[Show abstract][Hide abstract] ABSTRACT: Comparison of sequence data for Broadhaven (BRD) virus, a tick-borne orbivirus, and bluetongue virus (BTV), the type species of the genus, indicated that RNA segments 2 and 7 of BRD virus encode the two structural core proteins, VP2 and VP7, respectively. Segment 2 is 2792 nucleotides in length with a coding capacity for a protein (VP2) of 908 amino acids and a net charge of +8.5 at neutral pH. Segment 7 is 1174 nucleotides in length with a coding capacity for a protein (VP7) of 356 amino acids and a net charge of +11.5 at neutral pH. Comparison of the two sequences with BTV serotype 10 revealed amino acid identity of 35% between the product of segment 2 and BTV VP3, and 21% between the product of segment 7 and BTV VP7. The core proteins therefore show evidence of significant evolutionary divergence compared with that shown between different insect-borne orbiviruses. In particular, the amino terminus of BRD virus VP7 differed markedly from the equivalent region in VP7 of BTV and African horse sickness virus. This region is thought to interact with the outer capsid layer of insect-borne orbiviruses.
Journal of General Virology 11/1992; 73 ( Pt 10):2585-90. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The genome of orbiviruses (Reoviridae family) comprises 10 segments of double-stranded RNA. The fourth largest segment of the tick-borne Kemerovo (KEM) group orbiviruses is the genetic determinant of neurovirulence in experimentally infected mice, and segment 6 determines serotype. Reassortant viruses derived from a cross between two KEM-related viruses, Great Island (GI) and Wexford (WEX), that had the heterotypic gene combination W4G6 (segment 4 of WEX virus and segment 6 from GI virus) were nonpathogenic in mice. This apparent genetic modulation of neurovirulence may have resulted from steric interaction between the two outer capsid proteins of nonpathogenic reassortants. Further data are consistent with this hypothesis. Reassortants generated from additional KEM group viruses showed various degrees of enhanced neurovirulence in terms of their PFU/LD50 (ratio of infectivity in cell culture and in mice) and ASTmax (the average survival time at the highest virus dilution resulting in 100% mortality). Some reassortants were more pathogenic than either of their parental viruses. The results indicate that the gene determining neurovirulence dictates ASTmax, and the PFU/LD50 is a measure of the interaction between the products of the gene determining neurovirulence and that determining serotype. The nonpathogenic phenotype of a low passage isolate (St. Abb's 84-34 virus), derived from a single tick, generated neurovirulent reassortants. This result indicates that genetic modulation of KEM group viruses may occur in nature.
[Show abstract][Hide abstract] ABSTRACT: The complete nucleotide sequence of the smallest RNA segment (segment 10) of Broadhaven (BRD) virus, a tick-borne orbivirus, was determined from a full-length cDNA clone. The genome segment is 702 nucleotides in length and has a coding capacity for two proteins of either 205 or 199 amino acids, having net charges of +16.5 and +17.5, respectively, at neutral pH. Comparison of the sequence of RNA segment 10 of BRD, bluetongue, African horse sickness, and Palyam viruses revealed amino acid homology of 20 to 30% between the four orbiviruses, with one conserved region of 40 to 50% homology which, in segment 10 of BRD virus, is found between residues 26 and 71.
[Show abstract][Hide abstract] ABSTRACT: Genetic studies have been carried out on orbiviruses in the Great Island (GI) antigenic subgroup of the Kemerovo serogroup (Orbivrus, Reoviridae) to elucidate the functions of the 10 genomic double-stranded RNA segments. Such studies have shown that segment 4 is the major genetic determinant of neurovirulence (P.A. Nuttall, S.R. Moss, L.D. Jones, and D. Carey, 1989, Virology 172, 428-434), whereas segment 5 of Wexford (WEX) virus and segment 6 of GI virus are the major determinants of serotype specificity (S.R. Moss, C.M. Ayres, and P.A. Nuttall, 1987, Virology 157, 137-144; S.R. Moss, C.M. Ayres, and P.A. Nuttall, 1988, J. Gen. Virol. 69, 2721-2727). In studies with reassortants isolated following dual infection of cell cultures with WEX and GI viruses, the gene combination W4G6 (i.e., viruses deriving segment 4 from WEX virus and segment 6 from GI virus) resulted in nonpathogenic reassortants. Unlike the parental viruses, the avirulent reassortants did not produce clinical evidence of infection in inoculated 2-day-old mice although, suprisingly, they replicated in the brains of the mice. The alternate heterotypic gene combination, G4W5, resulted in typical neurovirulent reassortants. The results indicate that segment 6 of GI virus is able to modulate the phenotypic expression of segment 4 of WEX virus, but not vice versa. Modulation probably results from interactions between the products of these two genomic segments, possibly at the level of virion structure.
[Show abstract][Hide abstract] ABSTRACT: Three members of the Great Island antigenic subgroup (Kemerovo serogroup) of tick-borne obiviruses produced fatal infections following intracerebral inculation of 2-day-old mice. The average survival times and PFU/LD50 ratios of mice inoculated with Wexford (WEX) virus were significantly greater than those of either Nugget (NUG) or Great Island (GI) virus. Reassortant viruses were isolated following dual infections of cell cultures with a spontaneous temperature-sensitive (ts) mutant of WEX virus, and either NUG wild-type virus or a ts mutant of GI virus. The neurovirulence for mice and derivation of the genomic RNA segments were determined for the reassortants. Analysis of this data revealed that the pathogenic phenotype of the reassortant viruses depended on the parental origin of genomic segment 4. The major genetic determinant of serotype specificity was not shown to influence neurovirulence in these investigations.
[Show abstract][Hide abstract] ABSTRACT: The Kemerovo (KEM) serogroup of tick-borne orbiviruses (Reoviridae family) is currently classified into four antigenic subgroups: KEM, Chenuda (CNU), Great Island (GI), and Wad Medani (WM) (B. M. Gorman, J. Taylor, and P. J. Walker, 1983, In "The Reoviridae," pp. 287-357). Reassortment assays were carried out to determine the potential for gene exchange both within and between subgroups. Genome segment reassortment was demonstrated between members of two subgroups: KEM virus (a human pathogen) and representatives of the GI subgroup (viruses associated with seabirds). Neither KEM nor GI subgroup viruses reassorted with three viruses currently assigned to the CNU subgroup [CNU, Essaouira (ESS), and Mono Lake (ML)]. Within the CNU subgroup, CNU and ESS viruses reassorted, but there was no evidence of genome segment exchange between either of these two viruses and ML virus. The genetic data, and previously published antigenic data, suggest the need for reassigning these viruses. Four new serogroups are proposed to replace the extant KEM serogroup: KEM serogroup (comprising KEM and GI subgroups), CNU serogroup (including CNU and ESS viruses), Mono Lake serogroup, and WM serogroup.
[Show abstract][Hide abstract] ABSTRACT: The geographical distribution of members of the Great Island (GI) subgroup in the Kemerovo serogroup of orbiviruses extends from the Arctic to the Sub-antarctic. To examine the gene pool size of this group, five topotypes whose origins ranged from Iceland in the northern hemisphere to Macquarie Island in the Southern Ocean were tested for their ability to reassort in vitro. All the isolates were distinguishable by plaque reduction neutralization tests, and their genome profile in polyacrylamide gels. They showed high frequency reassortment following dual infection of cell cultures with temperature-sensitive (ts) mutants and/or wild-type virus. Analysis of the dsRNA profile of the reassortants by PAGE confirmed the observation from reassortment assays that the Great Island subgroup constitutes a single gene pool. A seventh reassortment group was identified, distinct from the six groups previously described. The ts lesions for reassortment groups I, V and VII were considered to be in genome segments 9, 3 and 2, respectively. Segment 6 of GI virus (in contrast to segment 5 of Broadhaven and Wexford viruses) was shown to be the major genetic determinant of serotype specificity.
Journal of General Virology 12/1988; 69 ( Pt 11):2721-7. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Reassortant viruses were produced from high-frequency recombination events between temperature-sensitive (ts) mutants of Broadhaven (BRD) (S. R. Moss and P. A. Nuttall, Virus Res. 4, 331-336, 1986) and Wexford (WEX) viruses, two serotypes in the Kemerovo serogroup of orbiviruses. The parental origin of each of the 10 genomic segments comprising each reassortant was determined by polyacrylamide gel electrophoresis. Comparison of neutralization titers with the results of genomic dsRNA analyses revealed that genome segment 5 codes for the neutralizing epitope(s). Kemerovo group viruses therefore differ from orbiviruses of the bluetongue serogroup in which segment 2 codes for the neutralizing epitopes (M. J. Grubman, J. A. Appleton, and G. J. Letchworth, Virology 131, 355-366, 1983; J. Kahlon, K. Sugiyama, and P. Roy, J. Virol. 48, 627-632, 1983). Results also indicated that the ts lesions in mutants of recombination groups II, III, and VI were in segments 1, 5, and 4, respectively. Reassortment of segments 2 and 10 appeared to be nonrandom, and evidence of possible "linkage" was obtained for segments 3 and 9.
[Show abstract][Hide abstract] ABSTRACT: . Viruses isolated from IXODES (CERATIXODES) URIAE collected in seabird colonies in the United Kingdom, Faeroe Islands, and Iceland are closely related to Great Saltee virus, a member of the Hughes serogroup (Bunyaviridae) isolated from Ornithodoros (Alectorobius) maritimus from Eire. With one exception, Hughes group viruses associated with seabirds have been recorded only from soft ticks of the O. (A.) capensis complex. The isolation of Hughes serogroup viruses from the hard tick I. uriae extends the host and geographical ranges of a group of viruses that have been associated with disease in humans.
Journal of Medical Entomology 07/1986; 23(4):437-440. · 1.82 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Eighteen stable temperature sensitive (ts) mutants of Broadhaven virus were isolated without the aid of mutagens. Spontaneous mutants were detected using 41 degrees C as the nonpermissive temperature and 36 degrees C as the permissive temperature. High frequency pairwise recombination defined five recombination groups. Four mutants belonged to group I, three to group II, six to group III, two to group IV, and two to group V. ts 7 was a possible double mutant representing lesions corresponding to those of groups III and V mutants. This is the first reported isolation of temperature sensitive mutants of a tick-borne orbivirus.
Virus Research 07/1986; 4(4):331-6. · 2.83 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Two viruses were isolated from a pool of three female Ixodes uriae ticks found on a dead puffin (Fratercula arctica) on a beach at Arbroath, Scotland. Complement fixation tests showed that one of the viruses was an orbivirus belonging to the Kemerovo serogroup and was related to Cape Wrath virus. Cross-reactions did not occur in neutralisation tests with 4 Kemerovo group viruses previously isolated from I. uriae collected in British seabird colonies. The orbivirus was therefore named Arbroath virus. The other virus was of the Uukuniemi serogroup (family Bunyaviridae) and reacted in complement fixation and neutralisation tests with a virus isolated from I. uriae collected from a seabird colony at St Abb's Head, Scotland. Both the orbi- and the uukuviruses replicated in a tick (Rhipicephalus appendiculatus) cell line, RA-243.
[Show abstract][Hide abstract] ABSTRACT: Three methods of isolating viruses from 10 tick pools were compared; none of the methods produced all 13 of the viruses isolated (7 viruses of the bunyaviridae and 6 orbiviruses). Inoculation of homogenised ticks into various cell lines was the most successful, yielding 11 virus isolations. Only 2 tick homogenates induced overt signs of infection following intra-cerebral inoculation of 2-day-old mice. However, when inoculated mouse brain was passaged in various cell lines, 8 of 12 isolations were made. The rates of success of the 3 methods of virus isolation appeared to vary according to the type and titre of the virus in the tick pool.
Journal of Virological Methods 09/1984; 9(1):27-33. · 1.88 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Viruses were isolated from 2 tick species collected from the nesting areas of seabirds on Great Saltee Island, Eire. Bunyaviruses of the Uukuniemi serogroup were isolated from hard ticks (Ixodes uriae and I. rothschildi), bunyaviruses of the Hughes serogroup from soft ticks (Ornithodoros maritimus), and orbiviruses of the Kemerovo serogroup from I. uriae and O. maritimus. The results indicate that the bunyaviruses, but not the orbiviruses, show "tick specificity". Neutralising activity against members of all 3 serogroups was detected in sera from chicks in the nesting areas; neutralising antibodies were probably maternal.
Archives of Virology 02/1984; 79(1-2):35-44. · 2.28 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Summary Viruses were isolated from two of three pools of the tickIxodes uriae collected from a puffin(Fratercula arctica) colony on the Shiant islands. One pool contained an orbivirus whereas evidence of both orbi- and bunyaviruses was found in the second pool. Serological tests showed that the orbiviruses were related to Cape Wrath virus in the Kemerovo serogroup; the bunyavirus appeared to be related to Clo Mor virus of the Sakhalin serogroup. The results indicate that an interchange of viruses may occur within seabird colonies of the north-west of Scotland.
Archives of Virology 02/1982; 74(4):259-68. · 2.28 Impact Factor