Five to six weeks old BALB/c mice of either sex were randomly distributed into 5 groups-Sham, JEV-infected, JEV-infected and treated with scrambled Morpholino (JEV+SC-MO), JEV-infected and treated with Morpholino against viral 39 conserved region (JEV+39 MO) and JEV-infected and treated with Morpholino against secondary structure in the 59UTR of viral RNA (JEV+59 MO). Initially each group contained 8 animals. Animals belonging to all groups except Sham were infected with 3610 5 plaque forming units (PFU) of JEV (GP78 strain) and that day was considered as day zero [20] . Animals of Sham group received equal volume of filtered MEM. Starting from 3 h post infection on day zero, 100 mg of SC-MO, 39 MO and 59 MO, diluted in 0.1 mL of sterile 16PBS (corresponding to 5 mg/kg body weight), were administered to animals belonging to JEV+SC-MO, JEV+39 MO and JEV+59 MO groups respectively, once per day, for 5 consecutive days. Animals belonging to the Sham-treatment group received equal volumes of sterile 16 PBS only. Survivality of animals in each group following JEV infection and Morpholino treatment were monitored daily upto 15 days post JEV infection (or till their death, whichever was earlier). Toxicity of the Morpholinos in mice was evaluated by weight loss and abnormal behavioral & clinical observations (including tremors, ruffled fur, hunching, ataxia, gait abnormalities), in a masked manner to minimize bias [14, 20] .