Virology
Introduction Early period identification Recent identificationWhat 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 classificationOld classification Type of host: human, animal, plant..etc 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 realasePathogenic effect on host cells
Permissive cells Destruction (lysis)
2. Cell fusion (syncytia)
3. Inclusion bodies4. Transformation
Non permissive cells Latent Chronic (persistent) Oncogenic SlowViral cultivation
Cell culture Organ culture: slice of organ Tissue culture: fragment of minced organ 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 cancerCell culture serves purposes Primary isolation Vaccine production Basic researches
Embryonated eggsLaboratory animals
F Viruses cannot be grown on sterile media, but require the presence of specific host cells.
Route and spread of viral infection
Vertical (congenital) ……. RubellaViral zoonosis from animal to human, OrfHorizontal Skin route warts Oral routeentrovirusRespiratory routerhinovirusUrogenital route (sexually transmitted) CMVViral spread
Direct lymphatic Viraemia CNS PNSViral Diagnosis
Viral infection clinical criteria(By the time virus isolation has been made, patient is either died or recovered)Importance of viral diagnosisManagement of the patient…. RubellaManagement of the patient’s contact.. HBVStudy the effectiveness of immunization HBV, HIVEpidemiological surveillance screening of blood donors distribution of particular virus investigation of new outbreakViral diagnostic techniques
Direct Electron microscope (stool exam for Rota virus) Detection of viral antigen in infected cell by FAT Viral isolation in TC or lab. animals2. Indirect serological tests to identify unknown virus by known antibodies ELISA RIA FAT CFT
Interferons
Low m.wt proteins confer cell ability to resist viral infection Host specific Non specific antiviral activity Types Alpha IF leukocytes Beta IF fibroblast Gamma IF lymphocytesMechanism 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 synthesisViral Vaccines
Traditional approach prevention rather than cure great success WHO programeradication of small pox
Why we use vaccines?Cheaper Prophylactic Prevent congenital abnormalities Control disease and eradicate it
Types of Viral Vaccines
Live attenuated vaccine attenuation for human not natural host treated in cell culture mutant e.g. polio virus disadvantage: revertant shelf life2. Killed or inactivated vaccines safer than live e.g. Rabies disadvantage: complete inactivation shelf life
3. Subunit vaccine recombinant DNA technology production of free N.A vaccine e.g. HBs Ag
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)
Ribavirin treatment of RSV, Lassa fever (inhibit binding of mRNA to ribosome) AZT act on reverse transcriptase of HIV