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Protozoa; Amebiasis; Dysentery; Colonic mucosa; Amebic liver abscess; Pathophysiology

Introduction

E. kistolytica's life cycle is straightforward and consists of two stages: the trophozoite (the host-tissue invasive stage) and the cyst (the host infective stage). Food or water contaminated with feces containing the cyst form of the parasite is the most common way to get the disease, but venereal transmission can also happen through oral-feces contact. The cyst is about 9 to 25 pm in diameter and contains four nuclei. The cysts excyst to form a total of eight trophozoites through nuclear and cytoplasmic division under unspecified intestinal tract stimuli. The parasite's motile feeding form, the trophozoites, has only one nucleus and pseudopodia. Trophozoites are the cause of invasive colonic disease, which can spread to the liver and result in an amebic liver abscess in some cases. Due to their rapid external degeneration and destruction by gastric acidity, trophozoites do not contribute to disease transmission. No host other than people is embroiled in the existence cycle, albeit normal contamination of primates has been reported. Trophozoites duplicate by paired parting. After two consecutive nuclear divisions of uninucleate cysts, they encyst produce the typical quadrinucleate cysts. Notably, the only comprehensive study of the life cycle of E. histolytica that has been published is based on a monkey-cultivated strain35. The lack of culture conditions that allow for encystation and excystation in vitro has limited the number of histolytica [1].

Epidemology

Many epidemio1ogic: studies of E. histolytica infection were performed before distinction between infection by E. dispar. Because the two species are morphologically indistinguishable, studies based on stool surveys reflect infection by both species. Because seroconversion does not appear to occur with E. dispar infection, however, seropositivity in a population should reflect the prevalence of infection with E. histolytica over the past 5 to 10 years. Although amebiasis can be found anywhere, developing nations have the highest prevalence rates. 8.4% of the population in Mexico City was infected with E.histolytica, according to a serologic study. High paces of amebic disease (both E. histolytica and E. dispar) have been observed in parts of Central and South America, the sub-Saharan and tropical regions of Africa, the Indian subcontinent, and Indonesia. Amebic liver abscesses and other extra intestinal diseases are three to ten times more common in men than in women, but the prevalence of colonic disease is the same for both genders. Children, particularly infants; pregnant women; also, ladies in the post pregnancy period have an expanded gamble for extreme illness and demise. Malnutrition, malignancy, and corticosteroid treatment are additional risk factors for more severe disease [2].

Pathophysiology

Entamoeba histdyfica trophozoites' interactions with the intestine more profound ulceration stretching out to the submucosa, then a resulting parallel extension through the submucosa with relative saving of the overlying epithelium, leads to the exemplary cup formed ulcer of amebiasis. The cooperation of E.histolytica trophozoites with the digestive mucosa has been demonstrated in animal with colonic ex plant and with digestive cell lines. Colonic attack is started after the trophozoites infiltrate the mucous hindrance. The mucous boundary is a significant host defensive component and may make sense of the relative opposition of rodents and different creatures to trial colonic infection. Ultrastructural studies uncover that there is dulling of microvilli in locales where single adaptable cell are in closeness to the brush line. Trophozoites begin their journey of penetration by piercing the interglandular epithelium. Extrusion of damaged epithelial cells has been observed alongside the separation of adjacent epithelia1 cells, the penetration of trophozoites between epithelial cells, and reaching the lumen. It has been hypothesized that the release of substances from the lysed neutrophils contributes to the tissue damage in neutrophils that are in close proximity to the ameba. These neutrophils frequently displayed a variety of degenerative changes. By stimulating intestinal secretion, trophozoites can cause diarrhea in addition to destroying tissue. Use of amebic lysate to the serosa yet not the mucosal side of stripped colonic mucosal arrangements creates a quick expansion in the short out current. Biochemical and immunochemical examinations demonstrate that amebic lysates contain serotonin, neurotensin, and subposition P. Lysates additionally seem to invigorate gastrointestinal discharge by excitement of mucosal creation of prostaglandin. Hatching of E. histolytica trophozoites with captivated human digestive Caco-2 cell monolayers become on permeabilized channels prompts a quick expansion in epithelial porousness, which goes before morphologic disturbance of monolayer integrity. Apical injury with loss of brush line in areas of contact between the epithelial cells and one celled critter is seen on electron microscopy. Before direct trophozoite invasion of the epithelium, this early increase in permeability may facilitate the subsequent transport of amebic toxins or secretagogues across the epithelium [3].

Cytopathogenicity

The presence of amebic trophozoites and tissue lysis and necrosis are hallmarks of invasive amebic infection. Z8The release of proteases and other degradative enzymes and secretagogues, amebic phagocytosis and motility, and the adhesion of amebic trophozoites to host epithelial cells have all been linked to the organism's invasion and destruction of tissue. A surface galactose inhabitable adhesion with 170 kDa and 35 kDa subunits is one of the most important molecules in mediating amebic adhesion to mucin and the intestinal epithelium. Genes encoding both subunits have been cloned and 6y, 133, lY. The 170-kDa subunit has the galactose binding activity and is encoded by both E. dispur and E.histolytica strains of Kistolytica Fecal antigen detection assays that distinguish infection with E. histolytica are based on monoclonal antibodies that bind to epitopes on the 170- kDa subunit of E. kistolytica strains but not E. dispur. The release of no oxidative products from lysed neutrophils as a result of amebic mediated cytolysis of neutrophils may contribute to the tissue damage seen in invasive amebiasis. A pore forming activity has been identified and purified from E. histolytica trophozoites, which has homology with the toxin melittin, a membranolytic peptide from bee squences present on plasmid rDNA have been identified as possible hemolysins. A pore forming activity has been identified and purified from E. histolytica trophozoites, which has homology with the amebic phospholipase .This play a role in cytolysis, as inhibitors of phospholipase A reduce amebic mediated cytolysis. Amebic microfilaments may play a significant role in contact dependent cytolysis, as Cytochalasin D also inhibits this process [4, 5].

Clinical Manifestation

Intestinal abnormalities

The clinical sign of digestive amebias is territory from gentle diarrhea to exemplary looseness of the bowels with stomach agony, tenesmus, and horrendous stools. Most of the time, the presentation is subacute and lasts less than a month. Dysentery is a sign of invasive amebic infection, and even stools that aren't particularly bloody almost always have occult blood, which is in line with the pathophysiology of amebic invasion of the colonic mucosa. Rarely, patients may present with severe, bloody diarrhea, fever, and more severe colitis. Although up to 75% of these patients may have peritonitis as a result of leakage through the severely ill colon, these patients typically do not present with a rigid surgical abdomen. Mortality from fulminant colitis is high. It is muddled whether these patients benefit from careful investigation instead of moderate administration with antiamebic and antibacterial. The gamble for fostering this disorder is higher in youngsters, pregnant ladies, and patients on corticosteroids. Corticosteroid administration to patients with intestinal amebiasis is associated with toxic megacolon, a rare but frequently fatal complication. Chronic nondysenteric E. histolytica infection, in which symptoms of diarrhea, abdominal pain, and weight loss can last for years, is an unusual presentation of intestinal disease. Case reports of appendiceal involvement exist. Shigellae, Cumpylobucter, and other invasive bacteria are among the differential diagnoses for invasive intestinal amebiasis; due to Clostridium dijficile, pseudomembranous colitis; colitis with cytomegalovirus; colitis ischemica; also, incendiary gut illness. Before making a diagnosis of inflammatory bowel disease, and especially before beginning corticosteroid therapy, amebiasis should be excluded from all patients by examination of stools or amebic serology because of the similarities in symptoms between the two conditions [6, 7].

Liver abscess

An elevated alkaline phosphatase is the most common finding in liver function tests. Rare is hyperbilirubinemia. Occasionally, abscess bacterial super infections are linked to severe jaundice. However, the symptoms that initially appear may frequently be nonspecific and resemble other febrile illnesses. A cough and an abnormal chest x-ray may present in some patients and be at first misdiagnosed as having pneumonia. Physical examination reveals hepatomegaly and point tenderness of the liver in approximately half of patients with an amebic liver abscess. Only one third of patients experience concurrent diarrhea. Most patients have a solitary canker; ordinarily in the right curve different abscesses are noticed all the more usually in patients with an intense show. Uncomplicated liver abscess mortality is less than 1% with early diagnosis and treatment. The majority of complications are caused by the amebic liver abscess rupturing into the chest, the peritoneum, and the pericardium. A cough that is caused by the necrotic contents of the liver abscess is a sign of the development of a bronco pleural fistula. In most cases, the necrotic material lacks amebae. Because it allowed the abscess to drain, the formation of such a fistula was a good indication for a spontaneous cure prior to the availability of effective antiemetic therapy [8, 9].

Conclusion

Various investigations have proposed that an immunization for amebiasis might be doable. In animal models of experimental amebic liver abscess, recombinant versions of three amebic antigens, the 170 kDa galactose inhibitable adhesin,lZ0,IS2 a Serine-Rich E. histolytica Protein (SREHP),lsO,152 a 29-kDa antigen,Iz1, and a combination of the SREHP and 170 kDa molecules1s2, have demonstrated .Progress has been made in fostering an oral immunization. The expression of recombinant SREHP vaccine strains with low levels of virulence raises the possibility of a vaccine that also protects against amebiasis and typhoid fever. In mice, oral vaccination with a peptide repeat of a serine-rich E. histolytica surface antigen fused to the cholera toxin B subunit induced mucosal IgA and systemic IgA and IgG antiamebic antibodies. It is unknown whether the promise of these prototype vaccine candidates can be realized in humans, with the ultimate goal of reducing or eliminating invasive amebiasis [10].

1. de le Muiioz M, Calderon J, Rojkind M (1982) . J Exp Med 155: 42-51.

 , ,

2. de la Munoz M, Moreno MA, Perez-Garcia JN (1991)  .Molec Microb 5: 1707-1714.

 , ,

3. de Lourdes MuAoz M, Rojkind M, Calderon J  (1984)  Entamoeba histolytica: Collagenolytic activity and virulence. J Protozool 31: 468-470.

  , ,

4. Denis M, Chadee K (1989) Cytokine activation of murine macrophages for in vitro killing of Entamoeba histolytica trophozoites. Infect Immunol 57: 1750-1756.

 , ,

5. Diamond L S (1968) Techniques of axenic cultivation of Entamoeba histolytica Schaudinn, 1903 and E . histolyticn-like amebae. J Parasitol 54715.

 

6. Dobell C (1928) . Parasitology 20357.

, ,

7. Edman U, Meraz MA, Rausser S (1990) . J Exp Med 1722: 379-888.

, ,

8. Edman U, Meza I, Agabian N M (1987) . Proc Natl Acad Sci USA 84: 3024-3028.

, ,

9. Flores BM, Reed SL, Ravdin JI (1993) Serologic reactivity to purified recombinant and native 29-kilodalton peripheral membrane protein of pathogenic Entumoeba histolytica. J Clin Microbiol 31: 1403-1407.

, ,

10. Garfmkel LI, Giladi M, Huber M (1989) . Infect Immunol 57: 926-931.

, ,

11. Ghadirian E, Bout DT (1988) In vitro killing of Entamoebu histolytica trophozoites by interferon-gamma-activated mouse macrophages. Immunobiol 176: 341-353.

, ,

12. Gonzalez-Ruiz A, Haque R, Rehman T (1994. J Clin Microbiol. 32: 964-970 .

, ,