dsRNA Viruses Flashcards
baltimore classification of dsRNAviruses
dsRNA viruses belong to Class III according ot the Baltimore classification of viruses
What is the most important group of dsRNA viruses
Reoviruses
Introduction to Reoviruses
- They are icosahedral shaped virus with segmented genome.
- They usually infect the respiratory and enteric tracts of humans and animals.
- Originally, the name ‘’reoviruses’’ came about based on early observations about the virus as follows:
Found in respiratory tract: R
Found in enteric tract: e
The disease was unknown at the time (ophan): o
The suffix ‘’virus’’ was added to make up the name Reovirus.
•Later, similar viruses have been observed to infect and cause disease in birds, mammals, fish, invertebrate (suck as insects), plant and fungi. Nevertheless, the group still retains the name reovirus
epidemeology of Reoviruses
in birds lol
- Reovirusesbelong to the family Reoviridae.
- Several genera have been named under the family for which the original reoviruseshave been incorporated into the genus Orthoreovirus.
- The genus Orthoreovirusinfect birds and mammals.
- The avian (bird) viruses are important pathological members of the genus orthoreovirus.
- Animal infection: majority of orthoreovirusinfecting animals are asymptomatic (show no symptom).
- Humaninfection: Most persons are exposed to orthoreovirusesinfection at childhood and have developed specific serum antibodies by early adult hoo
Reovirus(genus: Phytoreovirus) infecting plant
- Most of the reoviruses(Genus-Phytoreovirus) infecting plants are transmitted by vectorsthrough feeding. The virus undergo circulative transmission (insect saliva –body circulation-saliva) in the vector.
- Acquired virus replicatein the body circulation of the vector before returning to the saliva, ready to be injected into a new hosts.
- The vector suffers little or no harm in the process while the plant hosts suffer disease conditions due to the virus
Rotavirus infecting animals
ds RNA virus
Origin: The rotavirus was first discovered in faecelsamples from monkeys and mice using the electron microscope in 1963.
Human origin: In 1973, the rotavirus was discovered for the first time in faecalsamples from children with symptom of diarrhea using electron microscopy.
Shape: They are spherical shaped virionsmeasuring approximately 75 nm in diameter. Hence, the name rotavirus was derived from the shape of the virus which is round (rotain latin)
Rotavirus Capsid
- The capsid of rotaviruses has an icosahedral shape made up of three layers (triple layer).
- Each of the 3 capsid layers are made up of different virus proteins (VP).
- Inner layer: Have perforated channels made up of VP2.
- Middle layer: Have perforated channels made up VP6. It is arranged similar to a wheel’s spokes and serves as the major component of the virion.
- Outer layer: It is a glycosylated layer made up of VP7. VP7 is taken from a membrane within the cell and incorporated unto the surface of the virion.
- Innercore: Two protein species are associated with the inner core (VP1 and VP3) of rotaviruses.
- Spikes: VP4 forms the 60 spikes protruding from the surface of the rotavirus virion.
Rotavirus structure // enzymes
Figure 2: Rotavirus structureThe seven virionproteins are arranged based on sizes.
The 3 largest proteins are arranged toward the center of the virion
:VP2 is associated with the inner capsid layer.
VP1 and VP3 are enzymes associated with the genome with each made up of 12 copies.
VP1 has the RNA-dependent RNA polymerase activity
VP3 has guanylyltransferaseand methyl transferaseactivities
Rotavirus genome
- The genome of the rotavirus has 11 dsRNAsegments.
- Each of the 11 segments encode one protein except for one which encodes two proteins, making a total of 12 proteins.
`•Of the 12 encoded proteins, 6 codes for structural proteins while 6 codes for non-structural proteins
what cells do rotavirus replicate within?
•Rotaviruses infect and replicate in the enterocytes: These are cells at the ends of the villi (finger-like projections) in the small intestine.
Which cells do rotaviruses affect
- Rotaviruses infect and replicate in the enterocytes: These are cells at the ends of the villi (finger-like projections) in the small intestine.
- Attachment and Entry•Transcription•Translation•Genome replication and secondary transcription•Assembly•Exi
Rotavirus attachment and entry
- The mechanism of cell entry by rotaviruses are complex and remains relatively uncertain.
- First, the virionspike protein (VP4) is cleaved (cut) to smaller proteins VP5 and VP8, facilitating the entry of the virioninto the host cell
Mechanism of entry by rotaviruses
•Rotaviruses may enter the cells through two possible mechanisms
:1.Direct penetration via the plasma membrane
2.Endocytosis
Early events of rotavirus transcription
activation of transcription
- Activation of transcription: Once the virionenters a cell, the outer of the 3 layers is shed leaving the middle and inner layers in which transcription is activated.
- The 11 genome segments are seemingly linked with VP1 in the synthesis of new plus strand (+)RNA and a molecule of VP3 caps the 5’ end of the new RNAs.
- Nucleotides for RNA synthesis enter the particles via channels in the protein layers and are released via same rout
Figure 8: Early events in rotavirus replicatio
Figure 8: Early events in rotavirus replication:(+)
RNA is transcribed from each ofthe genome segments in the double-layered particle derived from the cell invading virion.
Initially this RNA functions as mRNA (green) and the 12 virus proteins are translated.
NSP2 and NSP5 play major roles in the assembly of viroplasm, and other virus proteins accumulate in these structures.
VP1 and VP3 bind to (+) RNA molecules (dark blue).
VP2 forms roughly spherical structuresaround the
(+)RNA (inner layer).
(–) RNA (light blue) is synthesized in the viroplasm
.VP6 is added to form progeny double-layeredParticles (middle layer
