Characterization of Isolates of Schistosoma mansoni from Egyptian Villagers that Tolerate High Doses of Praziquantel

Abstract

To determine if resistance/tolerance to the antischistosomal drug praziquantel (PZQ) is appearing in Egyptian villages within the Nile delta region, where it has been used extensively, we treated 1,607 infected villagers and observed that 321 required one additional treatment while 89 villagers required two additional treatments; 24 of the 89 were still not cured after a third dose of this drug. Eggs were isolated from fecal samples and serum was isolated from blood taken from seven villagers successfully treated after a single dose and from 14 villagers not successfully treated after two or three doses of PZQ. The eggs were used to establish infections in mice (isolates), which were then treated six weeks after infection with three different doses of PZQ. Serum was used to determine the concentration of PZQ in the infected humans. Three of the egg isolates from the 14 villagers that could not be treated with three doses of PZQ produced infections in mice that were statistically less responsive to PZQ when compared with isolates obtained from patients that were cured after a single dose of this drug. Pharmacokinetic parameters were the same in patients treated successfully after a single dose versus those not treated successfully following two or three doses, thus eliminating the possibility that poor cure rates among infected villagers was due to a decrease in PZQ bioavailability. From our data, approximately 1-2.4% of the villagers treated with PZQ could not be completely cured of their infection and three of every 1,000 treated villagers may harbor parasites that can tolerate high doses of PZQ. These results indicate that the extensive use of PZQ in the Nile delta region of Egypt has not resulted in a dramatic change in the efficacy of this drug. The isolation of schistosomes that are less susceptible to PZQ may be a warning signal that will require establishment of a monitoring system, similar to the one we have developed, to determine if the percentage of patients that cannot be cured by PZQ is increasing. Furthermore, if that percentage begins to increase over time, it will be critical to determine, by pharmacologic methods reported in this study, whether isolates obtained from uncured patients are becoming increasingly resistant to PZQ.

Resistance to praziquantel: direct evidence from Schistosoma mansoni isolated from Egyptian villagers.

“…The doses used were 25, 50, 100, and 200 mg/kg/day. Detailed information describing results concerning the response of these isolates to PZQ can be found in our previous publication 9 . Two weeks later, the mice were killed and worms were counted from liver and mesenteric veins.…”

“…The methods used to obtain schistosome eggs from infected Egyptian villagers, to infect the snails with miracidia, and to infect mice with cercariae have been described. 9 Briefly, the eggs obtained from patients were separated from fecal debris and rinsed in saline and dechlorinated tap water. Illumination induced hatching, and snails were exposed to the resultant miracidia.…”

“…8 In an effort to minimize the variability of these host factors, parasites isolated from patients not cured by antischistosomal drugs have been used to establish experimental infections in less-variable laboratory animal hosts. 9 If infections produced by these isolates are not cured by normal doses of PZQ, it suggests that the decreased responsiveness of the isolates is due to worm factors rather than host factors. However, this type of assessment is a rather toilsome process.…”

Schistosomes—proteomics studies for potential novel vaccines and drug targets

“…Reports of treatment failure in Senegal and Egypt [6,7], where isolates with reduced susceptibility to Praziquantel were obtained, have raised concerns about development of drug resistance. Further in vitro experiments confirmed the development of parasite resistance to Praziquantel compared with susceptible isolates [8][9][10][11].…”

Praziquantel: its use in control of schistosomiasis in sub-Saharan Africa and current research needs

“…6 % of the patients were still passing viable eggs. Several isolates were established in laboratory-maintained life cycles from eggs passed by uncured patients, and adult worms of these isolates were found to have PZQ ED 50 s 2-to 5-fold greater after PZQ treatment in mice than isolates that had been established from eggs passed before treatment by patients who had been cured (Ismail et al 1996).…”