Postmortem migration of Hymenolepis diminuta (Cestoidea: Cyclophyllidea) in the laboratory rat

Postmortem migration is of considerable concern in surveys and studies of parasite ecology where accurate estimates of parasite location is crucial. Yet, there is no quantitative information documenting this phenomenon. Twenty-seven Sprague-Dawley rats were each inoculated with 5 cysticercoids of Hymenolepis diminuta. Four weeks postinfection, 15 rats were killed by cervical dislocation. The small intestines of 3 rats were removed immediately and fast frozen. Additional groups of 3 rats each (experimentals) were processed at intervals of 30, 60, 120, and 240 min after death (AD). Four additional groups of 3 rats (controls) were killed and processed at 30, 60, 120, and 240 min in order to assess changes due to circadian movement. Changes in the position of the scolex and biomass (dry weight) were assessed as a proportion of small intestine length for the following criteria: anterior, median, and posterior location. The only significant within-group difference was an anterior shift in median biomass in the experimental group. Between-group differences were not evident at 30 min. Significant posterior shifts were found in anterior and median scolex position of the experimentals at 120 and 240 min AD, respectively. Median and posterior biomass shifted significantly anteriorly at 60 and 120 min AD in the experimental group, respectively, and worm range was significantly reduced in the experimentals at 120 min AD. There appears to be a 30-min period following host death in which H. diminuta does not change its position within the rat small intestine.