Pathophysiology of Reinfection with Trichinella spiralis in Guinea Pigs during the Intestinal Phase

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Guinea pigs with and without a history of previous Trichinella spiralis infection were challenged with a dose of 20,000 larvae. Segments of small intestine were tested in vitro for absorption of glucose on days 3, 7, 14, and 21. Malabsorption of glucose was detected on day 7 in segments from previously infected animals as compared to day 14 for challenge controls. In similar experiments, earlier onset of pathological changes of the gut, loss in body weight and blood eosinophilia were also noted in previously infected animals after challenge. Intestinal worm burden following a challenge of 20,000 larvae was, however, approximately the same during the 1st week postchallenge in previously infected and challenge control animals. It is suggested that the earlier onset of these changes reflects an allergic response of the gut to this nematode. A single dose of Trichinella spiralis larvae has been shown to cause intestinal malabsorption of glucose in guinea pigs (Castro et al., 1967). Under natural conditions, reinfection would seem to be a common occurrence. To what extent the immune status of the host influences the physiologic activity of the gut following reinfection is not clear. In nontropical sprue, an immune reaction to gluten appears to induce malabsorption (Taylor and Truelove, 1962). Bicks et al. (1967) demonstrated that D-xylose malabsorption induced by oral administration of 2,4-dinitrochlorobenzene was more severe in skin sensitized than in nonsensitized miniature pigs. On the other hand, Olson and Richardson (1968) reported protection against malabsorption of glucose in mice following reinfection. We are reporting here experiments in which changes in absorption and structure of the gut, body weight, and eosinophils of guinea pigs following reinfection were compared to those followix g primary infection. MATERIALS AND METHODS Trichinella spiralis was maintained by passage in Yale Swiss mice (Texas Inbred, Houston). Male guinea pigs were purchased at 200 to 225 g (Albino Farms, N. J.) and held 1 week prior to infection (Castro and Olson, 1967). Received for publication 23 October 1969. * This study was supported by the James W. McLaughlin Fellowship Fund for the Study of Infection and Immunity and by Research Grant AI-02732, NIAID, NIH, PHS. t Present address: Department of Pediatrics, University of Miami School of Medicine, Miami, Florida 33136. Glucose absorption was measured by the Crane and Wilson everted sac technique as employed by Castro et al. (1967). A 10-cm segment from the distal end of the anterior and posterior halves of the small intestine was tested. Intestinal tissues were fixed in formalin and sectioned as described by Castro et al. (1967). For electron microscopic study, the tissue was fixed in osmium tetroxide with or without prefixation with glutaraldehyde, embedded in Epon, and double stained with uranyl acetate and alkaline lead citrate (Pease, 1964). Eosinophil counts were made by the method of Olson and Schulz (1963). Adult worms were recovered from the intestine by the Larsh and Kent NaOH technique as modified by Castro and Olson (1967). Duncan's multiple range test (Steel and Torrie, 1960) was used to compare means, with a probability of 0.05 or less considered significant; ratios were transformed to arcsin values for analysis (Snedecor, 1956). Student's t test (Snedecor, 1956) and Wilcoxon's rank sum test (Wilcoxon et al., 1963) will be identified in the text when used. EXPERIMENTS AND RESULTS Glucose absorption of intestine In the first experiment, Group SC guinea pigs were sensitized with 2,500 larvae and challenged 4 weeks later with 20,000 larvae; anterior and posterior gut segments were tested on days 3, 7, 14, and 21. Other animals tested were given only the challenge (Group C) or sensitizing infection (Group S), or were uninfected controls (Group U). The capacity of segments to absorb and transport glucose is presented as the ratio of final glucose concentration of the serosal medium to that of the mucosal medium (S/M ratio). The S/M ratios for animals in Group S were approximately equal to those for uninfected controls; hence, these two groups were combined into a nonchallenge control, Group N.