Viruses 3 - Pathogenesis

Question 1

What are the stages of viral infection?

Answer 1

1) Entry 2) Replication 3) Dissemination 4) Shedding

Each stage plays a critical role in the life cycle of a virus.

Question 2

What must viruses overcome during entry?

Answer 2

Various defences of the body (physical or immunological)

Innate immune responses are often unspecified.

Question 3

Through which surfaces do many viruses enter the body?

Answer 3

Mucosal surfaces

These can include the skin, respiratory tract, alimentary tract, blood, genital tract, and transplacental routes.

Question 4

What is the primary barrier function of the skin against viral entry?

Answer 4

Keratinisation and cellular defences

Cellular defences include macrophages, neutrophils, dendritic cells, and natural killer cells.

Question 5

What are some examples of viruses entering through broken skin?

Answer 5

Orf virus, papillomavirus, rabies virus

Entry can occur through abrasions or bites.

Question 6

What are the defences of the respiratory tract against viral infection?

Answer 6

Ciliated epithelium, mucus, sneezing, coughing, alveolar macrophages, complement, cytokines, natural killer cells

The mucociliary escalator is a key mechanism for trapping and expelling pathogens.

Question 7

How can viruses be transmitted through the respiratory tract?

Answer 7

Inhalation of droplets from sneezing/coughing or saliva from infected individuals

Examples include Influenza and Canine parainfluenza virus.

Question 8

What are the defences of the alimentary tract?

Answer 8

Low pH in stomach, bile, enzymes, commensal microbiota

These factors contribute to competitive exclusion of pathogens.

Question 9

What are some examples of viruses that enter through the alimentary tract?

Answer 9

Norovirus, rotavirus, classic swine fever, feline infectious peritonitis

These viruses have adapted to survive the harsh conditions of the digestive system.

Question 10

What role do haematophagus insects play in viral transmission?

Answer 10

They transmit viruses through their bites into the bloodstream

Examples include Bluetongue virus and West Nile virus.

Question 11

What genital illnesses can infected semen result in?

Answer 11

• Equine viral arteritis
• Porcine Reproductive & Respiratory Syndrome (PRRS)

Question 12

What is the significance of climate change for arthropod vectors?

Answer 12

Milder winters allow vectors and viruses to move north (e.g., mosquitos)

This can lead to increased incidence of vector-borne diseases.

Question 13

What is the lifecycle of arthropod vectors such as midges?

Answer 13

Eggs laid in water; larva - nymph - adult

This lifecycle is crucial for the propagation of viruses they may carry.

Question 14

What are the effects of Schmallenberg virus in stillborn lambs?

Answer 14

1) Arthrogryposis (mmultiple contractures of the joints in more than one area of the body which are present from birth)
2) Scoliosis (a lateral curvature of the spine)
3) Torticollis (abnormal curving or twisting of the neck)
4) Brachygnathia inferior (shortened mandible)
5) Cerebellar/cerebral hypoplasia (underdeveloped cerebellum/ cerebrum)

These are severe congenital defects associated with the virus.

Question 15

What occurs during local dissemination of a virus?

Answer 15

Replication occurs in epithelium at the initial infection site; cell-to-cell spread occurs

The virus does not disseminate to other tissues at this stage.

Question 16

What is systemic dissemination of a virus?

Answer 16

Local replication followed by spread to other sites through lymph, blood, or nerves

This can lead to secondary sites of replication and more severe pathology.

Question 17

What is primary viraemia?

Answer 17

Presence of virus in the bloodstream following local infection

It occurs before the virus spreads to secondary sites.

Question 18

What is secondary viraemia?

Answer 18

Blood infection following the secondary site of replication

This indicates a more widespread infection.

Question 19

How does rabies virus enter the body and spread?

Answer 19

Introduced via bite, primary replication in muscle cells, uses motor nerves to reach CNS

Further replication occurs in the spinal cord and brain.

Question 20

What is the incubation period of a viral infection?

Answer 20

Time between exposure to virus and onset of disease

This can vary significantly based on the virus and host factors.

Question 21

What is shedding in the context of viral infections?

Answer 21

Critical step for transmission to new hosts; often occurs from the site of entry

Shedding can occur from different sites depending on the virus.

Question 22

What determines viral fitness?

Answer 22

Survival and transmission; viruses do not benefit from disabling the host

Co-evolution with hosts often results in minimal disease.

Question 23

What are cytopathic effects?

Answer 23

Structural changes in a host cell resulting from viral infection

These effects can lead to cell death and tissue damage.

Question 24

What is host shut-off in the context of viral infection?

Answer 24

Infecting virus takes over cellular machinery responsible for translation

This results in the production of viral proteins at the expense of host proteins.

Question 25

What is syncytia formation?

Answer 25

Fusion of multiple cells into a single multinucleated cell body ## Footnote This can occur in certain viral infections, leading to tissue damage.

Question 26

What are inclusion bodies?

Answer 26

Unique structures generated by viral proteins together with some cellular proteins as a platform for efficient viral replication ## Footnote Inclusion bodies can be cytoplasmic or nuclear. An example is the cytoplasmic inclusion bodies called negri bodies associated with rabies.

Question 27

What is the role of cytokines in viral infections?

Answer 27

Cytokines produced by host cells can cause fever as they are endogenous pyrogens ## Footnote They also contribute to immune responses and can lead to damage and clinical signs.

Question 28

What type of hypersensitivity reactions may contribute to immunopathology during viral infections?

Answer 28

Type 1-1V hypersensitivity reactions ## Footnote These reactions control individual cell responses during viral infections.

Question 29

List the host factors that influence virus interactions.

Answer 29

* Age * Gender * Nutritional status * Level of productivity * Species * Breed resistance * Immunity * Geographical origin * Physiological stress ## Footnote These factors can significantly impact the host's response to viral infections.

Question 30

What are the viral factors that affect virus interactions with the host?

Answer 30

* Virulence factors * Endemic or exotic status * Transmission route (insect vector, fomites, air-borne, feco-oral) * Co-infections with multiple pathogens * Infectiousness ## Footnote These factors determine how effectively a virus can infect and replicate within a host.

Question 31

What environmental factors influence virus interactions?

Answer 31

* Climatic conditions * Exposure to insect vectors * Contamination * Quality of pasture/feed * Stocking density * Management changes * Veterinary policy (e.g vaccination) ## Footnote These factors can affect the overall health of the host and the prevalence of viral infections.

Question 32

How is viral infection categorized?

Answer 32

Acute vs Persistent viral infection ## Footnote This categorization is based on the dynamics of viral growth within the host.

Question 33

What are the two types of persistent viral infections?

Answer 33

* Latent * Chronic ## Footnote Persistent infections exhibit different 'life strategies' compared to acute infections.

Question 34

True or False: Inclusion bodies can only be found in the cytoplasm.

Answer 34

False ## Footnote Inclusion bodies can be found in both the cytoplasm and nucleus.