A technique is described whereby a patent infection of known number, size, and sex of adult Ascaris suum may be established experimentally. The procedure involves the implantation of worms collected in the abattoir into miniature swine surgically prepared with enterocutaneous fistulas. The technique was used successfully to obtain a repeated infection, in 4 pigs, of 15 20-cm female worms. Infections were maintained for a 3to 4-week period, and were eliminated by dosage of pigs with Parbendazole. Evidence was obtained suggesting that the intestinal phase of ascaris, in the absence of prior somatic larval migration, may induce circulating antibody in the host. It is generally recognized that the somatic migration of ascaris larvae in pigs is easy to establish experimentally (Roneus, 1971). However, a subsequent development to the adult phase in the intestine is, paradoxically, difficult to achieve under experimental conditions (Green and Oldham, 1964; Kelly et al., 1958; Martin, 1926; Nickel, 1960; Ransom and Foster, 1920; Roberts, 1934; Schwartz, 1959). Roneus (1971) suggests the reason for this difficulty to be that the high eosinophilia, directly correlated with the large number (often tens of thousands) of infective ascaris eggs inoculated, impedes the development of larval worms to adulthood. Accordingly, Roneus found that a dosage of 500 infective eggs, which caused only insignificant bloodeosinophilia in pigs, gave the maximum return of adult worms. Galvin (1968), however, found that equivalent or greater numbers of adult worms in the intestine of pigs resulted from a single inoculation of 100, 1,000, or 5,000 infective eggs, but it appears impossible to predict with any precision the number of adult ascaris which will develop for any given dosage of eggs. Furthermore, the size of the worms in the resulting infection bears no apparent relation to their number (Galvin, 1968). An estimate by fecal egg count of the number of worms in an intestinal helminth infection is unreliable since several factors influence the number of eggs passed in the stool (Lane, 1930). In pig ascariasis, a count of the number of worms passed after anthelmintic medication may also be an unreliable estimate of the infection since it is suspected (Taffs, 1970) that a pig may eat some of these worms before the Received for publication 2 November 1973. researcher sees them (although this was not experienced in the present study). In consequence of the above, researchers have been obliged to conduct experimental work with pig-ascaris infections of very poorly controlled parasitological status. The present paper describes a technique for the repeatable establishment of patent, adult ascaris infections of precisely controlled number, size, and sex of worm by direct implantation into fistulated miniature swine. MATERIALS AND METHODS Six pigs, 3 male and 3 female, of the Hormel Miniature strain were used in this study. All animals were determined to be initially helminthfree. One male and 1 female were maintained uninfected, as controls, over the entire experimental period (duration approximately 4 months), at the beginning of which the pigs were approximately 10 months old and between 32 and 40 kg in weight. The design and surgical preparation of enterocutaneous (jejunal and ileal) fistulas in miniature swine, and the care, management, and restraint of these pigs for laboratory investigation are described elsewhere (Leigh-Browne and Harpur, 1974). The pigs were individually housed in concrete-floored, smooth-sided pens, and the bedding, in the form of wood shavings, was changed at 3-day intervals, at which time the pens were scrubbed out with hot water and the walls, floors, drinking appliances, and feeding pans were thoroughly hosed with steam to eliminate the possibility of any remaining ascaris eggs developing to the infective stage. The infection procedure was as follows. Adult, female worms were brought from the abattoir in a insulated flask of warm saline (325 mOsm, 37 to 39 C). Female worms were used because they are large and easy to see when passed in the feces and their presence in the host may be detected by the passage of eggs. The pig to be infected was fed, restrained, tranquilized, and the vinyl tube (length 50 cm, ID 12 mm, OD 16 mm)
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