Lecture 6 2/6/24 Flashcards
What is virus evolution?
-genomic changes in hereditary genomes that may result in phenotypic changes
-occurs within a viral population
Why is it important for mutation rate to be balanced?
-too high of a rate results in defective progeny
-too low of a rate does not allow progeny to adapt to changing environment
Why do RNA viruses tend to have more mutations than DNA viruses?
-higher error rates and lower stability
-viral polymerases lack proof-reading mechanisms
What are “hot spots”?
certain positions in viral genomes that have higher mutation rates
What are the characteristics of selection pressure?
-does not cause mutations
-selects for already existing mutants
What is a mutation?
change in the base sequence of a nucleic acid resulting in the alteration of the resulting protein
What happens when mutations occur in less tolerant proteins?
results in a non-infectious virus
What are the three types of drift/point mutations?
-silent
-substitution
-nonsense
What is a silent mutation?
mutation within a codon that produces the same viral protein sequence
What is a substitution mutation?
mutation within a codon that produces a different viral protein sequence
What is a nonsense mutation?
mutation within a codon that leads to the cessation of the viral protein sequence
What is a conservative substitution?
when a different amino acid is substituted, but it has similar properties to the original amino acid
What is a non-conservative substitution?
when a different amino acid is substituted that does not have similar properties to the original amino acid
What is a deletion mutation?
-deletion of nucleotides
-causes a frameshift mutation
-changes amino acid sequence downstream of mutation
What is an insertion mutation?
insertion of multiples of 3nt bases to a viral gene, resulting in the addition of amino acids
Which type of mutation is easy to revert back to wildtype?
point mutations
What is reassortment?
gene segments are mixed and matched when two different viruses strains end up in same host cell
What is recombination?
portions of gene segments are interchanged when two different virus strains are in the same host cell
What is antigenic drift?
-accumulation of small point mutations
-leads to minor antigenic changes with epidemic/seasonal potential
What is antigenic shift?
-viral reassortment of gene segments
-leads to major antigenic changes with pandemic potential
What are the characteristics of canine-parvovirus-2 evolving from feline panleukopenia virus?
-only 5 amino acid differences between the structural proteins
-these mutations provided CPV-2 with the ability to bind to the canine transferring receptor and infect dogs
What are the characteristics of feline enteric coronavirus and FIP?
-FECV is ubiquitous and causes mild enteric disease
-FIPV, a mutation of FECV, occurs in 10% of FECV cases and causes fatal systemic disease
-FIPV cannot be transmitted to other cats, but FIPV-infected cats can shed FECV
-FIPV is likely a mutant that undergoes autonomous infection
During which period of gestation can BVDV lead to a persistently infected fetus?
50-125 days of gestation
How does recombination play a role in BVDV?
-PI calves typically have non-cytopathic BVDV strains
-exposure of the PI calf to a cytopathic BVDV strain can lead to recombination between the two strains
-viral genome recombines with host mRNA, leading to expression of proteins that can be toxic
