9- PARASITOLOGY INTRODUCTION_Dr Ayesha (23-11-2020).pdf
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2020
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MEDICAL PARASITOLOGY MEDICAL PARASITOLOGY INTRODUCTION : The parasites which infect man The disease they produce The response generated by them Various methods of diagnosis Prevention. PARASITE : An organism that entirely dependent on another organism ie its host, for a...
MEDICAL PARASITOLOGY MEDICAL PARASITOLOGY INTRODUCTION : The parasites which infect man The disease they produce The response generated by them Various methods of diagnosis Prevention. PARASITE : An organism that entirely dependent on another organism ie its host, for all or part of its life cycle and metabolic requirements. Microparasite & Macroparasite On basis of their location – Ectoparasite & Endoparasite ECTOPARASITE – lice – causes infestation. ENDOPARASITE – all protozoan & helminthic – cause infection. OBLIGATE PARASITE : Cannot exist without a host eg. Toxoplasma gondii FACULTATIVE PARASITE : Live either a parasitic or free-living existence eg. Naegleria fowleri, Acanthamoeba spp., B. mandrillaris ACCIDENTAL PARASITE : Attack an unusual host eg. Echinococcus granulosus in man HOST : Harbours the parasite and provides the nourishment and shelter DEFINITIVE HOST : sexual reproduction INTERMEDIATE HOST : larval or asexual stages RESERVOIR HOST : Harbours the parasite and serve as imp. source of inf. to other hosts VECTOR : Usually an insect, that transmits an infection from one host to another e.g. housefly HOST-PARASITE RELATIONSHIP SYMBIOSIS : An association, one cannot live without the help of the other COMMENSALISM : Only parasite gets benefit without causing any injury to the host PARASITISM : Parasite gets benefits from the host and host always suffers from some injury SOURSES OF INFECTION CONTAMINATED SOIL AND WATER : Eggs of A.lumbricoids, Trichuris trichiura Cysts of E.histolytica, Giardia lamblia etc. RAW OR UNDERCOOKED PORK : T. solium, Trichinella spiralis RAW OR UNDERCOOKED BEEF : T. saginata BLOOD-SUCKING INSECTS : Plasmodium spp., Wuchereria bancrofti, Leishmania spp. etc. HOUSEFLY : E. histolytica DOG : Echinococcus granulosus CAT : T. gondii MAN : E.histolytica, Enterobius vermicularis and H. nana AUTOINFECTION: E.vermicularis & S.stercoralis Freshwater fishes , crab and crayfishes : Diphyllobothrium latum, Paragonimus westermani PORTAL OF ENTRY MOUTH : E.histolytica, G.lamblia, B.coli, etc. INHALATION : Eggs of E.vermicularis SKIN : A.duodenale, S.stercoralis, Plasmodium spp., Leishmania spp., W.bancrofti etc. CONGENITAL : T.gondii, Plasmodium spp. SEXUAL CONTACT : Trichomonas vaginalis etc. IATROGENIC INFECTION : Malaria parasites may be transmitted by transfusion or by contaminated syringes and needles PATHOGENICITY TRAUMATIC DAMAGE : By entry of filariform larvae of S.stercoralis etc. By attachment of Hookworms to the intestinal wall Eggs of S.haematobium and S.mansoni in urinary bladder and intestinal canal Large worms - A.lumbricoides and T.saginata may produce intestinal obstruction LYTIC NECROSIS – E.histolytica secretes lytic enzymes which lysis tissues. Plasmodium spp., Leishmania spp. cause necrosis during their growth and multiplication ALLERGIC MANIFESTATIONS : By secretions and excretions of the growing larvae and the products liberated from dead parasites. INFLAMMATORY REACTION : Most of the parasites provoke cellular proliferation and infiltration at the site of their location. Cause eosinophilia Anaemia Black water fever in malaria Inflammation of L.I (E.histolytica) NEOPLASIA : Schistosoma haematobium can cause vesical carcinoma. SECONDARY INFECTION : The migrating larvae e.g. strongyloidiasis, ascariasis - may carry bacteria and viruses from intestine to the blood & tissue. IMMUNITY IN PARASITIC INFECTIONS Less efficient than bacterial and viral infections CMI – Cytotoxic T (Tc) cells, Natural killer (NK) cells, Activated macrophages. AMI – Antibody (produced by B-cells) mainly IgM, IgG, IgE. PRESERVATION OF STOOL SPECIMENS : FORMALIN SOLUTION - 10% formalin saline – 3:1 (+) cysts, eggs and larvae (-) permanent stained smear, trophozoite, PCR POLYVINYL ALCOHOL (PVA) - Ethyl alcohol + HgCl2 + GAA + Glycerine + PVA 3:1 (+) cyst, trophozoites, trichrome staining (-) acid fast stain, safranine stain MERTHIONATE-IODINE- FORMALIN (MIF) SOLUTION - Sol. 1 – thiomersal + formaldehyde + glycerol Sol. 2 – Lugol's iodine Stains and fixes cysts, eggs, larvae without any need for further staining by wet mount Well preserved for 1 year or more SCHAUDINN'S SOLUTION - HgCl2 + Ethyl alcohol + GAA + Glycerol 14:1 It fixes and preserves the specimen for 1 year LABORATORY DIAGNOSIS DEMONSTRATION OF PARASITE : IN STOOL : Wet mount : Normal saline and Lugol's iodine (trophozoites, cysts, eggs) By concentration methods : Salt flotation or formal-ether con. method By Ziehl-Neelsen staining e.g. Cryptosporidium parvum, Isospora belli. EXAMINATION OF FAECES COLLECTION OF SPECIMEN : Normally passed stool No Barium enema specimen Three faecal samples x 3 days First two samples – During normal bowel movement 3 rd sample – After magnesium sulphate purge Amount – Whole stool, series of stool samples, milligram amount EXAMINATION OF STOOL SPECIMENS - Liquid stool specimens – within 30 min Semiformed stool specimens – within 60 min Formed stool specimens – within 24 hrs METHODS OF EXAMINATION Macroscopic Examination - Consistency, Colour, Odour, blood or mucous Adult helminths – A.lumbricoides, E.vermicularis, segments of Tapeworms Microscopic Examintion - Saline wet mount Iodine wet mount Stains – Iron-haematoxyline stain, Trichrome stain, Modified acid-fast stain CONCENTRATION METHODS : Floatation Technique Sedimentation Technique FLOATATION TECHNIQUE : SATURATED SALT FLOATATION TECHNIQUE: All the helminthic eggs float except unfertilized eggs of A.lumbricoides, eggs of taenia and all intestinal flukes ZINC SULPHATE (33%) CENTRIFUGAL FLOATATION TECHNIQUE – Concentrates cysts of protozoa, eggs of nematodes and small tape worms SEDIMENTATION TECHNIQUE : Simple sedimentation Formalin-ether sedimentation FORMALIN-ETHER SEDIMENTATION - Stool + 10ml water ----> filtrate ----> centrifuge x 2000rpm x 2min ----> discard supernatant Sediments + 10ml saline ----> centrifuge ----> discard supernatant Sediments + 7ml formalin saline ----> stand for 10min or longer ----> +3ml ether ----> mix it Centrifuge x 2000rpm x 2min Four layers --- ether --- debris --- formalin --- sediment Good method – Hypertonic sol. rupture the cysts and eggs QUANTIFICATION OF WORM BURDEN : Direct smear egg count Stoll's method Direct smear egg count - 2mg of faeces in a drop of saline Examine under low power Count the no. of eggs and calculate it per gram STOLL'S METHOD - 4gm of faeces + 56ml N/10 NaOH --- mix well Take 0.075ml on glass slide Count the eggs under low power ( a) (a) x 200 = eggs / gm x 24 hr faecal sample CORRECTION FACTOR (C.F) Mushy-formed stool – C.F – 1.5 Mushy stool – C.F – 2 Mushy-diarrhoeic stool – C.F – 3 Frankly diarrhoeic stool – C.F – 4 Watery stool – C.F - 5 In Blood : Wet mount – Trypanosomes and Microfilariae In Pbf – Thin & thick smear Staining – Leishman stain, Giemsa stain, Field stain, J.S.B stain Plasmodium spp., L.donovani, microfilariae of W.bancrofti BLOOD CONCENTRATION METHODS : MICROHAEMATOCRIT CENTRIFUGATION – For MP and trypanosome TRIPLE CENTRIFUGATION – 9ml blood + 1ml of 6% sod.citrate – centrifuge 100g x10min Supernatant -- centrifuge 250g x10min Supernatant -- centrifuge 700g x10min Sediments examined for trypanosomes BUFFY COAT CONCENTRATION – 5ml citrated blood For L.D, M.P, Trypanosomes MEMBRANE FILTRATION - For microfilariae in blood IN URINE : Trophozoites of T.vaginalis, eggs of S.haematobium GENITAL SPECIMENS : Trophozoites of T.vaginalis CSF : Trophozoites of N.fowleri, Acanthamoeba spp., B.mandrillaris SPUTUM : Eggs of Paragonimus westermani, E.histolytica During migratory phase - larvae of A.lumbricoides, Ancylostoma duodenale, Necator americanus, S.stercoralis TISSUE BIOPSY & ASPIRATION : E.h from liver abscess G.lamblia from bile larvae of T.spiralis, T.solium in the muscle biopsy Scolices and brood capsules in the fluid aspirated from hydatid cyst CULTURE : E.h & G.l in stool Leishmania spp. in blood IMMUNODIAGNOSIS : Skin Tests – By Intradermal injection- Immediate & Delayed hypersensitivity reaction Serological Tests – Detection of antibodies or antigens by ELISA, RIA, Agglutination Tests, CFT, IHA etc. MOLECULAR METHODS : DNA probes and Polymerase chain reaction (PCR) hypersensitivity, elisa, pcr