Abstract
Sentinel herds were used to study the epidemiology of arboviruses in Oman and North Yemen. The results indicate that bluetongue virus (BTV) is fairly widely distributed and is enzootic in Northern Oman, all year round. Virus type specific antibodies to five BTV serotypes (3, 4, 17, 20 and 22) were detected. Antibodies to epizootichaemorrhagic disease virus (EHDV) type 2 and EHDV318 were also present although to a lesser extent. No EHDV1 antibodies could be detected among the sentinel animals during the entire period. Prevalence of neutralizing antibodies against Akabane virus was found in a wide range of domestic animals in all countries of the Arabian Peninsula but the virus does not seem to be enzootic there. The possibility of windborne, infected vectors, from virus enzootic areas initiating these incursions into the Arabian Peninsula is discussed. A total of four arboviruses were isolated and identified (two BTV4 and two Akabane virus). Three of them from vertebrate hosts and one was from a species of Culicoides. This isolation of Akabane virus from C. imicola is the first record of this virus from this species of midge. Entomological investigations were undertaken, into the population dynamics of potential Culicoides vectors and the results correlated with the climatic conditions. Sixteen species of Culicoides were identified among which four were new to science, these included C. arabiensis, C. ibriensis, C. bueltikeri and C. neoschultzei. Vector competence studies have shown that the Omani virus isolates multiply in C. variipennis after oral ingestion and that both viruses are maintained for at least 10 days post-infection. Biochemical analysis and comparison of the proteins induced in infected cells and genomic profiles of the Omani virus isolates were analysed by polyacrylamide gel electrophoresis and formaldehyde-agarose gel electrophoresis and compared with several other prototype reference strains. Minor differences in BTV specific proteins and dsRNA profiles between various strains were observed. Akabane virus specific proteins were indistinguishable between the different Akabane strains, but minor differences were observed in their genomic profiles and that their RNA was polyadenylated.