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Virology 3rd Year lecture1 College of Dentistry Text book: Essenial Microbiology for Dentistry by Samaranayake Introduction Early period of identification Recent identification What is virus? Virus" is from the Greek meaning for "poison" and was initially described by Edward Jenner in 1798. Obligatory intracellular parasite Smallest infectious agent Has simple structure Has one type of nucleic acid Not true cell * lacks ribosome * mitochondria * cell wall * ribosome Viral structure Viral classification Old classification Type of host: human, animal, plant..etc 1 Tissue affinity: neurotropic, viscerotropic.etc Geographical location: Coxsackie, Newcastle Recent classification Nature of N.A: single, double stranded DNA or RNA Shape : icosahedra, helical, complex Envelop: enveloped or non-enveloped Assembly: cytoplasm, nucleus Physical and chemical nature: size, sensitivity, dimension Viral replication Attachment: Penetration Uncoating Replication Assembly and Realase Pathogenic effect on host cells Permissive cells 1. 2. 3. Destruction (lysis) Cell fusion (syncytia) Inclusion bodies 2 4. Transformation Non permissive cells 1. Latent 2. Chronic (persistent) 3. Oncogenic 4. Slow Viral cultivation Cell culture 1. Organ culture: slice of organ 2. Tissue culture: fragment of minced organ 3. Cell culture: Primary CT: variety of cells with limited growth(5-10) Diploid CT : single type divided up to 100 times derived from embryo Continuous CT: single type, indefinite growth, originated from cancer Cell culture serves purposes 1. Primary isolation 2. Vaccine production 3. Basic researches Embryonated eggs Laboratory animals Route and spread of viral infection Vertical (congenital) ……. Rubella Viral zoonosis from animal to human, Orf Horizontal 1. Skin route , warts 2. Oral route entrovirus 3. Respiratory route rhinovirus 4. Urogenital route (sexually transmitted) CMV Viral spread: direct, lymphatic, viraemia, CNS, PNS Viral Diagnosis Viral infection diagnosed by clinical criteria?? (By the time virus isolation has been made, patient is either died or recovered) 3 Importance of viral diagnosis Management of the patient…. Rubella Management of the patient’s contact.. HBV Study the effectiveness of immunization HBV, HIV Epidemiological surveillance * screening of blood donors * distribution of particular virus * investigation of new outbreak Viral diagnostic techniques 1. Direct Electron microscope (stool exam for Rota virus) Detection of viral antigen in infected cell by FAT Viral isolation in TC or lab. animals 2. Indirect serological tests to identify unknown virus by known antibodies (ELISA, RIA, FAT, CFT, etc Interferons Low m.wt proteins confer cell ability to resist viral infection Host specific Non specific antiviral activity Types Alpha IF Beta IF Gamma IF leukocytes fibroblast lymphocytes Mechanism of interferons Released IF from infected cell interact with membrane of surrounding cells resulting in the production of: Endonucleases: degrade RNA Protein kinases: block initiation of protein synthesis 4 Viral Vaccines •Traditional approach prevention rather than cure •great success WHO program eradication of small pox Why we use vaccines? • Cheaper • Prophylactic • Prevent congenital abnormalities • Control disease and eradicate it Types of Viral Vaccines • 1. Live attenuated vaccine attenuation for human not natural host treated in cell culture e.g. polio virus ; disadvantage: revertant s h e lf lif e 2. Killed or inactivated vaccines safer than live e.g. Rabies disadvantage: complete inactivation s h e lf lif e 3. Subunit vaccine recombinant DNA technology production of free N.A vaccine e.g. HBs Ag mutant Viral chemotherapy Type of viral infections lytic persistent latent Antiviral are nucleoside analogues (precursors of DNA or RNA) • • Acyclovir (zovirax): affect on herpes viruses (inhibit DNA synthesis) Amantadine : treatment of influenza virus (prevent shedding of virus) 5 • Ribavirin : treatment of RSV, Lassa fever (inhibit binding of mRNA to ribosome) •AZT act on reverse transcriptase of HIV Viriods •Smallest agents •Cause plant disease •Naked, closed circular ss RNA •Replicate using host cell enzymes •Not associated with human disease Prions (proteinaceous infectious particles) •Cause disease of long i.p. •Neither viruses nor viriods •Do not have either DNA or RNA •Ability to self replicate •Cause scrapie (CNS dis. of sheep) •Resistant to heat & chemicals • Transmitted to animals by ingestion • Neurological transmission has been reported Prions induced diseases • K u ru fatal neurological disease • Creutzfeldt-jakob chronic encephalopathy ** prions replicate first in lymph tissue spongy like appearance brain intracellular vacuoles Prevention & dental implication • No treatment or vaccines • Not consuming susceptible food • Disposable equipments in dental practice should be incinerated • Autoclave instruments at 131 for 18 min. 6