In albino mice infected with Trichinella spiralis when less than 5 weeks old, most of the adult worms were subsequently found in the anterior half of the small intestine. This is in agreement with the distribution reported for older mice by most workers, but is contrary to that reported for mice of this age. It is generally agreed that Trichinella spiralis spends its reproductive phase in the mammalian small intestine, and that mature worms found in other gastrointestinal locations are atypical or effete. It is further agreed that the distribution of trichinella within the small intestine is not uniform; but there is no agreement on the nature of this distribution. It has been reported that a clear-cut majority of the worms live in the anterior part of the small intestine in mature rats (Gursch, 1949; Larsh and Hendricks, 1949), in mature mice (Larsh and Hendricks, 1949), and in mice of unspecified age (Podhajecky, 1962). On the other hand, it has been reported that most worms inhabit the posterior part of the small intestine in young rats and mice (Larsh and Hendricks, 1949), and in rats, mice, and guinea pigs of unspecified age (Tyzzer and Honeij, 1916; Roth, 1939; Denham, 1965). The distribution of trichinella is affected by the immunological response of the host (Larsh, 1963). As an adjunct to immunological studies, it was therefore thought desirable to check the distribution pattern in the particular mouseparasite system used in our laboratory. The results differed from those of other investigators and are therefore recorded herewith. MATERIALS AND METHODS The mice used were male albino mice of the same Sharp and Dohme strain used in other reports from this laboratory. They were housed in groups of 10 and were fed a commercial laboratory feed (Ralston Purina Company) without restriction. The method of inoculation is described below. At necropsy, the entire small intestine of each mouse was removed, and divided into two equal lengths. Each length was promptly slit open, cut into short pieces, and dropped into warm saline. The anterior halves of the intestines of a group of mice were pooled for further processing, as were Received for publication 20 December 1966. the posterior halves. After incubation for approximately 1 hr at 37 C, a sufficient amount of 0.4% sodium hydroxide was added to give a final concentration of 0.04%o. These preparations were chilled for approximately 4 hr, and then washed through a metal sieve (10 mesh/inch) to remove the intestinal fragments. The worms were collected on a 200-mesh sieve and counted in aliquots drawn from a magnetically stirred suspension. Where the number of worms in the aliquots was very low (the posterior gut count of the light infection on Day 11 and all counts made on Day 21 of infection) the worms were allowed to settle, and a total count of the sediment was made. Because the mode of inoculation may influence the subsequent distribution of worms, the preparation of the inocula will be described in some detail. For Experiment 1 larvae were freshly harvested from mice with infections of at least 4 weeks' duration, and were suspended in water containing 5% gelatin. By repeated sampling and adjustment the larvae were prepared in two lots, one containing about 50 larvae/ml and the other about 300. A Stoll pipette in a calibrated mechanical holder was used to withdraw 8 aliquots of 0.075 ml from the first lot, which was magnetically stirred throughout. These yielded 5, 5, 3, 4, 3, 4, 4, and 5 larvae, indicating a concentration of 53.2 larvae/ml. By means of a larger pipette, four aliquots of 1.0 ml were drawn, yielding 55, 52, 53, and 53 larvae each, or a concentration of 53.23 larvae/ml. The appropriate mice received 1.0 ml of this suspension/mouse. From the second lot of larvae 8 aliquots of 0.075 ml yielded 26, 27, 22, 27, 26, 24, 26, and 23 larvae, indicating an original concentration of 333 larvae/ml. After this lot of larvae had been used to infect the mice (1.0 ml/mouse, by stomach tube) a single aliquot of the leftover suspension (1.0 ml) was found to contain 327 larvae. For Experiment 2 larvae were harvested and suspended as in Experiment 1, and adjusted to the desired concentration. As above, a magnetic stirrer and a Stoll pipette were used to withdraw 8 aliquots of 0.075 ml. These yielded 30, 34, 27, 30, 33, 26, 29, and 31 larvae, indicating a concentration of 399 larvae/ml. Each mouse was given 0.5 ml of the suspension by stomach tube. Tissues taken at necropsy were fixed in formalin and stained with hematoxvlin and eosin.
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Jan 1, 1992
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