The anthelmintic efficacy of natural plant cysteine proteinases against Hymenolepis microstoma in vivo F. Mansur 1,3 , W. Luoga 1,4 , D.J. Buttle 2 , I.R. Duce 1 , A. Lowe 1 and J.M. Behnke 1 * 1 School of Life Sciences, University of Nottingham, University Park, Nottingham, NG7 2RD, UK: 2 Department of Infection and Immunity, University of Sheffield Medical School, Beech Hill Road, Sheffield, S10 2RX, UK: 3 Faculty of Medicine and Health Sciences, Universiti Sains Islam Malaysia (USIM), Kuala Lumpur, Malaysia: 4 Department of Life Sciences, Mkwawa University College of Education, Iringa, Tanzania (Received 15 April 2014; Accepted 31 July 2014; First Published Online 16 September 2014) Abstract Little is known about the efficacy of cysteine proteinases (CP) as anthelmintics for cestode infections in vivo. Hymenolepis microstoma is a natural parasite of house mice, and provides a convenient model system for the assessment of novel drugs for anthelmintic activity against cestodes. The experiments described in this paper indicate that treatment of H. microstoma infections in mice with the supernatant of papaya latex (PLS), containing active cysteine proteinases, is only minimally efficacious. The statistically significant effects seen on worm burden and biomass showed little evidence of dose dependency, were temporary and the role of cysteine proteinases as the active principles in PLS was not confirmed by specific inhibition with E-64. Worm fecundity was not affected by treatment at the doses used. We conclude also that this in vivo host – parasite system is not sensitive enough to be used reliably for the detection of cestocidal activity of compounds being screened as potential, novel anthelmintics. Introduction The anthelmintic effects of plant-derived cysteine proteinases (CPs) from protease Family C1 (http:// merops.sanger.ac.uk; Rawlings et al., 2012) against nematodes in vivo have been demonstrated successfully in pigs (Satrija et al., 1994; Levecke et al., 2014), mice (Satrija et al., 1995; Stepek et al., 2006, 2007a, b), sheep (Buttle et al., 2011) and even chickens (Mursof & He, 1991). They are also highly effective against the three major human intestinal nematodes in naturally infected individuals (Ascaris lumbricoides, Trichuris trichiura and hookworms; Caldwell & Caldwell, 1929; Hansson et al., 1986). In comparison, little is known about the effects of CPs on cestode infections. Based on in vitro assays, there is evidence that CPs are detrimental to the survival of cestodes (He et al., 1992; Stepek et al., 2007c; Mansur et al., 2014) but data also indicate that this was not reflected in a reduction of parasite burdens when CPs were administered to infected hosts (He et al., 1992; de Amorin et al., 1999). To date, few results based on well-designed in vivo trials have been published, and whether CPs have in vivo activity against cestodes is still debatable. Nevertheless, it is clearly important to establish whether they are effective against cestodes in vivo if potential drugs based on CPs are to be taken *Fax: 44 115 951 3251 E-mail: jerzy.behnke@nottingham.ac.uk Journal of Helminthology (2015) 89, 601–611 doi:10.1017/S0022149X14000637 q Cambridge University Press 2014