Viral Classification & Structure PDF

Viral classification and structure Viral structure All viruses consist of core of single or double stranded DNA or RNA surrounded by a protective protein coat called Capsid The capsid is antigenic and enable the virus to attach to the surface of its specific host cells. The nucleic acid...

Viral classification and structure Viral structure All viruses consist of core of single or double stranded DNA or RNA surrounded by a protective protein coat called Capsid The capsid is antigenic and enable the virus to attach to the surface of its specific host cells. The nucleic acid together with the capsid form nucleocapsid In enveloped viruses, the nucleocapsid is surrounded by a lipid bilayer derived from the modified host cell membrane and the nucleocapsid is surrounded by a lipid bilayer interspersed with protein molecules (lipoprotin bilayer) envelope glycoproteins e.g. Herpesviruses (CMV,EBV,HSV,VZ) , Hepatitis B, Hepatitis C, Influenza, Rabies, Ebola, Corona, Mumps, Measles, RSV, rubella and HIV  DNA viruses Common virus Disease Common virus Disease Herpes simplex-1 Conjunctivitis, cold Herpes simplex-2 Genital herpes HSV-1 virus sores HSV-2 virus Neonatal herpes Varicella-zoster (VZ) Chicken pox Papilloma virus Skin Warts Cervical cancer, penile cancer and oral cancers Cytomegalovirus Infectious Epstein-Barr virus Infectious CMV mononucleosis EBV mononucleosis Congenital CMV Burkitt’s lymphoma Variola virus Small pox Adenovirus Respiratory &eye infection  RNA viruses Common virus Disease Common virus Disease Yellow fever virus Yellow fever Dengue fever virus Dengue hemorrhagic fever dengue shock syndrome Rotavirus Gastroenteritis Rabies virus Rabies Mumps virus Mumps Measles virus Measles Rubella virus Rubella Rabies virus Rabies Respiratory RSV pneumonia Poliovirus Poliomyelitis, Syncytial virus encephalitis Influenza A,B ,C Influenza Rhinovirus Common cold Coronavirus Upper respiratory Hepatitis C Hepatitis tract HCV (ssRNA)  Others (RT) Common virus Disease Common virus Disease Ebola virus Ebola haemorrhagic Hepatitis A Infectious hepatitis (ssRNA) disease HAV (RNA) Hepatitis B Serum hepatitis HIV-1, HIV-2 AIDS HBV (DNA) Liver cancer ssRNA (RT) Partially dsDNA (RT) Transmission of viruses Viruses of which man is the natural or most common host Rotavirus, Poliovirus , Hepatitis viruses, Rubella, Influenza , Rhinovirus …….. Viruses for which arthropod (mosquitos, sand-flies, ticks)and vertebrate animals (rodents , birds, monkeys) are the main host and human only accidental or secondary host Rabies virus, Yellow fever , Dengue fever Transmission route for human By direct contact : viruses released on the surface of the skin Chicken box Sexually transmitted includes Herpes simplex and Hepatitis B By ingestion of viruses: Lack of clean piped water supplies, inadequate disposal of faeces and poor personal hygiene are major factors for faecal-oral transmission ( faeces to mouth) such as Hepatitis A virus and Rotavirus By inhaling virus in airborne droplets or dust particles: Overcrowding greatly assists the spread of droplet infection. Also windy weather helps carried virus in dust particles. e.g. Influenza virus, Measles virus, Adenoviruses, RSV and Rhinovirus Transmission route for human By contact with contaminated articles such as floor mat or towel: Papilloma virus (wart virus) and eye infection viruses By infected mother to her child during pregnancy or birth: The virus cross the placenta and infects infants (transplacental) causing abortion, stillbirth or congenital anomalies such as CMV and Rubella By person to person carried on the body of insects: Houseflies and bedbugs can help in transfer of Hepatitis Unlike biological insect virus , no replication of viruses occur in insects. Only mechanical transfer of viruses Infection of cells by viruses When a virus infect a cell it is usually replicates and causes death of it is host cell. Occasionally, viruses infect cells and replicate without causing death of their host cells e.g. Rubella virus Some viruses do not replicate after infecting cells or they become inactive (latent). In response to certain stimuli, latent viruses can be reactivated and become active replicating particles such as Herpes viruses: HSV-1 &HSV-2, CMV, EBV and Varicella-Zoster virus A small group of viruses are able to change or transform their host cells fro normal cells into tumour producing cells (Neoplastic or Oncogenic) e.g. Papilloma virus, Hepatitis B virus and EBV Laboratory diagnosis Detection of viral antigen in cells (intracellular ) by fluorescent microscope (IF) using specific antibody and flourochrome e.g. influenza , HSV, VZ and rabies viruses Detection of soluble viral antigen by enzyme linked immunosorbent assay (ELISA) e.g. hepatitis B,C and Rotavirus Isolation of the virus by tissue culture , inoculation of embryonated eggs or inoculation of experimental animals (mice) Identification of viral particles by electron microscope e.g. hepatitis B and Rotavirus in faeces  Laboratory diagnosis Measurement of antibody in serum to detect a rise of antibody titre (serological diagnosis)→ 4 fold rise of antibody IgG titre Detection of IgM specific antibody in serum → early stages of infection e.g. congenital infections, Hepatitis A Haemagglutination assay: Many viruses attach to molecules present on the surface of red blood cells.e.g. influenza viruses Nucleic acid detection : Detection of virus encoded DNA and RNA is done with polymerase chain reaction (PCR) with virus- specific probes detects specific viruses. Molecular techniques are usually used to confirm positive serological results due to their higher sensitivity and specificity e.g. hepatitis C and HIV