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Precipitins in Serum from Men with Presumptive Reexposure to Cercariae of Schistosoma japonicum^*

Department of Microbiology, University of Chicago, Chicago, Illinois 60637, and Schistosomiasis Control Pilot Project, Palo, Leyte, Philippines

Using Schistosoma japonicum adult worm or egg extract as antigens, we examined, by immunoelectrophoresis, a series of sera from 35 laborers of the hyperendemic area of Palo, Leyte, in the Philippines, most of whom were stool-positive for S. japonicum. At three known periods during the 7 to 8 months of serum collection, these laborers were presumably reexposed to cercariae because of work in streams that contained Oncomelania quadrasi. During the first such period, laboratory white mice were simultaneously exposed to the water in which the men were working; the mice became infected. In 33 laborers (94.3%) no immunoelectrophoretic alterations were observed that indicated successful development of worms from the presumed reexposure. These results contrast sharply with the changes in immunoelectropherograms that are easily detectable 3 to 7 weeks after reexposure of rabbits to cercariae, indicating that schistosomes develop successfully after effective chemotherapy of an initial infection. Immunoelectrophoretic alterations indicative of successful development of worms were observed in the sera of the other 2 laborers. These results, with the unchanging clinical conditions of the laborers during a long period of observation, are presented as evidence that most of the infected male population of the hyperendemic area is resistant to superinfection with S. japonicum.

Accepted for publication July 29, 1970.

^* These investigations were supported by the United States-Japan Cooperative Medical Science Program administered by the National Institute of Allergy and Infectious Diseases of the National Institutes of Health, Department of Health, Education and Welfare, Grant 5 R22-A1-0 7724-03, by arrangement with and support of the authorities of the University of the Philippines, Quezon City, Philippines.

The Schistosomiasis Control Pilot Project is under the Department of Health, Republic of the Philippines, Manila.