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
Puerto Rico Nuclear Center, University of Puerto Rico, Tropical Disease Section, Ecological Investigations Program, National Communicable Disease Center, Health Services and Mental Health Administration, U.S. Public Health Service, San Juan, Puerto Rico
Quantitative laboratory tests were made on the cercariophagic activity of guppy fish, Lebistes reticulatus, by feeding them cercariae of Schistosoma mansoni labeled with radioselenium. Separate counts of radioactivity of the intestine of fish compared with the head and body proper were relatively high, indicating ingestion of cercariae. Heavily gravid females, which apparently find cercariae unattractive, served as controls. Otherwise, all classes studied—juveniles, adults, males, and females—ate many cercariae. When the same number of cercariae were placed in varying amounts of water, it was found that uptake of radioselenium is inversely related to volume. With a constant volume and increasing numbers of cercariae, increasing radioactivity was found in fed guppies. Guppies became radioactive much more quickly if they received feedings of untreated cercariae before being fed radioactive cercariae. Light enhanced cercariophagic activity. It appears possible that guppies may be useful in the biological control of schistosomiasis.
Immunology Unit, Tropical Disease Section, National Communicable Disease Center, Box 52, Old San Juan, Puerto Rico 00902. Please send requests for reprints to this address.
Puerto Rico Nuclear Center, University of Puerto Rico, Caparra Heights Station, San Juan, Puerto Rico 00935.
The Puerto Rico Nuclear Center is operated by the University of Puerto Rico under Contract AT-(40-1)-1833 from the U.S. Atomic Energy Commission.