Seasonal infection of Culex mosquitos and swine with Japanese encephalitis virus

A year-round study of the infection rates of JE virus in Culex mosquitos was made during 1970-71 in 2 hamlets in Taoyuan County, China (Province of Taiwan). JE virus was recovered from 5 of 314 pools of C. annulus, and from 1 of 22 pools of C. tritaeniorhynchus; these recoveries occurred during a 14-day period in July 1971. None of the 288 pools of C. p. fatigans, which had been collected between October and April, was positive. In addition, sentinel swine were assessed for antibody and virus. All the pigs became highly immune by 23 July; in each hamlet all the pigs had become infected within 1 week, virus being detected in them for only 1-2 weeks. Virus-positive mosquitos appeared to have obtained their infections at about the time that viraemia was occurring in the sentinel swine. These observations illustrate once again the lower infection rate and shorter duration of virus-positive mosquitos in China (Province of Taiwan) as compared with Japan.

Fatal Japanese encephalitis virus infection in immunosuppresed spider monkeys

Intracerebral inoculation of twelve spider monkeys with large doses of a virulent strain of Japanese encephalitis virus produced a subclinical encephalomyelitis. When an immunosuppressive dosage schedule of cyclophosphamide was given to a group of four monkeys concurrently with virus, all animals developed prostrating paralysis 12–14 days after infection. Virus was isolated more regularly from the blood and throat swabs of animals treated with cyclophosphamide than from controls. Monkeys inoculated with virus only developed serum antibody, but no antibody was detected in suppressed animals. At time of killing, all spinal cords from suppressed monkeys yielded virus and presented a histological picture resembling that of fatal poliomyelitis, but with a markedly reduced inflammatory response. Virus was isolated from only one of three cords from animals inoculated with virus alone, and histological examination indicated less severe neuronal destruction.