Comparison of recovery of schistosomula of Schistosoma japonicum from lungs of mice and rats.

Various strains of mice and rats were exposed to small doses of Schistosoma japonicum cercariae. At intervals, they were challenged with 200 to 230 cercariae per mouse and 500 to 520 cercariae per rat. Age-matched control animals received only the challenge infection from the same pool of cercariae. Recoveries of schistosomula from experimental and control groups were different on day 3 through day 5, with peak recovery on day 3 or 4 in four strains of mice examined (DBA/2, C57BL/6, C3H/He, and SWM) as well as in Fischer rats, indicating rapid migration of S. japonicum to the lung compared with that of S. mansoni. Significant reductions of recovery of schistosomula from lungs were demonstrated in DBA/2, C3H/He, SWM, and B10.S mice at week 3, but not in BALB/c, CBA, and C57BL/6 mice. Significant reductions were also demonstrated in Donryu, Wistar, Sprague-Dawley and Fischer rats at week 6. The degree of reduction depended on cercarial doses used for the initial exposure. Studies in DBA/2 mice revealed that the degree of reduction intensified biphasically, being greatest at week 5 and at week 12. The lowest recovery was demonstrated at week 6 in Fischer rats, when recovery of schistosomula tentatively increased in DBA/2 mice. A good correlation was found between recovery of schistosomula from lungs and recovery of adults by portal perfusion when DBA/2 and C57BL/6 mice, and Fischer rats were used for comparison. Thus, the present results provide basic information on the lung recovery of schistosomula of S. japonicum in suitable and unsuitable hosts.