Schistosoma mansoni: a method for inducing resistance to praziquantel using infected Biomphalaria glabrata snails

Abstract

To elucidate the mechanisms of antischistosoma resistance, drug-resistant Schistosoma mansoni laboratory isolates are essential. We developed a new method for inducing resistance to praziquantel (PZQ) The current strategy for schistosomiasis control is based on large-scale treatments of populations aimed at reducing disease morbidity (WHO 2002). Currently, praziquantel (PZQ) is the drug of choice (Utzinger & Keiser 2004, Fenwick & Webster 2006, with the main advantages of its use being oral administration, single dose, low toxicity and low cost (Fenwick et al. 2003, Utzinger & Keiser 2004. Despite the advantages of PZQ, there is concern about the development of Schistosoma mansoni resistance to PZQ, both under laboratory and field conditions (Abdul-Ghani et al. 2009). In the laboratory, induction of resistance is based on the treatment of mice infected with S. mansoni, initially using sub-curative doses of PZQ. Afterwards, the dosage is increased for at least seven passages in mice/snails to complete the life cycle of the parasite (Ismail et al. 1994, Fallon et al. 1995.The complete mechanism of action of PZQ is still unclear (Doenhoff et al. 2008). Obtaining resistant strains is important for the evaluation of such mechanisms as well as for the development of alternative drugs for schistosomiasis treatment and control. Studies show that PZQ is effective not only in adult worms, but also in the intramolluscan phase of the parasite (Coelho et al. 1988. We report a novel meth- od for the induction (or selection) of S. mansoni worms resistant to PZQ using successive treatments of infected Biomphalaria glabrata snails. SUBJECTS, MATERIALS AND METHODSParasites and hosts -The S. mansoni (LE strain) life cycle was maintained using B. glabrata (Barreiro de Cima strain) snails as intermediate hosts and Swiss mice as definitive hosts, according to Pellegrino and Katz (1968) and Souza et al. (1995).Perfusion of adult worms from infected mice -Two methods were used. The methodology described by Pellegrino and Siqueira (1956) used a needle attached to a Brewer's automatic pipetter to inject saline solution under pressure into the descendent aorta. Afterwards, saline was injected into the hepatic hilum of mice after sectioning the portal vein, allowing the perfusion of the portal system and mesenteric veins. Worms were recovered and counted. To recover the worms using the methodology described by Smithers and Terry (1965) the portal vein of the mice was sectioned and the culture medium was gently injected into the base of the left ventricle of the infected mice's hearts. It is not possible to recover all the worms using this methodology with a lower pressure injection, but the integrity of the parasite's tegument is preserved. Therefore, this methodology is ideal for the recovery of worms when the goal is to cultivate or evaluate other parameters such as tegumental integrity and/or excretory activity.Induction of resistance to PZQ in the intramolluscan phase -Two-hundred B. glabrata were individually infected with 10 S. man...

Evaluation of a method for induction of praziquantel resistance inSchistosoma mansoni

“…By comparing the number of worms recovered from different groups of mice infected with parasites previously unexposed to the drug during the intramolluscan phase with their corresponding exposed groups, the numbers were significantly higher in the groups infected with schistosomes previously exposed to the drug; significant differences were found between them (Table 2). These results were in agreement with the findings reported by Couto et al (2011), which may indicate that intra-molluscan exposure of S. mansoni has induced resistance to the drug in the adult stage. In mice infected with S. mansoni, oviposition begins about day 30 of post-infection.…”

“…In the mouse groups treated with PZQ, the increase of the drug dose from 200 mg/kg to 400 mg/kg, and then 800 mg/kg resulted in a gradual decrease in the number of recovered worms (Table 2). Comparable results were reported by Couto et al (2011). By comparing the number of worms recovered from different groups of mice infected with parasites previously unexposed to the drug during the intramolluscan phase with their corresponding exposed groups, the numbers were significantly higher in the groups infected with schistosomes previously exposed to the drug; significant differences were found between them (Table 2).…”

“…The food with PZQ and water was changed the second day after exposure. Exposure of snails to PZQ was repeated three times, with a 1-week interval between the treatments (Couto et al, 2011;Mattos et al, 2007).…”

“…They concluded that the stability of some of the isolates and the reversion of others indicate that the biological or genetic factors conferring decreased PZQ response vary among the isolates. Couto et al (2011) described a novel method for induction of PZQ resistance in a South American strain of S. mansoni. This was achieved by using successive exposures of the intramolluscan phase of the parasite in B. glabrata to PZQ.…”

Pharmacokinetics of the Antischistosomal Lead Ozonide OZ418 in Uninfected Mice Determined by Liquid Chromatography-Tandem Mass Spectrometry

“…This drug is safe, relatively inexpensive, and easy to distribute (13,14). However, it lacks efficacy against developing juvenile stages of Schistosoma, and its widespread use raises grave concerns about emerging resistance (15)(16)(17)(18)(19)(20). In addition, praziquantel's mechanism of action still requires further elucidation to intelligently design active derivatives (21)(22)(23)(24)(25)(26).…”