Studies on bluetongue disease in the People's Republic of China.

Bluetongue (BT) is an important infectious, non-contagious, insect-borne viral disease of ruminants, and is classified as a 'List A' disease in the OIE Terrestrial animal health code. Since the first discovery and diagnosis of this disease in the Shizong County of Yunnan Province in 1979, the authors have developed systematic studies of the epidemiology, experimental epidemiology, aetiology, pathology, viral molecular characteristics (nucleic acid), diagnostic techniques, virus identification (grouping and typing) methods, vaccines and immunisation methods of BT in the People's Republic of China. Viruses have been isolated from seven provinces and the major serotypes have been identified. Epidemiological surveys have been conducted in sixteen provinces and a distinct type of BT virus (BTV) epidemiology has been found in China. Sentinel herds were established to monitor BTV regularly from 1995 to 1998. Experimental epidemiological studies have revealed the regional distribution of BTV serotypes and the dynamic spread of BTV in different habitats of distinct natural conditions, ecological environment and climate in China. A technical system of diagnosis of BTV infection also has been developed, including the agar gel immunodiffusion (AGID), indirect ELISA, competitive-ELISA (c-ELISA) and virus neutralisation (VN) tests for detection of antibodies to BTV, and the serum neutralisation (SN), immunofluorescence (IF) and immunoperoxidase (IP), antigen capture-ELISA (ac-ELISA), virus inoculation methods for virus detection, and nucleic acid electrophoresis analysis, nucleic acid probe techniques, and polymerase chain reaction (PCR) methods for detection of BTV nucleic acid and/or proteins. Attenuated and killed vaccines of BTV serotypes 1 and 16 have been developed and new immunisation methods have been developed. The S7, S10 and portions of the L2 gene segment of Chinese prototype strains of BTV serotypes 1, 2, 3, 4, 12, 15 and 16 have been sequenced and compared to the same strains of prototype and field strains of BTV from the United States of America and Australia. Phylogenetic analyses indicate that the genetic relationships between these viruses correspond to their geographic origins or their serotype. The National Standards for Bluetongue Diagnosis, People's Republic of China has also been enacted. Remarkable social and economic benefits have been obtained through the application and dissemination of these achievements in China. This paper reviews the progress of studies and control of BT in China since 1995.