RNA was extracted using Trizol LS reagent (Invitrogen, Carslbad, CA) and suspended in RNase free water. RNA was quantified using Nanodrop 3300 (Thermo Scientific, Courtaboeuf, France). The M segment of RVFV was amplified with primers 59-CATGGATTGGTTGTCCGATCA-39 and 59-TGAGTGTAA-TCTCGGTGGAAGGA-39. Quantitative RT-PCR assays were performed using StepOne Plus Real-Time PCR System (Applied Biosystem, Courtaboeuf, France) in 96-well plates. Reverse transcription using MultiScribe Reverse Transcriptase (Applied Biosystem) at 48uC for 30 min was performed followed by a standard amplification program. The size of the amplification product was 108 pb. A standard curve was generated using duplicates of 10-fold serial dilutions of RNA of the M segment ranging from 10 9 to 10 2 copies. Quantification of viral RNA was done by comparison of the threshold cycle (Ct) values of the samples to the standards.