Medical Parasitology PDF

By Dr. Safa Mujahed Abdulateef  Medical Parasitology is the study of parasites and as such that does not include bacterial, fungal or viral infections. Human parasites are classified as : 1. intestinal parasites. blood borne parasites.  The association between two organis...

By Dr. Safa Mujahed Abdulateef  Medical Parasitology is the study of parasites and as such that does not include bacterial, fungal or viral infections. Human parasites are classified as : 1. intestinal parasites. blood borne parasites.  The association between two organisms may be one of the following: Mutualism: mutual benefit is derived from the association. 1. Symbiosis: mutual benefit, but the two organisms cannot live independently. 2. Commensalism: one partner benefits (commensal) while the other (host) is unaffected. It may be called a non-pathogenic parasite.  3. Parasitism: one organism (parasite) lives at the expense of the other (host). The latter usually suffers from the association with pathogenic parasite). Classification of Parasites  Phylum Protozoa General Features 1. Single-celled microorganisms belonging to the animal kingdom are classified as Protozoa (Greek Protos—first; zoon—animal). 2. Most of the protozoa are completely nonpathogenic but few may cause major diseases such as malaria, leishmaniasis, and sleeping sickness. Other protozoa act as opportunistic pathogens.  Phylum Protozoa General Features 3. Protozoa exhibit a wide range of size, shape, and structure. 4. Life cycle stages: a. Trophozoite: The active feeding and growing stage of the protozoa are called the trophozoite (G.trophos-nourishment). b. Cystic stage: resting or resistant stage which enables prolonged survival under unfavorable conditions  Phylum Protozoa General Features 5. Reproduction : a. Asexual: The most common method is binary fission by the mitotic division of the nucleus. b. Sexual stages are seen in ciliates and Sporozoa SubPhylum Sarcomastigophora Sub-ph :Sarcodina (Amoeba)  A- E. histolytica forms: A. Trophozoite: is growing stage of the parasite. It is the only form present in tissues. It is large and actively motile in freshly-passed dysenteric stool, erythrocytes seen in the endoplasm. Troph nucleus characterized by central karyosome B. precystic stage: Trophozoites undergo encystment in the intestinal lumen, does not occur in the tissues nor in feces.  Cystic Stage: Early cyst: Contains a single nucleus and two other structures a mass of glycogen, and 1- 4 chromatoid bodies or chromatoid bars, which are cigar-shaped. Mature cyst: the glycogen mass and chromidial bars disappear and the nucleus undergoes two successive mitotic divisions to form two and then four nuclei. 1he mature cyst is, thus quadrinucleate.  B- E. histolytica Infective Form Mature quadrinucleate cyst passed in feces of convalescents and carriers. The cysts can remain viable under moist conditions for about I0 days. C- E. histolytica mode of transmission Man acquires infection by swallowing food and water contaminated with cysts.  D- E. histolytica Life cycle: Excystation: Is hapened when the cyst reaches cecum or lower part of the ileum, due to the alkaline medium, the cyst wall is damaged by trypsin. Metacyst mean the cytoplasm gets detached from the cyst wall and ameboid movements appear causing a tear in the cyst wall, through which quadrinucleate ameba is liberated. Metacystic Trophozoites mean the nuclei in the metacyst immediately undergo division to form eight nuclei, each of which gets surrounded by its own cytoplasm to become eight small amebulae or metacystic trophozoites.  E-Pathogenesis and Clinical Features 1. Intestinal Amebiasis The lumen-dwelling amebae do not cause any illness. They cause disease only when they invade the intestinal tissues. This happens only in about 10% of cases of infection, the remaining 90% being Asymptomatic. 2. Amebic ulcer Is the typical lesion seen in intestinal amebiasis. The typical amebic ulcer is flask-shaped in cross section. FIG: Flask-shaped amebic ulcer F- Laboratory diagnosis of Entamoeba histolytica  Macroscopy: The stool is characterized by: Foul-smelling, copious, semiliquid, brownish -black in color, intermingled with blood and mucus, and it does not adhere to the container. Microscopy A. Saline preparation: The cellular exudate is scanty and consists of only the nuclear masses (pyknotic bodies) of a few pus cells, epithelial cells and macrophages. The RBCs are in clumps and yellow or brown -red in color. Charcot-Leyden crystals are often present. These are diamond- shaped, clear and refractile crystals. Actively motile trophozoites throwing pseudopodia can be demonstrated in freshly-passed stool. Presence of ingested RBCs clinches the identity of E. hislolytica. Nucleus is not visible but a faint outline may be detected. Cyst has a smooth and thin cell wall and contains round refractile chromatoid bars. Glycogen mass is not visible. B- Iodine preparation: For the demonstration of cysts or dead trophozoites, stained preparations may be required for the study of the nuclear character. Iodine-stained preparation is commonly employed for this purpose.