INFECTIOUS AGENTS - Viruses Flashcards
What are the three basic virus structural components?
Genome
Capsid
Envelope
What is the collective name for the viral genome and capsid?
Nucleocapsid
What is the function of the viral genome?
Codes for proteins required for replication and interaction with the host cell
Describe the different possible structures of viral genetic material
DNA or RNA genomes
Single or double stranded
Linear or circular
Segmented or non-segmented
Where are viral envelopes derived from?
Virus envelopes are derived from the lipid bilayer of the virus’ host cell
What is the function of the capsid and envelope surrounding a virus?
- Protection of the genome
- Facilitates the binding and entry of viruses into host cells
What are the two main groups of virus symmetry?
Icosahedral symmetry
Helical symmetry
Describe icosahedral symmetry
The viral genome is packaged within an icosahedral capsid
Describe helical symmetry
Capsid proteins wind around the viral genome
What are all helical viruses relevant to veterinary medicine surrounded by?
Envelope
What are the advantages of virus symmetry?
- Economy: viral symmetry means fewer genes are required for the virus to function so the viral genome can be more compact
- Redundancy: viral symmetry makes it more probable that if a virus is attacked more of the genes will survive for future replication
Describe the first step of virus replication (attachment)
- The virus attaches to the host cell through interactions between host cellular receptors and virus antireceptors
- Penetration of the virus into the cell via receptor mediated endocytosis; fusion; or translocation
- Uncoating of the virus
Describe the second step of virus replication (gene expression and genome replication) for DNA viruses
DNA VIRUSES:
DNA viruses tend to replicate in the host cell nucleus so need to replicate in actively dividing cells with a nucleus
Describe the second step of virus replication (gene expression and genome replication) for RNA viruses
RNA VIRUSES:
RNA viruses tend to replicate in the host cell cytoplasm and also have to encode for their own RNA polymerase in order to replicate
Describe the third step of virus replication (assembly and exit)
Viruses are released from the host cell through budding, host cell lysis or exocytosis
List six of the mechanisms that a virus can use to damage host cells
Inhibition of host cell nucleic acid synthesis
Inhibition of host cell transcription
Inhibition of host cell protein synthesis
Damage to the host cell membrane
Induction of apoptosis
Altered gene expression
What are some of the common routes of entry for a virus into the host?
Respiratory tract
Ingestion (gastrointestinal tract)
Skin trauma
Urogenital tract
Conjunctiva
What is tissue tropism?
Tissue tropism is the species of animal and types of cells that a virus infects
How do some viruses spread through their hosts?
Viruses can spread via the blood, lymph and neurones
What are some of the common effects viruses have on their hosts?
Cell/tissue destruction
Virus induced immunopathology
Viral oncogenesis
Increased susceptibility to other pathogens
‘Inapparent’ infection (undetected effects)
What determines the source of viral transmission?
The tissue tropism of the virus
What determines when the virus spreads and for how long?
The virus/host interaction
Describe three ways a virus can persist?
- Acute infection with rapid spread to other hosts
- Long term persistence in a host with continuous virus production
- Long term persistence in a host with intermittent virus production
List some strategies viruses have for persistence
Carrier animals (latent infection)
Long term persistence in the environment
Reservoir of infection in wildlife animals
Transmission via arthropod vectors
Evasion of the host immune system
Spread and adapt to new species
Which treatment control methods inhibit virus replication?
Antiviral drugs
Immune system modultors
Post exposure vaccination
Passive immunisation
Which technique has been the most efficient virus control method?
Vaccination (prophylactic treatment)
Which virus causes infectious canine hepatitis?
Canine adenovirus 1 (CAV-1)
Describe the structure of Canine adenovirus 1
DNA virus
Double stranded DNA
Non-enveloped
Icosahedral capsid
What is the function of the fibre present on CAV-1 virions?
Binding to and entering host cells
How many proteins required for the virus lifecycle are encoded for in the CAV-1 virus?
30 proteins
Describe the pathogenesis of the CAV-1 virus
- Dog is exposed to the virus in the saliva, urine or faeces of another infected dog
- Virus is inhaled/ingested by the dog and infects the tonsils followed by the lymph nodes and then the blood
- The virus travels through the blood to infect the liver, kidneys and eyes (primary sites of virus replication)
- The virus kills the cells it infects causing direct pathology and clinical symptoms
What are the clinical signs of infectious canine hepatitis?
Nausea
Vomiting
Pyrexia
Anorexia
Abdominal swelling
Which other tissues can be affected by the CAV-1 virus other than the liver?
Kidneys
Neurological tissue
Ocular tissue
Oral cavity
List some of the methods of persistence used by the CAV-1 virus
- Acute infection with fast spread to other hosts
- Environmental persistence
What can be used to diagnose infection by CAV-1?
PCR test on a nasopharyngeal, conjunctival or throat swap to detect the presence of canine adenovirus DNA
Which methods can be used to control CAV-1?
Vaccination (one of the routine puppy vaccinations)
- live attenuated vaccine based on CAV-2 (virus in the same family as CAV-1 that is antigenically similar)
Which virus can cause feline infectious peritonitis (FIP)?
Feline coronavirus (FCoV) but only 10% of the time, FCoV mainly causes mild enteric and respiratory disease
Describe the structure of the feline coronavirus virion
RNA virus
Single stranded RNA
Enveloped
Helical
What is the function of the spike protein present on the feline coronavirus?
Binding to and entering host cells
Describe the pathogenesis of the FCoV virus
- Cat is exposed to the virus secreted in the faeces of another infected cat
- The virus is inhaled/ingested by the cat
- The virus replicates within the gastrointestinal tract (primary site of replication)
What are the clinical signs of FCoV infection (usually)?
Mild/inapparent signs of a gastrointestinal tract infection (e.g. diarrhoea)
What are the clinical signs associated with feline infectious peritonitis (FIP)?
The clinical signs of FIP are associated with the apparent immune response of the host and the tissue tropism of the virus causing FIP
List some of the methods of persistence used by the FCoV virus
- Cycles of infection within the susceptible population
- Carrier animals
- Virus persistence in the environment
What can be used to diagnose FCoV infection?
- Immunofluorescence can be used to detect antibodies against the FCoV virus
- PCR can be used to detect the FCoV genome in the faeces
Which methods can be used to control FCoV?
Hygiene
Barrier methods
Isolation of cats
(T/F) There is a vaccine against FCoV available in the UK
FALSE
