Virology Introduction. Definitions. Introduction. Structure of virus. Virus transmission. Classification of virus. DNA Virus. RNA Virus. Treatment.

Transcription

1 DEVH

2 Virology Introduction Definitions. Introduction. Structure of virus. Virus transmission. Classification of virus. DNA Virus. RNA Virus. Treatment.

3 Definitions Virology: The science which study the virus and viral diseases. Virus: A genetic material containing either DNA or RNA genome that is able to alternate between intra and extra cellular states. OR Virus: Is a microscopic infectious agent that can reproduce only inside a host cell.

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5 Introduction The virus is usually very, very small compared to the size of a living cell ( nm). Viral components are assembled and don t replicate by division. Viruses need to host cell to produce their components for replication. Viruses have a naked capsid or an envelope morphology.

6 Structure of virus : 1- Nucleic acid(genome) : DNA or RNA not both. 2- Capsid(protein coat) : Which protect the genetic material. a)helical. b) Icosahedral. 3- Envelope : That surrounds them then they are outside the cell.

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8 Nature of Viruses Viral genome is packaged in protein coat

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11 Dr.T.V.Rao MD 11

12 Viruses classification DNA viruses remember HHAPPPy. Herpes. Adeno. Parvo. Hepadna. Pox. Papova=Polyoma+papilloma. all DNA viruses replicate in the nucleus except POX replicate in the cytoplasm. all DNA viruses are dsdna except PARVO ssdna. all DNA viruses are icosahedral except POX is complex. 3 DNA viruses are naked PAP(Parvo, Adeno and Papova).

13 Viruses classification RNA viruses: all RNA viruses are ssrna except Reoviridae is ds RNA. *all RNA viruses replicate in the cytoplasm except ORB (Orthomyxo, Retro and Borna) replicate in the nucleus. 3 RNA viruses are non enveloped PCR (Picorna, Calici And Reo). 5 RNA viruses have icosahedral PCR+FT ( Flavi and Toga).

14 VIRAL REPLICATION The basic process of viral infection and virus replication occurs in 7 main steps. 1. Adsorption 2. Penetration 3. Uncoating 4. Viral Genome Replication 5. Assembly 6. Maturation 7. Release

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18 PENETRATION

19 MATURATION

20 LYSIS OF CELL OCCUR

21 T4 Bacteriophage

22 VIRUS EXHIBITS TWO TYPE OF LIFE CYCLE : LYTIC CYCLE LYSOGENIC LIFECYCLE

23 LYSOGENIC CYCLE

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25 Introduction Etiologic agent of Acquired Immunodeficiency Syndrome (AIDS). Former names of the virus include: Human T cell lymphotrophic virus (HTLV-III) Lymphadenopathy associated virus (LAV) AIDS associated retrovirus (ARV) Leading cause of death of men aged and 4th leading cause of death of women in this age group in the US

26 Characteristics of the virus Icosahedral (20 sided), enveloped virus of the lentivirus subfamily of retroviruses. Retroviruses transcribe RNA to DNA. Two viral strands of RNA found in core surrounded by protein outer coat. Outer envelope contains a lipid matrix within which specific viral glycoproteins are imbedded. These knob-like structures responsible for binding to target cell.

27 Characteristics of the virus

28 Viral Replication First step, HIV attaches to susceptible host cell. Site of attachment is the CD4 antigen found on a variety of cells helper T cells macrophages monocytes B cells microglial brain cells intestinal cells T cells infected later on.

29 Life Cycle (a) HIV (red) attaches to two cell-surface receptors (the CD4 antigen and a specific chemokine receptor). (b) The virus and cell membrane fuse, and the virion core enters the cell. (c) The viral RNA and core proteins are released from the virion core and are then actively transported to the nucleus. (d) The viral RNA genome is converted into doublestranded DNA through an enzyme unique to viruses, reverse transcriptase (red dot). (e) The double-stranded viral DNA moves into the cell nucleus. (f) Using a unique viral enzyme called integrase, the viral DNA is integrated into the cellular DNA. (g) Viral RNA is synthesized by the cellular enzyme RNA polymerase II using integrated viral DNA as a template. Two types of RNA transcripts shorter spliced RNA (h) and full-length genomic RNA (j) are produced. (h) Shorter spliced RNAs are transported to the cytoplasm and used for the production of several viral proteins that are then modified in the Golgi apparatus of the cell (i). (j) Full-length genomic RNAs are transported to the cytoplasm (k). (l) New virion is assembled and then buds off. (m) Mature virus is released.

30 Viral Replication Methods of transmission: Sexual transmission, presence of STD increases likelihood of transmission. Exposure to infected blood or blood products. Use of contaminated clotting factors by hemophiliacs. Sharing contaminated needles (IV drug users). Transplantation of infected tissues or organs. Mother to fetus, perinatal transmission variable, dependent on viral load and mother s CD 4 count.

31 Transmission

32 Primary HIV Syndrome Mononucleosis-like, cold or flu-like symptoms may occur 6 to 12 weeks after infection. lymphadenopathy fever rash headache Fatigue diarrhea sore throat neurologic manifestations. no symptoms may be present

33 Primary HIV Syndrome Symptoms are relatively nonspecific. HIV antibody test often negative but becomes positive within 3 to 6 months, this process is known as seroconversion. Large amount of HIV in the peripheral blood. Primary HIV can be diagnosed using viral load titer assay or other tests. Primary HIV syndrome resolves itself and HIV infected person remains asymptomatic for a prolonged period of time, often years.

34 Clinical Latency Period HIV continues to reproduce, CD4 count gradually declines from its normal value of Once CD4 count drops below 500, HIV infected person at risk for opportunistic infections. The following diseases are predictive of the progression to AIDS: persistent herpes-zoster infection (shingles) oral candidiasis (thrush) oral hairy leukoplakia Kaposi s sarcoma (KS)

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36 Viruses spread by coughing and sneezing (Influenza viruses). Viruses are transmitted by the faecal-oral route such as (Norovirus), via contact with contaminated hands, food, or water. HIV is one of several viruses that are transmitted through sexual contact.

37 Parvovirus B19V cause Rash

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39 pox Virus Smallpox

40 Rhabdo Virus

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42 Simplified viral reproductive cycle Entry into cell and uncoating of DNA DNA Capsid VIRUS Replication HOST CELL Transcription Viral DNA mrna Viral DNA Capsid proteins Self-assembly of new virus particles and their exit from cell

43 5 Lytic cycle of phage T4, a virulent phage Release. The phage directs production of an enzyme that damages the bacterial cell wall, allowing fluid to enter. The cell swells and finally bursts, releasing 100 to 200 phage particles. 1 Attachment. The T4 phage uses its tail fibers to bind to specific receptor sites on the outer surface of an E. coli cell. 2 Entry of phage DNA and degradation of host DNA. The sheath of the tail contracts, injecting the phage DNA into the cell and leaving an empty capsid outside. The cell s DNA is hydrolyzed. Phage assembly Head Tails Tail fibers 4 3 Assembly. Three separate sets of proteins self-assemble to form phage heads, tails, and tail fibers. The phage genome is packaged inside the capsid as the head forms. Synthesis of viral genomes and proteins. The phage DNA directs production of phage proteins and copies of the phage genome by host enzymes, using components within the cell.

44 Lytic vs Lysogenic Lytic cycle (virulent phage) Release of virus bursts and kills host cell (lysis) Lysogenic cycle (temperate phage) Viral DNA integrates into host genome (provirus) Can be transmitted to daughter cells Can initiate lytic cycle in response to environmental signal (stress)

45 The lytic and lysogenic cycles of phage λ, a temperate phage Phage DNA Phage The phage attaches to a host cell and injects its DNA. Bacterial chromosome Phage DNA circularizes Occasionally, a prophage exits the bacterial chromosome, initiating a lytic cycle. Many cell divisions produce a large population of bacteria infected with the prophage. Lytic cycle Lysogenic cycle The cell lyses, releasing phages. Lytic cycle is induced Certain factors determine whether or Lysogenic cycle is entered Prophage/Provirus The bacterium reproduces normally, copying the prophage and transmitting it to daughter cells. New phage DNA and proteins are synthesized and assembled into phages. Phage DNA integrates into the bacterial chromosome, becoming a prophage (provirus).