9 - Viral infection and Prions* Flashcards
Requirements for successful infection
- Dose (enough virus)
- Access to target cells (susceptible, permissive)
- Absent or insufficient host immunity
Viral pathogenesis
The complex interaction between virus and host that results in disease
Pathogenicity
The comparison of the severity of disease caused by different microorganisms
Virulence
Comparison of the severity of disease caused by different strains of the same microorganisms
How can a virus enter through skin
- Abrasions (HPV)
- Inoculation with contaminated needles (HIV, Hepatitis B and C)
- Insect or animal bites (rabies)
How can a virus enter through mucous membranes
- Respiratory tract (Influenza, Corona)
- Gastrointestinal tract (eg. Poliovirus)
- Conjunctiva (Adenoviruses)
- Genital tract (Herpes, HIV)
- Transplacental, congenital and vertical (HSV, Rubella, CMV)
Virus dissemination after infection
- Localised at site of entry
- Spread from site of entry to one or more distant sites
Disseminated viruses
Viruses that have spread beyond the primary site (if many organs are infected becomes systemic)
What are the important target organs of infection
- Skin (measles)
- Lungs (pneumonia)
- Liver (yellow fever)
- CNS (polio, rabies)
Example of transplacental infection
Zika virus
Viral selective advantage
Drug stops replication of susceptible variants, favouring resistant variant to grow and dominate
Viral classification suffixes
- Order (‘-virales’)
- Families (‘-viridae’)
- Genera (‘-virus’)
How are viruses visualised
Using electron microscope. Does not require organism specific reagents (like in serological or biochemical identification)
Host range
Spectrum of host cells the virus can infect (invertebrates, vertebrates, plants, fungi and bacteria)
How is host range determined
by virus requirements for attachment to host cell
availability within host cell of factors required for replication
Zoonotic diseases
Viruses that cross species barriers
Smallpox
Caused by infection with variola virus. First human disease successfully eradicated by vaccination
Influenza
- In 1918 after WW1 spread around the globe in a series of waves killing > 50 million people
- No vaccine effective against all influenza as new strains continuously emerge
SARS-CoV
A novel coronavirus associated with severe acute respiratory syndrome.
Highly contagious, reservoir host identified as bats.
What is a prion
Proteinaceous infectious particle.
Abnormal pathogenic agents that are transmissible and able to induce abnormal folding of prion proteins that are found abundantly in brain. Results in large vacuoles in the brain
what are prions distinguished by
- Long incubation periods
- Characteristic spongiform changes associated with neuronal loss
- Failure to induce an inflammatory response
Cruetzfeldt-Jakob disease (CJD)
- Dementia
- Rapidly progressive and always fatal
- Infection leads to death usually within one year of onset of illness (4-5 months)
vCJD human form of BSE
- Varient of CJD
- Prominent psychiatric/behavioural problems, delayed neurological signs
- Infections leads to death usually around 13-14 months post onset of illness
Name another disease caused by prions
Fatal familial insomonia
name three diseases caused by prions in animals
- Scrapie in sheep
- CWD (chronic wasting disease)
- Mad cow disease
Mad cow disease (BSE)
- Originated as a result of feeding cattle meat and bone meal that contained BSE infected products
- Cattle experience progressive degeneration of nervous system and must be sacrificed
What does BSE stand for
Bovine spongiform encephalopathy
Kuru
First identified transmissible spongiform encephalopathy
Transmitted orally via the consumption of infected meat/nervous tissue - endocannibalism
