Microbiology 5 Flashcards
List the types of transmission of virus
- Respiratory
- Fecal oral
- Contact
- Zoonoses
- Blood
- Sexual contact
- Maternal-neonatal
- Germ line
What are fomites?
Snot.ect from a surface when an infected person touches them
What is intragenic transmission?
Where a health worker is the cause of infection.
What is a nosocomial infection?
An infection caught in the hospital.
What is vertical transmission?
From parent to offspring
What is horizontal transmission?
Any form of transmission not from parent to offspring.
What is germ line transmission?
Where the virus is part of the host genome.
What is viraemia?
Virus in the blood
What are the stages of dissemination from the site of entry?
Local infection to primary viraemia to amplification to secondary viraemia to the target organ.
What causes viral rashes?
- Systemic viral transmission
- Virus leaves the blood and enters the skin
- Cells are destroyed by virus replication
Define the term tropism.
The predilection of viruses to infect certain tissues and not others.
How is tropism determined?
- Can be defined by receptor interactions (susceptibility)
- Ability to use the host cell to complete replication (permissivity)
- Whether the virus can reach a tissue (accessibility).
How is the tropism of HIV determined?
- Receptor use - CD4 and CCR5 or CXCR4 co receptors
- Delta 32 mutation in CCR5 leads to HIV resistance
What receptors does measles use?
Two receptors - CD155/SLAM and Nectin 4
Describe the pathway taken by the measles virus.
- Virus enters new host - binds to SLAM on immune cells resulting in ummunosuppression
- Virus exits from the infected host using nectin 4 on the airway epithelia
What determines tropism of HA (influenza) virus?
- The virus enters through endosomes
- Low endosomal pH triggers fusion
- HA cleavage is required for exposure of fusion peptide (conformational change)
- Depends on availability of host proteases
Define the term pathogenicity
The ability of the virus to cause disease
Define the term virulence
The capacity of a virus to cause disease
What does viral disease depend upon?
Viral disease depends on how much replication the virus undergoes but is affected by other factors too such as the host response.
What are the different patterns of virus infection?
- Acute infection (followed by viral clearance)
- Acute infection with accidental tissue damage
- Persistence infection - latent& slow& transforming
- Long incubations
- Oncogenesis
Define acute viral infection
Rapid onset of disease
What are arboviruses?
Viruses spread by insects
What is a systemic infection?
Infection through the whole body
What is r0?
How many people will be infected by one infected person.
What is a latent persistent infection?
An infection that is hiding in the cell waiting to cause an episode of reactivation.
Give examples of acute infection
- Colds and influenza.
- Many unapparent or asymptomatic infections.
- Smallpox (variola virus) and dengue haemorragic fever causes death
- Poliovirus can cause poliomyelitis by accident& as can rubella
Give examples of persistent viral infections
- Chronic infection with low level replication of viruses in tissues which regenerate. Papillomaviruses in warts.
- Chronic carriers of hepatitis B and C viruses.
What are the strategies for viral persistence?
- Evading immune surveillance by infecting tissues unlikely to be infected
- MHC downregulation
- Escape by mutation
Give some examples of viruses that use strategies for viral persistence.
- Measles
- Herpes
- Papillomavirus
Give some examples of viruses that use latency.
Herpes simplex virus
How does herpes simplex virus latency and reactivation occur?
- Primary site of infection (epithelial cells)
- Secondary site of infection and site of latent infection (sensory neuron)
- Site of recurrent infection (epithelial cells)
How can viruses cause cancer?
- Viruses may encode oncogenes
- May interfere with the cell cycle to enhance their replication
Give examples of viruses that cause cancers
- Papillomaviruses encode inhibitors of tumour suppressor genes. This forces the cell into S phase.
- Polyoma virus
- HTLV-1 causes leukaemia
- Hep B and C increase chance of hepatocellular carcinoma
- Epstein Barr Virus causes lymphoma/carcinomas
What affects the outcome of virus infection?
- Virus sequence
- Virus load
- Host immune response/status
- Host co-morbidity
- Co infections
- Other medications
- Host genetics
- Host age & gender
Give an example of a virus whose sequence affects the outcome
- Poliovirus
- A single mutation in the genome can mean that one strain acts as a live attenuated vaccine
- Another invades the motor neurone and causes flaccid paralysis (poliomyelitis).
Give an example of a virus whose viral load affects the outcome
First child to be infected with chicken pox has a milder sibling than the second in the family.
Give an example of coinfections
- Secondary infection after influenza
- HIV infected individuals more likely to get Kaposis Sarcoma
- Hepatitis delta virus only affects people with hep B infection.
Give some examples of predisposing co-mobidities and conditions for severe influenza.
- Asthmatics and respiratory viruses
- Obesity
- Immunosuppression
- Immunodeficiency
- Elderly
- Diabetes mellitus
- Pregnancy
