Viruses 3 - Pathogenesis Flashcards
What are the stages of viral infection?
1) Entry 2) Replication 3) Dissemination 4) Shedding
Each stage plays a critical role in the life cycle of a virus.
What must viruses overcome during entry?
Various defences of the body (physical or immunological)
Innate immune responses are often unspecified.
Through which surfaces do many viruses enter the body?
Mucosal surfaces
These can include the skin, respiratory tract, alimentary tract, blood, genital tract, and transplacental routes.
What is the primary barrier function of the skin against viral entry?
Keratinisation and cellular defences
Cellular defences include macrophages, neutrophils, dendritic cells, and natural killer cells.
What are some examples of viruses entering through broken skin?
Orf virus, papillomavirus, rabies virus
Entry can occur through abrasions or bites.
What are the defences of the respiratory tract against viral infection?
Ciliated epithelium, mucus, sneezing, coughing, alveolar macrophages, complement, cytokines, natural killer cells
The mucociliary escalator is a key mechanism for trapping and expelling pathogens.
How can viruses be transmitted through the respiratory tract?
Inhalation of droplets from sneezing/coughing or saliva from infected individuals
Examples include Influenza and Canine parainfluenza virus.
What are the defences of the alimentary tract?
Low pH in stomach, bile, enzymes, commensal microbiota
These factors contribute to competitive exclusion of pathogens.
What are some examples of viruses that enter through the alimentary tract?
Norovirus, rotavirus, classic swine fever, feline infectious peritonitis
These viruses have adapted to survive the harsh conditions of the digestive system.
What role do haematophagus insects play in viral transmission?
They transmit viruses through their bites into the bloodstream
Examples include Bluetongue virus and West Nile virus.
What genital illnesses can infected semen result in?
- Equine viral arteritis
- Porcine Reproductive & Respiratory Syndrome (PRRS)
What is the significance of climate change for arthropod vectors?
Milder winters allow vectors and viruses to move north (e.g., mosquitos)
This can lead to increased incidence of vector-borne diseases.
What is the lifecycle of arthropod vectors such as midges?
Eggs laid in water; larva - nymph - adult
This lifecycle is crucial for the propagation of viruses they may carry.
What are the effects of Schmallenberg virus in stillborn lambs?
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.
What occurs during local dissemination of a virus?
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.
What is systemic dissemination of a virus?
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.
What is primary viraemia?
Presence of virus in the bloodstream following local infection
It occurs before the virus spreads to secondary sites.
What is secondary viraemia?
Blood infection following the secondary site of replication
This indicates a more widespread infection.
How does rabies virus enter the body and spread?
Introduced via bite, primary replication in muscle cells, uses motor nerves to reach CNS
Further replication occurs in the spinal cord and brain.
What is the incubation period of a viral infection?
Time between exposure to virus and onset of disease
This can vary significantly based on the virus and host factors.
What is shedding in the context of viral infections?
Critical step for transmission to new hosts; often occurs from the site of entry
Shedding can occur from different sites depending on the virus.
What determines viral fitness?
Survival and transmission; viruses do not benefit from disabling the host
Co-evolution with hosts often results in minimal disease.
What are cytopathic effects?
Structural changes in a host cell resulting from viral infection
These effects can lead to cell death and tissue damage.
What is host shut-off in the context of viral infection?
Infecting virus takes over cellular machinery responsible for translation
This results in the production of viral proteins at the expense of host proteins.
What is syncytia formation?
Fusion of multiple cells into a single multinucleated cell body
This can occur in certain viral infections, leading to tissue damage.
What are inclusion bodies?
Unique structures generated by viral proteins together with some cellular proteins as a platform for efficient viral replication
Inclusion bodies can be cytoplasmic or nuclear. An example is the cytoplasmic inclusion bodies called negri bodies associated with rabies.
What is the role of cytokines in viral infections?
Cytokines produced by host cells can cause fever as they are endogenous pyrogens
They also contribute to immune responses and can lead to damage and clinical signs.
What type of hypersensitivity reactions may contribute to immunopathology during viral infections?
Type 1-1V hypersensitivity reactions
These reactions control individual cell responses during viral infections.
List the host factors that influence virus interactions.
- Age
- Gender
- Nutritional status
- Level of productivity
- Species
- Breed resistance
- Immunity
- Geographical origin
- Physiological stress
These factors can significantly impact the host’s response to viral infections.
What are the viral factors that affect virus interactions with the host?
- Virulence factors
- Endemic or exotic status
- Transmission route (insect vector, fomites, air-borne, feco-oral)
- Co-infections with multiple pathogens
- Infectiousness
These factors determine how effectively a virus can infect and replicate within a host.
What environmental factors influence virus interactions?
- Climatic conditions
- Exposure to insect vectors
- Contamination
- Quality of pasture/feed
- Stocking density
- Management changes
- Veterinary policy (e.g vaccination)
These factors can affect the overall health of the host and the prevalence of viral infections.
How is viral infection categorized?
Acute vs Persistent viral infection
This categorization is based on the dynamics of viral growth within the host.
What are the two types of persistent viral infections?
- Latent
- Chronic
Persistent infections exhibit different ‘life strategies’ compared to acute infections.
True or False: Inclusion bodies can only be found in the cytoplasm.
False
Inclusion bodies can be found in both the cytoplasm and nucleus.
