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Animal Viruses

Introduction--Variation in size and shape  (10-300 nm)

 

Structure and Composition

           

Central nucleic acid core surrounded by capsid  (capsomere)

                        nucleocapsid surrounded by lipoprotein envelope

                                    symmetry may be masked

                                    enveloped--organic solvents-infectivity

                                    “naked” viruses

           

Morphology

                        Four groups of Classification

                                    Icosahedral--poliovirus--adenovirus

                                    Helical--rabies virus

                                    Enveloped--influenza virus

                                                nucleocapsid may be icosahedral or helical

                                                spikes--glycoprotein

                                                            erythrocyte agglutination

                                                pleomorphic

                                    Complex--poxviruses--vesicular stomatitis virus

                                                bullet shaped to indistinct capsids

           

Chemical Components

                       

Nucleic Acids   DNA or RNA

                                    Animal viruses:  1-DNA, 2-DNA, 1-RNA, 2-RNA

                                    Plant viruses:  1-DNA, 1-RNA, 2-RNA

                                    Circular or linear structure SV40 HVS

                       

Proteins--major component or capsid

                                    Enzyme present for nucleic acid replication

                                    Enzyme for RNA synthesis and DNA synthesis

                       

Lipid--predominant phospholipid enveloped viruses

                                    Glycopipids, fatty acids, aldehydes, cholestrol

                       

Carbohydrates--ribose or deoxyribose--spike

 

Viral Replication--replication with in susceptibale host

            Viruses have no independent metabolic activities

            Steps of viral infection:

1)      Attachment / adsorption

a)      preliminary ionic bond  (reversible--pH)

b)      irreversible attachment

2)      Penetration and uncoating

viropexis--phagocytic engulfment of whole virion

            capsid removed by lysosomal proteases

viral lipoprotein envelope fusion

            nucleocapsid released into host cytoplasm        

                                    ectodesmata--plants  (transient pores)

                                    latent period--uncoating process

3)      Replication and biosynthesis

nucleic acid replication-nucleus or cytoplasm

            replicase enzymes provided by virion

viral protein--cytoplasm  (ribosomes)

4)      Assembly and maturation--nucleus or cytoplasm

5)      Release--lysis, tubular secretion, budding / extrusion

thousand to millions are releases from cell

 

Classification

            Viral tissue affinity—neurotropic / dermatropic

            Physical, chemical, and biological characteristics

                        no nomenclature or taxonomy (vague)

 

Cultivation of Animal Viruses

            Embryonated hen’s egg

                        5-12 day fertile or embryonated eggs at 36 C

                        Chorioallantoic memebrane

                                    yolk-sac--allanoic cavity--embryo

            Tissue cultures--monolayer host cells

                        Vaccine preparation advantages

                                    Salks’s poliomyelitis vaccine

                                    HeLa line

                                    CPE--cytopahic effect--tissue deteriouration

 

Effects of Viral Infections—no symptoms to massive cell lysis

            Cell death  (plaques)

            Polykaryote formation

            Chromosomal breakage  (genetic change)

            Interferon induction

            Inclusion body formation--aggregates of unassembled viruses

                        Negri, Elementary, Guarnieri, Paschen bodies

 

Progressive and Fatal Viral Diseases

            Classic Slow Virus Diseases--Kuru and Creutzfeld-Jakob

                        degenerative CNS diseases

                        long incubation periods  (years)  atypic viruses

            Cancer

                        Leukemias--abnormal number leukocytes

                        Lymphomas--abnormal numer of lyphocytes

                        Sarcomas--mesodermal tumors

                        Carcinomas--epithlial tumors

                       

                        Characteristics of cancers

                                    Hyperplasia--uncontrolled poliferation

                                    Anaplasia--structural and functional abnormalties

                                    Metaplasia--malignant cell dispersal

 

                        Oncogenic viruses--tumor induction

                                    viral genome incorporated into host DNA

                                    host cell does no lyse

                                    RNA viral genome--reverse transcriptase

                                                2-DNA synthesis--provirus

                                                            induction of tumors / transformations