Transplantation of Larval Schistosoma mansoni from Infected to Uninfected Snails

Abstract

Schistosoma mansoni was transferred from infected Australorbis glabratus to normal A. glabratus by transplanting parasitized tissues or parasites into the cephalopedal sinus. Transplants of liver fragments from donors with mature infections resulted in erratic low-level cercarial emergence from recipients during the next 2 weeks; thereafter cercarial emergence rose sharply and became sustained. Cercariae of the early phase were apparently those already present in the transplant, while those of the later phase apparently derived from young daughter sporocysts which migrated from the transplant to the recipient's liver. Transplantation of tentacles bearing mother sporocysts resulted in sustained cercarial emergence after an incubation period of about 2 weeks; mature daughter sporocysts, producing cercariae, were found in the livers of recipients. Similar findings occurred when mature mother sporocysts were ruptured and the liberated immature daughter sporocysts were transplanted. Snails infected by transplants were susceptible to infection by miracidia which developed into mother sporocysts containing viable offspring. Transplanted daughter sporocysts produced infection in 77% of recipient A. glabratus; infection rates varied from 0% to 96% among eight other strains or species of snails receiving similar transplants. No reference has been found in the literature regarding transplantation of larval trematodes from infected to uninfected snails. Observations are now presented that larval Schistosoma mansoni derived from infected Australorbis glabratus can be transplanted into normal A. glabratus, and into certain other snails, and that infections thus established may proceed to maturity. MATERIALS AND METHODS 1. Infection and maintenance of donor snails Stock snails were a Puerto Rican strain (PR-2) of A. glabratus (see Cherin and Schork, 1959). Groups of 50 to 100 snails, 4 to 8 mm in diameter, were exposed in finger bowls to miracidia of a Puerto Rican strain of S. mansoni (see Chemin and Dunavan, 1962) and then maintained on lettuce, in darkness, in covered, aerated, stainlesssteel pans. These infected snails were the source of transplants. All donor and recipient snails were manipulated and maintained at 25 to 27 C. 2. Securing and processing transplants Dissections were done under a stereomicroscope. Sterile precautions were not taken although transplants were handled in an initially sterile antibioticfree solution (BSS) described elsewhere (Chernin, 1963). Three types of transplants were used. A. Parasitized liver (= digestive gland): Using a snail from which cercariae were emerging at Received for publication 29 October 1965. * These studies were supported in part by Research Grant AI-00513 and by a Research Career Award from the NIAID, U. S. Public Health Service. 40 to 42 days postinfection, the liver was excised (Cherin, 1963), placed in BSS, and cut into fragments about 2 by 1 by 1 mm (Fig. 1). These tissues were used within an hour; each snail received one fragment. Fragments used in an experiment were usually obtained from a single donor. B. Intact mother sporocysts: Snails with sporocysts in the tentacles were selected 18 days postinfection. (Mother sporocysts in other sites were not used in order to avoid dissections in dense tissues.) The snail body was pinned in a paraffinfilled dish flooded with BSS, and the infected tentacle was excised with iris scissors and placed in BSS in a depression slide. An untrimmed tentacle (Fig. 5) was transplanted at once into a recipient snail. C. Immature daughter sporocysts: Sporocyst-bearing tentacles were removed from snails infected for 14 to 20 days. Mother sporocysts were ruptured individually using fine needles, snail tissue was discarded, and the liberated daughter sporocysts were transplanted at once. Each recipient received the entire contents of one mother sporocyst. 3. Transplantation procedures Recipient A. glabratus (PR-2) from normal stock (Table I) were narcotized for 2 to 5 hr in 1.25 to 1.50% urethane. Each snail was clamped in a dish under a stereomicroscope, and, except as noted, the hook of a micro-retractor was inserted into the male genital opening and the snail extended by gentle traction (Michelson, 1958). Excess fluid was removed from the dish. The transplant was introduced into the extended neck of the snail, i.e., into the cephalopedal sinus, midway between the male genital opening and the anterior margin of the mantle. A fragment of liver or a tentacle was taken up in a small volume of BSS into the bore of a blunted 18or 19-gauge needle attached to a 0.25-ml syringe An incision was made into the sinus with