This paper describes a solid-phase microtitre plate enzyme-linked immunosorbent assay (ELISA) for the detection of antibodies to equine influenza viruses. Using egg-grown influenza viruses as the antigens attached to the solid phase, crossreactions were observed between an H7N7 equine virus (designated A1) and an H3N8 equine influenza virus (designated A2) when untreated antisera were tested. Absorption of antisera with egg-grown A/Porcine/Shope/1/33 influenza virus eliminated cross-reactive antibodies so that specific detection of anti-equine influenza A1 or A2 antibodies was possible.

Examination of horse sera following vaccination with A1 and/or A2 isolates showed that antibodies were produced against antigen associated with egg allantoic fluid as well as against virus. Such antibodies were eliminated following the absorption of antisera with porcine influenza virus. Results using sera from horses with known vaccination histories confirmed that the ELISA preferentially detected antibodies homologous to the antigen attached to the solid phase and methods to evaluate the current serological state of individual horses by relating the titres of specific antibodies against equine influenza A1 and A2 isolates are shown. This ELISA provides a simple and rapid method of assessing specific antibodies from horse sera and offers advantages over the ‘routine’ HI and SRH assessments since it gives high precision, is economical of reagents and has the capacity to handle large numbers of serum samples.

Infection 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.

In a preliminary seroepidemiological survey a total of 780 serum samples derived from various domestic animals of the Sudan were examined for Rift Valley fever (RVF) virus precipitating antibodies. The incidence was approximately 34·3% in sheep, 33·2% in cattle, 22%in goats, 7·9% in camels and 4% in donkeys. The findings indicated that RVF is mainly prevalent in the rich savanna areas of the south as well as the irrigated areas close to the Nile in the north.

Circumstantial evidence suggests that the detected antibodies were induced by a long-standing cryptically cycling infection and that resurgence of extensive epizootics is unlikely although limited outbreaks may occur. It is concluded that RVF virus circulates across the country in a south–north range along the Nile Valley with little or no extension to the drier lands to the east and west, and that ruminants are the primary species involved in virus maintenance. These species evidently serve as main amplifiers of infection during epizootics, but whether or not they also serve as sole virus reservoirs in inter-epizootic periods has yet to be determined.

Rotaviruses present in products of wastewater treatment were assayed in MA 104 cells by indirect immunofluorescence. Levels in settled sewage, activated sludge and effluent were greater than 103 per litre in March and April but virus was not detected during later months. This pattern correlated with the decline in laboratory reports of human rotavirus infection.