Lec 10: Reoviruses (dsRNA virus) Flashcards
Icosahedral viruses with dsRNA genomes isolated from…
Initially, no…
THEREFORE –>
…the Respiratory tracts and Enteric tracts of humans/animals
… no disease could be associated = Orphan
–> R + E + O = REOviruses
Reovirus host =
mammals, birds, fish, invertebrates including insects, plants and fungi
most of the plant reoviruses are transmitted between plants by =
The viruses replicate…
= insect vectors
…in BOTH the plant and the insect, generally causing disease in the plant, but little or no harm to the infected insect.
The most common cause of diarrhea is
a virus that infects the gut – “stomach flu.”
the cause of most types of food poisoning =
= Infection by bacteria
Rotaviruses are a major cause of
but…
gastroenteritis among children <5 y/o
…but other viruses such as Norovirus (+ssRNA) may also cause gastroenteritis
We focus on
Rotaviruses that infect human and animals
diarrhea death rate is high in
developing countries
Rotaviruses seasonality: (3)
- Winter months (Nov. through May in US)
- Gradual spread from West to East
- Year-round in the Tropics
Rotaviruses transmission
& vehicles?
mainly via fecal-oral route
& food, water, and fomites (ex: clothing/bedding)
Rotaviruses are very resistant to
environmental conditions in temperate climate months
Rotavirus virion shape =
spherical, with structures resembling the spokes of a wheel, so the viruses were named after the Latin word “rota” (= wheel)
Rotavirus virion structure =
triple-layered particle as the capsid has 3 layers, each constructed from a distinct Virus Protein (VP)
Rotavirus virion inner and middle layers =
constructed from VP2 and VP6 respectively, are perforated by channels
Rotavirus virion middle layer =
contains the ‘spokes’ of the ‘wheel’ and is the major component of the virion
Rotavirus virion outer layer =
constructed from VP7, which is glycosylated.
Rotavirus have __ _____ genome segments
11 dsRNA
Rotavirus genome segment codes…
…total of =
…to be exact,…
one protein, except one that codes 2 proteins.
So there are a total of 12 proteins.
to be exact –> 6 structural proteins (VP) and 6 non-structural proteins (NSP).
VP =
NSP =
structural proteins (VP) non-structural proteins (NSP)
NSP4 acts as
a viral enterotoxin
NSP4 is not
packed into the virions
NSP4 induces
dose- and age-dependent diarrhea in lab animals
NSP4 increases…
disturbing. ..
damages. ..
- intracellular Ca++ concentration
- disturbing the cellular electrolyte homeostasis,
- and also damages tight junction between cells.
To attenuate the symptoms of rotavirus-induced diarrhea:
Immunize mice with an NSP4-based vaccine, followed by specific antibody production
Rotaviruses infect cells called _______ @…
enterocytes @ the ends of the villi (finger-like extensions) in the small intestine.
2 possible ways in which a rotavirus virion can enter the cell:
- ) direct penetration of the virion across the plasma membrane
- ) endocytosis
rotaviruses =
7 Baltimore classes
class III dsRNA
first step of rotavirus replication:
The outer layer of the virion is removed, leaving a double-layered particle in which transcription is activated
A problem that dsRNA viruses must overcome is:
However, Most of these viruses, including the rotaviruses, have solved this problem by…
the fact that dsRNA is a potent inducer of a number of cell defense mechanisms including apoptosis, interferon production and RNA silencing
ensuring that the viral dsRNA is always enclosed within virus protein structures, and is never free in the cytoplasm to trigger these defenses.
The final stages of virion assembly involve:
the addition of the outer layer of the capsid and the spikes
Virions are released from the cell either by: (2)
lysis or exocytosis
as a result of rotavirus disease/infection…
- ) Enterocytes on the villi are destroyed, leading to reduced absorption of water, salts and sugars from the gut.
- ) tight junctions between cells are damaged by NSP4, allowing leakage of fluid into the gut.
- ) secretion of water and solutes by secretory cells, result in diarrhea and this can lead to dehydration
Rotavirus-mediated diarrhea 3 “punches”:
- ) reduced absorption of water, salts and sugars from the gut due to destroyed enterocytes
- ) leakage of fluid into the gut due to damaged tight junction between cells
- ) Secretion of water and solutes by secretory cells
(Diarrhea development)
After a short incubation period of one to two days,…
…the onset of the illness is sudden, with watery diarrhea lasting four to seven days, vomiting and rapid dehydration.
Diagnosis of a rotavirus infection is…
The main techniques are…
…relatively easy as such large numbers of virus particles (up to 1011 particles/ ml of faeces) are shed.
…ELISAs, EM, etc.
Rotavirus disease treatment =
Simple treatment: rehydrating the patient with a solution of salts and sugar
In some parts of the world, the means for rotavirus treatment are not…
…available.
~1/2 million deaths of infants and young children due to rotavirus infections worldwide.
most rotavirus infections are confined to…
sometimes the virus may…
…the gut,
…cross the gut and infect other tissues.
Rotaviruses are relatively resistant to…
and susceptible to…
…handwashing agents
…disinfection with 95% ethanol, ‘Lysol’, formalin
Rotaviruses Vaccines: (2)
RotaTeq (Live oral vaccine)
Rotarix (Live attenuated vaccine)
