Growth of Trichinella spiralis Larvae from Birth to Day 13 Postinoculation in the Male Albino Rat (1971)

Length measurements of Trichinella spiralis were made daily (from 5 to 13 days postinoculation) on larvae recovered from adult females from the small intestine, abdominal cavity fluid, thoracic duct lymph, blood, and the skeletal muscle of male albino rats. Mean length measurements obtained were as follows: newly born larvae (95 u); larvae from abdominal fluid (111 Au); larvae from lymph (105 ,t); larvae from blood (115 /u); and larvae from skeletal muscle on days 5 to 7 postinoculation (106 At). Analysis of the above data using Student's t test indicated significant differences (P 0.10). Using a 2-factor analysis of variance, effects of the two main pathways (blood vs. abdominal fluid), days postinoculation, and individual rats were significant (P < 0.001) influences on larval lengths. The data suggest that larval length is dependent upon the host's and the parasite's physiology. Explanations are given to account for the observed length differences. The life cycle of Trichinella spiralis (Owen, 1835) Railliet, 1895, is well established; nevertheless, certain discrepancies still persist. examining the literature, conflicting size measurements of newly born larvae, migratory larvae, and larvae recovered from skeletal muscle at the time of their first appearance became evident (Table I). Some workers (Roth, 1939; Pambuccian and Cironeanu, 1962; and others) give length measurements indicating that larvae released by females and those recovered from skeletal muscle at the time of their first appearance are similar in size. Ali Khan (1966) reported that the migratory larvae are 111 /, in length in fixed dry smears and 124 ju in length when heat-killed in saline. He also states that After 148 hr, larvae recovered from muscles were significantly shorter than the blood forms .. but offers no explanation to account for this observation. Other workers, such as Thomas (1965), give length measurements indicating differences between the size of newly born larvae, migratory larvae, and larvae recovered from skeletal muscle at the time of their first appearance. This report is therefore concerned with the growth of T. spiralis larvae from birth to day 13 postinoculation (PI) in the male albino rat. Since nematodes show a more pronounced inReceived for publication 7 April 1970. * Present address: Department of Biological Sciences, Eastern Kentucky University, Richmond, Kentucky 40475. cr ase in length while growing than they do in width (Lee, 1965), comparisons were made only on larval lengths vs. recovery sites. MATERIALS AND METHODS Host and parasite Male albino rats (Sprague-Dawley, Holtzman Co.) were used throughout. They were maintained individually in polycarbonate cages; Purina Laboratory Chow and fresh water were provided ad lib. The strain of T. spiralis used was one that has been maintained in this laboratory since 1956 by passage in albino rats. Infective larvae were recovered by pepsin-HCl digestion of skeletal muscles from stock rats infected at least 60 days previously. Experimental rats weighing 150 to 170 g (x = 159 ? 11) and 42 ? 2 days of age were infected by gavage with 3,000 100 excysted larvae. Recovery of larvae From females: In order to obtain uniform measurements at the time of larviposition, a standard procedure was utilized. On each day PI (from 5 to 13) the rat's entire small intestine was removed, slit lengthwise, and the contents scraped into a triple layer cheesecloth bag (24 by 20 mesh). The intestine was then cut into small segments and these added to the bag. The bag was suspended in a 250-ml beaker containing 0.85% saline. The bottom of each beaker was maintained at 37 C via a slide warming tray, thus creating a thermal gradient. The worms, being positively thermotropic, settled and/or moved to the bottom of the beaker and adult females continued to larviposit. The newly born larvae were then collected by pipette, concentrated by pooling, and suspended in nutrient broth (Difco) to which gelatin was added in order to slow down their movements so that accurate measurements could be made. Length measurements were made immediately thereafter