host virus interactions

Question 1

list the determinants of the interaction between host cell and virus.

Answer 1

• whether infection occurs
• the type of infection that is established (e.g. persistence/clearance)
• the outcome of the virus-host encounter

dependent on the pathogenicity of the infecting virus AND the susceptibility or resistance/tolerance of the host

Question 2

list the effects that virus interactions can have on host cells

Answer 2

- morphological - lysis, rounding and detachment from surface

**- functional ** - inhibition or stimulation of cell division

- biochemical - activation of cell signalling pathways, induction of immune response

- metabolic reprogramming - to support viral replication and rapid cell growth

**- immunological **- key strategies that could lead to resistance or infection (immune system is central to host-virus interactions)

these interactions are essential of virus replication and spread

Question 3

list the important events in pathogenesis of the virus lifecycle

Answer 3

1. invade the host, through skin or mucus membranes
2. at the cellular level, infect susceptible cells
3. overcome local defences (innate immune responses, to replicate permissive cells
4. virus assembly and spread from the site of infection often via the bloodstream to other organs to either:
   - undergo further rounds of replication
   - exit/shedding from the host in high umbers to infect other susceptible hosts to ensure spread and maintenance
   - routes include urine, feces, skin, respiratory tract (coughing, sneezing), sneezing, milk, blood

Question 4

explain how viruses exploit the host cell machinery

Answer 4

use of cell receptors for entry, host proteins for replication and translation, use of cell membrane for assembly and budding

Question 5

how would you diagnose a viral infection

Answer 5

• review of disease history and clinical signs
• clinical exam
• confirmation by laboratory testing

Question 6

list the different methods of laboratory diagnosis of viral infections

Answer 6

• detection and measure of infectious virus (isolation in cultured cells)
• detection of viral antigens (proteins/antigen)
• detection of viral nucleic acids (amplification of nucelic acid sequencing)
• detection of virus protein ( specific antibody response)
• use of serological tests to detect IgG, IgM or total antibody

such as immunofluorescence, immunohistochemistry, PCR, ELISA

Question 7

describe how PCR works to diagnose viral infection

Answer 7

• uses short lengths of DNA (primers) which are complementary to the virus sequence and amplifies a region spanned by primers
• thermostable DNA polymerase (Taq)
• recognise the presence of the amplification product using a gel-based method and stain for the DNA molecules

Question 8

what are the limitations of ELISA tests

Answer 8

• indicates previous exposure but not sufficient to indicate when infection occured
• false-negatives and positives can confuse diagnosis
• patient antibody can block test antibody binding
• cross reactions can occur (different virus members within virus family)
• a good knowledge of clincal symptoms, pathology and limitations needs to be applied
• direct detection of virus is more definitive

Question 9

list treatments/controls for viral infections

Answer 9

• supportive therapy (nutrition, fluids, treating symptoms)
• antivirals (not used in animals, targets must be specific, expensive, high potential for resistance => not relevant yet in vet med)
• vaccinations (most effective way to prevent viral disease, more cost effective)

Question 10

describe the mechanism of how vaccines work to control viruses

Answer 10

1. host exposure to vaccine antigen(s)
2. naive T and/or B cells that recognise this (not many) begin colonl expansion and differentiation
3. develope population memory cells
4. next encounter with same antigen(s) induces protective secondary response (more rapid and effective that primary response)

Question 11

list the different types of vaccines

Answer 11

• live vaccines
• inacativated (killed) virus vaccines
• viral-vector based vaccines (rabies)
• subunit vaccines
• DNA vaccines
• RNA vaccines (new - covid vacc)