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Introduction to Viruses of Medical Importance-1.ppt
- 1. Introduction to Medically Significant Human Viruses Virology 1
- 2. Learning objectives Upon completion of this lesson, the student will be able to: 1. Describe structure & properties of medically important viruses 2. Explain different criteria used to classify viruses 3. Illustrate classification of medically important viruses 4. List key viruses of medical importance 5. Describe the characteristics, mode of transmission, diseases they cause and laboratory specimens and tests required for preliminary diagnosis of ebola virus. 6. Describe characteristics, the mode of transmission, diseases they cause and laboratory specimens and tests required for preliminary diagnosis of yellow fever virus. 2
- 3. Structure of Medically Important Viruses Components of complete virus particles: Enveloped viruses comprise- Envelop (glycoprotein and membrane), nucelo- capsid (nucelic acid plus capsid) Naked capsid viruses comprise- only nucelo-capsid with no envelop 3
- 4. Fig. 1. From Medical Microbiology, 5th ed., Murray, Rosenthal & Pfaller, Mosby Inc., 2005, Basic Virus Structure 4
- 6. From Medical Microbiology, 5th ed., Murray, Rosenthal & Pfaller, Mosby Inc., 2005, Fig. 6-5. Basic Virus Structure http://www.med.sc.edu:85/mhunt/intro-vir.htm 6
- 7. Capsid Symmetry: 3 types Helical, Icosahedral and Complex 1. Helical Worm-like or coiled configuration 7
- 8. 8 Fig 2. components of complete virus particle : A) Enveloped virus with icosahedral symmetry. B) Virus with helical symmetry. Source : Medical Microbiology, 24 th ed; 2000
- 9. Capsid Symmetry 2. Icosahedral or Cubic Symmetry Most efficient arrangement for subunits in a closed shell Animal viruses in microscopy appear spherical but are icosahedral. An icosahedron has 20 faces, 12 vertices with five fold, three fold or twofold axes Composed of Exactly 60 identical structural subunits 9
- 10. Cubic or Icosahedron • 5:3:2 fold symmetry • 60 identical subunit Medical Microbiology, Jawtz,Melnick, & Adelberg’s,24th Edition, vishal
- 11. Capsid Symmetry 3. Complex Large brick or oval shaped or Irregular configuration 11
- 12. Medical Microbiology, 5th ed., Murray, Rosenthal & Pfaller, Mosby Inc., 2005. 12 Properties of Naked Viruses
- 13. From Medical Microbiology, 5th ed., Murray, Rosenthal & Pfaller, Mosby Inc., 2005, Fig. Box 6-5. Properties of Enveloped Viruses 13
- 14. Classification of Viruses 1. By Type of Nucleic Acid: DNA (Ss /Ds) or RNA Strategy of replication 2. By Size & morphology Type of symmetry (Icosahedral, Helical, Complex) Number of capsomers Presence or absence of envelope 14
- 15. Fig. Medical Microbiology, 5th ed., Murray, Rosenthal & Pfaller, Mosby Inc., 2005 Structures Compared 15
- 16. Other types of Classification 3. By Presence of specific enzymes E.g: RNA and DNA polymerase Neuraminidase Reverse transcriptase 4. By Host tissue or cell tropism E.g: Hepatitis viruses, HIV, etc 5. By Mode of Transmission 16
- 18. Other Types of Classification 6. Host range E.g. Animal, bacteria, plant 7. Type of disease E.g. encephalitis 18
- 19. Transmission of viruses • Route of transmission depends on the source and the ability of the environment and the body route to the target tissue. • Naked viruses can withstand drying, the effect of detergents, and extremes of pH and temperature. • Naked viruses are generally transmitted by the respiratory and fecal-oral routes and can often be acquired from contaminated objects.
- 20. Transmission of viruses • Enveloped viruses are comparatively fragile. • They require an intact envelope for infectivity. • These viruses must remain wet and are spread: A. In respiratory droplets, blood, mucus, saliva, or semen. B. By injection C. By organ transplantation
- 21. Susceptibility to Transmission • The persistence of a virus in a community depends on the availability of a critical number of immunologically naïve (sero negative), susceptible people. • Immunization produced by natural means or by vaccination, is the best way of reducing the number of such susceptible people. • The age of the person is an important factor in determining his or her susceptibility to viral infection.
- 22. Susceptibility to Transmission • Infants, children and the elderly are susceptible to different viruses. • The competence of a person’s immune response and his or her immune history determine how quickly and efficiently the infection is resolved and can also determine the severity of symptoms.
- 23. Epidemiology Terms • Epidemics occur over a larger geographic area and generally result from the introduction of a new strain of virus in to an immunologically naïve population. • Pandemics are worldwide epidemics, usually resulting from the introduction of a new virus (example, HIV). • The spread of a virus can be controlled by quarantine, good hygiene, changes in lifestyle, elimination of the vector, or immunization of the population.
- 24. Control of Transmission • Quarantine is restriction of freedom of movement of apparently well individuals who have been exposed to infectious disease, which is imposed for the maximal incubation period of the disease. • The proper sanitation of contaminated items and disinfections of the water supply are means of limiting the spread of enteric viruses. • The best way to limit viral spread, however, is to immunize the population.
- 25. HERPESVIRIDAE HEPADNAVIRIDAE ENVELOPED PAPILLOMAVIRIDAE POLYOMAVIRIDAE (formerly grouped together as the PAPOVAVIRIDAE) CIRCULAR ADENOVIRIDAE LINEAR NON-ENVELOPED DOUBLE STRANDED PARVOVIRIDAE SINGLE STRANDED NON-ENVELOPED POXVIRIDAE COMPLEX ds ENVELOPED DNA VIRUSES All families shown are icosahedral except for poxviruses 25
- 26. FLAVIVIRIDAE TOGAVIRIDAE RETROVIRIDAE ICOSAHEDRAL CORONAVIRIDAE HELICAL ENVELOPED ICOSAHEDRAL PICORNAVIRIDAE CALICIVIRIDAE NONENVELOPED SINGLE STRANDED + sense BUNYAVIRIDAE ARENAVIRIDAE ORTHOMYXOVIRIDAE PARAMYXOVIRIDAE RHABDOVIRIDAE FILOVIRIDAE SINGLE STRANDED negative sense REOVIRIDAE DOUBLE STRANDED RNA VIRUSES ENVELOPED HELICAL ICOSAHEDRAL NONENVELOPED 26
- 27. Viruses of medical importance include Examples such as O Flaviviruses (Yellow fever virus) O Ebola O Measles O Rubella O Polio O Mumps
- 28. Example Viruses • Two Example viruses will have an overview of key characteristics, the diseases they cause, mode of transmission and main laboratory tests for preliminary diagnosis.
- 29. Key Characteristics of Ebola Virus Characteristic of Ebola Virus • Ebola is a member of the Filovirus family • Ebola viruses are single-stranded RNA • Enveloped • The capsomer-covered nucleocapsid is helicoids in shape • The virion is tubular in appearance
- 30. Key Characteristics of Ebola Virus • Ebola haemorhagic fever (EHF): is a severe, often-fatal disease in humans and nonhuman primates that has appeared sporadically since its initial recognition in 1976. • Common found in West and Central Africa
- 31. Key Characteristics of Ebola Virus Mode of transmission • Is through contact with body fluids Preliminary Laboratory Diagnosis • Specimen: blood • Technique: serological tests
- 32. Key Characteristics of Yellow Fever Virus • Fall under the family flaviviridae • It is enveloped virus with an icosahedral capsid • Single stranded linear non segmented RNA • The envelope has three structural polypeptides, two are glycosylated • Yellow fever virus multiplies in many different types of animals and in mosquitoes
- 34. Key Characteristics of Yellow Fever Virus • Mode transmission of yellow fever is by infected mosquito of the genus Aedes • Disease Caused by Yellow Fever Virus • Yellow fever an acute, febrile, mosquito-borne illness characterized by liver and renal dysfunction and hemorrhage
- 35. Key Characteristics of Yellow Fever Virus Preliminary Laboratory Diagnosis • Specimen –Blood –Biopsy • Technique –Serology
- 36. Questions to Consider • Mention the mode of transmission for Yellow fever virus. • List three morphological characteristics of Ebola virus.
- 37. Key Points • Components of the virus include: Capsomers & nucelo-capsid and envelop unless the naked capsid virus. • Viruses can be classified according to: – Type of nucleic acid – Size & morphology – Presence of specific enzymes – Host tissue or cell tropism – Mode of transmission – Host range E.g. Animal, bacteria, plant – Type of disease E.g. encephalitis
- 38. References: • D Greenwood, R Slack, J Peutherer (2000)Medical Microbiology.15TH ed.Churchill Livingstone • Ivan M. Roitt & PJ.Delves Roitts (2004) Essential Immunology, 10th Edition, Replika press Pvt.ltd, India • Monica Cheesbrough (2003) Medical Laboratory Manual For Tropical Countries, part 2, Edition Cambridge University press, international sales department. • A Zuckerman (2009) Principles and practice of Clinical Virology,6th ed. Wiley & sons, Ltd.,Publishers
- 39. References: • Warren Levinson. MD,PHD(2004) Medical Microbiology & Immunology edition Mc Graw –Hill Companies • Satish Gupte, (2004) The Short Text Book For Medical Microbiology.10th Edition Replika press Pvt. ltd, India
- 40. • Edward K.Wagner, (2006) Basic Virology3rd ed., • Murray, Rosenthal & Pfaller (2005) Medical Microbiology, 5th ed., Mosby Inc., • Jawtz, Melnick, & Adelberg’s,24th Edition, Medical Microbiology, Vishal publishers.
Editor's Notes
- Icosahedron pattern: the most efficient arrangement subunits in closed shell Advantage - The subunits can be smaller and thus economizing on genetic information - Avoids physical restraints which prevents the tight packing o subunits in other symmetry
- People are exposed to viruses through out their lives. Some situations, vocations, lifestyles, and living arrangement increase the likelihood that a person will come in contact with certain viruses. Many viruses are ubiquitous (found every where), as borne out by the fact that evidence of exposure (antibodies to the virus) can be detected in most young children (HSV –1, HHV6, varicella – zoster virus, parvovirus B19) or early adult hood (EBV and respiratory and enteric viruses). Poor hygiene and crowded living, school, and job conditions promote exposure to respiratory and enteric viruses. Day care centers are consistent sources of viral infections, especially viruses spread by the respiratory and fecal-oral routes.
- Travel, summer camp, and vocations that bring people in contact with a virus vector such as mosquitoes, put them at particular risk for infection by arbo-viruses and other zoonoses. Sexual promiscuity also promotes the spread and acquisition of several viruses. Health care workers, such as physicians, dentists, nurses, and technicians, are frequently exposed to respiratory and other viruses but are uniquely at risk for acquiring viruses from contaminated blood (HBV, HIV) or vesicle fluid (HSV). Animals can also act as vectors that spread viral disease to other animals or humans. Animals can also be reservoirs. Viral diseases that are shared by animals or insects and humans are called zoonoses. Arthropods, including mosquitoes, ticks, and sand f lies can act as vectors for toga viruses, flavi-viruses, bunya viruses, and reo-viruses. These viruses are often referred to as arbo-viruses because they are arthropod born.
- The source of the virus is the tissue site of viral replication and secretion. Non-enveloped viruses are also called naked viruses.
- Unlike the non-enveloped viruses, enveloped viruses are comparatively fragile.
- The geographic distribution of a virus is usually determined by whether the requisite cofactors or vectors are present or whether there is an immunologically naïve, susceptible population. Seasonal difference in the occurrence of viral disease corresponds with behaviors that promote the spread of the virus. Out breaks of a viral infection often results from the introduction of a virus (such as hepatitis A) in to a new location. The out breaks originate from a common source (e.g. food preparation)
- Viruses of medical importance are numerous hence we have selected only the above to deal with)
- Source: Maggiano & Thomas, 2010
- 1. Mode transmission of yellow fever is by infected mosquito of the genus Aedes. 2. Characteristic of Ebola Virus Ebola is a member of the Filovirus family Ebola viruses are single-stranded RNA Enveloped The capsomer-covered nucleocapsid is helicoids in shape The virion is tubular in appearance