Isolation of bluetongue and related viruses from Culicoides spp. in the Sudan

Abstract

SummaryInfection of domestic ruminants with bluetongue virus (BTV) is widespread in the Sudan but there are no records of vector species of Culicoides in that country. Therefore, light-trap collections of Culicoides for virus isolation procedures were made in the Khartoum and Um Benein areas of the Sudan during September–October 1982.Two virus isolates were made from pools of unengorged, female Culicoides. An isolate from a pool of C. kingi (schultzei gp) is a member of the Epizootic Haemorrhagic Disease (EHD) serogroup. The other isolate from a pool of C. imicola, a known BTV vector in other parts of Africa, is type-5 BTV.In laboratory experiments, the North American vector of BTV, C. variipennis, supported replication of both Sudanese isolates to a high titre and transmission occurred after 10 days' incubation.This paper records the first isolation in the Sudan of arboviruses from Culicoides, with the identification of a BTV serotype and the presence of a member of the EHD (genus orbivirus, family Reoviridae) serogroup.

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

“…The isolation of BTV-2 from C. imicola confirms the previously acknowledged status of this species as a major vector of BTV in Africa and in the Sudan [3,11]. However, the isolation of a BTV from a mixed pool of Culicoides consisting of C. neavei, C. distinctipennis, C. similis, C. circumscriptus, C. ravus, C. grahami and C. milnei suggests that in the Sudan other species of Culicoides may also be involved in BTV transmission.…”

“…The procedures used were similar to those described by Mellor and colleagues [3]. Pools of unengorged female midges totalling 200 or fewer were ground in Griffiths tubes containing 3.5 ml of phosphate-buffered saline, supplemented with 2 % bovine serum albumen and 1 % antibiotic stock.…”

“…Electron micrographs (Fig. 3) demonstrated the presence of spherical virus particles ranging in size between 60-70 nm and which showed the diffuse appearance typical of orbiviruses for each of the 14 virus isolates [3]. (ii) Reciprocal cross neutralization -The results of cross-neutralization tests are shown in Table 5.…”

“…Isolate Gp 7 and EHDV-4 were both strongly neutralized by Gp the antiserum of EHDV-318. Isolates 3838, 3843 and 3856 were tested against all six EHDV antisera and also against an extra antiserum raised against 3863 virus (related to Su48 [3]). Isolate 3856 was only neutralized by the antiserum Su48 while isolates 3838 and 3843 were both neutralized by the antiserum of 3863 virus.…”

“…Since C. imicola is the classical Old World vector of BTV [11] and has previously been shown to be involved in BTV transmission in the Sudan [3] it is likely that the seasonal incidence of BT in Central Sudan, described by Mohammed and Taylor [1], is due directly to the seasonal prevalence of this midge as influenced by the movements of the ITCZ. Other arboviruses which may be transmitted in Central Sudan either by C. imicola or by C. schultzei will probably have, for the same reasons, a similar seasonal incidence to BTV.…”