Viral Pathogenesis Flashcards
What does a virus need to initiate an infection?
- Sufficient virus at site of entry
- Host cells must be susceptible
- Host cells are permissive (factors needed for replication and dissemination)
- Local antiviral defense must be breached
What does it mean for a cell to be susceptible?
Susceptible cells have receptors required for viral entry
What are some viral entry sites?
Aerosol transmission
Oral-fecal transmission
Sexually transmitted
Arthropod vector
Contact with blood/secretions
What will stomach acid degrade?
Membrane viruses
What is R0?
The number of people an infected person can pass the virus onto
What are acute infections like?
Rapid and self-limiting
The virus can be present before symptoms
What are some viruses that cause acute infections?
Rhinovirus
Rotavirus
Influenza
Coronavirus
Poliovirus
How is influenza spread and what type of infection is it?
An acute infection spread by aerosolized droplets
How long can viruses remain infectious on surfaces?
As long as they are wet
What are persistent infections like?
On-going infections
Viruses can persist and overwhelm the immune system later
What is an advantage of a virus with a persistent lifestyle?
The virus doesn’t have to find a new host for a long time
What virus causes persistent infections?
Hepatitis B
What type of infections can hepatitis B be?
Acute or persistent
What are the symptoms of acute HBV?
Fever, loss of appetite, nausea, vomiting, abdominal pain, yellow colouring of the eyes, dark urine, clay-colored or light stools
What percentage of people with acute HBV fail to clear it?
5%
What percentage of people clear chronic HBV?
5-10% of adults
95% of perinatally infected infants
What might people with chronic HBV develop?
Chronic hepatitis
Permanent liver damage
Liver cancer
How can we diagnose an HPV infection?
PCR, antigen screen
What are latent infections like?
An extreme persistent infection that can hide from the immune system
What is an example of a latent, reactivating infection?
Herpes simplex complex
Where does herpes simplex hide?
In the trigeminal ganglia and can reactive when you are stresses as nerves are typically protected from immune responses
What percentage of the population has recurrent symptoms of herpes?
20%
What is a worry with latent infections?
Symptoms may not always be present while virus is infectious
What are slow infections like?
Slow viruses have a long latency period followed by acute infection
The virus may be present at times during latency (HIV) or undetectable for years (measles SSPE)
What is SSPE?
Measles subacute sclerosing panencephalitis
What types of infections does measles cause?
Acute infections and a rare latent disease
What are the symptoms of measles?
Rash, hypersensitivity reaction, fever, cough, conjunctivitis
Why is measles so contagious?
The virus can remain in the air for up to 2 hours after the infected person leaves an area
It has a long incubation period, people are contagious 4 days before the rash starts through four days after
What are some injuries that can be caused by viruses?
- Cytopathic effects on cells directly = cells may be lysed
- Viruses can be oncogenic
- Immunopathology = damage as a result of local inflammation
How can viruses be oncogenic?
Cells lose contact inhibition and their normal anchorage-independence interactions and become immortal
Can be transformed by virally encoded oncoproteins
Viral disruption of host genes
What is poliomyelitis?
Paralysis caused by poliovirus, affects 1% of infected individuals as the virus becomes neurotrophic and causes rupture of neurons
Why was there an increased incidence of poliomyelitis in the early 1900’s?
Sanitation improved so babies were not exposed to poliovirus while still protected by maternal antibodies
What effect can develop from poliovirus?
Cytopathic effect = cell rounding and lysis
What are avian cells transformed by?
Two forms of Rous sarcoma virus
What does loss of contact inhibition mean?
Cells normally do not pile up on each other and start piling up
What does anchorage independence mean?
Cancer cells lose their attachments and become mobile
What did the filtration of sarcomas in chickens prove?
That tumorigenesis was not due to a primitive transplantation-like effect but rather a virus
What do viral oncogenes cause?
Cancer
What can retroviruses do?
Take up cellular DNA and integrate a provirus form into the genome
What does Rous sarcoma virus take up?
A src gene that is used as a cell signalling molecule that phosphorylates proteins involved in signal transduction
Unregulated cell signalling from v-src causes cancer
