A survey of 558 pigs for serological evidence of infection with Japanese encephalitis virus (JEV) performed during the summer of 1968 is recorded. Antibodies were detected by the goose red cell haemagglutination-inhibition test. A high incidence of infection was recorded among mature stock in the New Territories (75.4 per cent) with lower degrees of infection on Hong Kong Island (35"8 per cent) and in Kowloon (26.5 per cent). Of 57 pigs under one year of age only four showed evidence of infection.In view of the widely recorded incidence of JEV in Asia, its occurrence in Hong Kong was to be expected. The regional variation in level of infection within the Colony is probably due to differences in terrain and agricultural development, with consequent differences in availability of mosquito breeding sites. ,It is concluded that JEV is probably a significant pathogen of pigs and humans in the Colony.
SUMMARYTwo flocks of chicks from parents not immune to Newcastle disease (ND) virus and six flocks from immune parents were vaccinated intranasally with 10 e'~ to 106"s8 mean embryo infective doses ofF strain ND virus on the fifth day of life. A group of chicks from each flock was left unvaccinated. Vaccinated and unvaccinated chicks from each flock were killed on days one to ten and then every other day until 39 to 61 days. Serums were examined by the ND virus haemagglutination-inhibition (HI) test, and tissues were inoculated into fertile hens' eggs for recovery of vaccine virus. Vaccine virus was recovered from vaccinated nonparentally-immune chicks daily from two to 14 days post-vaccination. Their serological response was detectable two days post-vaccination and reached peak levels nine to 14 days post-vaccination. In contrast, vaccine virus was recovered rarely or not at all from parentally-immune chicks and their serological response was much less than in chicks with no parental immunity. It is concluded that parentally-acquired antibodies neutralised vaccine virus so reducing the amount of immunizing virus antigen to which the host was exposed.
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