k? (L16) Flashcards
Virus encounters can lead to various outcomes IN CELLS
Acute cytopathic infection Persistent infection Latent infection Cell transformation Abortive infection Null infection
Virus encounters can lead to various outcomes IN ORGANISMS
Acute infection (disease) Subclinical infection Persistent and chronic infections Latent infection Slowly progressive disease Virus-induced tumour
How do we define disease?
SYMPTOM:
Any subjective evidence of disease or of a patient’s condition, i.e. such evidence as perceived by the patient, a change in a patient’s condition indicative of some bodily or mental state (how ill you feel)
CLINICAL SIGN:
An objective physical finding found by the examiner.
- Infection may or may not result in overt disease. In the absence of observable disease, an infection is said to be subclinical or silent.
- An immune response measured in vitro may not correlate with recovery or protection
define Virus Virulence
Virulence is the capacity to cause disease.
Virulence among viruses is relative and varies from avirulent (no disease) to lethal.
Few viruses are 100% lethal. e.g. ‘virulent’ poliovirus causes paralysis in only 1% of infected individuals.
Different strains of a virus can vary in virulence
define attenuation
Attenuation is the reduction in the virulence of a virus
define pathogenicity
Pathogenicity is the ability of the virus to cause pathology: this can be microscopic or macroscopic.
Since avirulent viruses can be pathogenic the terms are not synonymous.
Pathogenicity has come to mean ‘ability to cause disease’
Virulence has come to mean ‘relative disease-causing capacity’
what does virulence depend on?
Virulence depends on a combination of viral and host factors:
Virus factors
strain/isolate - genetically determined
dose
route of infection
Host factors
species
genetic constitution e.g. MHC proteins expressed
age, sex, nutritional status
The virulence of a virus cannot be described without reference to the conditions of infection
The Iceberg Principle of Infection
TOP OF ICEBERG Death of host Classical and severe illness Mild illness Subclinical or silent infection No infection BOTTOM OF ICEBERG
this shows a spectrum
Immune Control of Virus Infections
DIAGRAM IN L16 S12
Regulation of virus infection by the immune system (IS)
The IS is made up of many different responses:
- each is graded, not all or nothing
- quality and quantity of responses vary among people
The IS is not homogeneous throughout the body:
- e.g. CNS not subject to the full range of systemic IR until the blood-brain barrier is breached
- e.g. mucosal IS comprises all mucosal surfaces, and is in many ways distinct from the systemic IS
Regulation of virus infection by the immune system (IS):
Multiple elements of the IS combine to control a virus infection
Often only one part of the IS is effective in combating a particular infection, even though all parts of the immune response are mounted:
— each virus infection may be combated by different responses
The target of the immune response can be the virion or the infected cell or both
Intracellular virus is beyond the reach of adaptive immunity, unless virus antigens are displayed on the cell surface
Network of antiviral immunity
LOOK AT L16 S15
INNATE IMMUNITY AND VIRUS INFECTION
TITLE
types of Interferons
Type 1 Interferons α and β:
closely related cellular proteins made in response to virus infection.
have antiviral activity
can upregulate expression of proteins that are antiviral
can upregulate the expression of MHC I proteins (builds adaptive response)
Type 2 Interferon γ:
a cellular protein made by activated T cells in response to their cognate antigen
is a cytokine
different in sequence from interferons α and β
has antiviral activity
can upregulate the expression of MHC I and II proteins
how are interferon responses elicited
STEPS
- induction
- priming an antiviral state
- antiviral action of ISGs
