Serology of Schistosoma spindale (Montgomery, 1906)

Abstract

The Cercarien-Hiillen-Reaktion (CHR) was used to determine the serological relationship of human and cattle schistosomes. Complete pericercarial membranes (Cercarienhiillen) were formed during 1 hr and 35 min of incubating Schistosoma spindale cercariae in the unheated, undiluted sera of mice with moderate Schistosoma mansoni infections. Dilution and the 4 C storage time of antisera affected the intensity and completion time of CHRs. Specificity of CHR with S. spindale was evaluated. The reaction was not affected by using the sera of mice infected first with a bacterium, Salmonella typhimurium, and subsequently with S. mansoni. There were no CHR cross-reactions using sera of mice infected with Hymenolepis nana, H. diminuta, or sera of rats infected with Hydatigera taeniaeformis. Schistosoma spindale, a parasite of cattle, has received considerable attention in parasitology. The life history and the morphology of the cercarial stage have been studied in detail (Soparkar, 1921; Fairley et al., 1930). Occurrence of this species in Thailand was reported only a decade ago by Yokogawa (1961), who thus identified the fork-tailed cercariae discharged by a freshwater snail, Indoplanorbis exustus. Prapasarathorn et al. (1963) identified adult worms obtained from experimentally infected animals. It was also demonstrated that the cercariae were not able to develop after penetrating human skin, being eliminated by a tissue reaction (Harinasuta et al., 1965). Thus, the parasite caused only a cercarial dermatitis in man, but no other known pathology. Although much work has been done on the life cycle of the parasite, serological studies have been neglected. The only information stems from Fairley (1926), who developed a complement fixation test (CFT) using infected I. exustus snail liver as antigen. The value and limitations of this CFT test were examined by Schofield (1959). Present work was undertaken to supplement our information concerning the serological reactions of infections with S. spindale. Since S. spindale is congeneric with human schistosomes, a serological relationship might be expected. However, it would be interesting to demonstrate this with actual cross-reactions since previous studies (Le Flore, 1961; Donges, 1966, 1967) have shown that phyletic relationReceived for publication 6 July 1971. *Present address: The Rockefeller University, New York, New York 10021. ships among the strigeid trematodes do not always correlate with serological similarities. Le Flore failed to demonstrate a CercarienHiillen-Reaktion (CHR) of avian schistosome cercariae from Cerithidea californica in human S. mansoni antisera. D6nges, however, was successful in using cercariae of Posthodiplostomum brevicaudatum (Diplostomatidae) in such tests, obtaining 93% positive results in West African patients infected with S. haematobium. This paper is limited to the in vitro crossreactivity of S. spindale and Schistosoma mansoni infections. Intensity of cross-reaction was studied with respect to several variables: (1) general appearance of the reaction; (2) length of reaction time; (3) relation of reaction intensity to the worm load in serum donors; and (4) effect of storing antisera. To determine the specificity of the reaction, several sorts of immune sera were tested against cercariae of S. spindale: those of mice that had been infected sequentially with bacteria, Salmonella typhimurium, and Schistosoma mansoni, as well as those of animals with natural cestode infections. The latter included sera of mice with Hymenolepis nana and H. diminuta, and of rats with cysticerci of Hydatigera taeniaeformis. MATERIALS AND METHODS From among the several serological tests, the CHR was chosen because of its simplicity, practicality, and clear-cut results. The CHR (Vogel and Minning, 1949), which occurs when living cercariae of Schistosoma spp. are placed in homologous antisera, involves the formation of a transparent membrane around the cercarial tegument, the latter functioning as a structural antigen.