| Bluetongue (BT), caused by Bluetongue virus (BTV), is a kind of hemorrhagic disease affecting ruminants. Which 27 serotypes have been identified. BT is widespread in temperate, subtropical and tropical areas, BT is transmitted when hematophagus sucked blood with the virus and bit susceptible animals. All ruminants can be infected, among which, sheep and cattle are more susceptible.In this study,2032 serum samples with antibody positive in 6683 serum samples of cattle and sheep in 13 cities of Guangxi province during 2009-2015. 500 serum samples with strongly positive antibody were screened by C-ELISA method, after which, they were used to for a Micro-serum neutralization test with the standard strains of BTV type 1-24 be released by OIE. The result shows that there were 17 serotypes of BTV:BTV-1,2,3,4,5,8,9,10, 11,15,16,17,18,19,20,22,23 and 24 in Guangxi. In which, BTV-5, 8,11,13,17,18,19,20,22 are first reported in China. The dominant types are BTV-1, BTV-2 and BTV-4 by statistical analysis. In addition, the result also shows that multiple infection with diverse serotypes in Guangxi.In this stusy, three monitoring points-Longan county (Nanning city), Xingye county (Yulin city) and Hepu county (Beihai city)-are established and collected the insect vector. The identification of the insect shows that there were 7 Culicoides -- Culicoides oxystoma, Culicoides humeralis, Culicoides peregrinus, Culicoides arakawai, Culicoides pallidicornis, Culicoides impunctatus and Culicoides innoxius--in these areas. In which, Culicoides pallidicornis, Culicoides impunctatus and Culicoides innoxius are first reported in Guangxi.From 100 samples of heparin sodium taken from the anticoagulant of sentinel animals in October and November,23 strains of virus were isolated by way of chicken embryo inoculation (E), BHK 21 cells (B), and C6/36 cells (A),18 BTV strains were identified among 23 strains by c-ELISA and real-time PCR. So far,3 serotypes (BTV-1, BTV-16 and BTV-21) were identification among which 5 of 18 by Micro-serum neutralization test and VP2 gene amplification. In which,5172E was BTV-1,5204B,5097A & 5097B were BTV-16, and 5149E was BTV-21. Phylogenetic analysis-based on the VP2, VP7 and NS3/3A gene -shows that the majority strains of Guangxi belonged to the subtype eastern and had closed relationship with the isolations from Japan and India. It was worth nothing that the VP7 gene from 5024B belonged to the subtype western. It means that this segment may came from enthetic strain and integrating into virus genome by reassortment.The BTV isolate 5097 B strain was selected for a preliminary study on the pathogenicity of the virus in cattle and swine. Despite, hyperemia on nasal and pharyngeal mucosa and blood spots on the testis were observed after 8 dpi, the classical pathological change--the tongue of cyanosis, stomatocace pneumonemia and pneumonedema--were not observed. The most virus titer was detected in peripheral blood by real-time PCR, and lung and spleen were followed. The result of the distribution of virus in cattle was accord with the previous report. Meanwhile, the BTV nucleic acid did not detected from swinish organs in all 40 day test period, which means that the isolate 5097B cannot proliferation in swine. |
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