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Structure ofย Coltivirus
- Coltivirusparticles are 60โ80ย nm in diameter having two concentric capsid shells with a core that is about 50ย nm in diameter.
- They have a relatively smooth surface capsomeric structure and icosahedral symmetry.
- Non enveloped, icosahedral virion with a triple capsid structure, about 60-80 nm in diameter.
- Each virion contains a fullโlength copy of 12 segments of linear, doubleโstranded, positiveโsense RNA.
- The buoyant density of the virus in CsCl is 1.38ย gย cmโ3.
Genome ofย Coltivirus
- The genome consists of 12 dsRNA segments coding for 13 proteins that are numbered in order of decreasing size.
- The genome comprises approximately 29,000ย bp, with segment lengths that range between 675 and 4350 bp.
- The terminal 5โฒ- and 3โฒ-sequences of theย coltivirusgenome are conserved.
- The 12 segments are VP1(Pol)- RNA-dependent RNA polymerase, VP2-Methyltransferase, cell-receptor recognition site, VP3- RNA replication factors, VP4, VP5-Guanylyltransferase, VP6-Nucleotide binding, NTPase, VP7-RNA replication factors, VP8, VP9-Kinase, helicase, VP10, VP11, VP12-RNA replication factors.
Epidemiologyย ofย Coltivirus
- The virus that causes Colorado tick fever is the second most common Arbovirus in the United States, and several hundred cases are reported to the Centers for Disease Control and Prevention (CDC) annually.
- It has been found in California, Colorado, Idaho, Montana, Nevada, New Mexico, Oregon, South Dakota, Utah, Washington, and Wyoming, as well as the Canadian provinces of British Columbia and Alberta.
- CTFVย is caused by aย Coltivirus, and is a member of the Reoviridae. It is found in the mountain regions of western USA and Canada, especially in the Rocky Mountain area in Colorado.
Replicationย ofย Coltivirus
- Attachmentย toย host receptorsย and mediatesย endocytosis of virus into host cell.
- Particles are partially uncoated in endolysosomes, but not entirely, and penetrate in the cytoplasm.
- Earlyย transcription of the dsRNA genomeย by viral polymerase occurs inside the sub-viral particle (naked core), so that dsRNA is never exposed to the cytoplasm.
- Full-length plus-strand transcripts from each of the dsRNA segments are synthesized. These plus-strand transcripts are used as templates for translation.
- Viral proteins and genomic RNAs aggregates inย cytoplasmic viral factories.
- (+)RNAs are encapsidated in a sub-viral particle, in which they areย transcribedย 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.
Pathogenesisย ofย Coltivirus
- Colorado tick fever is a viral infection transmitted by the bite of the wood tickย Dermacentor andersoni.
- The virus circulates between ticks and rodents, with humans being the secondary hosts.
- 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.
- The virus replicates in those bone marrow cells, which disrupts the development and replication ofย leukocytes(white blood cells),ย eosinophils, andย basophils.
- Because of this,ย thrombocytopeniacould also a potential result.
- Erythrocytes, which are enucleated red blood cells, seem to be infected while they areย erythroblasts, their nucleated 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.ย
- 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.
Clinical manifestationsย ofย Coltivirus
- Clinical illness consists of headache, fever, myalgia, arthralgia, retro-orbital pain, photophobia and neck stiffness, accompanied by a macular, maculopapular or petechial rash in about 10% of cases and leukopenia are the cardinal features
- It is biphasic in about half the patients, characterized by 2โ3 days of illness, then 2 days of remission, followed by 2โ3 days’ more illness.
- The acute illness lasts 5โ10 days.
- Children may develop CNS infection encephalitis or hemorrhagic fever may occur.
- Prolonged convalescence characterized by weakness and fatigue is common in adults.
Lab Diagnosisย ofย Coltivirus
- Culture and RT-PCR during first 2 weeks of illness.
- Serologic assays (e.g., IgM-capture EIA, indirect fluorescent antibody, and plaque-reduction neutralization) on convalescent samples.
- Conventional blood tests are also generally not helpful, although leukopenia is a common finding in many patients.
- However, it is likely that many cases of Colorado tick fever are attributed to other viral infections and never correctly diagnosed.
Treatmentย ofย Coltivirus
- No specific antiviral treatment is available.
- Patients with suspected CTF are given supportive care as appropriate.
Prevention and controlย ofย Coltivirus
- No vaccine to prevent CTF.
- Use of insect repellent
- Wearing long sleeves and pants
- Avoidance of wooded and bushy areas with high grass
- Performing thorough tick checks after spending time outdoors
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