Introduction To Parasitology PDF

Introduction to Parasitology Dr Nina von Knorring January 2024 CMID/NHLS [email protected]  Objectives To define terms applicable to medical parasitology To describe the classification of medically important parasites To describe the life c...

Introduction to Parasitology Dr Nina von Knorring January 2024 CMID/NHLS [email protected]  Objectives To define terms applicable to medical parasitology To describe the classification of medically important parasites To describe the life cycle, clinical features, treatment and prevention of commonly encountered protozoa and helminths in Southern Africa To explain the laboratory diagnosis of medically important parasites To discuss the public health importance of parasitic diseases in our setting  Introduction Parasites are an important cause of morbidity and mortality in Southern Africa Immuno-compromised patients, travel to foreign countries, growing population of immigrants Knowledge of common pathogens is necessary to ensure accurate identification and appropriate treatment Parasitic infections can be difficult to diagnose, need collaboration between laboratory and health care worker (adequacy of submitted specimen, clinical details etc.)  Important definitions Eukaryotes = cells have membrane bound nuclei and organelles e.g. animals, plants Prokaryotes = cell lacks membrane bound nucleus, contains nucleoid, e.g. bacteria Parasites = eukaryotes either single-celled (protozoa) or multicellular (metazoa) e.g. macroscopic helminths (worms). An organism that lives in or on another organism (its host) and benefits by deriving nutrients at the host's expense Vector = any living carrier, most often an arthropod, which transports an infectious parasite from an infected individual or its wastes to a susceptible host  Important definitions …cont’d Host Single host – require one host species to complete life cycle (e.g. Entamoeba histolytica) Multiple hosts – require two or more hosts to complete life cycle o Definitive host = parasite reproduces sexually within host or adult forms are present within host o Intermediate host = parasite reproduces asexually within host or larval development takes place within host (e.g. snail host in schistosomiasis) Infective form = stage of development which is infective to a susceptible host Life cycles Direct life cycle – no intermediate host. Transmission usually occurs amongst same species. Sexual reproduction takes place Indirect life cycle – one or more intermediate hosts, which may be of different species. Maturing of the parasitic stage or sexual/ asexual reproduction takes place in these hosts (offspring from single organism)  Working classification of medically important parasites Intestinal Entamoeba histolytica Amoebae Tissue Acanthamoeba Flagellates Intestinal/body cavity Giardia lamblia Protozoa (single-celled) Tissue Trypanosoma species Sporozoans Blood Plasmodium species Ciliates Intestinal Balantidium coli Coccidia Intestinal Cryptosporidium parvum Platyhelminths Trematodes Schistosoma species (flat worms) (flukes) Cestodes Taenia solium Metazoa (tapeworms) (multicellular) Intestinal Nematodes Intestinal Roundworms’ (round worms) Tissue Wuchereria bancrofti ( filariasis)  Entamoeba histolytica Diagnosis: Direct stool wet mounts Clinical: Spectrum from asymptomatic carriage to colitis or extra-intestinal complications e.g. liver abscess Transmission: Faeco-oral Distribution: World wide. Travellers and recent immigrants at Treatment: risk Metronidazole [Luminal agent] Prevention: Sanitation, water quality, hand hygiene, fly control  Giardia lamblia Diagnosis: Direct wet mounts Clinical: Asymptomatic to severe diarrhoea and malabsorption. Recurs if not treated. Treatment: Metronidazole Prevention: Good hygiene Transmission: (personal, food), Faeco-oral improved water Distribution: quality World wide, more common in children  Trypanosoma species Chancre Haemolymphatic Travel history important Meningo- encephalitic  Two types of African Trypanosomiasis: East African: Trypanosoma brucei rhodesiense (Zimbabwe, Tanzania, Zambia, Angola) Rapidly progressive (death within months); possible chancre at site of bite. Wild game/cattle are reservoir host West African: Trypanosoma brucei gambiense (DRC, CAR, Sudan) Classic ‘sleeping sickness’, chronic progression (CNS involvement after 1-2 years). Humans are main reservoir host, although domestic animals have been implicated Diagnosis: lab diagnosis as clinical features not specific; microscopy of body fluid (blood, lymph node fluid)/tissue and CSF Treatment: depends on type of infection and disease stage; five different drugs available, side effects/toxicity common Prevention: no vaccine available; prevention of tsetse fly bite; reduction of disease reservoir and vector  Cestodes Tapeworms – Taenia solium Diagnosis: Direct wet mount: ova Clinical: Asymptomatic to malabsorbtion. Important complication neurocysticercosis - leading cause of adult onset epilepsy in SA Distribution & Transmission: World-wide, eating undercooked pork, close proximity to pigs Prevention: Treatment: Cooking meat Mebendazole thoroughly; Albendazole improved sanitation and toilets  Nematodes: Roundworms 5 important intestinal roundworms: Ascaris lumbricoides (roundworm) Ancylostoma duodenale and Necator americanus (hookworms) Trichuris trichuria (whipworm) Enterobius vermicularis (pinworm) Strongyloides stercoralis (threadworm) Asymptomatic but may lead to iron deficiency, malabsorption, malnutrition and growth defects Distributed world-wide with some predominantly found in hot humid climates Most transmitted via soil contaminated with human faeces May have direct or indirect life-cycles, with S. stercoralis having a free-living stage (outside host- geohelminths) Faeco-orally transmitted Prevention possible through basic hand and food hygiene, safe water and improved socio-economic conditions Treated with mebendazole or albendazole Examples of nematodes seen in SA E. vermicularis – common worldwide esp. A. lumbricoides – worldwide esp. lower in children of all socio-economic classes. socio-economic conditions.  Laboratory diagnosis 1) Pre-analytic 2) Analytic Stool: Stool microscopy: fecal Never freeze, thaw or place in concentration; direct wet mount incubator or permanent stained smear for Specifically request for ova, trophozoites, cysts parasites as special concentration technique used. Blood microscopy: thin and thick Add clinical details, date/time of Giemsa stain e.g. malaria, collection trypanosomiasis Loose stool: should be examined within 30 min. after Others: histological examination passing (for detection of motile of biopsy tissues, microscopy of trophozoites) sputum, vaginal discharge, CSF Formed stool: may be Serological techniques examined within 24 hrs (if and molecular detection (PCR) trophozoites not expected) Blood: EDTA fresh blood 3) Post-analytic (malaria; trypanosomiasis) Rapid turn around time Others: Report as soon as possible to clinicians, CSF (trypanosomes) esp. malaria. Blood for serology (amoebiasis, schistosomiasis)  Public Health Importance Serious and ‘neglected’ diseases Considerable morbidity and mortality Malaria Amoebiasis Schistosomiasis Helminth burden in young children leading to malnutrition and impaired growth. Economically developing world suffers most Vicious cycle of poverty, malnutrition, impaired development Conditions suitable for sustaining parasites, vectors and intermediate hosts. Economically developed world at risk too Travellers Military activity ?Climate change  Objectives To define terms applicable to medical √ parasitology To describe the classification of medically important parasites To describe the life cycle, clinical features, treatment and prevention of commonly encountered protozoa and helminths in Southern Africa To explain the laboratory diagnosis of medically important parasites To discuss the public health importance of parasitic diseases in our setting  References Koneman’s Color Atlas and Textbook of Diagnostic Microbiology (6th edition) Manual of Clinical Microbiology (10th edition) Textbook of Diagnostic Microbiology (4th edition) CDC (parasitology life cycles) and WHO websites (soil-transmitted helminth infections)