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Questions and Answers
Through which route is the Hepatitis A virus excreted?
Through which route is the Hepatitis A virus excreted?
What is the term for the ability of a virus to infect specific cells or tissues?
What is the term for the ability of a virus to infect specific cells or tissues?
Which of the following is a host factor that determines the severity of a viral disease?
Which of the following is a host factor that determines the severity of a viral disease?
What is the term for the presence of a virus in the blood?
What is the term for the presence of a virus in the blood?
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Which of the following is NOT a route of viral excretion?
Which of the following is NOT a route of viral excretion?
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What is the term for the ability of a virus to cause disease?
What is the term for the ability of a virus to cause disease?
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Which of the following is a factor that can influence the immune response to a viral infection?
Which of the following is a factor that can influence the immune response to a viral infection?
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What is the term for the initial symptoms that occur before the onset of a specific disease?
What is the term for the initial symptoms that occur before the onset of a specific disease?
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What is pathogenicity?
What is pathogenicity?
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What is meant by viral tropism?
What is meant by viral tropism?
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What is an example of tissue tropism?
What is an example of tissue tropism?
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What is an example of host tropism?
What is an example of host tropism?
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What is viral virulence?
What is viral virulence?
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What determines the ability of a virus to cause disease?
What determines the ability of a virus to cause disease?
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What is an example of cellular tropism?
What is an example of cellular tropism?
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What is the relationship between viral virulence and pathogenicity?
What is the relationship between viral virulence and pathogenicity?
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What determines the specific target tissues that a virus can infect?
What determines the specific target tissues that a virus can infect?
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What is the term for the period between exposure to an infection and the appearance of the first symptoms?
What is the term for the period between exposure to an infection and the appearance of the first symptoms?
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What is the primary route of transmission for rhinoviruses?
What is the primary route of transmission for rhinoviruses?
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What is the term for the early symptom(s) that might indicate the start of a disease before specific symptoms occur?
What is the term for the early symptom(s) that might indicate the start of a disease before specific symptoms occur?
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What is the term for the spread of a virus from the initial site of infection to other parts of the body?
What is the term for the spread of a virus from the initial site of infection to other parts of the body?
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What factor can influence the length of the incubation period?
What factor can influence the length of the incubation period?
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What is the term for the process by which a virus enters the body and initiates infection at a primary site?
What is the term for the process by which a virus enters the body and initiates infection at a primary site?
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What type of cells does HIV infect?
What type of cells does HIV infect?
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Study Notes
Severity of Disease
- Host factors that determine severity of disease include age, genetic predisposition, malnutrition, immunosuppression, other underlying illnesses, and psychological factors.
Excretion
- The virus is excreted via various routes after replication and spread, including:
- Skin via vesicles/lesions (e.g. HSV 1 and 2)
- Respiratory tract (e.g. RSV or influenza)
- Genito-urinary tract (GUT) (e.g. measles or CMV - in urine, e.g. HIV or HBV - in semen)
- Gastro-intestinal tract (GIT) (e.g. rotavirus or Hepatitis A)
- Body fluids (breast milk) (e.g. HIV or HBV)
Viral Tropism
- Viral replication at specific target tissues often defines the symptoms of the disease
- Examples of viral tropism include:
- Hepatitis viruses infecting hepatocytes
- Varicella-zoster virus infecting neurons and epithelial cells
- HIV infecting CD4 cells
- Determined by the presence of specific receptors on cells that can be used by the virus
Spread in the Host
- Local spread: restricted to cells where the virus entered, replicates, and is released from infected cells, then spreads to neighboring cells
- Systemic spread: virus breaches epithelial barrier, invades sub-epithelial tissues, breaks through basement membrane, and allows spreading to other parts of the body via blood, lymphatics, or nerves
- Examples of localized infections:
- Rhinoviruses: upper respiratory tract (URT)
- Rotaviruses: intestinal epithelium
- Papillomaviruses/poxvirus: epidermis
- Examples of systemic infections:
- Enteroviruses: intestinal epithelium, lymphoid tissues, CNS
- Herpesviruses: oropharynx or GUT, lymphoid cells, CNS
Systemic Infection
- Acquisition: virus enters the body
- Primary replication at the site of entry
- Incubation period: virus is amplified and may spread to a secondary site
- Primary viraemia: spread via neurons/lymph
- Secondary site of replication
- Secondary viraemia
- Prodrome: early symptom(s) that might indicate the start of a disease before specific symptoms occur
Incubation Period (IP)
- Period between exposure to an infection and the appearance of the first symptoms
- Factors that influence the length of the IP include:
- Dose or inoculum of infectious agent
- Route of inoculation
- Rate of replication of infectious agent
- Host susceptibility and immune response
Pathogenicity and Viral Virulence
- Pathogenicity: ability of an organism (e.g. virus) to cause disease in a susceptible host
- Viral virulence: capacity of a virus to cause disease, often used as a measure of pathogenicity
- Viral tropism: specificity of a virus for a particular host, tissue, or cell, i.e. where the virus can infect and replicate
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Description
This quiz covers factors that determine the severity of disease caused by viruses, including host factors and modes of viral excretion. Test your knowledge of virology!
