Parasitology Introduction PDF

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