Lecture 31: Viral Structure and Replication Dr. P. K. Rajesh Clinical Microbiologist Also-Learning outcomes of Virology (Element 6) Plus plan for E & RE symposium

Lecture 31: Viral Structure and Replication OBJECTIVES: The objectives of this lecture are to describe the general properties of viruses. explain how viruses replicate and how this process differs from bacterial replication. explain how viral replication can cause damage the host cell and result in disease. introduce basic principles involved in the laboratory diagnosis of viruses

Learning Outcomes At the end of this lecture, students should be able to: compare and contrast the general properties of viruses with those of the prokaryotes. classify viruses based on their nucleic acid, capsid and envelope. enumerate the methods by which viruses can be identified in the laboratory. recall and apply the knowledge gained regarding the lab diagnosis of viruses to specific viruses discussed later. (to be assessed during the symposium)

General properties of viruses Viruses possess only one type of NA Obligate intracellular ‘parasites’ Cannot grow in artificial cell free medium Lack enzymes for protein & NA synthesis Complex process of replication* Unaffected by antibiotics-(affected by antivirals) (Can a virus b differentiated from a bacterium?)

Classification is based on Nucleic acid- DNA or RNA Capsid- Icosahedral or Helical Envelope- Enveloped or Non enveloped “Ether solubilty”

ENVELOPE CAPSID NUCLEIC ACID

The Rajesh formula-1 HUMAN DISEASE CAUSING DNA VIRUSES 1) POX 2) HERPES GROUP (Hsv1,2,Vzv,,Ebv, Cmv,6,7,8) 3) HEPATITIS B 4) ADENO (Non enveloped=NE) 5) PAPILLOMA, POLYOMA (NE) 6) PARVO (NE) ALL THE OTHER VIRUSES ARE RNA

Colour’s ready A virus structure is made in the order from inside to outside as A. genome; capsid; envelope B. genome; envelope; capsid C. capsid; genome; envelope D. envelope; capsid; genome E. envelope; genome; capsid

Colour’s ready Which ONE of the following is a DNA virus? A. Human immuno deficiency virus B. Measles virus C. Dengue virus D. Adeno virus

FLIP SIDE Which ONE of the following is a RNA virus? A. Rota B. Pox C. Hepatitis B D. Adeno

The Rajesh formula-2 All helical viruses are ENVELOPED All ENVELOPED viruses are Ether soluble Icosahedral viruses may be E or NE Picorna and Reo are important RNA non enveloped icosahedral viruses Reo is the only double stranded RNA

Replication of viruses Adsorption (virus-cell interaction) Penetration (entry into cytoplasm) Uncoating (separation of genome from capsid) Synthesis (DNA-nucleus, RNA cytoplasm) (Pox, Orthomyxo and HIV exceptions) Release (Enveloped,Non enveloped)

Thot spot! Antivirals to stop replication? Influenza HIV

Lab diagnosis of viruses 1)Electron Microscopy-Direct visualization 2)Tissue culture- cytopathic effects (Egg inoculation, animal models used earlier) 3)PCR-Viral DNA/RNA detection 4)ELISA/IF/LA etc- Antigen detection 5)Serology- ELISA/IF/LA etc – IgG / IgM antibody detection. (Disclaimer-some viruses have not yet been cultured )

Tissue culture (TC) Growing the virus in tissue similar to tissue of infection Eg. Lung tissue for Respiratory viruses (Human cell culture is ideal) Earlier used….. Chicken egg/chick embryo Monkey kidney etc were used for TC

Tissue culture-cytopathic effect On tissue culture, growth of virus can be observed by Changes in the tissue-cytopathic effects Finding Inclusion bodies-microscopy or IF PCR of TC Use of neutralising antibodies. (remember Chlamydia inclusion bodies?)

Self study Detailed reading of VIRAL 1)structure 2)replication 3)affinity to tissues 4)pathogenesis 5)prophylaxis

Recommended textbooks 1) Text book of Microbiology R. Ananthanarayan and CKJ Paniker 2) Jawetz, Medical Microbiology

Lecture 32: Common Viral Diseases OBJECTIVES: The objectives of this lecture are to discuss DNA viruses concentrating on -classification of Human Herpes viruses -Herpes simplex virus-modes of transmission, pathogenicity, laboratory diagnosis and preventive methods assign Adeno and Hepatitis B viruses (Hepatitis B would be dealt in detail in GI system in year 2) as a SDL exercise

Learning Outcomes At the end of the lecture, students should be able to: tabulate, classifying Human Herpes viruses according to officail name, common name, subfamily, cytopathology and sites of infection describe the microbiology laboratory identification of Herpes simplex viruses discuss the immuno-prophylaxis of Herpes virus review literature on Adeno and Hepatitis viruses so that the knowledge gained would help when the topic is dealt in detail in GI system in Year 2 (to be assessed during the symposium)

Lecture 33: Common Viral Diseases OBJECTIVES: The objectives of this lecture are to discuss RNA viruses concentrating on -serotypes of Dengue virus - Dengue virus -modes of transmission, pathogenicity, laboratory diagnosis and preventive methods assign rabies and poliomyelitis virus (which would be dealt in detail in CNS in year 2) as a SDL exercise assign measles, mumps and rubella viruses and their vaccines as a SDL exercise.

Learning Outcomes At the end of the lecture, students should be able to: categorize dengue viruses into serogroups and denote their significance in disease describe the microbiology laboratory identification of Dengue viruses judge the reasons for the unavailability of a safe and effective vaccine for dengue review literature on rabies and poliomyelitis virus so that the knowledge gained would help when the topic is dealt in detail in CNS system in Year 2.(to be formatively assessed during the symposium) review measles, mumps and rubella viral infections and their prophylaxis. (to be formatively assessed during the symposium)

Lecture 34: Common Viral Diseases OBJECTIVES: The objectives of this lecture are to describe the structure of HIV and highlight the significance of the structure in pathogenicity and lab diagnosis. discuss the mode of transmission of HIV describe the laboratory diagnosis of HIV specifying the screening and confirmatory tests Outline the general aspects in the prevention of HIV

Learning Outcomes At the end of the lecture, students should be able to: describe the morphological features of HIV and to relate its significance in pathogenicity and in the lab diagnosis describe the laboratory diagnosis of HIV discuss the prophylactic measures of HIV judge the reasons for the unavailability of a safe and effective vaccine for HIV(New from batch 16-Discuss briefly on the HIV candidate vaccines)

Lecture 35: Common Viral Diseases OBJECTIVES: The objectives of this lecture are to introduce emerging viral infections such as SARS, Influenza, Nipah viruses discuss the mode of transmission and pathogenicity of these viruses describe laboratory diagnosis of these viruses discuss the methods of prevention

Learning Outcomes At the end of the lecture, students should be able to: describe the pathogenicity and laboratory diagnosis of SARS, Influenza and Nipah viruses. discuss the prophylactic measures available to prevent an epidemic.