• 1.

    Engels D, Chitsulo L, Montresor A, Savioli L, 2002. The global epidemiological situation of schistosomiasis and new approaches to control and research. Acta Trop 82: 139146.

    • Search Google Scholar
    • Export Citation
  • 2.

    Wang LD, Utzinger J, Zhou XN, 2008. Schistosomiasis control: experiences and lessons from China. Lancet 372: 17931795.

  • 3.

    Zhou XN, Wang LY, Chen MG, Wu XH, Jiang QW, Chen XY, Zheng J, Utzinger J, 2005. The public health significance and control of schistosomiasis in China–then and now. Acta Trop 96: 97105.

    • Search Google Scholar
    • Export Citation
  • 4.

    Zhou XN, Guo JG, Wu XH, Jiang QW, Zheng J, Dang H, Wang XH, Xu J, Zhu HQ, Wu GL, Li YS, Xu XJ, Chen HG, Wang TP, Zhu YC, Qiu DC, Dong XQ, Zhao GM, Zhang SJ, Zhao NQ, Xia G, Wang LY, Zhang SQ, Lin DD, Chen MG, Hao Y, 2007. Epidemiology of schistosomiasis in the People's Republic of China, 2004. Emerg Infect Dis 13: 14701476.

    • Search Google Scholar
    • Export Citation
  • 5.

    World Health Organization, 2002. Prevention and control of schistosomiasis and soil-transmitted helminthiasis: report of a WHO expert committee. WHO Technical Report Series 912. Geneva: WHO.

  • 6.

    Xiao SH, Keiser J, Chen MG, Tanner M, Utzinger J, 2010. Research and development of antischistosomal drugs in the People's Republic of China: a 60-year review. Adv Parasitol 73: 231295.

    • Search Google Scholar
    • Export Citation
  • 7.

    Chen MG, 2005. Use of praziquantel for clinical treatment and morbidity control of schistosomiasis japonica in China: a review of 30 years' experience. Acta Trop 96: 168176.

    • Search Google Scholar
    • Export Citation
  • 8.

    Fallon PG, Doenhoff MJ, 1994. Drug-resistant schistosomiasis: resistance to praziquantel and oxamniquine induced in Schistosoma mansoni in mice is drug specific. Am J Trop Med Hyg 51: 8388.

    • Search Google Scholar
    • Export Citation
  • 9.

    Liang YS, Li HJ, Dai JR, Wang W, Qu GL, Tao YH, Xing YT, Li YZ, Qian K, Wei JY, 2011. Resistance of Schistosoma japonicum to praziquantel is experimentally induced in laboratory. Chin J Schisto Control 23: 605610.

    • Search Google Scholar
    • Export Citation
  • 10.

    Ismail M, Metwally A, Farghaly A, Bruce J, Tao LF, Bennett JL, 1996. Characterization of isolates of Schistosoma mansoni from Egyptian villagers that tolerate high doses of praziquantel. Am J Trop Med Hyg 55: 214218.

    • Search Google Scholar
    • Export Citation
  • 11.

    Ismail M, Botros S, Metwally A, William S, Farghally A, Tao LF, Day TA, Bennett JL, 1999. Resistance to praziquantel: direct evidence from Schistosoma mansoni isolated from Egyptian villagers. Am J Trop Med Hyg 60: 932935.

    • Search Google Scholar
    • Export Citation
  • 12.

    Fallon PG, Sturrock RF, Niang AC, Doenhoff MJ, 1995. Diminished susceptibility to praziquantel in a Senegal isolate of Schistosoma mansoni. Am J Trop Med Hyg 53: 6162.

    • Search Google Scholar
    • Export Citation
  • 13.

    Melman SD, Steinauer ML, Cunningham C, Kubatko LS, Mwangi IN, Wynn NB, Mutuku MW, Karanja DM, Colley DG, Black CL, Secor WE, Mkoji GM, Loker ES, 2009. Reduced susceptibility to praziquantel among naturally occurring Kenyan isolates of Schistosoma mansoni. PLoS Negl Trop Dis 3: e504.

    • Search Google Scholar
    • Export Citation
  • 14.

    Herwaldt BL, Tao LF, van Pelt W, Tsang VC, Bruce JI, 1995. Persistence of Schistosoma haematobium infection despite multiple courses of therapy with praziquantel. Clin Infect Dis 20: 309315.

    • Search Google Scholar
    • Export Citation
  • 15.

    Alonso D, Muñoz J, Gascón J, Valls ME, Corachan M, 2006. Failure of standard treatment with praziquantel in two returned travelers with Schistosoma haematobium infection. Am J Trop Med Hyg 74: 342344.

    • Search Google Scholar
    • Export Citation
  • 16.

    Yu DB, Li Y, Sleigh AC, Yu XL, Li YS, Wei WY, Liang YS, McManus DP, 2001. Efficacy of praziquantel against Schistosoma japonicum: field evaluation in an area with repeated chemotherapy compared with a newly identified endemic focus in Hunan, China. Trans R Soc Trop Med Hyg 95: 537541.

    • Search Google Scholar
    • Export Citation
  • 17.

    Liang YS, Dai JR, Ning A, Yu DB, Xu XJ, Zhu YC, Coles GC, 2001. Susceptibility of Schistosoma japonicum to praziquantel in China. Trop Med Int Health 6: 707714.

    • Search Google Scholar
    • Export Citation
  • 18.

    Wang W, Dai JR, Li HJ, Shen XH, Liang YS, 2010. Is there reduced susceptibility to praziquantel in Schistosoma japonicum? Evidence from China. Parasitology 137: 19051912.

    • Search Google Scholar
    • Export Citation
  • 19.

    Balen J, Zhao ZY, Williams GM, McManus DP, Raso G, Utzinger J, Zhou J, Li YS, 2007. Prevalence, intensity and associated morbidity of Schistosoma japonicum infection in the Dongting Lake region, China. Bull World Health Organ 85: 519526.

    • Search Google Scholar
    • Export Citation
  • 20.

    Hong QB, Yang K, Huang YX, Sun LP, Yang GJ, Gao Y, Gao Y, Zhang LH, Zhou M, Steinmann P, Liang YS, 2011. Effectiveness of a comprehensive schistosomiasis japonica control program in Jiangsu province, China, from 2005 to 2008. Acta Trop 120S: S151S157.

    • Search Google Scholar
    • Export Citation
  • 21.

    Chen XY, Wang LY, Cai JM, Zhou XN, Zheng J, Guo JG, Wu XH, Engels D, Chen MG, 2005. Schistosomiasis control in China: the impact of a 10-year World Bank Loan Project (1992–2001). Bull World Health Organ 83: 4348.

    • Search Google Scholar
    • Export Citation
  • 22.

    Yu S, 1981. Studies on the methodology of egg collection with nylon bag for the diagnosis of Schistosoma japonicum infections. Chin J Med Lab Technol 4: 210213.

    • Search Google Scholar
    • Export Citation
  • 23.

    Gönnert R, Andrews P, 1977. Praziquantel, a new broad-spectrum antischistosomal agent. Z Parasitenkd 52: 129150.

  • 24.

    Jordan P, Webbe G, Sturrock RF, 1993. Human Schistosomiasis. UK: CAB International.

  • 25.

    Wu GL, 2002. A historical perspective on the immunodiagnosis of schistosomiasis in China. Acta Trop 82: 193198.

  • 26.

    Zhu YC, 2005. Immunodiagnosis and its role in schistosomiasis control in China: a review. Acta Trop 96: 130136.

  • 27.

    Katz N, Chaves A, Pellegrino J, 1972. A simple device for quantitative stool thick-smear techniques in schistosomiasis mansoni. Rev Inst Med Trop Sao Paulo 14: 397400.

    • Search Google Scholar
    • Export Citation
  • 28.

    Lin DD, Liu JX, Liu YM, Hu F, Zhang YY, Xu JM, Li JY, Ji MJ, Bergquist R, Wu GL, Wu HW, 2008. Routine Kato-Katz technique underestimates the prevalence of Schistosoma japonicum: a case study in an endemic area of the People's Republic of China. Parasitol Int 57: 281286.

    • Search Google Scholar
    • Export Citation
  • 29.

    Yu JM, de Vlas SJ, Jiang QW, Gryseels B, 2007. Comparison of the Kato-Katz technique, hatching test and indirect hemagglutination assay (IHA) for the diagnosis of Schistosoma japonicum infection in China. Parasitol Int 56: 4549.

    • Search Google Scholar
    • Export Citation

 

 

 

 

 

The Sensitivity of Schistosoma japonicum to Praziquantel: A Field Evaluation in Areas with Low Endemicity of China

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  • Jiangsu Institute of Parasitic Diseases, Wuxi, Jiangsu Province, People's Republic of China; Key Laboratory on Technology for Parasitic Disease Prevention and Control, Wuxi, Jiangsu Province, People's Republic of China; Dantu District Center for Disease Control and Prevention, Zhenjiang, Jiangsu Province, People's Republic of China

The purpose of the current study was to investigate the susceptibility of Schistosoma japonicum to praziquantel in low endemic foci of China. During the non-transmission period of schistosomiasis, a total of 43 of 1,242 subjects were identified as being infected with the parasite using parasitological stool examinations in two low-endemicity areas of China, with a prevalence rate of 3.46%. All stool-egg-positive subjects were treated with praziquantel in a single oral dose of 40 mg/kg or 30 mg/kg for two successive days. Six weeks post-treatment, no S. japonicum eggs were detected in the 43 treated villagers. The results indicate that the current efficacy of praziquantel against S. japonicum seems satisfactory and has not changed over the past three decades in the low endemic areas of China. It is also suggested that no evidence of tolerance or resistance to praziquantel in S. japonicum is detected in areas with low endemicity in China.

Human infection by the blood-fluke Schistosoma japonicum remains a major public health concern in the People's Republic of China, the Philippines, and parts of Indonesia.1 In China, concerted control efforts since the 1950s have dramatically reduced the number of the areas endemic for the parasite and the burden of disease among humans.2,3 Nevertheless, in the remaining core endemic regions, mainly located along the middle and lower reaches of the Yangtze River and some mountainous areas of provinces of Yunnan and Sichuan, over 0.7 million people are estimated to be infected, with a further 30 million at risk of infection.4

Because of high efficacy, excellent tolerance, few and transient side effects, simple administration, and competitive cost, praziquantel is currently the drug of choice for treatment of human schistosomiases.5 Treatment of schistosomiasis japonica has shown great advances with the introduction of the drug into the therapeutic arsenal in China,6 and praziquantel-based chemotherapy was considered as a priority control strategy for the national schistosomiasis control program.7 Under laboratory conditions it is possible to induce resistance of Schistosoma mansoni and S. japonicum to praziquantel in mice following treatment with multiple subcurative doses of the drug,8,9 and a decreased sensitivity to praziquantel in field isolates of S. mansoni has also been found in many endemic foci.1013 In addition, there are several schistosomiasis cases caused by infections with S. haematobium in which repeated standard treatment failed to clear the infection.14,15 Extensive, long-term, repeated praziquantel chemotherapy has been used to control the morbidity and reduce the prevalence and intensity of S. japonicum infection for about 30 years7; it is, therefore, of great importance to monitor the current efficacy of praziquantel in areas where the drug is widely used because there is concern that continued use of praziquantel may result in drug resistance in schistosomes, and there are currently few other drugs being developed that are likely to be alternatives to praziquantel. Previously, there were several studies reporting the sensitivity of praziquantel in areas with moderate or high endemicity.1618 However, the majority of schistosome-endemic areas in China are currently characterized by a low endemicity, which is mainly caused by praziquantel-based comprehensive control.19,20 Given that many populations in these areas received praziquantel for treatment or prevention of S. japonicum infection many times, it is essential to investigate the susceptibility of S. japonicum to praziquantel in low endemic areas. Here, a field investigation was carried out in two foci with low endemicity in China, to evaluate the current efficacy of praziquantel against S. japonicum.

Two villages that are endemic for S. japonicum, namely Xuguang and Sanshan villages located in Dantu District of Zhenjiang City and Jiangpu District of Nanjing City, Jiangsu Province, were involved in this study, with populations of 1,045 and 1,152, and 2.7% and 1.9% of the people infected, respectively (local epidemiological data in 2006). The praziquantel-based integrated control program, including mass synchronous chemotherapy for both humans and domestic animals (mainly bovine) with praziquantel, control of the snail host of S. japonicum, health education, etc., has been successively implemented in both villages for more than 10 years with the World Bank Loan Project for Schistosomiasis Control.21 During the period of schistosomiasis non-transmission (from November 2007 to February, 2008), a random sample of 1,242 volunteers 6–70 years of age from the two study villages was included in this study, however pregnant women were excluded. Schistosoma japonicum infection was detected by parasitological stool examinations using the miracidium hatching test,22 and the total number of eggs detected in each stool specimen (about 30 g) was counted and recorded, and the intensity of infection was expressed as the number of eggs per gram of feces. Epidemiological case surveys were conducted in those subjects with positive stool examinations, to obtain information including name, age, sex, history of treatment of schistosomiasis, etc. Praziquantel tablets (Nanjing Pharmaceutical Factory Co. Ltd, Nanjing, China; batch no. 20070607) were given to those subjects whose fecal examinations were positive at a single oral dose of 40 mg/kg or 30 mg/kg for two successive days recommended by the Ministry of Health, China. Fecal samples were collected for parasitological stool examinations 6 weeks post-treatment.

This study was approved by the Ethics Review Committees of Jiangsu Provincial Department of Health and Jiangsu Institute of Parasitic Diseases. Informed consents were obtained from all participants following a detailed description of the purpose and potential benefits of the current study. Praziquantel (oral dose of 40 mg/kg or 30 mg/kg) was offered to those cases with stool eggs for free, and all subjects accepted the treatment protocol.

Of the 1,242 residents examined in both villages, 43 had S. japonicum eggs in the first stool examination, with a prevalence rate of 3.46%. The infection rate, age range, sex ratio, intensity of infection, history of infection, history of treatment with praziquantel, and treatment interval of the infected patients are shown in Table 1. Among the 43 infected subjects, 13 received praziquantel treatment at a single dose of 40 mg/kg, and 30 were treated with praziquantel at a dose of 30 mg/kg for two successive days. Six weeks after treatment, all of the treated villagers were re-examined and no S. japonicum eggs were detected.

Table 1

Demographical features of the detected schistosomiasis patients in the two study villages

CharacteristicXuguang VillageSanshan Village
Infection rate (%)3.123.64
No. villagers examined417825
No. cases infected with S. japonicum1330
Age range (years)10–619–60
SexMale717
Female613
Intensity of infectionEPG 24–961023
EPG 216–31237
No. cases with history of infection921
No. cases with history of treatment with praziquantel1228
Treatment interval< 1 year412
1–3 years410
> 4 years58

Since praziquantel, a highly effective and safe anti-schistosomal drug, was developed,23 it has replaced all other schistosomicidal agents to become the only anti-schistosomal drug of choice for treatment against all the major species of schistosome.5 Praziquantel makes mass chemotherapy possible as a priority control strategy in almost all countries worldwide where schistosomiasis is endemic.5

Diagnosis is central to schistosomiasis control.24 Currently, definitive diagnosis of S. japonicum infection still requires the demonstration of eggs or miracidia in feces,25,26 either by means of the Kato-Katz technique27 or the miracidium hatching method.21 It has been shown that the routine Kato-Katz technique underestimates the real prevalence of S. japonicum in areas with low endemicity.28 Therefore, the miracidium hatching test was used for detection of S. japonicum infection in this study. However, considering the result of the hatching test depends on environmental factors such as temperature and water quality,29 a failure to detect S. japonicum-infected residents cannot be excluded.

Our findings indicate that the current efficacy of praziquantel against S. japonicum seems satisfactory and has not changed after about three decades of repeated, long-term extensive use in the low endemic areas of China. Together with our previous findings,17 it seems that the susceptibility of S. japonicum to praziquantel remains high in China. Therefore, periodical monitoring of the efficacy of the drug against schistosomes and systematic survey of praziquantel sensitivity in different geographical isolates of S. japonicum in China are required, and development of tools that can be used for field surveillance of drug resistance in S. japonicum in China seems justified.

ACKNOWLEDGMENTS:

We thank the villagers in the study areas for their active cooperation during the examinations and treatment.

  • 1.

    Engels D, Chitsulo L, Montresor A, Savioli L, 2002. The global epidemiological situation of schistosomiasis and new approaches to control and research. Acta Trop 82: 139146.

    • Search Google Scholar
    • Export Citation
  • 2.

    Wang LD, Utzinger J, Zhou XN, 2008. Schistosomiasis control: experiences and lessons from China. Lancet 372: 17931795.

  • 3.

    Zhou XN, Wang LY, Chen MG, Wu XH, Jiang QW, Chen XY, Zheng J, Utzinger J, 2005. The public health significance and control of schistosomiasis in China–then and now. Acta Trop 96: 97105.

    • Search Google Scholar
    • Export Citation
  • 4.

    Zhou XN, Guo JG, Wu XH, Jiang QW, Zheng J, Dang H, Wang XH, Xu J, Zhu HQ, Wu GL, Li YS, Xu XJ, Chen HG, Wang TP, Zhu YC, Qiu DC, Dong XQ, Zhao GM, Zhang SJ, Zhao NQ, Xia G, Wang LY, Zhang SQ, Lin DD, Chen MG, Hao Y, 2007. Epidemiology of schistosomiasis in the People's Republic of China, 2004. Emerg Infect Dis 13: 14701476.

    • Search Google Scholar
    • Export Citation
  • 5.

    World Health Organization, 2002. Prevention and control of schistosomiasis and soil-transmitted helminthiasis: report of a WHO expert committee. WHO Technical Report Series 912. Geneva: WHO.

  • 6.

    Xiao SH, Keiser J, Chen MG, Tanner M, Utzinger J, 2010. Research and development of antischistosomal drugs in the People's Republic of China: a 60-year review. Adv Parasitol 73: 231295.

    • Search Google Scholar
    • Export Citation
  • 7.

    Chen MG, 2005. Use of praziquantel for clinical treatment and morbidity control of schistosomiasis japonica in China: a review of 30 years' experience. Acta Trop 96: 168176.

    • Search Google Scholar
    • Export Citation
  • 8.

    Fallon PG, Doenhoff MJ, 1994. Drug-resistant schistosomiasis: resistance to praziquantel and oxamniquine induced in Schistosoma mansoni in mice is drug specific. Am J Trop Med Hyg 51: 8388.

    • Search Google Scholar
    • Export Citation
  • 9.

    Liang YS, Li HJ, Dai JR, Wang W, Qu GL, Tao YH, Xing YT, Li YZ, Qian K, Wei JY, 2011. Resistance of Schistosoma japonicum to praziquantel is experimentally induced in laboratory. Chin J Schisto Control 23: 605610.

    • Search Google Scholar
    • Export Citation
  • 10.

    Ismail M, Metwally A, Farghaly A, Bruce J, Tao LF, Bennett JL, 1996. Characterization of isolates of Schistosoma mansoni from Egyptian villagers that tolerate high doses of praziquantel. Am J Trop Med Hyg 55: 214218.

    • Search Google Scholar
    • Export Citation
  • 11.

    Ismail M, Botros S, Metwally A, William S, Farghally A, Tao LF, Day TA, Bennett JL, 1999. Resistance to praziquantel: direct evidence from Schistosoma mansoni isolated from Egyptian villagers. Am J Trop Med Hyg 60: 932935.

    • Search Google Scholar
    • Export Citation
  • 12.

    Fallon PG, Sturrock RF, Niang AC, Doenhoff MJ, 1995. Diminished susceptibility to praziquantel in a Senegal isolate of Schistosoma mansoni. Am J Trop Med Hyg 53: 6162.

    • Search Google Scholar
    • Export Citation
  • 13.

    Melman SD, Steinauer ML, Cunningham C, Kubatko LS, Mwangi IN, Wynn NB, Mutuku MW, Karanja DM, Colley DG, Black CL, Secor WE, Mkoji GM, Loker ES, 2009. Reduced susceptibility to praziquantel among naturally occurring Kenyan isolates of Schistosoma mansoni. PLoS Negl Trop Dis 3: e504.

    • Search Google Scholar
    • Export Citation
  • 14.

    Herwaldt BL, Tao LF, van Pelt W, Tsang VC, Bruce JI, 1995. Persistence of Schistosoma haematobium infection despite multiple courses of therapy with praziquantel. Clin Infect Dis 20: 309315.

    • Search Google Scholar
    • Export Citation
  • 15.

    Alonso D, Muñoz J, Gascón J, Valls ME, Corachan M, 2006. Failure of standard treatment with praziquantel in two returned travelers with Schistosoma haematobium infection. Am J Trop Med Hyg 74: 342344.

    • Search Google Scholar
    • Export Citation
  • 16.

    Yu DB, Li Y, Sleigh AC, Yu XL, Li YS, Wei WY, Liang YS, McManus DP, 2001. Efficacy of praziquantel against Schistosoma japonicum: field evaluation in an area with repeated chemotherapy compared with a newly identified endemic focus in Hunan, China. Trans R Soc Trop Med Hyg 95: 537541.

    • Search Google Scholar
    • Export Citation
  • 17.

    Liang YS, Dai JR, Ning A, Yu DB, Xu XJ, Zhu YC, Coles GC, 2001. Susceptibility of Schistosoma japonicum to praziquantel in China. Trop Med Int Health 6: 707714.

    • Search Google Scholar
    • Export Citation
  • 18.

    Wang W, Dai JR, Li HJ, Shen XH, Liang YS, 2010. Is there reduced susceptibility to praziquantel in Schistosoma japonicum? Evidence from China. Parasitology 137: 19051912.

    • Search Google Scholar
    • Export Citation
  • 19.

    Balen J, Zhao ZY, Williams GM, McManus DP, Raso G, Utzinger J, Zhou J, Li YS, 2007. Prevalence, intensity and associated morbidity of Schistosoma japonicum infection in the Dongting Lake region, China. Bull World Health Organ 85: 519526.

    • Search Google Scholar
    • Export Citation
  • 20.

    Hong QB, Yang K, Huang YX, Sun LP, Yang GJ, Gao Y, Gao Y, Zhang LH, Zhou M, Steinmann P, Liang YS, 2011. Effectiveness of a comprehensive schistosomiasis japonica control program in Jiangsu province, China, from 2005 to 2008. Acta Trop 120S: S151S157.

    • Search Google Scholar
    • Export Citation
  • 21.

    Chen XY, Wang LY, Cai JM, Zhou XN, Zheng J, Guo JG, Wu XH, Engels D, Chen MG, 2005. Schistosomiasis control in China: the impact of a 10-year World Bank Loan Project (1992–2001). Bull World Health Organ 83: 4348.

    • Search Google Scholar
    • Export Citation
  • 22.

    Yu S, 1981. Studies on the methodology of egg collection with nylon bag for the diagnosis of Schistosoma japonicum infections. Chin J Med Lab Technol 4: 210213.

    • Search Google Scholar
    • Export Citation
  • 23.

    Gönnert R, Andrews P, 1977. Praziquantel, a new broad-spectrum antischistosomal agent. Z Parasitenkd 52: 129150.

  • 24.

    Jordan P, Webbe G, Sturrock RF, 1993. Human Schistosomiasis. UK: CAB International.

  • 25.

    Wu GL, 2002. A historical perspective on the immunodiagnosis of schistosomiasis in China. Acta Trop 82: 193198.

  • 26.

    Zhu YC, 2005. Immunodiagnosis and its role in schistosomiasis control in China: a review. Acta Trop 96: 130136.

  • 27.

    Katz N, Chaves A, Pellegrino J, 1972. A simple device for quantitative stool thick-smear techniques in schistosomiasis mansoni. Rev Inst Med Trop Sao Paulo 14: 397400.

    • Search Google Scholar
    • Export Citation
  • 28.

    Lin DD, Liu JX, Liu YM, Hu F, Zhang YY, Xu JM, Li JY, Ji MJ, Bergquist R, Wu GL, Wu HW, 2008. Routine Kato-Katz technique underestimates the prevalence of Schistosoma japonicum: a case study in an endemic area of the People's Republic of China. Parasitol Int 57: 281286.

    • Search Google Scholar
    • Export Citation
  • 29.

    Yu JM, de Vlas SJ, Jiang QW, Gryseels B, 2007. Comparison of the Kato-Katz technique, hatching test and indirect hemagglutination assay (IHA) for the diagnosis of Schistosoma japonicum infection in China. Parasitol Int 56: 4549.

    • Search Google Scholar
    • Export Citation

Author Notes

*Address correspondence to You-Sheng Liang, Jiangsu Institute of Parasitic Diseases, 117 Yangxiang, Meiyuan, Wuxi, Jiangsu Province, 214064, People's Republic of China. E-mail: wxliangyousheng@yahoo.cn

Financial support: W.W., J.R.D., and Y.S.L. were supported by the National Science and Technology Pillar Program of China (grant no. 2009BAI78B06). W.W. and H.J.L. were supported by a grant from the Jiangsu Department of Health (grant no. X200912) and the Jiangsu Provincial Scientific Foundation of Preventive Medicine (Y201031).

Authors' addresses: Wei Wang, Jian-Rong Dai, Hong-Jun Li, and You-Sheng Liang, Jiangsu Institute of Parasitic Diseases, Key Laboratory on Technology for Parasitic Disease Prevention and Control, Ministry of Health, Wuxi, China, E-mails: wangweijipd@yahoo.com.cn, wxdaijianrong@yahoo.cn, li3982@163.com, and wxliangyousheng@yahoo.cn. Xue-Hui Shen, Dantu District Center for Disease Control and Prevention, Zhenjiang City, Danyang, Jiangsu Province, China, E-mail: zjdtxf@163.com.

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