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Presentation on theme: "Viruses."— Presentation transcript:

1 Viruses

2 Overview of Topic What is a virus? Human virus infections Treatment
Definition Structure and replication Human virus infections Treatment Antivirals Vaccines Vaccination against viruses Inactivated vaccines Live vaccines Interferon

3 What is a Virus? A virus is a non-cellular particle made up of genetic material and protein that can invade living cells Structure Core of nucleic acid surrounded by a protein coat called a capsid Capsid can be DNA or RNA, but not both Core can be several to several hundred genes

4 1 nanometer (nm) = one billionth of a meter
SO HOW BIG ARE VIRUSES? Viruses are REALLY small. Size – 20 to 400 nanometers (one nanometer is one billionth of a meter) They are much smaller than bacteria. They can only be seen with an electron microscope. prokaryotic cells ,000 nm 1 nanometer (nm) = one billionth of a meter eukaryotic cells 10, ,000 nm viroids nm viruses nm prion 2-10 nm

5 VIRUS SHAPES Round Herpes virus There are two types: Genital oral
Rod-shaped Tobacco mosaic virus Many sided (icosohedral)

6 SHAPES MAY DIFFER BUT… All viruses have
1. Chromosome-like part that carries hereditary information – The Core 2. Protein coat: Protects hereditary information and provides the shape! The Capsid Influenza Virus Tobacco Mosaic Virus T4 Bacteriophage DNA capsid tail sheath tail fiber

7 Virion Structure Lipid Envelope Nucleic Acid Protein Capsid Virion
Spike Projections Protein Capsid Lipid Envelope Virion Associated Polymerase ·        


Specificity – usually infect specific organisms Cannot infect animals if it infects plants Some can infect wider variety Rabies – all mammals, some birds Common cold: infects cells on airway passage to lungs Tobacco mosaic virus: only tobacco plants…not wheat or corn Rabies: only nervous system cells of mammals

10 Viroid A viroid is made only of single-stranded RNA.
causes disease in plants can stunt plant growth passed through seeds or pollen

11 Bacteriophage E coli bacteria
Bacteriophages are viruses that infect bacteria Bacteriophage Head – capsid and DNA Tail – with fibers to attach to bacteria T group Most commonly studied are T group – T1, T2, T3, T4 etc... T4 has a DNA core within a protein coat, and tail with tail fibers to attach to bacteria. E coli bacteria

12 Viruses need living organisms in order to reproduce and form more viruses!
Injecting DNA virus

13 Retroviruses RNA viruses
When they infect a cell, they produce DNA copies of their RNA genes. Retroviruses have their genetic information copied backwards. RNA  DNA One retrovirus is HIV. Others cause cancer in animals and humans.

14 Viruses enter host cell in different ways:
Bacteriophages pierce host cells Viruses of eukaryotes enter by endocytosis Viruses of eukaryotes also fuse with membrane


16 Virus Replication 1 2 3 4 5 6 7 8 Virus attachment and entry
Uncoating of virion 3 Migration of genome nucleic acid to nucleus 4 Transcription 5 Genome replication 7 Virion assembly 6 Translation of virus mRNAs 8 Release of new virus particles

Section 19-3 Bacteriophage protein coat Bacteriophage DNA Bacterial chromosome Bacteriophage attaches to bacterium’s cell wall Bacteriophage enzyme lyses the Bacterium’s cell wall, releasing new bacteriophage particles that can attack other cells. Lytic Cycle Bacteriophage injects DNA into bacterium Bacteriophage proteins and nucleic acids assemble into complete bacteriophage particles Bacteriophage Bacteriophage DNA Bacteriophage protein Bacteriophage takes over bacterium’s metabolism, causing synthesis of new bacteriophage proteins and nucleic acids

18 Lytic Infection Cause cells to lyse or burst Infection
chance contact virus with right kind of bacterium. Virus attaches to bacterium and injects its DNA. Most times, complete virus particle does not enter. Growth Bacterium cannot tell difference between bacterial and viral DNA. RNA polymerase causes mRNA to be made from cell for virus. Viral DNA takes over and produces more DNA and viral proteins. Replication Virus uses bacterial material to make thousands of copies of the protein coat and DNA. Cell becomes filled with virus particles. (All three stages can happen with E. coli within 25 minutes!) DNA serves as central point for virus particles to be assembled. Cells fill with virus and lyse (burst). New viruses can now infect new cells.

19 Lysogenic cycle- a virus imbeds its DNA into the DNA or the host cell and is replicated along with the host cell’s DNA. Bacterial DNA called prophage.

20 Types of Infections Cell death – Cytopathic effect
This is the end result of many lytic virus infections in which the cell is killed following virus infection. Persistent infection The outcome of some virus infections is not cell death but the development of a persistent (or chronic) virus infection. Latent Infection The capacity of herpes virus to establish a latent infection is essentially another form of persistent infection. In this case the virus is not actually replicating but lying dormant in the host cell Transformation A transformed cell in vitro or a tumour developing in vivo is essentially a cell-type, which shows no control over its cell division with unregulated growth.

21 Transmission of Viruses
Respiratory transmission Influenza A virus Fecal-oral transmission Enterovirus Blood-borne transmission Hepatitis B virus Sexual Transmission HIV Animal or insect vectors Rabies virus ·        

22 Targeting of the virus to specific tissue and cell types
Receptor Recognition CD4+ cells infected by HIV CD155 acts as the receptor for poliovirus Acute Virus Infections Localised to specific site of body Development of viraemia with widespread infection of tissues

23 Viruses and Disease Examples are: Small Pox Polio Measles AIDS Mumps
Influenza Yellow Fever Rabies Common Cold Herpes Ebola etc…

24 Human immunodeficiency virus
HIV Human immunodeficiency virus Is a retrovirus (virus that contains RNA and uses an enzyme to make a DNA copy). DNA is usually made from RNA Can remain dormant for many years Destroys white blood cells of the host’s immune system HIV-infected white blood cell

25 Chicken Pox - Shingles Chicken Pox and shingles are both caused by varicella-zoster, a member of the herpes virus family. Chicken Pox is an uncomfortable, highly contagious and sometimes serious disease. Chicken Pox preventable by vaccine and it’s very unusual to acquire more than once in immunocompetent persons. The virus remains in your body and can later reactivate and become shingles.  

26 Hepatitis A A liver disease that results from infection with the Hepatitis A virus. It can range in severity from a mild illness lasting a few weeks to a severe illness lasting several months. Hepatitis A is usually spread when a person ingests fecal matter — even in microscopic amounts — from contact with objects, food, or drinks contaminated by the feces or stool of an infected person. Almost all people who get Hepatitis A recover completely and do not have any lasting liver damage, although they may feel sick for months.

27 Hepatitis B Inflammation of the liver due to the hepatitis B virus (HBV). It can also be transmitted via needle sticks, body piercing and tattooing using unsterilized instruments, the dialysis process, sexual and even less intimate close contact, and childbirth. Symptoms include fatigue, jaundice, nausea, vomiting, dark urine, light stools. Diagnosis is by blood test. Treatment is via anti-viral drugs and/or hepatitis B immunoglobulin (HBIG).

28 Hepatitis C Liver disease that results from infection with the Hepatitis C virus. It can range in severity from a mild illness lasting a few weeks to a serious, lifelong illness. Hepatitis C is usually spread when blood from a person infected with the Hepatitis C virus enters the body of someone who is not infected. (Most commonly by sharing needles or other equipment to inject drugs). Before 1992, when widespread screening of the blood supply began in the United States, Hepatitis C was also commonly spread through blood transfusions and organ transplants. Hepatitis C can be either “acute” or “chronic.” Acute Hepatitis C virus infection is a short-term illness that occurs within the first 6 months after someone is exposed to the Hepatitis C virus. For most people, acute infection leads to chronic infection. Chronic Hepatitis C is a serious disease than can result in long-term health problems, or even death.

29 Influenza A virus Properties of the virus Myxovirus
Enveloped virus with a segmented RNA genome Infects a wide range of animals other than humans Undergoes extensive antigenic variation Major cause of respiratory infections

30 Influenza A virus Infection
Spread by respiratory route Virus infects cells of the respiratory tract Destruction of respiratory epithelium Secondary bacterial infections During a sneeze, millions of tiny droplets of water and mucus are expelled at about 100 miles per hour with 100,000 germs into the air.

31 Common Cold There are more than 200 viruses that can cause a cold
They can mutate SARS Severe Acute Respiratory Syndrome is a viral respiratory disease. Causes fever, coughing, difficulty breathing

32 Poliovirus ·       

33 Poliovirus Poliovirus vaccines Properties of the virus Enterovirus.
B Enterovirus. Possesses a RNA genome. Transmitted by the fecal oral route. Cause of gastrointestinal illness and poliomyelitis. 40 30 20 10 1950 1960 1970 1980 Number of cases (in thousands) Poliovirus vaccines A: Salk – killed inactivated vaccine. B: Sabin – live attenuated vaccine

34 Poliovirus Infection Gut Viraemia Paralysis Non-neuronal tissues
Virus excretion in the faeces Non-neuronal tissues Viraemia Neuronal tissues Paralysis ·        

35 Generation of Novel Influenza A Viruses
Avian H3N8 Human H2N2 ANTIGENIC SHIFT Genetic Reassortment Human H3N2 Point mutation of HA and NA genes ANTIGENIC DRIFT

36 Viruses and Human Tumours
Epstein Barr Virus Burkitt’s Lymphoma Human papillomavirus Benign warts Cervical Carcinoma Human T-cell Leukaemia Virus (HTLV-1) Leukaemia Hepatitis C virus Liver carcinoma

37 Virus-induced tumours
Infection Uninfected Cell Uncontrolled cell growth and tumour formation [ ] ?

38 Virus-induced transformation
Normal cells Transformed cells Virus transformed cells show a complete deregulation of their normal growth. They tend to pile up over each other and do not stop growing as is typical of normal uninfected/non-transformed cells. This change in the phenotype is due to the virus influencing the gene regulation of the cell. Many of the cellular genes affected that lead to the transformed phenotype are associated with growth regulation and signal recognition.

39 Treatment and Prevention of Virus Infections
Antivirals Target: Attachment/Entry Picornaviruses Nucleic acid replication Human immunodeficiency virus (AZT) Herpes simplex virus (Acyclovir) Virus protein processing HIV (Protease inhibitors) Virus maturation Influenza A virus (Neuraminidase blockers) Vaccines and immunizations The body’s own defenses must be used Vaccine – dead or weakened viruses that stimulate the bodies defense system Symptoms can be treated sometimes, but once someone is infected by a virus, there is not much science can do

40 Problems with Antivirals
Identification of virus-specific target. Difficulty in finding a virus specific site against which to direct the antiviral Generation of resistant variants. As with the use of antibiotics – resistant mutant scan be readily generated that are resistant to antivirals – this is particularly a problem with those against HIV where the drug has to be used for prolonged periods of time.

41 Interferon Interferons are a family of naturally-occurring proteins that are made and secreted by cells of the immune system (for example, white blood cells, natural killer cells, fibroblasts, and epithelial cells). Since interferons enhance the immune system in many ways, they are used for many diseases that involve the immune system. Examples: Interferon alfa-2a (Roferon-A) Interferon alfa-2b - malignant melanoma, chronic hepatitis C, and chronic hepatitis B. Ribavirin combined with interferon alfa-2b, interferon alfacon-1 (Infergen), pegylated interferon alfa-2b, or pegylated interferon alpha-2a, all are approved for the treatment of chronic hepatitis C. Interferon beta-1b (Betaseron) and interferon beta-1a (Avonex) are approved for the treatment of multiple sclerosis. Interferon alfa-n3 (Alferon-N) is approved for the treatment of genital and perianal warts caused by human papillomavirus (HPV). Interferon gamma-1B (Actimmune) is approved for the treatment of chronic granulomatous disease, and severe, malignant osteopetrosis.


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