into sterile 10-ml tubes without anticoagulant or serum colt activa-tor (Vacutainer®, Becton-Dickinson, UK). Samples wer elabelled and transported in a refrigerated box at 4◦C.Blood samples were centrifuged at 400 × g for 15 min. Serasamples were then aliquoted and stored at −25◦C until serological analysis.