Biological and molecular characteristics of orbiviruses and orthomyxoviruses isolated from ticks
Tick-borne orbiviruses and tick-borne “orthomyxoviruses” possess segmented RNA genomes. Consequently, they have the potential to undergo reassortment following co-infection of a cell with related viruses. Most orbiviruses (family Reoviridae) isolated from ticks are members of the Kemerovo (KEM) serogroup, possessing a genome comprised of 10 segments of double-stranded RNA. In vitro studies have demonstrated reassortment between Great Island (GI) subgroup viruses (associated with seabirds) and KEM virus (a human pathogen), but not between GI subgroup viruses and other members of the group that are associated with birds. Such genetic relationships presumably reflect the evolutionary pathways followed by the virus as it circulates in a vertebrate-arthropod infection cycle. Evidence that rapid evolution, via genetic reassortment, can occur in both the vertebrate and tick hosts of an arbovirus has been demonstrated with Thogoto (THO) virus, an unclassified tick-borne virus that shows structural and morphogenetic properties characteristic of orthomyxoviruses. The genome of THO virus is composed of 6 segments of single-stranded, negative-sense RNA. Using is mutants, reassortment of THO virus has been demonstrated in naturally infected ticks and in a vertebrate host. However, in these studies the potential for reassortment was shown to be limited by interference. This paper discusses the relative roles of the vertebrate host and the tick vector in terms of virus evolution resulting from genetic reassortment.
KeywordsVertebrate Host Tick Infestation Infected Tick Bluetongue Virus Arthropod Vector
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