Absence of viraemia in cattle after experimental infection with Japanese encephalitis virus.

Cow calves were infected with Japanese encephalitis virus (JEV) by parenteral inoculation. One batch was reinfected with JEV, followed by West Nile virus (WNV), while another batch was reinfected directly with WNV. No viraemia due to either JEV or WNV was demonstrated in any of the calves. Culex tritaeniorhynchus mosquitoes fed on 4 of the calves infected with JEV during the first 10 d had no detectable virus, nor did they transmit the virus by bite to susceptible baby chickens. In another experiment, calves did not develop viraemia after infected C. tritaeniorhynchus mosquitoes were allowed to feed on them. Neutralizing and/or haemagglutination-inhibiting antibodies against JEV were demonstrated in 6 of the 11 calves, which explains the high proportion of JE seropositives among cattle in India. All the 5 calves that were infected with WNV subsequent to JEV developed neutralizing and haemagglutination-inhibiting antibodies against WNV also. The study indicates that cattle do not play a role in the maintenance of JEV in nature.