Introduction to Medical Parasitology PDF

INTRODUCTION TO MEDICAL PARASITOLOGY DR MICHELLE G BROWN/PROF J LINDO DEPARTMENT OF MICROBIOLOGY, UWI MONA OBJECTIVES OF LECTURE To introduce terminology used in the discipline Appreciate the relevance of the taxonomy of these organisms To define host/parasite relationships To introduce students to...

INTRODUCTION TO MEDICAL PARASITOLOGY DR MICHELLE G BROWN/PROF J LINDO DEPARTMENT OF MICROBIOLOGY, UWI MONA OBJECTIVES OF LECTURE To introduce terminology used in the discipline Appreciate the relevance of the taxonomy of these organisms To define host/parasite relationships To introduce students to the range of parasites causing disease in humans SYMBIOSIS Mean literally Living Together There are several symbiotic relationships in the animal kingdom Pathogen A pathogen causes harm (= disease) COMMENSALISM 1 host benefits other not harmed Entamoeba coli and E. dispar - intestine Cyst of Entamoeba coli a common commensal in patients at UHWI PHORESIS Symbiont carried by host There is no physiological dependence Host often called transport host Transported symbiont is called phoront Egg of Trichuris trichiura which may be transported by the housefly NEUTRALISM Neither incur cost or benefit PARASITISM One symbiont (parasite) benefits the other (host) is harmed in some way Highly successful lifestyle PARASITE LIFE CYCLES All parasites pass through a series of developmental stages to complete their life cycles If the parasite only requires one host to do this the life cycle is direct If the parasite requires two or more hosts to do this the life cycle is indirect OBLIGATE PARASITE (SYMBIONT) Organism which is physiologically dependent on establishing a symbiotic relationship with another Plasmodium – causes malaria Trichuris – whipworm Ascaris lumbricoides– large round worm Necator americanus – common hookworm EXAMPLES OF OBLIGATE SYMBIONTS Plasmodium in blood film Hookworms in situ Ascaris lumbricoides (round worm) FACULTATIVE PARASITE (SYMBIONT) Organism can exist physiologically independently of another but may establish a relationship if opportunity presents itself Acanthamoeba Naegleria fowleri ENDOPARASITE Parasite lives inside the host Ascaris lumbricoides Trichuris trichiura Necator americanus Entamoeba histolytica ECTOPARASITE Parasite lives on exterior of host, eg. Phthirus pubis – Pubic louse Cochliomyia hominovorax - screwworm Sarcoptes scabei - scabies Parasite/host relationships Very specific - humans only, eg. Taenia solium, Trichuris trichiura Less specific - humans and several other hosts; eg. Strongyloides stercoralis - Trypanosoma cruzi Not specific -range of mammals eg. Trichinella spiralis Definitive host - host in which sexual reproduction takes place eg. mosquito in malaria Intermediate host - development of parasite occurs, but no sexual reproduction, eg. Man in malaria Mosquito-definitive host Man-intermediate host Reservoir host - maintains parasitic infection and acts as a source of infection to human. Rats in Angiostrongylus cantonensis infections Paratenic host - host in which no development takes place but parasite survives. Prawn in Angiostrongylus cantonensis infections Zoonosis - parasitic infection which is principally of animals but which can be transmitted to humans, eg. Toxoplasma gondii, Toxocara canis, Ancylostoma caninum SOME ZOONOSES Toxocara canis Cutaneous larva migrans ANTHROPONOSIS “a disease that is spread from humans to humans … – E.g. smallpox, malaria – Usually implies a pathogen normally (but not absolutely) limited to infecting humans – Excludes rare/unusual cases Superinfection - a new infection with the same species of parasite Autoinfection - superinfection by a parasite originating in the same individual, e.g. Strongyloides stercoralis Autoinfection SOURCES OF EXPOSURE TO PARASITIC INFECTION Contaminated food or water Food with the infective stage Blood sucking/biting arthropod Close contact with infected person Oneself (autoinfection) PORTALS OF ENTRY Mouth Skin Inhalation Transplacental Sexual intercourse PORTALS OF ENTRY Entry via Ingestion Cyst of Entamoeba histolytica Life cycle of Entamoeba histolytica Eggs of Ascaris lumbricoides Life Cycle of Ascaris lumbricoides Entry via Skin Entry via Inhalation Eggs of Pinworm Life Cycle of Enterobious vermicularis (Pinworm) Entry via Sexual Transmission Trichomonas vaginalis Congenital Route Sub-Kingdom Protista 1. Sarcomastigophora 2. Apicomplexa 3. Ciliophora 4. Microspora Phylum Sarcomastigophora Subphylum: Mastigophora Class: Zoomastigophora flagellates Subphylum: Sacrodina - Amoebae Order: Amoebida - Entamoeba Sarcomastigophora Class: Zoomastigophora Giardia duodenalis - GI tract Trypanonosoma cruzi -Blood Leishmania donovani -Skin Trichomonas vaginalis - GU tract Trichomonas tenax - Mouth commensal PHYLUM: APICOMPLEXA Class Sporozoea Tissue parasites (alternate sexual and asexual cycles) Plasmodium - 4 sp causes malaria Toxoplasma - congenital infection Cryptosporidum, Cyclospora, Isospora opportunistic in AIDS PHYLUM: CILIOPHORA Move using cilia Many are free-living or commensal Typically 2 types of nuclei Typified by Balantidium coli PHYLUM MICROSPORA Emerging infection - 1st case 1959 Unicellular spores Opportunistic in AIDS patients Transmitted via spores Symptoms - diarrhoea, neurological Prevalence and Intensity Prevalence - % of population infected Intensity – mean number of parasite/host Worm burden-measure of intensity Increased Worm burden = increased Disease PHYLUM: PLATYHELMINTHES Often hermaphroditic Cestoidea - tapeworms - stages often in vital organs Trematoda - flukes (Schistosomes) IH present Flat worms, various habitats PHYLUM: NEMATODA Round worms - dioecious Intestines- Ascaris, Trichuris, Strongyloides Blood - Wuchereria bancrofti, Onchocerca volvulus Tissue - Dracunculus INTESTINAL NEMATODES TISSUE NEMATODE Phylum: Arthropoda Insects and their ilk Important ectoparsites Important vectors of disease SAMPLE COLLECTION Container Dry, clean, leak proof with tight fitting lid Labeled clearly Patient’s name, registration number, date and time of Exclude Urine, water, soil, all other materials PHYSICAL CHARACTERISTICS OF THE SPECIMEN Macroscopic parasites ⮚ Pinworms may be seen on the surface ⮚ Tapeworm proglottids on the surface or within sample ⮚ ⮚ Ascaris adults often seen in heavy infections Break up sample with applicator sticks to check for helminths STOOL CONSISTENCY VS DISTRIBUTION OF PROTOZOA SUBSTANCES THAT INTERFERE WITH STOOL EXAMINATIONS Kaolin Antacids Mineral oil Barium/bismuth Antimicrobial agents Gall bladder dyes 1st sample negative- repeat 3 specimens- interval 2-3 days LABORATORY DIAGNOSIS Direct smear – trophozoites Formalin-ether concentration (OVA, CYST & PARASITE) Eggs, cysts, larvae Kato Katz Thick walled eggs (Ascaris, Trichuris, schistosomes) Quantitative Culture of Strongyloides Harada Mori Charcoal Agar plate LABORATORY DIAGNOSIS Direct Smear Kato katz smears with Ascaris LABORATORY DIAGNOSIS Blood Tests Serology- detection of antibodies or antigen eg ELISA LABORATORY DIAGNOSIS Blood smear- detection of parasites found in the blood –eg for detection of parasites in malaria, filariasis LABORATORY DIAGNOSIS LABORATORY DIAGNOSIS (RAPID TESTS) Rapid test for Schistosomiasis