Lecture 3: General Virology 3

Question 1

Define vial transmisson

Answer 1

Virus Transmission: passing of viral infection between hosts (ether naive or susceptible)

Question 2

Describe the transmission between species of influenza virus

Answer 2

• Bird reservoir with minimal clinic signs
• Infect domestic poultry and swine from wild birds
• Infect people from domestic poultry and swine

Question 3

What is the most important influenza virus type

Answer 3

• Type A is the most important because it infects the most number of species

Question 4

what are 2 types of transmission

Answer 4

vertical
horizontal

Question 5

What are the mechanisms of vertical transmission? Add examples of diseases and consequences of infection

Answer 5

• Vertical: parent to offspring
  o in utereo: BVDV/Blue tongue/feline parvo
  o birth: canine herpes
  o After birth/milk: CAE/Meadi-visna
  o Causing abortion (PRRS)/congential dz (BVDV/border dz)/congenital defects (akabana virus/blue tongue/feline parvo)

Question 6

What are horizontal transmission mechanisms

Answer 6

• Horizontal: Between individuals in a population
  o Direct:
  o Indirect:
  o Aerosols:
  o Arthropods:
  o Iatrogenic:
  o Nosocomial:

Question 7

What are mechanisms of direct viral transmission + examples

Answer 7

o Direct: lick/rub/bite (rabies)/ sexual contact (herpes)/abrasions (papilloma)
o Indirect: iatrogenic/fomite

Question 8

What are mechanisms of aerosol viral transmission + examples

Answer 8

o Aerosols: smaller particles travel farther (Marek’s dz)

Question 9

What are mechanisms of arthropod viral transmission + examples

Answer 9

o Arthropods: mosquito (equine encephalitis)/ticks (African swine fever)/culicoides (blue tongue dz)

Question 10

What are mechanisms of iatrogenic viral transmission + examples

Answer 10

o Iatrogenic: non-sterile/poor hygiene (equine infectious anemia/bovine leukemia)

Question 11

What are mechanisms of nosocomial viral transmission + examples

Answer 11

o Nosocomial: canine parvo/calci virus

Question 12

How is equine encephalitis virus transmitted

Answer 12

o Ex. equine encephalitis: equine/humans are dead end hosts – virus cycles between birds and mosquitoes

Question 13

How is bovine leukemia virus controlled

Answer 13

o Ex. bovine leukemia controlled by good hygiene – milk pasteurization/reduce flies/disinfect equipment

Question 14

Compare features of low and high stability viruses in the environment (with examples)

Answer 14

• Low environmental stability: respiratory transmission, enveloped
  o Except Marek’s dz (wrapped in keratin)
• High environmental stability: fecal-oral, non-enveloped (adeno/circo viruses)

Question 15

Compare the stability of viruses in a clinical vs subclinical infection

Answer 15

• Clinical infection = more productive
• Subclinical infection = better used for dissemination

Question 16

What are the strategies are used to impact viral survival/stability

Answer 16

• Factors: maintenance of serial infections
  o Acute/self limiting: Transmission affected by population size
  o Persistent infection
  o Vector maintenance

Question 17

What are the features of transmission of a virus that causes acute/self limiting dz (+examples)

Answer 17

o Acute/self limiting: Transmission affected by population size
 Virus disappear with recovery + high load during dz
 Require consistent supply of hosts
 Ex. influenza/rota viral diarrhea/infectious bursal dz

Question 18

What are the 3 features of transmission of a virus that causes persistent dz (+examples)

Answer 18

 Persistent: clinical dz after years of subclinical shedding (BVDV)
 Chronic: similar to acute initially (high viral shedding) + low level shedding for years after (foot and mouth/feline calcivirus)
 Latent: intermittent shedding without clinical consequence (herpes)
* +/- clinical signs during re-activation
* Cannot detect infection in latent period (no viral protein prod.)

Question 19

What type of strategy does bovine herpes virus use to maintain infection/transmission

Answer 19

• Ex. BVH-1 (bovine herpes) replicated in nasal mucosa – latent in trigeminal ganglia/t cells in tonsils -> stress/low immunity re-activates to create productive infection in primary replication sites

Question 20

What are 3 factors that affect how emerging viral dz develop

Answer 20

• Host: must overcome host defences
• Environmental change: ecological or human (translocation of virus/vector)
• Viral determinants: evolution with short generation time/high mutation rate

Question 21

What are some mechanisms viruses evolve slowly/gradually

Answer 21

o Variants depend on selective pressure – vary in virulence/tropism
o Antigenic drift: DNA virus (except Pox) use cell proofreading – RNA virus don’t = mutate more
o Higher mutation size = lower genome size
o Quasi species: small variations in virus due to mutation

Question 22

What are some mechanisms viruses uses to evolve quickly

Answer 22

o Recombination;
o Reassortment:

Question 23

How do viruses change via recombination + an example

Answer 23

o Recombination; 2 viral genomes combine – require co-infection
 Ex. sinbis-like virus + eastern equine encephalitis = western equine encephalitis
 Single stranded RNA or DNA viruses

Question 24

How do viruses change via reassortment + examples

Answer 24

o Reassortment: exchange segments of genome
 2 segments: arena/birna
 3 segments: bunyaviridae
 6-8 segments: orthomyzoviridae
 12 segments: Reoviridae

Question 25

What is the mechanism influenza uses to evolve

Answer 25

 Influenza A: can do triple reassortment (swine + human + avian = NA swine flu, + euro-asian swine flue = H1N1 ) * HA binds sialic acid receptors on host * Avian = highest affinity for 2-3 sialic receptors in gut/lung * Human = affinity for 2-6 sialic receptors in airway * Quail and pig type viruses have both types of receptors * Receptor types/affinities can change due to reassortment and antigenic shift (quail/pig) * Quails and pigs act at ‘mixing pot’ for reassortment – because both types of viruses can enter one cell * Infected cell will produce both initially infecting viruses + new reassorted virus

Question 26

Briefly explain the genetic interaction you can expect if a quail is infected with human adapted H1N1 and avian adapted H6N2 influenza A viruses. (3 marks)

Answer 26

mark 1:Quail have a2-3 and a2-6 (human and avian) receptors for influenza. mark 2: If they infect the same cell, reassortment can occur. mark 3: If reassortment occurs there will be a novel progeny that is different from the initially infecting parent viruses.

Question 27

Which animal species can act as a mixing vessel for influenza virus reassortment A Cattle B Chicken C Swine D Felines E Bovines

Answer 27

C

Question 28

During latency of herpes virus infection, you may observe A Virus replication B Viral protein synthesis C Mild clinical signs D Severe clinical signs E No virus shedding

Answer 28

E

Question 29

Can a virus replicate in a target cell with nonfunctional ribosomes? Briefly explain your answer. (2 marks)

Answer 29

No. Viruses rely on host cell machinery to produce viral proteins. Without ribosomes no protein production can occur.

Question 30

What are the consequences (at least 2 points) of mutation in viral genome? (2 marks)

Answer 30

mark 1: A mutation may lead to a new biological variant that mark 2: The tropism may change. Resulting in the colonization of different host or organs. mark 3: A change in virulence may occur. It can increase or decrease mark 4: The virus may be non-viable.

Question 31

What is meant by 'vertical transmission'? How is this different from 'horizontal transmission? (2 marks)

Answer 31

Vertical transmission occurs between mother and offspring. It can occur trans-placentally, during birth, or via milk. Horizontal transmission occurs between individuals in the population at risk. It can be direct or indirectly transmitted for example via airborne aerosols, consumption of milk/meat, nosocomial.

Question 32

What are the 3 types of 'emerging' viral dz

Answer 32

Types: * Newly recognized * Newly evolved * Increased incidence