Further studies on bluetongue and bluetongue-related Orbiviruses in the Sudan

Abstract

SUMMARYThe seasonal incidence of bluetongue virus (BTV) in Central Sudan is related primarily to fluctuations in the prevalence of the vector, Culicoides imicola. Population densities of this midge begin to rise with the onset of precipitation and peak during October, before falling sharply at the end of the rainy season in November. These are also the months of BTV transmission. Populations of C. schultzei, the commonest midge in Central Sudan, are also related to the rainy season but this species does not seem to be involved with BTV transmission.BTV serotype 2 was isolated from C. imicola confirming the status of this midge as a known vector but a second isolate of the same serotype was made from a mixed pool of Culicoides not including C. imicola. This suggests that BTV transmission in the Sudan may involve more than one species of Culicoides. Epizootic haemorrhagic disease virus (EHDV) serotype 4 and a palyam virus were isolated from C. schultzei which indicates that this species may be involved in the transmission of BT-related viruses. Seven further virus isolates from sentinel calves at Shambat (Khartoum) confirmed the presence of BTV serotypes 1, 4 and 16, and an untyped EHDV (designated 318) in the Sudan. All of the viruses isolated and identified during the course of this work are recorded from the Sudan for the first time.

Isolation and identification of arboviruses from the Sultanate of Oman

“…Virus was not isolated from C. schultzei in the present study, but only relatively small numbers of this species were examined. In the Sudan C. schultzei group midges have been implicated in the transmission of the BT-related epizootic haemorrhagic disease viruses (EHDV) [23], at least two serotypes of which occur in Oman (Al-Busaidy and Mellor, unpublished observations). Also, Akabane virus has recently been isolated from C. schultzei group midges in Japan [13].…”

“…Also, Akabane virus has recently been isolated from C. schultzei group midges in Japan [13]. C. schultzei midges have not been implicated as vectors of BTV and it is unlikely that they are significantly involved in the transmission of this group of viruses [23].…”

Detection of a novel reassortant epizootic hemorrhagic disease virus (EHDV) in the USA containing RNA segments derived from both exotic (EHDV-6) and endemic (EHDV-2) serotypes

“…Three serotypes have been recognized in Africa: EHDV-3 (proposed to be EHDV-1) and EHDV-4, which were initially isolated from Culicoides spp. in Nigeria in 1967and 1968, respectively (Lee et al, 1974, and EHDV-318 (proposed to be EHDV-6), which was first isolated from cattle in Bahrain in 1983 and subsequently described from sentinel calves in the Sudan (Mohammed & Mellor, 1990;Rabenau et al, 1993;Anthony et al, 2009). EHDV serotypes 5, 7 and 8, along with the prototype strain of EHDV-6 (CSIRO 753), were initially isolated from sentinel cattle herds in Queensland and the Northern Territory of Australia during 1977-1982(St George et al, 1983.…”

Epidemiology of bluetongue and related orbiviruses in the Sultanate of Oman

“…This is a different pattern to that shown by BTV and may be related to the fact that these two groups of virus seem to be transmitted by different species of Culicoides. Strains of EHDV have been shown to be transmitted by C. schultzei group midges in the Sudan [20]. However, in Northern Oman peak populations of this group of insects occur at Rumais between April and November (Fig.…”