Structured epidemiological studies based on sentinel herds in Indonesia and Malaysia have provided much information regarding the bluetongue (BT) viruses (BTV) and their likely vectors in South-East Asia. Serotypes 1, 2, 3, 7, 9, 12, 16, 21 and 23 have been isolated. Molecular analyses show all group within the Australasian topotype, with four genotypic sub-groupings identified to date. There are relationships to isolates from both India and Australia. Strains of BTV in South-East Asia do not appear to be highly virulent, since BT disease is not seen in local sheep. Known vector species identified include Culicoides fulvus, C. actoni, C. wadai and C. brevitarsis. C. imicola has not been identified in Malaysian or Indonesian studies. Molecular analyses indicate movement of South-East Asian strains of BTV into northern Australia, and the gradation in observations between India and eastern Australia regarding serotype, genotype, virulence and vector species suggests movement along a conceptual gradient through South-East Asia.
The authors have characterised the genetic diversity of the bluetongue virus (BTV) RNA segments 3 and 10 from Indonesia, Malaysia and Australia. Analysis of RNA segment 3, which codes for the core protein VP3, showed conserved sequences in the previously defined Australasian topotype, but which further divided into four distinct clades or genotypes. Certain genotypes appeared to be geographically restricted while others were distributed widely throughout South-East Asia. Ongoing surveillance programmes in Australia have identified the movement of Indonesian genotypes into northern Australia and possible reassortment among them. Similarly, analysis of RNA segment 10, which codes for the non-structural protein NS3/3A, showed they were also conserved and grouped into five clades or genotypes, three Asian and two North American/South African.
After the outbreak of Nipah virus (NiV) in 1998-99, which resulted in 105 human deaths and the culling of more than one million pigs, a search was initiated for the natural host reservoir of NiV on Tioman Island off the east coast of Malaysia. Three different syncytia-forming viruses were isolated from fruit bats on the island. They were Nipah virus, Tioman virus (a novel paramyxovirus related to Menangle virus), and a reovirus, named Pulau virus (PuV), which is the subject of this study. PuV displayed the typical ultra structural morphology of a reovirus and was neutralised by serum against Nelson Bay reovirus (NBV), a reovirus isolated from a fruit bat (Pteropus poliocephalus) in Australia over 30 years ago. PuV was fusogenic and formed large syncytia in Vero cells. Comparison of dsRNA segments between PuV and NBV showed distinct mobility differences for the S1 and S2 segments. Complete sequence analysis of all four S segments revealed a close relationship between PuV and NBV, with nucleotide sequence identity varying from 88% for S3 segment to 56% for the S1 segment. Similarly phylogenetic analysis of deduced protein sequences confirmed that PuV is closely related to NBV. In this paper we discuss the similarities and differences between PuV and NBV which support the classification of PuV as a novel mammalian, fusogenic reovirus within the Nelson Bay orthoreovirus species, in the genus Orthoreovirus, family Reoviridae.
Bluetongue viruses (BTV) were isolated from sentinel cattle in Malaysia and at two sites in Indonesia. We identified eight serotypes some of which appeared to have a wide distribution throughout this region, while others were only isolated in Malaysia or Australia. Nearly half of the 24 known BTV serotypes have now been identified in Asia. Further, we investigated the genetic diversity of their RNA segments 3 and 10. Using partial nucleotide sequences of the RNA segment 3 (540 bp) which codes for the conserved core protein (VP3), the BTV isolates were found to be unique to the previously defined Australasian topotype and could be further subdivided into four distinct clades or genotypes. Certain of these genotypes appeared to be geographically restricted while others were distributed widely throughout the region. Similarly, the complete nucleotide sequences of the RNA segment 10 (822 bp), coding for the non-structural protein (NS3/3A), were also conserved and grouped into the five genotypes; the BTV isolates could be grouped into three Asian genotypes and two Nth American/Sth African genotypes.
The nucleotide sequence of the RNA segment 3 of bluetongue virus (BTV) serotype 2 (Ona-A) from North America was determined to be 2772 nucleotides containing a single large open reading frame of 2703 nucleotides (901 amino acid). The predicted VP3 protein exhibited general physiochemical properties (including hydropathy profiles) which were very similar to those previously deduced for other BTV VP3 proteins. Partial genome segment 3 sequences, obtained by polymerase chain reaction (PCR) sequencing, of BTV isolates from the Caribbean were compared to those from North America, South Africa, India, Indonesia, Malaysia and Australia, as well as other orbiviruses, to determine the phylogenetic relationships amongst them. Three major BTV topotypes (Gould, A.R. (1987) Virus Res. 7, 169-183) were observed which had nucleotide sequences that differed by approximately 20%. At the molecular level, geographic separation had resulted in significant divergence in the BTV genome segment 3 sequences, consistent with the evolution of distinct viral populations. The close phylogenetic relationship between the BTV serotype 2 (Ona-A strain) from Florida and the BTV serotypes 1, 6 and 12 from Jamaica and Honduras, indicated that the presence of BTV serotype 2 in North America was probably due to an exotic incursion from the Caribbean region as previously proposed by Sellers and Maaroof ((1989) Can. J. Vet. Res. 53, 100-102) based on trajectory analysis. Conversely, nucleotide sequence analysis of Caribbean BTV serotype 17 isolates suggested they arose from incursions which originated in the USA, possibly from a BTV population distinct from those circulating in Wyoming.