2nd Lecture - Parasitology PDF

2nd LECTURE  Introduction Scientific Nomenclature Each parasite has: Phylum , class, order, family, genus & species King Phillip Came Over For Good Spaghetti  Scientific Nomenclature …cont The scientific name of the parasite is binomial: Genus & species...

2nd LECTURE  Introduction Scientific Nomenclature Each parasite has: Phylum , class, order, family, genus & species King Phillip Came Over For Good Spaghetti  Scientific Nomenclature …cont The scientific name of the parasite is binomial: Genus & species The Genus starts with a Capital letter and species name starts with small letter Loading… The scientific name of the parasite should be written in Italic letter or Under lined.  Human Parasites Parasites infect human fall into 2 categories: 1- Unicellular Parasites (Protozoa). 2- Multicellular Parasites (Metazoa).  Kingdom: Protista Phylum: Protozoa (Unicellular Parasites) 1- Subphylum: Sarcomastigophora Superclass: Sarcodina – Entamoeba Superclass: mastigophore Loading… – Trypanosoma – Leishmania 2- Subphylum: Ciliophora – Balantidium 3- Subphylum: Apicomplexa (Sporozoa): – Toxoplasma – Plasmodium  Entamoeba histolytica Phylum: Protozoa Subphylum: Sarcomastigophora Superclass: Sarcodina Class: Rhizopoda Order: Amoebida Genus: Entamoeba  Entamoeba histolytica Disease: Amoebiasis, amoebic dysentery, amoebic colitis, amoebic liver abscess. Geographical distribution: Cosmopolitan especially in tropics and subtropics and wherever sanitary conditions are bad. Habitat: Large intestine, occasionally extra-intestinal (liver, lung, brain, …). Hosts: Definitive host: man. Reservoir host: monkey, dog and rat.  Morphology Three stages [Trophozoite - precyst - cyst] 1- Trophozoite: Trophozoite is the motile, feeding and pathogenic stage Size: (average 20 µ). It has clear ectoplasm and granular endoplasm with food vacuoles containing RBCs in the invasive forms. The pseudopodium is well developed with active, progressive motility. It reproduces asexually by binary fission in the wall of large intestine of man.  2- Precyst: Some of the daughter amoebae that are entered into the lumen of intestine and transform into precystic stage. Has blunt pseudopodium that does not help in locomotion, sluggish movement. Smaller than trophozoite but larger than the cyst. It is the nonmotile , nonfeeding and nonpathogenic stage. either uninucleate or binucleate. The cytoplasm does not contain RBC and food particles.  3- Cyst: It is found in the lumen of the large intestine It has four nuclei It is surrounded by a thin and highly resistant wall. It contains cigar- shaped chromatoid bodies and diffuse glycogen mass are present that represent storage food. It is the infective stage. Loading…  Life cycle Ingestion of mature cyst Excystation in the small intestine Migration to the wall of large intestine. Multiplication by binary fission: Metacyst with 4 nuclei then 8 nuclei. 8 separate metacystic trophozoites from one cyst. The trophozoites proceed downstream to colonize the lumen of the colon and multiply by binary fission. Encystation.. Infective stage: quadrinucleated mature cyst. Mode of infection: ingestion of cysts in contaminated food and drinks. Life cycle of E. histolytica Definitive host: Human Reservoir host: Monkey, dog & rat Infective stage: Quadrinucleated mature cyst Diagnostic stage: Cyst & trophozoite Mode of infection: Ingestion of mature cyst  Clinical aspect *Asymptomatic infection: The infected persons are usually healthy carriers who excrete millions of cysts / day without any clinical symptoms. Very dangerous as a source of infection and spread. *Symptomatic infection: 1- Intestinal Amoebiasis A- acute dysentery (diarrhea alternating with constipation, tenesmus with blood & mucus in stool). B- chronic non-dysenteric amoebiasis. 2- extra-intestinal amoebiasis: The trophozoites may disseminate via blood to other extra-intestinal sites e.g. in the liver, lung, brain … etc. Intestinal Amoebiasis Intestinal Amoebiasis …… cont.  Extraintestinal amboebiasis *Hepatic amoebiasis: Amoebic hepatitis: sudden rise of temperature & enlarged tender liver Amoebic liver abscess: Fever, pain in the right hypochondrium that usually refers to the right shoulder and enlarged liver. If not treated the abscess may rupture and trophozoites may go to pleural cavity, lung, peritoneal cavity, pericardium, gall bladder and skin. Aspiration of the abscess yields anchovy sauce (thick chocolate-coloured pus) with trophozoites. *Amoebic lung abscess  Extra-intestinal Amoebiasis Direct Extension Through blood Haematogenous spread Perianal amoebiasis  Diagnosis A- Clinical: clinical picture and endemicity. B- Laboratory: I- Intestinal amoebiasis: Direct: 1-Stool examination by: -Direct smear: Cyst or trophozoite can be detected in stool. Trophozoite appears more in diarrheic stool while cysts are present more in well-formed stool. - Concentration techniques as zinc sulfate-flotation may be needed when cysts are few. Diagnosis …. Cont 2- Stool culture. 3- Rectal scraping: to detect trophozoites. 4-Sigmoidoscopy or total colonoscopy for: Visualization of the lesions- Biopsy- Aspiration. Diagnosis …. Cont II- Extra-intestinal amoebiasis: X-rays. Ultrasonography. Computed tomography (CT) and magnetic resonance imaging (MRI). Immunological tests. Examination of aspirates for trophozoites by smear or culture. Leucocytic count: leucocytosis.  Prevention and Control Environmental sanitation Anti-vector measures Proper sewage disposal Safe water supply Not to use excreta as fertilizer or storage before use Health education Washing of green raw vegetables Washing hands before eating and after defecation Treatment of carriers, particularly food handlers  Differences between E. histolytica & E. coli E. Histolytica E. coli Pathogenic commensal non pathogenic Trophozoite 10-20µm , 20-30µm. Mature cyst 4- nucleated 8- nucleated Suggested Reading Chiodini, P.L.; Moody, A.H. and Manser, D.W. (2001): Atlas of Medical Helminthology and Protozoology. 4th ed. Churchill Livingstone, P. 48-53. http://www.dpd.cdc.gov/dpdx/HTML/Para_Health.htm http://www.dpd.cdc.gov/dpdx/HTML/Amebiasis.htm