Presence of bluetongue and epizootic hemorrhagic disease viruses in Egypt in 2016 and 2017

Abstract

BTV and EHDV are closely-related orbiviruses that are transmitted between domestic and wild ruminants via the bites of hematophagous midges. Previous studies have reported seropositivity against BTV antibodies in sheep and goats in two Egyptian governorates (Beni Suef and Menoufia). However, no recent data are available on the BTV serotype(s) circulating in Egypt and the likely presence of EHDV has never been explored. This study investigated the presence of BTV and EHDV among cattle which had been found BTV-seropositive by ELISA method. These cattle living in proximity to sheep and goats previously found BTV-seropositive. These cattle displayed no clinical signs of BT but reproductive problems had been reported in herds. A total of 227 cattle blood samples were therefore collected in 2016 and 2017. Ninety-four of the 227 animals tested by a BTV ELISA were positive for BTV antibodies (41.4%). Of these 94 ELISA-positive cattle, only 83 EDTA-blood samples were available and therefore tested for BTV and EHDV genome detection by RT-PCR and sequencing.Of the cattle sampled in 2016, results revealed that two were RT-PCR-positive for BTV and seven for EHDV. Sequencing showed the presence of EHDV-1 and BTV-3 genome sequences. EHDV-1 S2 shared 99.5% homology with an EHDV-1 S2 from a strain isolated in 2016 in Israel. BTV-3 S2 and S8 sequences shared >99.8% nucleotide similarity with the BTV-3 Zarzis S2 and S8 sequences (Tunisian BTV, also detected in 2016). Of the 66 blood samples tested following their collection in 2017, they were all EHDV-negative by RT-qPCR while five were BTV- positive by RT-qPCR. However, attempts to identify the BTV serotype of these five samples were unsuccessful. Only part of BTV S8 was sequenced and it showed 79% nucleotide similarity with S8 of atypical BTV serotypes (particularly with BTV-26 and another BTV serotype strain isolated from a sheep pox vaccine). Overall, these findings demonstrate that both BTV and EHDV were circulating in Egypt in 2016 and 2017.