Lec_4_Bacteria - Zoonotic Viruses • Zoonoses are diseases...

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Unformatted text preview: Zoonotic Viruses • Zoonoses are diseases of vertebrate animals that can be transmitted to man: either directly or indirectly through an insect vector. • When an insect vector is involved, the disease is also known as an arboviral disease. • However, not all arboviral diseases are zoonosis: where the transmission cycle takes place exclusively between insect vector and human e.g. dengue and urban yellow fever. • Examples of viral zoonoses that can be transmitted to man directly include rabies, hantaviruses, lassa and ebola fevers. Rabies Virus • member of the Lyassavirus of the Rhabdoviridae • ssRNA enveloped virus, characteristic bullet-shaped appearance with 6-7 nm spike projections. • virion 130-240nm * 80nm •-ve stranded RNA codes for 5 proteins; G, M, N, L, S • Exceedingly wide range of hosts • There are 5 other members of Lyassavirus : Mokola, Lagosbat, Duvenhage, EBL-1, and EBL-2 • Duvenhage and EBL-2 have been associated with human rabies. Rabies Virus Structure of rabies virus (Source: CDC) Rabies virus particles Epidemiology • Rabies is a zoonosis which is prevalent in wildlife. The main animals involved differs from continent to continent. • Europe fox, bats • Middle East wolf, dog • Asia dog • Africa dog, mongoose, antelope • N America foxes, skunks, raccoons, insectivorous bats • S America dog, vampire bats Spongiform Encephalopathies and Prions Prion • Smaller than smallest known virus • Not yet completely characterized • Most widely accepted theory – Prion = Proteinaceous infectious particle • Normal Protein – PrP C (C for cellular) – Glycoprotein normally found at cell surface inserted in plasma membrane Normal protein • Secondary structure dominated by alpha helices • Easily soluble • Easily digested by proteases • Encoded by PRNP gene (in humans) – Located on human chromosome 20 Abnormal Protein • Insoluble in all but strongest solvents • Highly resistant to digestion by proteases – Survives in tissues post-mortem • Extremely resistant – Heat, normal sterilization processes, sunlight • No detectable immune response spongiform encephalopathies of humans and other animals • humans – Kuru (Fore people in New Guinea) – Creutzfeldt-Jakob disease (CJD) – Gerstmann-Straussler-Scheinker (GSS) – fatal familial insomnia – new variant CJD • Animals – Scrapie – exotic ungulate encephalopathy – bovine spongiform encephalopathy (BSE) – transmissible mink encephalopathy – feline spongiform encephalopathy – chronic wasting disease (CWD) Bacterial Pathogens Turbidity Pathogenic Bacteria Pathogenic bacteria possess virulence properties in the form of structures or chemical constituents that contribute to pathophysiology – Endotoxins – Exotoxins Pili: for attachment and effacement to cells and tissues Invasins: to invade cells Some bacteria make spores: – highly to physical and chemical agents and – very persistent in the environment Peptidoglycan...
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This note was uploaded on 04/05/2010 for the course ENVH 451 taught by Professor Meschke during the Fall '09 term at University of Washington.

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Lec_4_Bacteria - Zoonotic Viruses • Zoonoses are diseases...

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