WEEK 11: 11.6 Viral Transmission and Pathogenesis

Question 1

What are 3 different modes of virus transmission

Answer 1

1. Direct contact
   contact with tissues/fluids of an infected individual, leading to entry through mucous membrane (eyes/mouth) and skin (open wounds, grazes, bites)
2. indirect transmission
   fomite, vector-mediated
3. zoonotic (can be direct or indirect too)

Question 2

What are the different routes of virus entry, describe each

Answer 2

airbone: transfer pathogens via small particles in air, through coughing/sneezing. replicate in resp tract, enveloped, eg. influenza
faecal/oral: ingestion of contaminated food/water due to faeces, urine or saliva. virus replicates in intestinal tract, released in the faeces for eg. rotavirus
sexual transmission: virus present in blood & body secretions, transmitted through sex, infest cells at mucosal surfaces, eg. Hep B
blood-borne virus infection: virus replicated in target cells & released into bloodstream, circulates in blood (viraemia), transmitted by exposure to infected blood (like sharing needles) eg. HIV
vector borne virus infection: eg. mosquito spreading dengue

Question 3

What are the 5 simple facts related to pathogenesis of virus infection

Answer 3

1. viruses are obligate intracellular parasites
2. viruses must bind to cellular receptors to deliver the viral genome
3. genomes can only function inside living cells
4. virus replication requires a polymerase either carried within the virus particle or is part of the genetic code (the genome)
5. viruses must make mRNA, to be translated by host ribosomes

Question 4

What are the the 4 stages of the pathogenesis of virus infection

Answer 4

1. transmission, virus must evade host physical defenses and move form one host to another . routes of entry can be those listed before.
2. viral replication: establishment of single cell infection. attachment to cell, penetration (passive diffusion), uncoating of genome, gene expression through production of mRNA, replication (copying of RNA/DNA), assemply of nucleocaspids, packaging of genomes/enzymes, release of virus via cell lysis or budding
3. spread within the body, either localised (warts) infection or systemic infection (infection followed by entry into circulatory/nervous system)
4. host defense systems aim to eliminate infected cell and clear the host of the virus, and outcomes result in transient infection (successful clearing of viral infection) or persistent infection (inability to clear the infection)

Question 5

What are the 5 different effects of virus infection at the cellular level?

Answer 5

1. cytopathic effect (CPE)
   - cell death
   - rounding of cell due to cytoskeletal changes
2. multinucleated giant cell formation
3. malignant transformation - cancer
4. inclusion bodies (protein aggregates) eg. rabies
5. no change (viral genome remains dormant)

Question 6

What is the effectiveness of an immune response affected by?

Answer 6

the rate of virus application, size of virus dose, route of infection, age of host & the ability of the virus to escape an immune response