Evidence Against Rapid Emergence of Praziquantel Resistance in Schistosoma haematobium, Kenya

Charles H. King, Case Western Reserve University School of Medicine and University Hospitals of Cleveland, Cleveland, Ohio, USA; Eric M. Muchiri, John H. Ouma, Ministry of Health, Nairobi, Kenya

Disclosures

Emerging Infectious Diseases. 2000;6(6) 

In This Article

Abstract and Introduction

We examined the long-term efficacy of praziquantel against Schistosoma haematobium, the causative agent of urinary schistosomiasis, during a school-based treatment program in the Msambweni area of Coast Province, Kenya, where the disease is highly endemic. Our results, derived from treating 4,031 of 7,641 children from 1984 to 1993, indicate substantial year-to-year variation in drug efficacy. However, the pattern of this variation was not consistent with primary or progressive emergence of praziquantel resistance. Mathematical modeling indicated that, at current treatment rates, praziquantel resistance will likely take 10 or more years to emerge.

Schistosomiasis remains a public health problem in many regions, including Africa, the Middle East, Asia, and South America[1]. For many of the Schistosoma species that infect humans, isoquinolin-4-one, praziquantel, is the only effective drug[2,3]. Its minimal side effects and high degree of efficacy against both trematodes and cestodes have made it the drug of choice for many human and veterinary parasitic infections[2,4]. However, praziquantel has been in use for more than 20 years[5], and concern is increasing that resistance has emerged, or will soon emerge, in human parasites[6,7].

Loss of praziquantel efficacy would set back helminth control efforts. Many community-based programs depend on praziquantel for treating patients with schistosomiasis, cysticercosis, echinococcosis, and tapeworm and other fluke infections[5,8,9,10,11,12,13]. Concern over possible loss of efficacy prompted the European Commission to establish an International Initiative on Praziquantel Use, which met in February 1998[14] and again in February 1999[15]. The group reviewed reports of low efficacy in clinical trials in Senegal and Egypt[16,17,18,19] and of laboratory isolation of schistosome strains resistant to standard and high doses of the drug[20,21,22,23]. Although there was no definitive laboratory evidence of genetically transmissible and drug-selectable resistance (as had been demonstrated for the antischistosome drug hycanthone[24]), concern was raised over possible low-level resistance. The need was expressed for continued monitoring for resistant strains under the pressure of widespread praziquantel use[14].

We examined drug efficacy in the community and among schoolchildren given repeated praziquantel treatment for S. haematobium in Coast Province, Kenya. Year-to-year variation in treatment response was assessed, and the likely time-to-emergence of resistance was evaluated through the use of mathematical modeling of resistance-gene transmission in this obligately diecious parasite.

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