Viral Infections Flashcards
What are the 7 groups of viruses
dsDNA, ssDNA, dsRNA, +ssRNA, -ssRNA, rtDNA, rtRNA
The Baltimore classification system is based on…
Nucleic acid present in the virion particles and the pathway for expression of the genetic material
+ssRNA vs -ssRNA: infectivity
\+ssRNA = infectious right away, directly translated into proteins -ssRNA = not infectious right away, needs to be converted to +ssRNA first
Ambisense ssRNA
Virus resembles a negative sense RNA virus, but they can also translate genes from the positive strand
Viral entry is initiated by… (3)
- Conformational changes in virus that expose receptors for membrane fusion and penetration
- Transmit signals through membrane to prepare cell for invasion
- Induction of endocytic pathway
2 ways RNA viruses replicate their genomes
- RNA dependent RNA synthesis
2. RNA dependent DNA synthesis (RT) followed by DNA replication and transcription (Retroviruses)
What is a downside of a high error rate for RNA viruses
Error rates impose an upper limit on genome size (most are 5-15kb)
Virus assembly: non-enveloped vs enveloped
Non-enveloped can assemble in the cytoplasm or nucleus
Enveloped must get a lipid bilayer from a host cell membrane during assembly
4 steps of non-enveloped virus assembly
- Macromolecules form empty capsids
- Viral DNA is inserted via packaging sequence at one end
- Precursor core proteins are also packaged
- Proteolytic cleavage of precursors proteins by proteinase makes infectious virion
3 pathways of enveloped virus assembly
- Proteins transported to PM and capsid assembly and envelopment occur simultaneously
- Capsid assembly happens in cytoplasm and virus buds from PM to get its membrane
- Capsid assembly happens in ER, gets its envelop from ER and is exocytosis
Enteric viruses do not multiply in…
Food systems
What is poliovirus associated with
Milk and milk products
What kills polio in milk
Pasteurization above 70C for 30 seconds
How is polio transmitted
Fecal oral route, it multiplies in the intestine
What does polio do in the body
It invades the nervous system and can cause total paralysis in hours
Initial symptoms of polio in the body
Fever, fatigue, headache, vomiting, stiffness of neck
Genome and capsid of polio
RNA genome (+ssRNA) Non-enveloped
What are the 3 serotypes of the polio and what is different about them
PV1, PV2 and PV3
Each has a slightly different capsid
What is the most common polio serotype
PV1, localized in Pakistan and Afghanistan
Polio: 5’ NTR region
Harbors 2 domains, cloverleaf and internal ribosome entry site
Covalently linked to viral protein VPg
What does the cloverleaf structure do
Regulates viral RNA replication and the initiation of translation
What does the IRES domain do
Mediates translation of viral mRNA
How is polio mRNA translated
As one long polypeptide, later cleaved into mature structural and non-structural proteins by proteolytic processing
P1 precursor protein of polio is cleaved into what
VP1, VP3 and VP0
What does HAV effect
The liver
Duration and symptoms of HAV
8 weeks
Nausea, vomiting, diarrhea, jaundice, fever, abdominal pain
How is HAV spread
Fecal oral route, and undercooked contaminated seafood
If you get HAV once…
You are immune for life
Genome and capsid of HAV
RNA genome (+ssRNA) Non-enveloped
How many proteins does HAV encode
A single polyprotein
What part of the HAV polyproteins codes for the major capsid proteins
The N-terminal (the rest encodes series of nonstructural proteins required for HAV RNA replication)
What is the function of VPg on the 5; end of HAV genomic RNA
A protein primer for RNA synthesis
How does HAV spread in the body
By secretion from infected hepatocytes via the biliary system
When does fecal shedding of the virus reach its max
Just before the onset of hepatocellular injury (individual is most infectious)
What accompanies fecal shedding in HAV infection
Extended viremia, but at a lower magnitude
What is indicative of hepatocellular injury
Serum alanine aminotransferase
When are norovirus outbreaks most common
In fall and winter months
What is the contagious period of norovirus
The moment they feel ill to 3 days after recovery (sometimes two weeks)
Where is norovirus found in human secretions
The stool and vomit
3 ways someone can be infected with norovirus
- Direct contact
- Touching surfaces
- Eating/drinking contaminated sources
How is norovirus spread
Fecal oral route, sometimes shellfish
Main symptoms of norovirus
Diarrhea, vomiting, nausea, stomach cramps (less common can be headache, chills, fever)
Genome and capsid of norovirus
RNA genome (+ssRNA) Non-enveloped virus
What norovirus genogroup is the most prevalent in humans
Genogroup II
What NoV genogroups infect: humans, bovine, mice
Humans: I, II, IV
Bovine: III
Mice: V
What does ORF1 in NoV encode
A single nonstructural polyprotein
What does ORF2 in NoV encode
VP1 capsid protein (divided in shell and protruding domains)
What does ORF3 in NoV encode
Minor structural protein VP2
What does ORF4 in NoV encode and where is it found
Only in mice NoV
Encodes virulence factor 1 (newly defined)
Why are rotavirus infections rare in adults
Because you get it as a kid (before the age of 5) and immunity develops with each infection so subsequent infections are less severe
How is rotavirus transmitted
Fecal oral route
Treatment for rotavirus
Oral rehydration and vaccination to prevent infection
Rotavirus symptoms
Nausea, vomiting, watery diarrhea and low-grade fever
What is the most common cause of death related to rotavirus infection
Diarrhea
Genome and capsid of rotavirus
RNA genome (dsRNA) - segmented, linear Non-enveloped virus
How does rotavirus achieve rapid evolution through genetic reassortment
If someone is co-infected with two strains, the segmented genome allows them to be mixed and packaged into a new virion
What is the surface of the rotavirus made of
The VP7 glycoproteins and embedded with the VP4 spike attachment protein
Why is the dsRNA genome of the rotavirus never completely uncoated
To prevent activation of the an antiviral state by the cell in response to the dsRNA
