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
Barrio San Antonio is a coastal settlement on the San Juanico straits in the municipality of Basey on the island of Samar, the Philippines. It has a population of approximately 1,900 in 320 households. Initially, 851 residents (45%) of 240 households participated in this survey to determine the prevalence and intensity of Schistosoma japonicum infection, and morbidity as indicated by associated hepatomegaly and splenomegaly. As a result of an initial single stool examination of 1 ml by a modified formalin concentration technique, 40% of this population was found to be infected. On subsequent examinations, with the addition of serologic techniques and recording the history of therapy, approximately 70% of this population was found to be infected with S. japonicum after the age of 10 years. If judged by the number of eggs produced per milliliter of feces, infection intensity in this population might be considered to be low. However, 25% (73 of 391) positives on single examination) exhibited schistosomal hepatomegaly or hepato-splenomegaly and had a mean egg count of 10.9. Those infected but without hepatomegaly had a slightly lower mean egg count of 8.4. Of the infected males with hepatomegaly, 75% were 19 years of age or less and 45% of these were producing less than 10 eggs/ml of stool. Of infected females with hepatomegaly, only 28% were 19 years of age or less, and 68% of these were producing less than 10 eggs/ml. Abdominal pain, distress, diarrhea, and dysentery were significantly more frequent in the infected than uninfected persons, and this frequency was related to egg output. The heights and weights of these infected individuals were less than those of the uninfected members of this population and significantly less than the Filipino norm. The small percentage of the infected population (6.6%) that were producing 51% of the eggs had a mean egg count of approximately 260 with a mean age of 33.7. In this group, 7 of the 22 individuals were in the age group 10–14 years and 15 were above 20 years of age. Although some individuals of Barrio San Antonio have sought therapy, this population and area have been largely unstudied and have not up to the present been involved in control or mass chemotherapy programs. The findings of this survey give an opportunity to determine the impact of such programs when they are instituted in this area.