Colitivirus presentation

1. Coltivirus
BY- Sanju Sah
St. Xavier’s College, Maitighar, Kathmandu
Department of Microbiology

3. Introduction
• Reo: from Respiratory enteric orphan
• In 1959, Sabin proposed the name reovirus to reflect
the fact that viruses of this group had been isolated
from the respiratory and enteric tracts and were orphan
(reo) viruses without known associated disease.
• The family Reoviridae is divided into several genera.
• Four of the genera are able to infect humans and
animals: Orthoreovirus, Rotavirus, Coltivirus, and
Orbivirus.
• Other genera infect only the plants, insects, and fish.

4. • These genera can be divided into two groups; one group
contains viruses with large spikes at the 12 vertices on the
particle (eg, Orthoreovirus) whereas members of the second
group appear more smooth, lacking the large surface
projections (eg, Rotavirus).
• The Reoviridae viruses are non-enveloped viruses with
double-layered protein capsids.
• The genome consists of a 10–12 segmented double-stranded
RNA with a total genome size of 16–27 kbp depending on
the genus
• Rotaviruses contain 11 genome segments, whereas
orthoreoviruses and orbiviruses each possess 10 segments
and coltiviruses have 12 segments.

5. Important Properties of Reoviruses

7. Structure
of
family
Reoviridae

8. REPLICATION:CYTOPLASMIC
• Attachement to host receptors probably mediates
endocytosis of virus into host cell.
• Particles are partially uncoated in endolysosomes,
but not entirely, and penetrate in the cytoplasm.
• Early transcription of the dsRNA genome by viral
polymerase occurs inside this sub-viral particle
(naked core), so that dsRNA is never exposed to
the cytoplasm.
• Transcription from each of the dsRNA segments
produces mRNA templates for translation.
• Viral proteins and genomic RNAs aggregates in
cytoplasmic viral factories.

9. • (+)RNAs are encapsidated in a sub-viral
particle, in which they are transcribed to give
RNA (-) molecules with which they become
base-paired to produce dsRNA genomes.
• The capsid is assembled on the sub-viral
particle.
• Mature virions are released presumably
following cell death and associated breakdown
of host plasma membrane.

10. Viral
replication

11. Diseases associated with reoviruses
*Biliary atresia is
a rare condition
in newborn
infants in which
the common bile
duct between the
liver and the
small intestine is
blocked or absent

12. Coltivirus
• Coltiviruses resemble the orbiviruses in size and
in having 2 capsids.
• These viruses contain 12 RNA segments.
• Colorado tick fever (CTF), Salmon River virus (in
Idaho), Eyach virus (in Germany and France),
isolate S6-14-03 (in California), Banna virus,
Beijing virus, and Gansu virus (in China) either
are proved or suspected of causing human disease.

14. wood tick (Dermacentor andersoni)

15. • Colorado tick fever is an acute viral
infection transmitted by the bite of wood
tick (Dermacentor andersoni) caused by
Colorado tick fever virus.
• Colorado fever was so named because the
illness was believed to occur predominantly
in Colorado and was used to distinguish this
clinical illness from that of Rocky Mountain
spotted fever caused by Rickettsia species.
• The causative agent of this fever was
recognized as a virus in 1946

16. • The virus infects and replicates in the bone
marrow, lymph nodes, spleen, and liver of
rhesus monkey, but without producing any
histological abnormalities.
• The virus has been shown to replicate in
erythroid precursor cells without severely
damaging them and is present in mature red
blood cells.
• Larval and nymphal stages of D. andersoni ticks
usually transmit the virus among all rodents, but
only adult ticks transmit the virus to humans.

17. • The ticks acquire the infection on feeding an infected
viremic host.
• The infected ticks subsequently transmit the virus through
their saliva during act of feeding on a new susceptible host.
• Squirrels, rabbits, and deer are the natural animal hosts for
the virus.
• The virus generally causes a nonspecific febrile illness.
• The incubation period is short and varies from 3 to 6 days.
• The clinical manifestations of the acute condition are
characterized by the sudden onset of fever, chills, headache
with retro-orbital pain, malaise, nausea, and occasionally
vomiting.

18. • A rash is generally absent by which Colorado tick fever
is differentiated from the Rocky Mountain spotted
fever.
• The fever is typically biphasic (i.e., with two episodes
of fever), each of which lasts 2–3 days, separated by a
remission of approximately equal duration, in most
cases, the febrile period is followed by moderate to
marked weakness and malaise.
• Complications are rare, but may include hepatitis,
pericarditis, epididymoorchitis, atypical pneumonitis,
encephalitis, and aseptic meningitis.
• Viruses are present in the erythrocytes during the first 2
weeks of disease.

19. • This is followed by a period during which the
viruses infect and replicate within the
erythropoietic cells.
• In the infected red blood cells, the viruses can live
for the life of the cells, which is nearly 120 days.
• A single attack of infection usually produces
lifelong immunity.
• No specific antiviral treatment is available for
Colorado tick fever.
• The condition is usually self-limited and can be
prevented by avoiding contact with the wood tick

22. Pathogenesis
• Coltiviruses replicate in the cytoplasm in cells of
both arthropods and vertebrates, but they are only
transmitted by the arthropods.
• When the virus replicates, the virion outer shell has to be
removed in order for RNA polymerase to be activated to
continue the replication of the virion's RNA.
• Reassortment of the RNA segments in progeny is common,
and this plays a role in some of the genetic diversity
between the serotypes.
• Infection takes place when the tick larvae feed on rodents,
like squirrels, that are already infected with virus.
• The tick's saliva then contains the virus, and it becomes
infectious for life. The adult tick then transmits the virus to
humans through a bite, where it infects bone marrow cells

23. • The virus replicates in those bone marrow cells, which
disrupts the development and replication
of leukocytes (white blood cells), eosinophils,
and basophils.
• Because of this, thrombocytopenia could also a
potential result.
• Erythrocytes, which are enucleated red blood cells,
seem to be infected while they are erythroblasts, their
precursor stage.
• The virus stays in these red blood cells without harming
it for up to four months. Here, it is protected from the
immune system's attacks.
• Antibody to the virus is found only about two weeks
after symptoms begin to show, but the virus can still be
found in blood cells for about six weeks.

24. Symptoms
• Colorado tick fever virus can cause a fever, chills,
headache, photophobia, myalgia, arthralgia, and
lethargy.
• Children, in particular, may develop a
hemorrhagic disease.
• Leukopenia with both lymphocytes and
neutrophils is very common for Colorado tick
fever virus, In either case, the infection can lead
to encephalitis or meningitis.

25. Diagnosis
• For diagnosis, the erythrocytes can be isolated by
injecting them into a tissue culture and checking
to see if they are infected.
• Also, the antigen for Colorado tick fever virus can
be identified using the immunofluorescence
microscopy.
• In this method, the antigens on the surface of the
erythrocytes are marked with fluorescence and
examined under a fluorescence microscope.

26. • Colorado tick fever virus can be detected in a
patient with a reverse transcription polymerase
chain reaction (RT-PCR), where even a single
virion and its genetic material can be detected.

27. Treatment
• There is currently no known vaccine or
treatment available to treat these Coltiviruses,
but 3'-fluors-3'-deoxyadanosine, a nucleoside
analog, halts replication of Colorado tick fever
virus in vitro.

28. Control
• The virus circulates between ticks and rodents,
with humans being the secondary hosts.
• People at risk for catching the disease are hikers
and campers that are in the risk areas.
• Also, April, May, and June are when the
infections mainly occur, because this is the time
when the adult ticks are prevalent in the
environment.
• The best way to avoid getting bitten and catching
this disease is wearing long sleeves or pants,
avoiding high tick-infested areas, and wearing
tick repellent.