water supply.
- It can also be spread by anal-oral contact with contaminated objects or hands.
- Cysts can develop a tolerance to the chlorine in drinking water, rendering it useless over a particular concentration.
- In underdeveloped countries like India, Africa, and some sections of Central and South America, poor socioeconomic conditions and sanitation are a primary cause of endemic sickness.
- Parasitic infections in the United States are most commonly brought in by immigrants and tourists from endemic regions.
- Asymptomatic carriers, particularly those working with food, are a major contributor to the epidemic’s persistence and spread.
- Food crops and aquatic animals irrigated with fecally tainted water are another potential source of exposure.
- It has also been noted that gays are a vulnerable population for sexually transmitted diseases.
- The parasite illness caused by Entamoeba histolytica ranks as the third biggest cause of death worldwide.
- In spite of the fact that 90% of E. histolytica infections are asymptomatic, up to 100,000 people each year still end up with symptoms.
- Colonization by E. histolytica or E. dispar predominates in Entamoeba infections. The amoebic colitis and extraintestinal amoebiasis caused by E. histolytica pathogen. It has been determined that E. dispar is not pathogenic and does not produce any clinical symptoms.
- Infection is a global problem, but it is most pervasive in nations with weak healthcare systems and low living standards.
- India, Africa, Mexico, and Central and South America all have a comparatively high infection rate. Among preschool-aged children, for instance, E. histolytica was shown to be the causative agent in 2.2% of cases of dysentery in a Bangladeshi research spanning three years.
- The seroprevalence of E. histolytica has been observed to reach 42% in rural parts of Mexico.
- Having poor hand hygiene, defecating in public places like rivers, and living in close quarters with animals are all major risk factors for infection owing to fecal-oral transmission.
- Amebiasis infections are uncommon in affluent countries like the United States, where they cause at least 5 deaths annually among immigrants and recent visitors who have been to an endemic region.
- Amoebic colitis is equally common in males and females of all ages. Risk of fecal-oral contamination through oral and anal sex has been cited as a reason why gay and bisexual men pose a greater threat of transmitting disease.
- Pregnancy, corticosteroid medication, cancer, malnutrition, and drinking are all related with an elevated risk for complex infection and mortality.
- At least three times as many men in their 30s and 40s as women in their 50s and 60s get amoebic liver abscess infections.
Pathophysiology of Amebiasis
- E. histolytica has two distinct life cycles, the inactive and non-invasive cyst form and the active and potentially dangerous trophozoite stage.
- Ingestion of the cyst form results in the formation of trophozoites, which are capable of invading and penetrating the intestinal mucosa and killing epithelial cells and inflammatory cells.
- The adhesion of colonic epithelial cells by trophozoites is facilitated by a particular galactose-N-acetylgalactosamine lectin, which contributes to the pathophysiology of infection.
- Colonic epithelial cells die off by cytolysis and apoptosis after being directly adhered to by trophozoites; this triggers the release of interleukin-1 and precursor interleukin-1.
- Cytokines and other inflammatory mediators, including as cyclooxygenase-2 (COX-2), interleukin-1 (IL-1), and IL-8, are produced after IL-1 stimulates nuclear factor-kappa B (NF-kB) in distant cells. An additional step that can be made easier by amoebic cysteine proteinases is the conversion of pro-IL-1 to active IL-1.
- Neutrophils and macrophages are drawn to the scene after being lured there by these cytokines and inflammatory mediators.
- Direct contact with trophozoites can be harmful to neutrophils, which in turn can damage colonic epithelial cells and trigger the production of additional mediators.
- Macrophages also secrete other mediators, such as TNF, which contribute to inflammation.
- Inflammation, thickening, ulceration, necrosis, and ultimately perforation are all part of the pathological spectrum associated with mucosal tissue.
- Cysteine proteinases produced by amoebae can cleave and inactivate anaphylatoxins C3a, C5a, IgA, and IgG, hence aiding in the trophozoite’s capacity to inhibit the host’s immunological response.
- Liver necrosis and abscess formation can be caused when trophozoites go to other organs.
Detection of Amebiasis
- E. histolytica-specific diagnostic assays are superior to microscopic identification of the parasite in stool, liver abscess pus, or colonic biopsies (see following discussion).
- Although E. histolytica is more likely to be the cause of erythrophagocytic amebae, E. dispar trophozoites have been discovered to include eaten red blood cells as well.
- Only between 8 and 44 percent of patients with amebic liver abscess had the parasite detected through repeated stool investigations.
- Despite best efforts, identifying the parasite in aspirated pus from liver abscesses has a 20% sensitivity rate even in the most skilled hands.
- To far, the only faecal antigen test that can reliably differentiate between E. histolytica, E. dispar, and E. moshkovskii is the TechLab E. histolytica II enzyme-linked immunosorbent assay.
- Numerous investigations in both E. histolytica endemic and nonendemic regions have demonstrated the sensitivity and specificity of a test based on the identification of the Gal/ GalNAc lectin in stool, while a single study has reported a discrepancy between PCR and antigen detection.
- Amebic liver abscess can also be diagnosed with the help of antigen detection. Before undergoing antiamebic treatment, 96% (22/23) of patients with amebic liver abscess had Gal/GalNAc lectin in their serum, according to a study. If the parasite was present in pus from a liver abscess, then the detection rate was between 41% and 74%.
Polymerase Chain Reaction
- Comparable sensitivity to that of stool antigen detection can be achieved with real-time PCR (qPCR).
- When it comes to detecting E. histolytica DNA in bodily fluids like stool and liver abscess pus, qPCR is a more sensitive assay than standard PCR.
- Differentiating E. histolytica isolates using PCR might be valuable for epidemiological studies and for elucidating the virulence characteristics of individual isolates.
- For the diagnosis of amebic liver abscess and amebic colitis, the IHA test for anti-amebic antibody has a sensitivity of 70% in the beginning of the illness and increases to greater than 95% after recovery.
- Current serologic assays suffer from the problem of being persistently positive for years after an episode of amebiasis has resolved.
- It follows that between 10% and 35% of people living in underdeveloped nations have anti-amebic antibodies, as measured by standard serologic tests.
- There may be a lack of specificity in serologic tests because most patients with invasive amebiasis in affluent countries are immigrants from developing countries.
- As an illustration, between 80% and 96% of patients in five recent series of amebic liver abscess cases in the United States were foreign-born.
- Therefore, one should not make the diagnosis of amebiasis in a native of a country where amebiasis is endemic on the basis of a serologic test alone, as current serologic assays may be inadequate for the separation of acute from previous amebiasis, even in industrialised nations.
- Since the disease may only be present in the cecum or ascending colon, colonoscopy is the preferred diagnostic method.
- Preparing the patient with cathartics or enemas is not recommended since they may obscure the parasite’s true identity.
- Examining and testing for E. histolytica antigen in wet preparations of material aspirated or scraped from the base of ulcers is recommended.
- Granular, friable, and diffusely ulcerated mucosa may characterise amebic colitis, a condition that can superficially resemble inflammatory bowel disease.
- Pseudomembranes and large geographic ulcers may also be present. Histopathologic analysis of colonic biopsy specimens from individuals with amebic colitis has a detection rate of 0% to 100% of trophozoites, depending on the study.
- Take biopsy samples from the ulcers’ borders. Staining parasites with periodic acid-Schiff makes them more visible in biopsies because of their distinctive magenta hue.
- It has been established that E. histolytica can infiltrate carcinomas, leading to misdiagnosis.
- In order to diagnose amebic abscesses in the liver, any of the three most used diagnostic modalities—ultrasound, CT, or MRI—are equally effective.
- An amebic abscess cannot be distinguished from a pyogenic abscess using any of the three methods.
- Six months after treatment, only one-third to two-thirds of amebic liver abscesses were resolved on repeat ultrasonography.
Clinical manifestation of Amebiasis
- Nearly 80% of E. histolytica infections are asymptomatic, but they can linger in the colon for a long time and spread disease.
- Symptoms of intestinal amoebiasis, which include diarrhoea, slight fever, abdominal pain, and cramping, typically manifest between two and four weeks after infection.
- Obstruction of the gut due to trophozoite masses is an uncommon complication of chronic intestinal amoebiasis, which typically manifests as nonspecific gastrointestinal distress, bloody or mucousy diarrhoea, and ulceration of the colonic mucosal surfaces.
- Depending on the host and the parasite’s developmental stage, symptoms might range widely.
- Diarrhea, abdominal pain, loss of appetite, fever, and chills are all symptoms of amoebic dysentery, which is brought on by an invasive trophozoite infection.
- When trophozoites breach the intestinal wall and spread through the circulation, it causes amoebic dysentery, which manifests as amebic abscesses in extraintestinal tissue.
- Abcesses in the liver and brain, as well as peritonitis, pleuropulmonary abscesses, and cutaneous and vaginal amoebic lesions, are the most common extraintestinal organ diseases to be contaminated.
- When trophozoites enter the bloodstream from the intestinal mucosa, hepatic amoebiasis is a common result.
The symptoms may last for weeks and include fever, weakness, stomach swelling, nausea, jaundice, cough, and pain in the upper right quadrant.
- All E. histolytica infections need to be treated due to the risk of transmission and the risk of acquiring extraintestinal symptoms.
- Those who suffer from intestinal amebiasis or amebic liver abscess should start with metronidazole and then switch to a luminal drug. Adults typically take 500 mg to 750 mg of metronidazole three times day orally for 7-10 days.
- Metronidazole is safe for usage in children at daily dosing of 35 mg/kg to 50 mg/kg split into three equal doses.
- Paromomycin, diiodohydroxyquin, and diloxanide furoate are all examples of luminescent agents. Paromomycin is administered at a dose of 25 mg/kg to 30 mg/kg daily, split into three doses, for 7 days; diiodohydroxyquin is administered at a dose of 650 mg orally for 20 days; and diloxanide furoate is administered at a dose of 500 mg orally thrice daily for 10 days.
- There are several alternatives to metronidazole, including tinidazole, ornidazole, and nitazoaxanide.
- Treatment of patients with fulminant amoebic colitis or peritonitis symptoms necessitates the use of broad-spectrum antibiotics. Bowel perforation or toxic megacolon may necessitate surgical intervention.
- It has been established that drainage, when added to medical treatment, is of no help in cases of amebic liver abscess that are otherwise simple.
- Clinical failure to respond to antimicrobial therapy may necessitate aspiration or catheter drainage.
- Antimicrobial therapy, such as metronidazole with a luminal drug, is recommended for the treatment of pleuropulmonary infections after aspiration of amebic pleural effusion.
Prevention and control measures of Amebiasis
- Standard methods for treating water for human consumption, such as sedimentation, coagulation, filtration, and disinfection, should be put into place.
- Properly heating food to 68 degrees Celsius for 5 minutes is enough to kill cysts, therefore do so before eating.
- One major source of disease spread is the practise of using human waste as an agricultural fertiliser. Thus, it is important to properly wash and cook produce and to use disinfectants.
- Avoiding raw or untreated water is a must for anyone visiting an endemic area.
- It is necessary to use iodine at 200 ppm or heat food and water to over 68 degrees Celsius to kill cysts, as cysts are resistant to chlorine.
- People with amoebic infections should not be allowed to prepare or handle food due to the fact that asymptomatic carriers shed millions of cysts per day for years.
E. histolytica infections
While the vast majority of people who become infected with E. histolytica show no symptoms at all, as many as 10% of those people may eventually become ill. Although E. histolytica most often affects the intestines, it can also harm the liver, lungs, heart, and brain.
- Gastrointestinal: Symptoms of gastrointestinal issues normally develop slowly over a period of one to three weeks. Common symptoms include diarrhoea, bloody stools, weight loss, and stomach pain.
- Liver: Amoebic liver abscess is the most prevalent extraintestinal consequence. Months to years after visiting an endemic region, symptoms may begin to appear. High body temperature and pain in the upper right quadrant are symptoms. Hepatomegaly and soreness of the liver may be present on physical examination. Less than 10 percent of patients exhibit jaundice. Leukocytosis without eosinophilia, high alkaline phosphatase levels, transaminitis, and an increased erythrocyte sedimentation rate are typical laboratory results.
- Respiratory tract: Atelectasis and transudative pleural effusions are the result of pleuropulmonary involvement, an uncommon consequence of the respiratory system. Rupture of an amoebic liver abscess into the pleural space can result in empyema or a hepato-bronchial fistula, both of which can lead to high body temperature, coughing, and difficulty breathing.
- Cardiac infection: This even rarer complication than pleuropulmonary disease occurs when an abscess in the liver ruptures into the pericardium, causing the patient to experience the symptoms of pericarditis or cardiac tamponade.
- Brain infection: Amoebic brain abscesses are an uncommon form of brain infection characterised by the quick onset of severe symptoms, including headache, vomiting, and changes in mental status, and ultimately, death.
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