7 - The world of Parasitology Parasitism Intimate and...

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The world of Parasitology
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Parasitism • Intimate and obligatory symbiotic relationship between two organisms of different species • Parasite is metabolically dependent on host • Short term (mosquito) or permanent (tapeworm) • Very common way of life (50% of animal species)
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“Success” of Parasites • Success in terms of prevalence, number of hosts (dispersion), geographic range, number offspring, potential for transmission to next host, etc. • Transmission depends on many factors such as water quality, hygiene, proximity to animals, agricultural practices, climate, sanitation, over- crowding, poverty, travel, international trade, traditional foods, susceptible populations, etc.
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Modes of Transmission • person-to-person (faecal-oral route) • water • food • zoonotic • insect vectors • blood / organ transplant • congenital • penetration through skin
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Phylum Protozoa (single-celled eukaryotes) Subphylum Sarcomastigophora Superclass Mastigophora (flagellates) - Giardia, Trichomonas Superclass Sarcodina (amoeba) - Entamoeba Subphylum Ciliophora (ciliates) - Balantidium Subphylum Apicomplexa (sporozoans) - Cryptosporidium, Cyclospora, Toxoplasma, Plasmodium Subphylum Microspora (microsporidians) - Encephalitozoon, Nosema (spore forming protozoans)
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Helminths and Arthropods Phylum Platyhelminthes Class Digenea (flukes) – Schistosoma Class Cestoidea (tapeworms) – Diphyllobothrium, Taenia Phylum Nematoda (roundworms) – Enterobius , Trichinella, Ascaris, Anisakis Phylum Arthropoda (act as parasites and vectors) Class Arachnida (ticks, mites) Class Insecta (mosquitoes, blackflies, fleas, lice)
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Giardia lamblia (syn. G. duodenalis , G. intestinalis ) HISTORY first described by Leeuwenhoek in 1681: “…I have sometimes also seen animalcules a-moving very prettily, their belly which was flatlike, furnisht with sundry little paws…” • Demonstrated to be a true pathogen in the early 1900’s • Most freq. identified intestinal parasite worldwide
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Symptoms – G. lamblia • Most infections are asymptomatic (carriers) • acute giardiasis: diarrhea, weight loss, abdominal discomfort, nausea, vomiting • retardation of growth and development in young children (failure to thrive)
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Prevalence - G. lamblia • most common protozoan infection of intestinal tract worldwide • 2-5% in industrialized world and 20-30% in developing world; • prevalence rises through infancy and childhood and declines in adolescence (related to faecal-oral route of transmission) • Other high risk groups include travellers and immunocompromised
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Life cycle – G. lamblia -excystation -trophozoites in small intestine -longitudinal binary fission -encystation -cysts shed with faeces
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Giardia lamblia genotypes (zoonotic transmission) Zoonotic: • Assemblage A – humans, livestock, cats, dogs, beavers • Assemblage B – humans, livestock?, dogs, beavers Non-zoonotic: • Assemblage C – dogs • Assemblage D – dogs • Assemblage E – hoofed livestock • Assemblage F – cats • Assemblage G – rats
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7 - The world of Parasitology Parasitism Intimate and...

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