Plaque assay
Collecting RBCs were suspended in 1 mL PBS, then repeatedly frozen and thawed to release the virus. Vero cells were seeded in 12-well plates and grown to confluent monolayers. Then cells were infected with 500 μL serial ten-fold dilutions of the frozen and thawed samples for 1 h at 37 °C. After infection, cells were overlaid with 0.7% low melting point agarose (Solarbio) in Dulbecco’s Modified Eagle’s Medium (DMEM) containing 2% FBS and incubated at 37 °C for 72 h. Plaques were visualized by staining with crystal violet.