V. Evaluation of Cross-Immunity against Type 1 Dengue Fever in Human Subjects Convalescent from Subclinical Natural Japanese Encephalitis Virus Infection and Vaccinated with 17D Strain Yellow Fever Vaccine
With standardized technics and a Coca's extract of Schistosoma japonicum worms (Philippine-Leyte strain) at 27 to 30 µg N/ml as antigen, the intradermal test (immediate reaction) for schistosomiasis japonica in the Philippines showed an overall sensitivity of 88.2% among known infected individuals and a non-specificity of 3% among uninfected Filipinos. Sensitivity was 95% or better in those 12 years or older, but significantly less (65%) in younger individuals. A false-positive rate of up to 9% was found among American Peace Corps volunteers in the Philippines; a false-positive response of 37.5% was found in Filipinos infected with Capillaria philippinensis. Antigens prepared from S. mansoni and Schistosomatium douthitti worms were significantly less sensitive in detecting schistosomiasis japonica; however, an antigen prepared from the Japanese strain of S. japonicum had a comparable sensitivity to the antigen prepared from the Philippine-Leyte strain.