Lecture 12: Viruses, Pathogenesis, Role, Diagnosis - Chap 36, 37, 38, 39 Flashcards
Who proposed the term ‘virus’ in the 1890s?
Louis Pasteur.
What discovery did Ivanovski and Beijerinck make about viruses?
They found that a disease in tobacco was caused by a virus (filterable agent).
What is the general size range for viruses?
20 to 200 nm.
What is a nucleocapsid?
The capsid and nucleic acid together.
What term describes a fully formed virus capable of infection?
Virion.
How do enveloped viruses differ from naked viruses in terms of stability?
Enveloped viruses are sensitive to drying, acid, and detergents, while naked viruses are more stable.
What is the main function of viral spikes?
To attach to host cells and stimulate the immune response.
How do helical and icosahedral capsids differ in structure?
Helical capsids are spiral, while icosahedral capsids have a 20-sided structure.
What is a common feature of complex capsids found in bacteriophages?
They include tail fibers and a capsid head.
How are enveloped viruses typically released from host cells?
By budding or cell lysis.
What role do matrix proteins play in enveloped viruses?
They link the envelope to the capsid and help in virus assembly.
What are viral genomes primarily composed of?
DNA or RNA, but not both.
Which viruses contain single-stranded DNA as an exception?
Parvoviruses.
How do RNA viruses differ from DNA viruses in replication location?
RNA viruses generally replicate in the cytoplasm, DNA viruses in the nucleus.
What mechanism do viruses use to ensure survival in the gut environment?
Naked capsids, which are resistant to acid and enzymes.
What is the primary function of reverse transcriptase in retroviruses?
To convert viral RNA into DNA.
What is the initial step in the viral multiplication cycle?
Adsorption, where the virus attaches to the host cell.
During viral penetration, how does an enveloped virus enter a cell?
By fusing with the host cell membrane.
What is the purpose of uncoating in viral infection?
To release the viral genome into the host cell.
In which part of the host cell are most DNA viruses assembled?
In the nucleus.
How do lytic viruses damage their host cells?
By replicating and lysing the cell.
What is a latent viral infection?
A dormant infection where the virus is present but not actively replicating.
What process allows oncoviruses to transform host cells?
By inactivating or altering cell growth suppressors, such as p53.
Which viruses are commonly associated with causing human cancers?
HTLV-1, HBV, HCV, HPV 16/18, EBV, and HHV-8.
What are cytopathic effects in viral infections?
Visible damage to host cells, such as syncytia and inclusion bodies.
What is syncytia formation in viral infections?
Fusion of infected cells to form multinucleated cells.
How can viruses transmit via aerosols?
Through respiratory droplets.
What type of viruses are transmitted through blood transfusion or organ transplant?
Hepatitis B, C, D, HIV, and HTLV-1.
How do prions differ from viruses in structure?
Prions are misfolded proteins without nucleic acid.
What laboratory method is often used to detect viral DNA or RNA?
PCR.
What are the basic structural components of viruses?
Capsid, nucleic acid (DNA or RNA), and sometimes an envelope with spike proteins
How does a viral capsid protect the virus?
Provides a rigid outer shell that protects viral genetic material and aids in host cell attachment
What roles do spike proteins play in viral infection?
Aid in cell attachment, immune evasion, and sometimes enzymatic functions (e.g., neuraminidase in influenza)
Differentiate between naked and enveloped viruses in terms of stability.
Naked viruses are more stable, surviving acidic conditions and drying; enveloped viruses are labile, sensitive to drying and detergents
Describe the six main stages of viral replication.
1) Adsorption, 2) Penetration, 3) Uncoating, 4) Synthesis, 5) Assembly, 6) Release
What is adsorption in the viral replication cycle?
Attachment of viral spikes to specific receptors on host cell membranes
How do viruses enter host cells?
By fusion (for enveloped viruses) or endocytosis (for both naked and enveloped viruses)
Define viral tropism.
The specificity of a virus for a particular host cell type, determined by receptor binding
What is tissue tropism, and why is it important?
Refers to the preference of viruses for certain tissues or organs, impacting disease severity and symptoms
How do lytic infections cause cellular damage?
By replicating within and lysing the host cell, releasing new virions
What is a non-lytic infection?
Infection where viruses replicate without killing the host cell, often releasing virions through budding
Give an example of a cytopathic effect (CPE).
Syncytia formation in RSV infection, where infected cells fuse into large multinucleated cells
How do oncogenic viruses contribute to cancer?
By altering host cell genes related to growth (e.g., HPV affecting p53 and RB proteins)
What is immune-mediated damage in viral infections?
Tissue damage resulting from immune response, such as inflammation from cytokine release
List common viral transmission modes.
Respiratory droplets, fecal-oral route, bloodborne, and direct contact
What are common symptoms of respiratory viral infections?
Cough, fever, sore throat, and nasal congestion
Describe the typical disease progression for HSV.
Starts with skin or mucosal lesions (cold sores), can progress to encephalitis in severe cases
How does HIV affect the immune system?
Infects and destroys CD4+ T cells, leading to immunodeficiency
Which laboratory technique is commonly used to detect viral RNA?
PCR (Polymerase Chain Reaction)
What is the purpose of serology in viral diagnostics?
To detect antibodies against specific viruses, indicating current or past infection
How is immunofluorescence used in viral diagnosis?
Detects viral antigens in infected tissues or cells using fluorescent antibodies
Define the term ‘viremia.’
Presence of viruses in the bloodstream, often spreading infection to secondary sites
Describe the cytokine response in viral infections.
Release of cytokines like TNF and IL-1, which induce fever and inflammatory symptoms
What role does humoral immunity play in viral defense?
Production of antibodies that neutralize viruses and mark them for destruction by phagocytes
How do viruses evade the immune system?
Through methods like antigenic variation, hiding in host cells, or producing immune-modulating proteins
What is a cytokine storm, and how does it relate to viral infections?
An excessive immune response that causes tissue damage, seen in severe viral infections like SARS
Name a common method for diagnosing herpesvirus infections.
Observation of syncytia or inclusion bodies in infected tissue samples
How do viruses utilize host cell machinery for replication?
By redirecting host enzymes and ribosomes to synthesize viral proteins and genomes
What is antigenic drift, and in which viruses is it common?
Minor mutations in viral genes over time, common in influenza viruses, causing seasonal variation
Describe the mechanism of viral latency.
Virus remains dormant in host cells, reactivating under certain conditions without immediate symptoms
How does the immune system control latent viral infections?
Through cytotoxic T cells and memory B cells that target reactivated viruses
What is a viral oncogene?
A viral gene that can transform host cells and promote uncontrolled cell growth
List viruses associated with hemorrhagic fevers.
Ebola, Marburg, and Dengue viruses
Describe viral encephalitis and a common causative agent.
Brain inflammation caused by viruses like HSV-1, leading to fever, headache, and seizures
What diagnostic technique is used for chronic hepatitis virus infections?
Serology for hepatitis B surface antigen (HBsAg) and hepatitis C antibodies (anti-HCV)
