Colitivirus
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Coltiviruses are a genus in the Reoviridae family that infect both arthropods and vertebrates. They contain 12 segmented double-stranded RNA genome segments and replicate in the cytoplasm of infected cells. Colorado tick fever virus is a prominent Coltivirus that causes a febrile illness in humans transmitted through the bite of the wood tick. It infects and replicates in bone marrow cells, disrupting leukocyte development. The virus remains in erythrocytes for up to 4 months without harm, protecting it from the immune system. There is no vaccine or treatment available, so prevention focuses on avoiding wood tick bites.
Colitivirus
- 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
- 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.
- 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.