introduction to medical parasitology for PT.pptx

Introduction to Medical Parasitology John F. Lindo, PhD Department of Microbiology Email: [email protected] Objectives of lecture 1. To introduce terminology used in the discipline 2. To define host/parasite relationships 3. To introduce students to the range of parasites causing disease in...

Introduction to Medical Parasitology John F. Lindo, PhD Department of Microbiology Email: [email protected] Objectives of lecture 1. To introduce terminology used in the discipline 2. To define host/parasite relationships 3. 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 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 Dermatobia hominis Phorant is the egg Transport host is mosquito Parasitism One symbiont (parasite) benefits the other (host) is harmed in some way Highly successful lifestyle Obligate parasite (symbiont) Organism which is physiologically dependent on establishing a symbiotic relationship with another 1. Plasmodium – causes malaria 2. Trichuris – whipworm 3. Ascaris lumbricoides– large round worm 4. Necator americanus – common hookworm Some obligate symbionts Plasmodium in a blood film Hookworms in situ Some obligate symbionts Trichuris trichiura (whipworm) Ascaris lumbricoides Facultative parasite (symbiont) Organism can exist physiologically independently of another but may establish a relationship if opportunity presents itself 1. Acanthamoeba 2. Naegleria fowleri 3. Balamuthia mandrillaris – Mud bathe in St Thomas, Jamaica Facultative symbionts Naegleria fowleri from CSF Acanthamoeba cyst in corneal scraping Endoparasite Parasite lives inside the host 1. Ascaris lumbricoides 2. Trichuris trichiura 3. Necator americanus 4. Entamoeba histolytica Endoparasites Ascaris Hookworms Endoparasites Entamoeba histolytica – intestine, liver Ectoparasite Parasite lives on exterior of host, eg. 1. Phthirus pubis – Pubic louse 2. Cochliomyia hominovorax - screwworm 3. Sarcoptes scabei - scabies Ectoparsite Screwworms in ear Hand of scabies patient 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 Host/parasite relationships Very specific Plasmodium (malaria) Trichuris trichiura - whipworm Taenia solium – pork tapeworm Trypanosoma cruzi - Less specific Armadillo Trypomastigote – infective stage Several mammalian hosts Not specific Trichinella spiralis – found in muscle of bears, pigs, mongoose??? 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 Human - The intermediate host Mosquito – The definitive 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 Angiostrongylus cantonensis – adult worms in the heart of a rat the DH. Is this a zoonosis? Name a paratenic host? Intermediate host Giant land snail – IH for Angiostrongylus 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 Ancylostoma caninun Anthroponosis An infection that is spread from humans to humans … – –E.g. smallpox, malaria, Trichuriasis –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 - Strongyloides Autoinfection Sources of Exposure to Parasitic Infection 1. Contaminated food or water 2. Food with the infective stage 3. Blood sucking/biting arthropod 4. Close contact with infected person 5. Oneself (autoinfection) Portals of Entry 1. Mouth 2. Skin 3. Inhalation 4. Transplacental 5. Sexual intercourse Portals of entry Neonatal toxoplasmosis - congenital Entry via the skin Reduviid bud – Vector of Trypanosoma cruzi Hookworm larva – penetrates skin Entry via inhalation Pinworn – Enterobius Ingestion Egg of Ascaris lumbricoides Cyst of Entamoeba histolytica Sexual transmission Trichomonas vaginalis Protozoan stages Trophozoite: the feeding, growing and dividing stage of a protozoan –Note that many organisms have specific names for life-cycle stages that could be described as trophozoites Cyst: at least two distinct meanings: –In the tissue, a distinct walled off cavity containing multiple organisms, often important in transmission (e.g. Trichinella,Toxoplasma). - Microscopic, resistant form shed into the environment and responsible for transmission (e.g. Entamoeba 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: Sarcomastigophora Sarcodines and flagellates Trypomastigote of T. cruzi Entamoeba histolytica 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: Apicomplexa Plasmodium Toxoplasma Life cycle of Plasmodium Life cycle of Cryptosporidium PHYLUM: CILIOPHORA Move using cilia Many are free-living or commensal Typically 2 types of nuclei Typified by Balantidium coli Trophozoite of Balantidium coli PHYLUM MICROSPORA Emerging infection - 1st case 1959 Unicellular spores Opportunistic in AIDS patients Transmitted via spores Symptoms - diarrhoea, neurological Microsporidia spore – Stool of HIV patient Prevalence and Intensity Prevalence - % of population infected Intensity – mean number of parasite/host Worm burden-measure of intensity ↑ Worm burden ≡ ↑Disease PHYLUM: PLATYHELMINTHES Often hermaphroditic Cestoidea - tapeworms - stages often in vital organs Trematoda - flukes (Schistosomes) IH present Flat worms, various habitats Class: Cestoidea - Tapeworms Adult Taenia solium Taenia solium –segments or proglottids Larvae of T. solium in brain of human Class: Trematoda Fasciola haepatica Flukes Schistosoma sp. PHYLUM: NEMATODA Round worms - dioecious Intestines- Ascaris, Trichuris, Strongyloides Blood - Wuchereria bancrofti, Onchocerca volvulus Tissue - Dracunculus Intestinal nematodes Trichuris trichiura Enterobius vermicularis pinworm Hookworms – in situ Strongyloides stercoralis Tissue nematode(s) Wuchereria bancrofti - microfilaria Phylum: Arthropoda Insects and their ilk Important ectoparsites Important vectors of disease Some arthropods Ectoparasites PT may encounter Screwworm infection of the scalp in a Kingston resident - Courtesy Dr S. Hemmings Adult crab louse on hair Adult head louse Hard to see - often confused for dandruff or hair spray droplets. Cemented at the base of the hair shaft nearest the scalp 0.8 mm by 0.3 mm, oval and usually yellow to white Nits take about 1 week to hatch (range 6 to 9 days) Viable eggs are usually located within 6 mm of the scalp. Thank You