Microbiology Chapter 13
Most viruses infect only
A certain type of host
Enveloped viruses may be damaged by
increased temperature freezing temperature pH below 6 or above 8 lipid solvents some chemical disinfectants
Enveloped RNA virus that has the surface antigen of another virus
Hepatitis D
Viroids
Naked strands of RNA (no capsid or envelope) 1/10th size of normal virus Cause diseases in plants
Transmission of viruses
Respiratory transmission Fecal-oral transmission Blood-borne transmission Sexual Transmission Animals or insect vectors
A helical capsid of a virus
Rod or thread shaped
How many stages are in animal viral replication?
Six
Damage to host cell cytopathic effects (CPE) - Visual effects of virus on a cell
Shape change Detachment from adjacent cells Swelling Fusion into giant, multinucleate cells (syncytia)
Oncogenic viruses, oncoviruses
Epstein-Barr virus Human papillomavirus (HPV) Human Herpes virus 8 Human T-cell leukemia virus 1 & 2
Where does an enveloped virus get its envelope from?
From its host cell during viral replication or release.
Non- enveloped RNA virus that is transmitted by the fecal-oral route
Hepatitis A
Enveloped DNA virus that is transmitted by blood
Hepatitis B
Purified surface protein of this virus is the immunogen in a vaccine
Hepatitis B
Where is an envelope found?
In some viruses (mostly animals)
What is it know as if cell is lysed?
Lytic replication
Hepatitis B is an infectious disease of major import. The causative virus belongs to which family of viruses: a. paramyxoviridae b. poxviridae c. hepadnaviridae d. orthomyxoviridae
C
What do all viruses have?
Capsid and nucleic acid
Where do viruses have to be to replicate?
Inside the cell
Polyhedral (Icosahedral) capsid of a virus
Most are 20 sided polygons
Capsid of a virus.
Protein coat surrounding virus and protects nucleic acid Consists of one or more proteins unique to the virus Determines shape of virus
Animal viruses
Proteins or glycoprotein spikes that correspond to glycoproteins on the surface of animal cells.
Modes of viral multiplication of Attachment (adsorption)
Bacteriophage - tail fibers to cell wall proteins Animal virus - spikes, capsid, envelope to cell membrane
Each of the following statements concerning viral surface proteins is correct EXCEPT: a. They elicit antibody that neutralizes infectivity of the virus. b. They determine the species specificity of the virus-cell interaction. c. They participate in active transport of nutrients across the viral envelope membrane. d. They protect the genetic material against nucleases.
C
What is a non-enveloped or naked virus?
No membrane around capsid
Describe a virus
Obligate intracellular parasite Can only replicate inside cell Cannot make proteins without a host Strands of nucleic acid surrounded by protein coat Cannot be destroyed by antibiotics
What are viruses dependent on for replication?
On host's organelles and enzymes to produce new virions
What is an envelope composed of?
Phospholipid bilayer and proteins outside of capsid
Diseases caused by non -enveloped or naked viruses:
Poliomyelitis Warts Common cold
Bacteriophages
Proteins in their tail fibers that attach to proteins on the surface of bacterial cells.
Prions
Small, proteinaceous, infectious particle no nucleic acid, no envelope, no capsid not destroyed by heat to 90o C not sensitive to radiation treatment not destroyed by enzymes that digest nucleic acids sensitive to protein denaturing agents
Satellites
Small, single stranded RNA molecules Must have "helper" virus to replicate Replication "revolves around" helper virus Mostly associated with plant viruses Exception = hepatitis delta virus (HDV) Smallest genome of any known animal virus Primarily transmitted by blood or blood products Vaccination for HBV prevents infection Increases Hepatitis B death rate 10x
How are viruses classified?
Type of nucleic acid Presence of an envelope Shape Size Host cell specificity Animal, plant, bacterial
Modes of viral multiplication of Biosynthesis
Using host cell's metabolic machinery Bacteriophage - in cytoplasm Animal virus - in cytoplasm (RNA viruses) or nucleus & cytoplasm (DNA viruses)
Non-cellular infectious agents
Viroids, Satellites and Prions
Chronic or latent state of damage to a host cell
Virus remains dormant in nerve cells Activated by stress, immunosuppression (cold, fever) All Herpesviruses capable of causing latent infections
Replication usually causes the host cell to
lyse and die (may be immediate or long term)
Complex capsid of a virus
Variety of shapes
Some viruses can cause cancer attributed to the presence of oncogenes. Which of the following is NOT an example of this? a. Hepatitis A virus b. Epstein Barr virus c. Human Papilloma virus d. Hepatitis B virus
A
Viruses may be so specific that they infect
A particular cell of the host organism
What is a Virus?
A submicroscopic, parasitic, filterable agent consisting of a nucleic acid surrounded by a protein coat.
Maturation
Assembly of new components into complete virons- occurs spontaneously
What are the five stages in bacterial viruses? (bacteriophages)
Attachment Penetration/Entry Biosynthesis Maturation Release
Specificity
Attraction of viral surface molecules to proteins/glycoproteins on the surface of the host cell. receptors
Each of the following viruses possesses an outer envelope of lipoprotein EXCEPT: a. Varicella-zoster virus b. Papillomavirus c. Influenza virus d. Human immunodeficiency virus
B
Latency is an outcome particularly characteristic of which one of the following viral groups? a. Polioviruses b. Herpesviruses c. Rhinoviruses d. Influenza viruses
B
The "common cold" syndrome has been associated with several viral agents. Which of the following viral agents is not associated with the "common cold" syndrome? a. rhinovirus b. variola c. corona virus d. adenovirus
B
Modes of viral multiplication of Release
Bacteriophage host cell lysis* enzyme = lysozyme Animal virus budding (enveloped viruses) cell rupture (non-enveloped viruses)
Modes of viral multiplication of Maturation
Bacteriophage - addition of parts (collar, sheath, tail fibers, etc.) Animal virus - assembly of capsid; insertion of viral nucleic acid into capsid RNA viruses in cytoplasm DNA viruses in nucleus
Modes of viral multiplication of Penetration or entry into a host cell
Bacteriophage - injection of NA through cell wall Animal virus - endocytosis or fusion
Modes of viral multiplication of uncoating
Bacteriophage - none needed Animal virus - enzymatic (lysosomal) digestion of viral proteins
Cultivation and Replication in vitro methods
Cell or tissue culture
What are naked viruses more resistant to?
Changes in temperature and pH
Persistent Infections of damage to a host cell
Continual production of viruses over many months or years Serious effects; often fatal
Transformation
Conversion of normal cells into malignant cells
The ability of a virus to produce disease can result from a variety of mechanisms. Which one of the following mechanisms is LEAST likely? a. Cytopathic effect in infected cells. b. Malignant transformation of infected cells c. Immune response to virus-induced antigens on the surface of in fected cells. d. Production of an exotoxin that activates adenylate cyclase.
D
The herpes simplex viruses cause specific disease entities and this includes the following except: a. gingivostomatitis b. encephalitis c. Kaposi's vericelliform eruption d. infectious mononucleosis
D
Nucleic acid core of a virus
DNA or RNA, never both. RNA genomes only occur in viruses. May be double or single stranded.
Release
Departure of new virons from host cell, generally kills host cell
How can viral diseases be prevented and treated?
Good hygiene Vaccines Anti-viral drugs
Enveloped RNA virus that is the most common cancer of non-A, non-B hepatitis
Hepatitis C
Cultivation and Replication in vevo methods
Laboratory animals Embryonic bird tissues
Biosynthesis
Making of new nucleic acid molecules, capsid proteins, and other viral components
Diseases caused by enveloped viruses:
chickenpox shingles mononucleosis herpes simplex (cold sores/genital herpes)