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sarcomastigoproa Intestinal E his. E Flagellates - hartmanni opportunistic/ Heinoflagellates Ecki I - non-pathogenic E hand- , F Mutschilii- Chapter 2. ciliophoraciliates Extra intestinal protozoan Infections E gingivalis-nonpathogenic coccidia spolson. Naegleria fowler Acanthamoeba upp. Intestinal Amebae Pilarita T. Rivera, Windell L. Rivera, Juan Antonio A. Solon S even species of amebae occur in humans. These include the pathogenic Entamoeba histolytica, and the commensals E. dispar, E. reaction (PCR) restriction fragment length polymorphism (RFLP), and typing with monoclonal antibodies, these three species are moshkovskii, E. hartmanni, E. coli, Endolimax now differentiated. E. hartmanni, formerly nana, and Iodamoeba butschlii. Entamoeba referred to as “small race” of E. histolytica, is polecki is an intestinal ameba of pigs and differentiated primarily on the basis of size. monkeys that has been occasionally detected Parasite Biology in humans, and is a probable cause of diarrhea. They are mainly differentiated on the basis of Entamoeba histolytica is a pseudopod- structure and size. Trophozoites divide by binary forming non-flagellated protozoan parasite. It fission. Most cyst-forming amebae go through is the most invasive of the Entamoeba parasites nuclear division, and then divide again after (which includes E. dispar, E. moshkovskii, E. excystation in a new host. hartmanni, E. polecki, E. coli, and E. gingivalis), and the only member of the family to cause colitis Entamoeba histolytica and liver abscess. The life cycle of E. histolytica Entamoeba histolytica is currently classified consists of two stages: an infective cyst (Plate within the subphylum Sarcodina, superclass 2.1) and an invasive trophozoite form. No host Rhizopoda, class Lobosea, order Amoebida, other than humans is implicated in the life cycle, family Entamoebidae, and genus Entamoeba. The members of this genus are characterized by having a vesicular nucleus, a centrally (or near central) located small karyosome, and varying numbers of chromatin granules adhering to the nuclear membrane. These nuclear and other morphologic differences distinguish the species of Entamoeba except E. histolytica, E. dispar, and E. moshkovskii (previously known as the Laredo strain). The three said species are morphologically identical and of the same size. It was only recently that this E. histolytica species complex was resolved. Plate 2.1. Entamoeba histolytica cyst (Courtesy Through isoenzyme analysis polymerase chain of the Department of Parasitology, UP-CPH) Two STAGES : ENTAMOEBA- cyst-chromatical bars 20 glycogen vacuoles most have : smooth a rounded ENDOLIMA-large Kartosome several achromatic grales walls more than 1 , nucher, ENYAMOEIA-large Karto some rich in chromatin lendosome) vacuole , large glorogen -well formed stool TROPHOzole-contain bacteria a food particles feeding stage , , stool : water contain RBC-indicate invasiveness motile- pseudopods - mostly : irregular in shape - due to pseudopod · uninuclear easily destroyed by gastric Chapter 2: protozoan Infections 21 - juices of the stomach - susceptible to the outside environment although natural infection of primates has been Infection with E. histolytica occurs when cysts reported. The quadrinucleate cyst is resistant to are ingested from fecally-contaminated material gastric acidity and desiccation, and can survive (Figure 2.1). Other modes of transmission in a moist environment for several weeks. include venereal transmission through fecal-oral · Figure 2.1. Life cycle of Entamoeba histolytica (Accessed from www.dpd.cdc.gov/dpdx) 22 MedICal parasItology In the phIlIppInes contact or direct colonic inoculation through contaminated enema equipment. Excystation occurs in the small or large bowel, where a cyst undergoes nuclear followed by cytoplasmic division to form eight trophozoites. The E. histolytica trophozoites are highly motile and possess pseudopodia (Plate 2.2). They vary in size from 12 to 60 µm in diameter (about 20 µm in average). Microscopic examination of fully- passed stool specimens reveals the characteristic progressive and directional movement of trophozoites, with pseudopodia as locomotory Plate 2.2. Entamoeba histolytica trophozoite organelles. The hyaline pseudopodium is (From World Health Organization. Bench Aids for formed when the clear, glasslike ectoplasm, the Diagnosis of Intestinal Parasites. or outer layer is extruded, and the granular Geneva: World Health Organization; 1994) endoplasm flows into it. Ingested red blood cells are observed as pale, greenish, refractile bodies in the cytoplasm of the ameba. Cysts are usually spherical, and the size may vary from 10 to 20 µm. They are characterized by a highly refractile hyaline cyst wall, one to four nuclei, and rod-shaped (or cigar-shaped) chromatoidal bars. Trophozoites have the ability to colonize and/or invade the large bowel, while cysts are never found within invaded tissues. E. histolytica trophozoites multiply by binary fission. They encyst producing uninucleate cysts, which then undergo two successive nuclear divisions Plate 2.3. Entamoeba histolytica quadrinucleate to form the characteristic quadrinucleate cysts cyst (From World Health Organization. Bench Aids (Plate 2.3). for the Diagnosis of Intestinal Parasites. Geneva: *E. histolytica is a eukaryotic organism but World Health Organization; 1994) has several unusual features, including the lack of organelles that morphologically resemble lack of glutathione metabolism, the use of mitochondria. Because nuclear-encoded pyrophosphate instead of ATP at several steps mitochondrial genes such as pyridine nucleotide in glycolysis, and the inability to synthesize transhydrogenase and hsp60 are present, E. purine nucleotides de novo. Glucose is actively histolytica, at one time may have contained transported into the cytoplasm, where the mitochondria. There is no rough endoplasmic end products of carbohydrate metabolism are reticulum or Golgi apparatus, although cell ethanol, carbon dioxide, and under aerobic surface and secreted proteins contain signal conditions, acetate. sequences, and tunicamycin inhibits protein * Pathogenesis and Clinical Manifestations glycosylation. Ribosomes form aggregated crystalline arrays in the cytoplasm of the The proposed mechanisms for virulence trophozoite. Some differences in biochemical are: production of enzymes or other cytotoxic pathways from higher eukaryotes include the substances, contact-dependent cell killing,  spontaneous indestionas of Chapter 2: protozoan Infections 23 ↑ and cytophagocytosis. In vitro, amebic killing study involving 206 patients with probable of target cultivated mammalian cells involve ALA as diagnosed by ultrasound, the two receptor-mediated adherence of ameba to most frequent manifestations were fever in target cells, amebic cytolysis of target cells, 77% and RUQ pain in 83%. Pain is either and amebic phagocytosis of killed or viable localized in or referred to the right shoulder. target cells. E. histolytica trophozoites adhere The liver is tender, especially in acute cases, to the colonic mucosa through a galactose- and hepatomegaly is present in 50% of cases. inhibitable adherence lectin (Gal lectin). Then, Chronic disease (>2 weeks duration) is found the amebae kill mucosal cells by activation of in older patients and it involves wasting with their caspase-3, leading to their apoptotic death significant weight loss rather than fever. Only engulfment. 30% of ALA cases have concurrent diarrhea. Recent studies have shown that susceptibility However, daily stool cultures revealed that 72% of humans to E. histolytica infection is associated harbored trophozoites even in asymptomatic with specific alleles of the HLA complex. infections. Mortality in uncomplicated ALA is Majority of cases present as asymptomatic less than 1%. infections with cysts being passed out in The onset of amebic colitis may be sudden the stools (cyst carrier state). The recent after an incubation period of 8 to 10 days, or differentiation of E. dispar and E. histolytica after a long period of asymptomatic cyst carrier by PCR has confirmed the high prevalence state. ALA may have all acute presentation of of non-pathogenic E. dispar compared to the less than 2 weeks duration or a chronic one of pathogenic E. histolytica. However, studies also more than 2 weeks duration. The recurrence revealed that most E. histolytica infections in rate was found to be 0.29% in a five-year study endemic communities are asymptomatic. of ALA in Mexico. Amebic colitis clinically presents as gradual The most serious complication of amebic onset of abdominal pain and diarrhea with or colitis is perforation and secondary bacterial without blood and mucus in the stools. Fever peritonitis. Colonic perforation occurs in 60% is not common and it occurs only in one third of fulminant colitis cases. of patients. Although some patients may only In ALA, the most serious complications are have intermittent diarrhea alternating with rupture into the pericardium with a mortality constipation, children may develop fulminant rate of 70%, rupture into the pleura with colitis with severe bloody diarrhea, fever, and mortality of 15 to 30%, and super infection. abdominal pain. Intraperitoneal rupture, which occurs in 2 to Ameboma occurs in less than 1% of 7.5% of cases, is the second most common intestinal infections. It clinically presents as complication. However, it is not as serious as a mass-like lesion with abdominal pain and colonic perforation because ALA is sterile. a history of dysentery. It can be mistaken for Secondary amebic meningoencephalitis carcinoma. Asymptomatic ameboma may also occurs in 1 to 2%, and it should be considered occur. in cases of amebiasis with abnormal mental Amebic liver abscess (ALA) is the most status. Renal involvement caused by extension common extra-intestinal form of amebiasis. of ALA or retroperitoneal colonic perforation is The cardinal manifestations of ALA are fever rare. Genital involvement is caused by fistulae and right upper quadrant (RUQ) pain. Several from ALA and colitis or primary infection studies have shown these two as the most through sexual transmission. frequent complaints, particularly in acute Natural or innate immunity to E. histolytica cases (