HELMINTHS OF GEH SYSTEMAscaris lumbricoides Trichuris trichiura Necator americanus Ancylostoma duodenale Strongyloides stercoralis Oxyuris vermicularis Trichinella spiralis Taenia saginata Taenia solium Hymenolepis nanaHymenopelis diminuta Dipylidium caninum Diphyllobothrium latum Echinostoma ilocanum PROTOZOA OF GEH SYSTEMEntamoeba histolytica Pathogenic Entamoeba hartmanni Entamoeba coliEndolimax nanaIodamoeba butschlii Dientamoeba fragilis Giardia lamblia PathogenicChilomastix mesnili Enteromonas hominis Retortamonas intestinalis Trichomonas hominis Balantidium coli PathogenicIsospora belli PathogenicBlastocystis hominis PathogenicPARASITIC INFECTIONS IN GEH SYSTEM

Fasciola hepaticaClonorchis sinensis Opisthorchis felineus Opisthorchis viverrini Dicrocoelium dendriticum

Entamoeba histolyticaHost : HumanDisease : Amebiasis Geographic distribution : CosmopolitanMorphology : 1. Trophozoite 2. Precyst 3. Cyst

Trophozoite

Shape : indefiniteSize : 10 - 60 mThe clear, refractile, hyaline ectoplasm,sharply separated from the endoplasm, Ectoplasm in outer part, endoplasm in inner part The thin, finger-like ectoplasmicpseudopodia are extended rapidly, so its motility is quick. The fine granular endoplasm contains rbc It has single nucleus not visible in unstained preparation . With stain, the nucleus has a small, compact karyosome located centrally nucleus, clearly nuclear membrane, and uniform fine granules of chromatin .

The trophozoites are pathogenic, live in lumen and wall of the colon, liver, lung, brain, and other tissues, multiply by binary fission, and can destruct the tissuePrecyst

Shape : indefiniteSize : 10 - 30 m The ectoplasm unclear, only visible when pseudopodia are formed slowly, so its motility is slow. The fine granular endoplasm contains bacteria and food particles without rbc .It has one nucleus; the structure of nucleus is similar to the nucleus in trophozoite .

The precyst lives commensal in lumen of the colon, multiplies by binary fission, is essential stage because it can change to trophozoite or cyst.Cyst

Shape : round or ovalSize : 10 - 20 m Wall : thinIt has 1, 2 or 4 nucleiIn 1-, and 2-nucleate cysts (immature cysts) contain glycogen vacuole and sausage-shaped chromatoid bodies with blunty rounded ends In 4-nucleate cysts (mature cysts) glycogen vacuole and chromatoid bodies are usually not found.

The cysts are formed in lumen of the colon, non-pathogenic, but infective stages

LIFE CYCLE The life cycle of E. histolytica is comparatively simple. Mode of infection is ingestion of cysts. The cysts pass out in the feces, and immediately infective. On ingestion the mature cysts, which are resistant to the acidic gastric juices, pass to the lower part of small intestine. Here, under influence of neutral or alkaline digestive juices and the activity of the ameba, the cyst wall desintegrated (excystation), liberating a four-nucleated metacyst that ultimately divides into eight small metacystic trophozoites, then these metecystic trophozoites move downward to the large intestine. Intestinal stasis often enables the amebas to establish a site of infection in the cecal region of the colon, but they may be swept along to the sigmoidorectal region or even out of body. Once the ameba begin feed and grow, they develop into normal trophozoites. The changes of establishing a foothold in the intestinal epithelium are reduced when the organisms are few, the volume of food large, or there is intestinal hypermotility. In the lumen of colon, under condition not yet known, the trophozoite discharges food and condenses into a spherical mass, this is the precyst. Then a relatively thin, tough wall is secreted, so that the unripe cyst (immature cyst) is formed (encystation). Ripening (maturing) of the cyst consists of two consecutive mitotic divisions of the nucleus to produce four nuclei. Trophozoites do not become encysted after evacuation from the bowel. In semiformed stools, it is sometimes possible to find precysts, uninucleate, binucleate, and occasionally 4-nucleate cysts. In well-formed stools, it is customary to find the 4-nucleate cysts (mature cyst). Fluid or semifluid stools usually contain trophozoites rather than cysts.