viral pathogenesis Flashcards
What are the requirements for successful infections?
dose
access to target cell
absent or insufficient host immunity
Why is the knowledge of incubation periods important?
aids diagnosis and is essential tool in tracing spread of disease outbreaks
What are the different lengths of incubation?
short (<1 week) - localised infections - Arboviruses
medium (7-21 days) - generalised infections - Measles
long (weeks to month) - Rabies
very long (years) - usually fatal - prion disease
Why is knowledge of disease patterns important?
aids in disease management and public health response
What are the different types of disease patterns?
Acute none persistent - rapid and self limiting
Latent - persistence of viral genome in the host cell
Persistent - asymptomatic
Persistent pathogenic
Insidious infections with fatal outcomes
What is viral pathogenesis?
Complex interaction between virus and host that results in disease
What is pathogenicity?
the comparison of the severity of disease caused by different microorganism
What is virulence?
the comparison of the severity of disease caused by different strains of the same microorganism
What are common sources of animal-to-human transmission?
rodents
bats
Where can viruses invade a host?
entry through the skin
entry through mucous membranes (most)
What are the skin entry routes?
abrasions
inoculation and contaminated needles
insect or animal bites
What are the entry routes via mucous membranes?
respiratory tract
gastrointestinal tract
conjunctiva
genital tract
transplacental
What happens after viruses reach the basement membrane?
directional release of virus particles from polarised cells at the mucosal surface
How are virus particles released from polarised cells?
Apical release (no underlying penetration)
Basolateral release (penetrates underlying, may allow systemic spread)
Both released (= disseminated infection)
What is haematogenous spread?
disseminate by entering bloodstream
How can viruses be taken up?
by local lymphatic vascular system, replicate in endothelial cells or inoculation by a vector bite
What is viraemia?
describes the presence of infectious virus particles in blood
What is active viraemia?
produced by virus replication
What is passive viraemia?
virus particles are introduced into the blood without viral replication at the site of entry
What is secondary viraemia?
subsequent disseminated infections
What are cellular factors for viral invasion?
Presence of appropriate receptors
Physical and molecular environment
Morphological changes in host cell caused by viral invasion (cytopathic effects)
What are some cytopathic effects?
lysis
syncytium formation
What is syncytium formation?
fusion of an infected cells with neighbouring cells leading to the formation of multi-nucleate enlarged cells or syncytia
What are the different types of skin rash’s (exanthem features)?
enanthem
vesicular eruptions
maculopapular rash
purpuric rash
haemorrhagic rash
What are Maculopapular rashes?
destruction of infected cell by CTL
What is a purpuric rash?
thrombocytopenia
What can cause a Haemorrhagic rash?
disseminated intravascular coagulopathy
Where does dissemination of infection occur?
localised at the site of entry
spread from site of entry to one or more distant site
What are the important target organs for dissemination?
lungs
liver
central nervous system
What are some CNS viral infections?
aseptic meningitis
encephalitis
myelitis
paralysis
What is aseptic meningitis?
inflammation of meninges
What is encephalitis?
infection of the brain
What are some symptoms of Encephalitis?
headache, fever, confusion, drowsiness, convulsions, seizures, hallucinations
What is acute flaccid paralysis?
acute onset of flaccid paralysis in one or more limbs
What causes acute flaccid paralysis (AFP)?
may be caused by anterior horn cell infection with wild or vaccine polio virus
What can primary HIV disease lead to?
AIDS dementia complex (brain)
vacuolar myelopathy (spinal cord)
peripheral neuropathy (nerve)
meningitis (acute or chronic)
What are the 7 stages of HIV replication cycle?
binding
fusion
reverse transcription
integration
replication
assembly
budding
What is the measles infection pathway?
- virus entry
- primary replication
- spread and cell tropism
- cell injury and clinical illness
- recovery from infection
- virus shedding and transmission
How can a virus shed?
from primary site of multiplication or from target organ
How can a virus shed?
from primary site of multiplication or from target organ
What is R0?
is the average number of secondary cases generated by one primary case in a susceptible community
