Microbiology Mod 1: Virology PDF

MICROBIOLOGY 8/21/2024. MOD 1: INTRODUCTION...

MICROBIOLOGY 8/21/2024. MOD 1: INTRODUCTION TO VIROLOGY Dr. Ma. Teresa A. Barzaga, M.D., FPSP Trans Group: We Bare Bears I. VIRUS virion. A genetic material contained within an organic Each virion contains at least one particle that invades living cells unique protein synthesized by Uses their host’s metabolic processes to produce a specific genes in its nucleic acid. new generation of viral particles. Microorganisms that are smaller than a bacteria and cannot grow or reproduce apart from a living cell. II. 2 MAJOR COMPONENTS OF THE VIRUS USED IN CLASSIFICATION A. ORIGIN OF VIRUSES Viruses contain nucleic acid, either as RNA or DNA. The origin of viruses is not known. These molecules possess all the genetic information of There are two hypotheses for the two evolutionary the virus necessary for its replication. origins of viruses. 1. ESCAPE HYPOTHESIS MAJOR DESCRIPTION COMPONENT Suggests that viruses were once part of the genetic material of host cells, the DNA or RNA, but escaped Molecular weight cell control and later evolved independently. Structure Single-strandedness or 2. REDUCTION HYPOTHESIS Nucleic acid double-strandedness Associates the origin of viruses to cells (RNA/DNA) Circular or linear Considers viruses to be the reduced forms of Segmented or unsegmented intracellular parasitic organisms. Size B. CHARACTERISTICS OF A VIRUS Size Invades living cells and uses their chemical Symmetry machinery to keep itself alive and to replicate itself. Whether it is enveloped The smallest infectious agents (20-300 nm in Surrounds the virus and is diameter). Capsid composed of a finite number of Contains only one kind of nucleic acid (DNA or RNA) protein subunits known as as the genome. capsomeres (usually associated ○ The viral nucleic acid contains information with or found closed to viral necessary for programming the infected host cell to nucleic acid). synthesize virus-specific macromolecules required for the production of viral progeny. Inert in the extracellular environment. III. DNA VIRUS CLASSIFICATION AND DISEASES Replicate only in living cells. Viruses cause many human infections and are also responsible for rare diseases. C. STRUCTURE OF VIRUSES Researchers have grouped viruses together into several All viruses contain nucleic acid, either DNA or RNA, but major families based on their shape, behaviour, and NOT both. other characteristics. Some viruses are enclosed by an envelope of fat and The table below includes the adenoviruses, protein molecules. herpesviruses, parvoviruses, poxviruses, papovaviruses, and hepadnaviruses, among others. STRUCTURAL DESCRIPTION COMPONENT DNA Virus Classification and Diseases A protein shell or coat enclosing FAMILY VIRUSES DISEASES Capsid the nucleic acid genome. Sore throats; Adenoviridae Adenoviruses Nucleocapsid Capsid + enclosed nucleic acid. Conjunctivitis Lipid-containing membrane Herpes simplex; Herpes labialis; Envelope surrounding viral particles. Varicella-Zoster Herpes genitalis; Cytomegalovirus; Chickenpox; Herpesviridae The complete virus particle Epstein-Barr; Shingles; Virion In its infective form outside the Human Infectious cell, a virus particle is called a Herpesvirus mononucleosis Microbiology - Mod 2 Introduction to Virology 1 of 7 The use of trans, practice questions, and evals ratio must be used discreetly and social media/public exposure of the aforementioned shall be strictly prohibited.  Erythema Febrile Parvoviridae Parvovirus infectiosum diseases Variola; Smallpox; Encephalitis; Poxviridae Molluscum molluscum Togaviridae Alphavirus Febrile contagiosum contagiosum diseases Warts; Progressive V. EFFECTS OF PHYSICAL AND CHEMICAL AGENTS ON Papilloma; VIRUSES Papovaviridae multifocal polyoma leukoencephaly- pathy AGENT DESCRIPTION Acute and Viruses are generally inactivated HepaDNA virus Hepatitis B virus chronic hepatitis when exposed at 56 degrees centigrade for 30 minutes or 100 IV. RNA VIRUS CLASSIFICATION AND DISEASES Heat degrees centigrade for a few seconds. Major families include the picornaviruses, including the Exception to this: Hepatitis B rhinoviruses, caliciviruses, paramyxoviruses, virus and Polyomavirus orthomyxoviruses, rhabdoviruses, filoviruses, and retroviruses. There are dozens of smaller virus families within these Stable at low temperatures and major classifications. can be stored at -40 to -70 Many viruses are host-specific, capable of infecting degrees centigrade and partially Cold and causing disease in humans or in specific animals inactivated by thawing and only. freezing, especially the enveloped viruses. RNA Virus Classification and Diseases Reaction to drying is variable. Some are able to survive well Drying FAMILY VIRUSES DISEASES while some are rapidly inactivated. Lymphocytic Arenaviridae choriomeningitis; Meningitis Ultraviolet Inactivates viruses. Lassa virus irradiation Caliciviridae Calicivirus Gastroenteritis Inactivates viruses with Chloroform envelopes, while those without and ether Coronaviridae Coronavirus Colds envelopes are resistant. Acute Oxidizing and Inactivates viruses. Marburg virus; reducing E.g., formaldehyde, chlorine, Filoviridae hemorrhagic Ebola virus agents iodine, and hydrogen peroxide fever Dengue virus; Most viruses are resistant to Phenol Japanese B Hemorrhagic phenols. Flaviviridae encephalitis fever; virus; Encephalitis Inactivates viruses. Yellow fever virus Radiation E.g., UV, X-ray, high-energy particles Acute Orthomyxoviridae Influenza respiratory Antibiotics Have no effect at all on viruses. disease Measles; VI. COMMON METHODS USED FOR INACTIVATING Measles; VIRUSES Mumps Parotitis; Viruses may be inactivated to: Paramyxoviridae Parainfluenza; Respiratory ○ Sterilize laboratory supplies and equipment. Respiratory tract infections ○ Disinfect surfaces or skin syncytial virus ○ Make drinking water safe Meningitis; ○ Produce inactivated vaccines Enterovirus; Poliomyelitis; Picornaviridae Rhinoviruses; colds; METHOD EXAMPLES Hepatitis A Hepatitis A Sterilization of Gamma irradiation Infantile Laboratory Ethylene oxide Reoviridae Rotavirus diarrhea Supplies and Dry heat Equipment Steam under pressure Rhabdoviridae Rabies Encephalitis; Microbiology - Mod 1 Introduction to Virology 2 of 7 The use of trans, practice questions, and evals ratio must be used discreetly and social media/public exposure of the aforementioned shall be strictly prohibited.  Peracetic acid membrane Surface Formaldehyde Disinfectants Glutaraldehyde 3 The protein coat of the virus Sodium hypochlorite is removed by the host cell enzymes Uncoating Iodophors Viral nucleic acid is then Skin 70% ethanol released for the production of Disinfectants Chlorhexidine the virus’ mRNA 4 Part of the replication step along VII. REPLICATION (VIRUS GROWTH CYCLE) with translation Viruses differ from all other infectious organisms in their Production of virus’ mRNA structure and biology, particularly in their reproduction. ○ Key to the successful Although viruses carry conventional genetic information infection of the cell in their DNA or RNA, they lack the synthetic The virus takes over the machinery for information to be processed into new Transcription cellular biosynthetic virus material. machinery, utilizing the virus’ They can replicate only after infecting a host cell and genome or nucleic acid parasitizing the host’s ability to transcribe or translate The information coding for the genetic information. virus’ protein is passed to the Viral DNA replication occurs in the host’s nucleus ribosomes ○ Exception: Poxviruses — occurs in the cytoplasm 5 mRNA attaches to the A. STEPS IN THE VIRUS GROWTH CYCLE ribosomes and directs synthesis of various specific proteins such as: ○ Structural proteins: Translation capsid proteins and envelope proteins ○ Nonstructural proteins: enzymes required for virus replication especially virus nucleic acid synthesis 6 Newly synthesized nucleic acid molecules and structural proteins come together to form the new virus progeny Assembly Can take place in the: ○ Nucleus ○ Cytoplasm ○ Cell membrane Stages involved in the infection of the host's cells. 7 Gradual process of extrusion or budding through the cell Release VIRUS GROWTH CYCLE membrane Rupture of the cell membrane 1 Viruses show host specificity ○ Usually infect only one or a VIII. ROUTES BY WHICH VIRUSES ENTER THE BODY restricted range of host species Initial basis of specificity: the Attachment ability of the virus particles to (Adsorption) attach to the host cell In many instances, there is a specific interaction with specific receptors on the host cell plasma membrane 2 Virus particle is taken up inside the cell Temperature dependent — takes place at 37°C Virus may enter the host by: Penetration 1. Fusion of envelope with (Entry) cell’s plasma membrane 2. Receptor-mediated endocytosis 3. Direct penetration of virus Routes by which the viruses enter the body.. particles across the plasma Microbiology - Mod 1 Introduction to Virology 3 of 7 The use of trans, practice questions, and evals ratio must be used discreetly and social media/public exposure of the aforementioned shall be strictly prohibited.  ROUTES BY WHICH VIRUSES ENTER THE BODY ○ Interferons are a complex of protein regulatory 1 Through contaminated molecules released from Oral Transmission virus-infected cells food, drink, or saliva ○ When taken up by 2 Droplet Through inhalation of uninfected cells, these are Transmission particles rendered resistant to virus infection 3 Injections, trauma, or Direct Inoculation 2 Phagocytosis Cellular components of the insect bites immune response are also 4 Sexual Transmission involved in controlled viral infections 5 Trans-placental Viruses elicit a tissue response different from the response to pathogenic 6 Direct Skin Contact bacteria Infiltration with mononuclear IX. MODES OF TRANSMISSION OF VIRUSES cells and lymphocytes, characterizes the inflammatory reaction of uncomplicated viral MODES OF TRANSMISSION OF VIRUSES lesions 1 Droplets or aerosols 3 Respiratory Constant upward movement ○ Influenza virus tract action of ciliated epithelium ○ Measles and effect of mucus ○ Smallpox Sexually 4 Stomach acid Inactivates acid-label viruses ○ HIV ○ Hepatitis B virus 5 Skin Forms an impermeable ○ Herpes Simplex Type barrier Direct transmission 2 (HSV-2) from ○ Papilloma person-to-person Hand-to-mouth, B. SPECIFIC DEFENSE MECHANISM by contact Hand-to-eye, Mouth-to-mouth ○ Epstein-barr virus SPECIFIC DEFENSE MECHANISM ○ Herpes Simplex virus ○ Rhinoviruses 1 Humoral Immunity Due to antibodies Exchange of contaminated blood 2 Cell-mediated Immunity ○ Hepatitis B virus ○ HIV C. FACTORS WHICH INFLUENCE INFECTION 2 Indirect Enteroviruses transmission by the Rotaviruses FACTORS WHICH INFLUENCE INFECTION fecal-oral route Hepatitis A virus 1 Age Factor of viral pathogenicity 3 Humans are accidental More severe disease is often hosts through: more produced in newborns ○ bites by rabies virus Viral infections are generally Animal to animal ○ droplets or aerosols acquired in childhood and ○ rodent-contaminate are followed by long lasting d partners immunity 4 Bites of arthropod Arboviruses 2 Immune Deficiency vectors Flaviviruses 3 Pregnancy X. HOST RESPONSE TO VIRUS INFECTION The outcome of viral infections involve the interplay XI. ABILITY OF VIRUSES TO CAUSE DISEASES CAN BE between viral and host factors. VIEWED ON 2 LEVELS A. NONSPECIFIC DEFENSE MECHANISM ABILITY OF VIRUSES TO CAUSE DISEASES Usually shown very soon after viral infections There are 4 main effects: The changes NONSPECIFIC DEFENSE MECHANISM 1. Death of cell that occur 1 2. Fusion of cells to form within 1 Interferon Most prominent among the multinucleated cells individual cells innate immune response 3. Malignant Microbiology - Mod 1 Introduction to Virology 4 of 7 The use of trans, practice questions, and evals ratio must be used discreetly and social media/public exposure of the aforementioned shall be strictly prohibited.  transformation remain infections 4. No apparent morphologic or function 4 Location within an Brain change immunologically sheltered sanctuary 1. Transmission of the virus and its entry to the host 5 Rapid antigenic variation 2. Replication of the virus and damage to the cells 6 Intracellular spread The 3. Spread of the virus to other pathogenesis cells and organs 7 Immunosuppression Acquired immune 2 that takes 4. The immune response, both deficiency syndrome place in the as a host defense and as a infected patient contributing cause of certain diseases XIV. LABORATORY DIAGNOSIS OF VIRUS INFECTIONS 5. Persistence of the virus in some cases A. VIRUS ISOLATION 1. TISSUE CULTURE XII. EFFECTS OF VIRUSES ON CELLS Virus growth is recognized by the presence of: ○ Cytopathic effect EFFECTS OF VIRUSES ON CELLS ○ Heme absorption ○ Immunofluorescence When infection is lethal Cell death Kills the cell causing Cytopathic 2. CHICK EMBRYO Effect (CPE) Main routes of inoculation: ○ Chorioallantoic membrane When the cell is not killed but is ○ Allantoic cavity Cell changed from a normal cell to ○ Amniotic cavity transformation one with the properties of a Virus route is recognized by the appearance of malignant or cancerous cell. “pocks” which are virus lesions present in the chorioallantoic membrane, or presence of When the virus remains within hemagglutinins in the amniotic fluids or allantoic fluids. the cell in a potentially active Latent infection 3. CULTIVATION IN LABORATORY ANIMALS state but there is no obvious effect on the cell’s function. Mice, guinea pigs, hamster, rabbits, primates Suckling mice: less than 48 hrs old are most commonly used, and they are inoculated by: XIII. PERSISTENT VIRAL INFECTIONS ○ Intracerebral ○ Intranasal A. TYPES ○ Intraperitoneal ○ Subcutaneous 1. ESCAPE HYPOTHESIS Presence of virus is recognized by observing for signs Replicating viruses can be continuously detected often of diseases or death. at low levels. Virus is identified by testing for neutralization of their Mild or no clinical symptoms may be evident. pathogenicity for animals by standard antiviral sera. Requires proper collection of appropriate specimens 2. LATENT INFECTIONS and inoculation of suitable cell cultures, susceptible Virus persists in an occult form animals or embryonated eggs. ○ Most of the time when new known viruses are produced. When to do virus isolation? There may be intermittent flare ups of the clinical When new epidemics occur. disease, when infectious virus can be recovered. When serological tests overlap. When it is necessary to confirm a presumptive 2. SLOW VIRUS INFECTIONS diagnosis made by direct microscopic observation. Chronic, progressive, fatal infections of the CNS. When the same clinical illness may be caused by many different agents. B. MECHANISMS B. DIRECT DEMONSTRATION OF VIRUS OR ANTIGEN IN MECHANISMS OF PERSISTENT VIRAL INFECTIONS MATERIALS Most widely used and fast method of diagnosis 1 Integration of a DNA Retroviruses provirus into host cell DNA DIRECT DEMONSTRATION OF VIRUS OR ANTIGEN IN MATERIALS 2 Immune tolerance NO neutralizing antibodies are formed 1 Immunofluorescence 3 Formation of virus-antibody complexes which 2 Solid-phase immunoassays Microbiology - Mod 1 Introduction to Virology 5 of 7 The use of trans, practice questions, and evals ratio must be used discreetly and social media/public exposure of the aforementioned shall be strictly prohibited.  A. ATTENUATED LIVE-VIRUS VACCINES 3 Electron Microscopy Virus with reduced pathogenicity to provide immune response without disease. C. SEROLOGY Methods used for isolating attenuated strains are the Demonstration of virus antibody. repeated passage of human pathogens in other host Monitors the immune system’s antibody response to species. viral antigen exposure, including both infection and Results in variants with reduced virulence in humans. immunization. Traditional basis of serologic diagnosis of a viral ADVANTAGES AND DISADVANTAGES OF infection is demonstration of sera conversion or a ATTENUATED LIVE-VIRUS VACCINES significant increase in circulating homologous viral antibody over the course of illness. ADVANTAGES DISADVANTAGES 1. SPECIMEN Good immunogen Unstable SPECIMEN Induces long-lived, May produce persistent appropriate immunity infections in vaccines 1 Acute Induces good Possible contamination 2 Convalescent Sera cell-mediated immune with Simian Papovavirus response SV40 2. SEROLOGICAL TESTS Induces antibody Storage and limited shelf production and life SEROLOGICAL TESTS resistance at the portal of entry 1 Complement fixation test (CFT) B. INACTIVATED VIRUS VACCINES (KILLED VIRUS 2 Hemagglutination Inhibition test VACCINES) Method of production is through exposure of purified 3 Neutralization test virus preparations to denaturing agents. Results in loss of infectivity without loss of 4 Immunofluorescence antigenicity. 5 Enzyme-immunoassay (EIA) ADVANTAGES AND DISADVANTAGES OF INACTIVATED VIRUS VACCINES 6 Radio-immunoassay ADVANTAGES DISADVANTAGES 7 Detection of IgM More effective than the Careful manufacturing 3. RECENT INFECTION CAN ONLY BE DIAGNOSED BY subunit vaccines practices THE FOLLOWING: Stable May not protect for a long period HOW RECENT INFECTIONS CAN BE DIAGNOSED Little or no risk Not as effective at Increase in the level of virus preventing infections as Rising titer antibody at least 4 fold from acute to live viruses convalescent. Not possible for all Detection of viruses Earliest antibody to appear. IgM Cell-mediated immune High If the virus antibody is higher than response is generally poor stationary titer that found in the population. C. SUBUNIT VACCINES XIV. LABORATORY DIAGNOSIS OF VIRUS INFECTIONS The newest type of vaccines. Used to boost the immune system and prevent serious life-threatening diseases. Most cost-effective method of prevention of serious ADVANTAGES AND DISADVANTAGES OF SUBUNIT viral infections. VACCINES Immunity to a viral infection is based on the development of an immune response to specific ADVANTAGES DISADVANTAGES antigens located on the surface of virus particles or virus-infected cells. Completely safe Relatively poor For enveloped viruses, the most important antigens antigenicity – do NOT are the surface-lipoproteins. elicit the same range of antibodies as a virus does Microbiology - Mod 1 Introduction to Virology 6 of 7 The use of trans, practice questions, and evals ratio must be used discreetly and social media/public exposure of the aforementioned shall be strictly prohibited.  Rare adverse reactions Vaccine delivery — requires carries/adjuvants TWO TYPES OF SUBUNIT VACCINES SYNTHETIC VACCINES RECOMBINANT VACCINES Not very effective but has Better than synthetic great potential. vaccines. Currently, there are none There have been some in use. successes which have been achieved. e.g. Hepatitis B vaccines which are now produced in yeast XVI. AVAILABLE VACCINES VACCINES THAT ARE AVAILABLE FOR THE PREVENTION OF SEVERAL SIGNIFICANT HUMAN DISEASES CAUSED BY VIRUSES INCLUDING THEIR MOVES OF ADMINISTRATION ATTENUATED INACTIVATED VIRUS RECOMBINANT LIVE (KILLED) X HEPATITIS A (intramuscular) X HEPATITIS B (intramuscular) INFLUENZA A X X AND B (intranasal) (intramuscular) JAPANESE B X ENCEPHALITIS (subcutaneous) MEASLES, MUMPS, X RUBELLA (intramuscular) (MMR) X PAPILLOMA (intramuscular) X X POLIOVIRUS (oral) (intramuscular) X RABIES (intramuscular) X ROTAVIRUS (oral) X SMALLPOX (subcutaneous) TICK-BORNE X ENCEPHALITIS (intramuscular) VARICELLA-ZO X STER (intramuscular) YELLOW X FEVER (subcutaneous) X ADENOVIRUS (oral) Microbiology - Mod 1 Introduction to Virology 7 of 7 The use of trans, practice questions, and evals ratio must be used discreetly and social media/public exposure of the aforementioned shall be strictly prohibited.