Patterns of Viral Infection Flashcards
What is pathogenesis?
Is the complex interaction between virus and host that results in disease
What is pathogenicity?
A comparison of the severity of disease caused by different microorganisms
What is virulence?
A comparison of the severity of disease caused by different strains of the same microorganism
What are the 2 components of pathogenicity in viruses?
Effects of viral replication on the host
Effects of host response on virus and host
What are the fundamental questions of pathogenesis in regards to viral infections?
How does a virion enter the host?
How does it overcome local defences?
How does it spread to other areas of the body?
How does it exit from the host to infect other susceptible hosts?
Why is one viral strain more virulent than another?
Replication rate
Tropism
Ability to evade host immune defences
Changes in ability to disseminate within the host
How can virulence change?
Very small changes in the viral genome (eg influenza B can change to bind to human entry protein as well)
What cellular factors determine pathogenicity of viruses?
Presence of receptors for binding
Physical and molecular environment of host cell must enable initial replication cycle (eg upper respiratory viruses may ideally want 33 degrees cells)
What is the cytopathic effect?
Many viruses kill the cells in which they replicate. Infections induce characteristic appearance.
What can CPE be used for?
Diagnosis of infecting virus
How can viruses enter host through the skin?
Through abrasians
Entry via inoculation with contaminated needles
Through insect or animal bites
How can viruses enter host through mucous membrane?
Entry via respiratory tract
Entry via GI tract (faecal-oral route, eg poliovirus causing poliomyelitis)
Entry via conjunctiva (Enterovirus type 70 causes conjunctiva)
Entry via genital tract (eg. STIs)
How do viral infections of the respiratory tract manifest themselves?
Could show symptoms above the neck and below the neck.
How do viruses spread?
Through blood (either through capillaries by replicating in endothelial cells or through insect bite)
Through lymphatic capillaries they can enter circulation as well
What is viraemia?
Presence of infectious virus in the blood
What causes active viremia vs passive viremia?
Virus replication causes active
Virus introduction causes passive
What is primary viremia?
Virus enters blood after initial replication at site of entry
What is secondary viremia?
Virus produced by disseminated infections
How is there diagnostic value in viremia?
The secondary viremia is stronger allowing blood samples to give us more information
What are the important target organs for viral infections?
Skin
Lungs
Liver
Kidneys
CNS
What do viral infections of the skin typically look like?
A skin rash or exanthem
Vesicular erutions caused by replication of viruses in epthelial cells
Maculopapular rash (destruction of cells by Cytotoxic T Lymphocytes)
Purpuric rash causing haemorrhaging (as seen in dengue virus)
What type of infections hit the lungs?
Most respiratory infections are localized
Some are part of a generalized infection (e.g. Measles –
pneumonitis is a common feature)
What type of infections hits the liver?
Hepatitis viruses
Also infected during generalized infections like yellow fever