Medical Parasitology PDF

MEDICAL PARASITOLOGY Roderick D. Balce INTRODUCTION TO PARASITOLOGY A. HOST-PARASITE RELATIONSHIPS 1. SYMBIOSIS – living together of phylogenetically different organisms e.g. host and parasite 2. MUTUALISM – beneficial to both organisms 3....

MEDICAL PARASITOLOGY Roderick D. Balce INTRODUCTION TO PARASITOLOGY A. HOST-PARASITE RELATIONSHIPS 1. SYMBIOSIS – living together of phylogenetically different organisms e.g. host and parasite 2. MUTUALISM – beneficial to both organisms 3. COMMENSALISM – beneficial to one organism, neutral to the other 4. PARASITISM – beneficial to one organism, harmful to the other B. COMPONENTS OF PARASITIC INFECTION 1. HOST Definitive Harbors the adult or sexual stage of a parasite Intermediate Harbors the larval or asexual stage of a parasite Paratenic Harbors a parasite that does not develop but remains alive and is infective to the next host Reservoir Allows the parasite’s life cycle to continue and serves as a source of human infection 2. PARASITE Obligate Depends entirely upon its host for existence Facultative Capable of parasitic and free-living existence Transitory Larval stage is passed in a host while the adult is free living Permanent Completes its life cycle in ____________ Periodic Requires ____________________ for the larval and adult stages Zoonotic Primarily infects animals and may be acquired by man Accidental Occurs in an unusual host Erratic Occurs in an unusual organ or habitat Spurious or Passes through the intestinal tract without coprozoic causing any disturbance Endoparasite Lives inside the body of a host; invasion is called ________________ Ectoparasite Lives on body surfaces; invasion is called Lice (Pediculus spp., Phthirus pubis), ______________________ itch mite (Sarcoptes scabiei) Intermittent Visits the host only during feeding time Bed bug, mosquito, flea, tick, biting fly parasite 3. VECTOR a. Biologic – transmits a parasite only after the latter has completed part of its development b. Mechanical / Phoretic – not essential in the parasite’s life cycle and is responsible only for transporting the parasite Vectors Parasites transmitted Mosquitoes Plasmodium spp., Wuchereria bancrofti, Brugia malayi Biting flies Leishmania spp., Trypanosoma brucei, filariae Kissing bugs Trypanosoma cruzi Ticks Babesia spp. Cockroaches, house flies 4. PORTALS OF ENTRY AND MODES OF TRANSMISSION Portal of entry Mode of transmission Examples Ingestion Most intestinal parasites Mouth/ oral cavity Oral-anal intercourse Larval skin penetration Skin Skin inoculation (vector-borne) Urogenital tract Sexual intercourse (venereal) Nasal passages Intranasal Transplacental Vertical transmission (mother to fetus) *Autoinfection – internal (within the intestine) or external (hand to mouth) 5. PORTALS OF EXIT – _____________________________________________ 1|  MEDICAL PARASITOLOGY Roderick D. Balce C. PARASITE NOMENCLATURE AND CLASSIFICATION 1. BINOMIAL SYSTEM OF NOMENCLATURE ▪ Genus – represents the taxon to which the species belongs; first letter is capitalized ▪ Specific epithet – trivial name that distinguishes the species within the genus ▪ Both parts of the organism’s name are italicized in normal text or underlined in handwriting 2. CLASSIFICATION OF MEDICALLY IMPORTANT PARASITES a. PROTOZOA 1) Phylum Sarcomastigophora – amebae and flagellates 2) Phylum Ciliophora – Balantidium coli 3) Phylum Apicomplexa – sporozoans or coccidians b. OTHER UNICELLULAR PARASITES – Blastocystis spp. and microsporidians c. HELMINTHS 1) Phylum Nemathelminthes – nematodes (roundworms) 2) Phylum Platyhelminthes – trematodes (flukes) and cestodes (tapeworms) d. ARTHROPODS 1) Class Arachnida – ticks, mites, chiggers 2) Class Insecta – lice, fleas, cockroaches, bugs, beetles, flies, mosquitoes, midges 3) Class Crustacea – crabs, crayfish, copepods DIAGNOSTIC PROCEDURES A. STOOL 1. Specimen collection a. Clearance period following ingestion of certain drugs and compounds: ▪ Antacids, antidiarrheals, barium, bismuth, laxatives (leave crystalline residues) – ________ ▪ Antimicrobial agents (decrease the number of protozoans) – __________ ▪ Gallbladder dyes – __________ b. Collect sufficient quantity of stool: __________________________________ c. Avoid contamination with urine, water, or soil. d. Place the specimen in a dry, clean, leak-proof, waxed container with a screw top. e. Label the specimen with the patient’s name, age, sex, date and time of collection and other pertinent information. f. Number of specimens examined before confirming a truly negative result: ________________________ 2. Specimen handling and preservation a. Maximum time between collection and examination: Liquid specimens ________ Soft/semi-formed specimens ________ Formed specimens _________ b. Stools must not be left at room temperature, incubated, or frozen a. Beyond one hour, the stool must be _____________________ for up to 24 hours. b. For longer periods of preservation, use two-vial system: ___________________________ c. Ratio of stool to preservative _______ Fixative Comments WM CT PS IA 10% formalin All-purpose fixative Merthiolate-iodine-formalin Fix and stain Sodium acetate-acetic acid formalin Can be used for permanent stains Schaudinn's fluid Contain ______________ Polyvinyl alcohol Mod. PVA Contains ___________________ *WM=Wet mount; CT=Concentration technique; PS=Permanent staining; IA=Immunoassay 3. Macroscopic examination a. Color/Appearance: Brown ________ Black/tarry _______________ Mucoid, bloody _____________ b. Consistency: Soft to well-formed Gives clues on parasite stages present Determines sensitivity of ____________________________ c. Macroscopic structures: adult worms, scolices, proglottids 4. Microscopic examination (O & P Examination) a. Wet mount ▪ prepared by mixing _______ of stool with a drop of ____________ ▪ useful in the detection of motile protozoan trophozoites, helminth eggs, and larvae ▪ may be stained by temporary dyes: _______________________________ 2|  MEDICAL PARASITOLOGY Roderick D. Balce b. Concentration techniques Sedimentation Procedures 1) Formalin-ether (or ethyl acetate) concentration technique ▪ Formalin _____________________ ▪ Ether/ethyl acetate ______________________ ▪ Can be used with specimens preserved in formalin, MIF or SAF ▪ Efficient in recovering most protozoan cysts and helminth eggs and larvae, including operculate eggs, and is moderately effective for schistosome eggs ▪ Less distortion of protozoal cysts compared to zinc sulfate flotation 2) Acid-ether concentration technique ▪ 40% HCl __________________ ▪ Recommended for animal parasites, Trichuris, Capillaria and Schistosoma eggs ▪ Parasites may be lost to the plug of debris; possible destruction of protozoan cysts Flotation Procedures 1) Zinc sulfate centrifugal flotation ▪ 33% ZnSO4 with SG of _____ for processing fresh feces (adjusted to ____ if specimen is formalinized) ▪ yields a cleaner preparation than is provided by FECT, but it is unreliable for the recovery of nematode larvae, infertile eggs of Ascaris, and the eggs of Taenia, schistosomes and many other cestode and trematode eggs 2) Brine’s flotation ▪ uses saturated salt solution with a specific gravity of ___ ▪ no centrifugation is required ▪ not applicable for operculate and thin-shelled eggs 3) Sheather’s flotation ▪ uses boiled sugar solution preserved with phenol ▪ preferred for concentrating coccidian oocysts c. Permanent staining a. Iron Hematoxylin – __________________ b. Trichrome – __________________ c. Modified Trichrome – ___________________________________________________ d. Modified acid-fast stain – used to demonstrate Cryptosporidium, Cytoisospora, and Cyclospora oocysts d. Artifacts that resemble parasites Type of Artifact Resemblance Neutrophils __________________________ Macrophages, squamous and columnar epithelial cells Amebic trophozoites Yeast, fungal conidia, mushroom spores, diatoms Protozoan cysts or helminth eggs Mite eggs _________________________ Pollen grains _________________________ Plant cells Helminth eggs Plant hairs/fibers Helminth larvae Starch granules, fat globules, air bubbles, mucus Protozoan cysts 5. Additional techniques a. Kato thick smear – _____ mg stool placed over a glass slide and covered with cellophane that has been soaked in a mixture of _________________________________ ; useful in mass stool examination b. Egg counting techniques – useful for assessing worm burden and monitoring the efficacy of antihelminthics especially in cases of ____________________________________________ 1) Kato-Katz – a modification of the Kato thick smear which uses a measured amount of stool which has been sieved through a wire mesh Eggs per gram feces (epg) = number of eggs counted x factor (depends on template used) ▪ 1-mm thick template with a 9-mm hole delivers ___ mg feces → factor used is ___ ▪ 0.5-mm thick template with a 6.5 mm hole delivers ___ mg feces → factor used is ___ 2) Stoll dilution – makes use of 0.1 N ______, a flask calibrated at 56 mL and 60 mL, and Stoll pipettes calibrated at 0.075 mL and 0.15 mL 3) Faust-Malloney egg hatching technique – used to determine severity of Schistosoma infection WHO classification of intensity of STH and Schistosoma infections Organism Light Moderate Heavy Ascaris lumbricoides