mod 3

• Amoebae are distributed worldwide, especially in developing countries of the tropics, and are more common in areas where sanitation is poor.
• The majority of cases of Amoebae are asymptomatic.
• Amoebae are found in the human colon.
• Amoebae occur in three forms: Trophozoite, Precyst, and Cyst.
• The Trophozoite is the vegetative form of the parasite and the only form present in tissues.
• The mature cyst of Sappinia diploidea is round and measures 15 – 30 μm.
• The characteristic feature of Sappinia diploidea is that both the trophozoite and cyst stages are binucleated.
• The Trophozoite is irregular in shape and varies in size from 12 to 60 μm; the average being 20 μm.
• Sappinia diploidea can be cultivated on a nonnutrient agar plate coated with bacteria.
• Mandrillaris does not feed on bacteria.
• The trophozoite of Sappinia diploidea is oval, measures 40 – 70 μm.
• Sappinia diploidea is a newly recognized pathogenic free living amoeba found in soil and water.
• Treatment for GAE caused by Balamuthia includes a combination of flucytosine, pentamidine, fluconazole, sulfadiazine and either azithromycin or clarithromycin.
• There are currently no known ways to prevent infection with Balamuthia.
• Only one case of amoebic encephalitis has been reported due to Sappinia diploidea.
• The Trophozoite's cytoplasm consists of ectoplasm and endoplasm.
• Ectoplasm is clear and transparent.
• Endoplasm is finely granular and contains nucleus, food vacuoles and phagocytosed erythrocytes.
• Pseudopodia are finger-like projections formed by movements of ectoplasm in one direction.
• The Trophozoite's nucleus is spherical and contains a central karyosome.
• The nuclear membrane of the Trophozoite is lined by a rim of evenly distributed chromatin.
• The Trophozoite reproduces by binary fission.
• The Trophozoite is killed by drying, heat and chemical sterilization.
• Before encystment, the Trophozoite extrudes its food vacuoles and rounds up to form a precystic stage, measuring 10 – 20 μm in size.
• The Trophozoite contains a large glycogen vacuole and chromatoid bars.
• The Trophozoite secretes a cyst wall to become a cyst.
• Amoebic antigen in serum is found only in patients with active infection and disappears after clinical cure, so its presence in serum indicates recent and active infection.
• Serum antibodies appear only in the later stages of intestinal amoebiasis.
• When these isoenzymes are subjected to electrophoresis, based on the electrophoretic pattern (zymodeme pattern) and mobility of the isoenzymes, E. histolytica can be speciated.
• E. histolytica can also be used to differentiate E. histolytica and E. dispar.
• Real time PCR can be used as an alternative to the conventional PCR.
• Microscopy of stool is not useful in the diagnosis of amoebiasis.
• E. histolytica possesses several isoenzymes like malic enzyme, hexokinase, isomerase, and phosphoglucomutase.
• Various tests for antibodies against E. histolytica include ELISA, Indirect fluorescent antibody (IFA) test, Indirect hemagglutination (IHA) test, IHA using crude antigens.
• Microscopy of liver pus can detect trophozoites (but never cyst) with less than 25% sensitivity.
• Nested multiplex polymerase chain reaction (PCR) is available targeting small subunit ribosomal ribonucleic acid (rRNA) genes that can differentiate E. histolytica, E. dispar and E. moshkovskii with a sensitivity of nearing 90% and specificity of 90 – 100 %.
• ELISA for amoebic antigen uses monoclonal antibody specific for lectin antigen and is usually positive in the early stage of the disease with a sensitivity of 65%.
• Other methods for antigen detection include CIEP, Coagglutination test, Slide agglutination test.
• Motile trophozoite containing a spherical nucleus with large karyosome is the clue for identification.
• Naegleria fowleri undergoes transformation to a pear shaped flagellate form when the scrapping of the non nutrient agar is transferred to sterile tubes containing distilled water, a process known as enflagellation test.