A Preliminary Study on Susceptibility of Mice of Various Strain to Hymenolepis nana Eggs

Mice of various strain were given orally eggs of Hymenolepis nana maintained by ddY mice and sacrificed for the adult wormrecovery 2 weeks after the administration of the eggs. The mice of ddY, ICR, C3H and BALB/C were highly susceptible to the eggs while those of DBA/2 and C57BL/6 were less susceptible. key words: Hymenolepis nana, mouse, infectivity Mice-Hymenolepis nana model is useful for the experimental chemotherapy of infection with cestodes (Thomas and Gonnert, 1977). However, no detailed information has been reported so far in terms of the susceptibility of various-strain mice to H. nana eggs. The present paper, though a preliminary one, deals with this matter. The life cycle of H. nana was routinely maintained using female ddY mice without intermediate hosts as follows. Faecal pellets in the rectum of mice infected 2 weeks previously were suspended in normal saline, macerated and filtered through a wire mesh to remove large debris. The filtrate was washed 3 times in saline with centrifugation at about 1,200 r.p.m. and was stirred for 10 min for their shell removal in a cylindrical glass vessel containing a magnetic stirrer and glass beads (diameter: about 1mm). This method was originally reported by Berntzen and Voge (1965). In the present authors' investigation, the shells of more than 90% H.nana eggs were removed. After counting the number of the eggs, the suspension was diluted with saline to adjust the egg concentration. Each mouse was given 0.4 ml of the suspension containing 50 shell-removed (deshelled) eggs using a stomach tube. Two weeks after the inoculation with the eggs, faecal pellets excreted by the mice were examined to be positive for H.nana eggs. The rectal eggs from these mice were used for another passage. In the present study, 7-week-old female mice of 6 strains, ddY, ICR, DBA/2, C57BL/6, C3H and BALB/C were orally inoculated with 50 deshlled eggs from the mice used for the maintenance of H. nana. Two weeks after the inoculation, the mice in all the groups were sacrificed for the adult wormrecovery from the mouse intestine. The number of the scolex of the adult worms was counted under a stereoscopic microscope. In the present study, eggpositive rates in faecal pellets were not examined, though infection with adult worms was confirmed in each mouse strain. R eceived for publication, April 30, 1998