You-Sheng Liang

In vitro responses of praziquantel-resistant and -susceptible Schistosoma mansoni to praziquantel

The resistance status of five praziquantel-susceptible and five praziquantel-resistant isolates was confirmed by chemotherapy in CD(1) mice with 3 x 200mg/kg micronised praziquantel. Micronised praziquantel had higher efficacy than two other praziquantel formulations (prepared without milling). The five resistant isolates were less responsive to praziquantel than the five susceptible isolates (59-74% reduction in worm burden in resistant isolates compared with 92-100% in susceptible isolates). Observations were made on the in vitro responses of different stages of 10 isolates to praziquantel. There were different in vitro responses to praziquantel at the egg, miracidial, cercarial and adult stages of Schistosoma mansoni between praziquantel-resistant and praziquantel-susceptible isolates. There were differences in the response of resistant and susceptible isolates following exposure of freshly hatched miracidia to 10(-6)M praziquantel for 1 min and observing the percent change in shape. Using this test it should be possible to determine whether failed therapy in patients infected with S. mansoni is due to the presence of praziquantel-resistant worms. Similarly, by exposing freshly shed cercariae to 4 x 10(-7)M praziquantel and observing the percent of tail shedding over 80 min it should be possible to monitor for the presence of praziquantel-resistant worms in snails collected in the field.

Detection of praziquantel resistance in schistosomes.

This article presents a detailed description of the clinical procedure in detecting praziquantel resistance in schistosomes. The effect of praziquantel on miracidia hatched from eggs obtained from the feces of mice infected with Schistosoma mansoni was observed in 24-well flat bottom microplates. 2 isolates were praziquantel-susceptible; 4 isolates were praziquantel-insusceptible including a laboratory-selected praziquantel-resistant population and 3 Senegalese isolates. The cessation of swimming of miracidia was observed in different concentrations of praziquantel at various times and then the morphological changes were checked by adding a drop of Lugols iodine. An objective measure of susceptibility was obtained by the addition of Lugols iodine and by determining whether miracidia had stopped swimming. However the latter procedure was less easy to read as a test than change in shape. Further investigation on whether failed therapy of Schistosoma mansoni is due to the presence of praziquantel-tolerant worms will be done in field trials in China.

Susceptibility of Schistosoma japonicum to praziquantel in China

To look for possible evidence of the development of resistance in Schistosoma japonicum to praziquantel, we conducted a field study in China. During the non‐transmission period of schistosomiasis a random sample of 2860 individuals from six villages in three provinces of China were examined using a parasitological stool examination. Of the 372 stool‐positive subjects, 363 subjects were treated with a single oral dose of 40 mg/kg of praziquantel. Six to Seven weeks after treatment, of 334 subjects examined using the same stool examination, stool‐negative results were found in 319 patients which represents a 95.5% parasitologic cure rate. Fifteen subjects still excreting eggs were treated a second time with the same dose of praziquantel. All stool samples, including those from participants re‐treated with praziquantel, were re‐examined 12 weeks after the first treatment and no stool‐positive subjects were found. The results indicate that there was no evidence for reduced susceptibility of S. japonicum to praziquantel despite its extensive use in the main endemic areas of China for more than 10 years. The in vitro responses to praziquantel of cercariae, miracidia and eggs of S. japonicum compared with S. mansoni demonstrate that the cercariae, miracidia and eggs of S. japonicum are more sensitive to praziquantel than those of S. mansoni. More sensitive worms would be less likely to develop resistance and this could explain why no evidence for resistance was found in S. japonicum in China.

Biological characteristics of praziquantel-resistant and -susceptible isolates of Schistosoma mansoni.

If there is a change in the biological characteristics of schistosomes associated with the development of resistance to praziquantel, this could affect the transmission and pathology of the diseases they cause. To investigate this possibility, the host-parasite relationships of five praziquantel-resistant and five praziquantel-susceptible isolates of Schistosoma mansoni were compared in Biomphalaria glabrata snails and outbred CD(1) albino mice. Whether praziquantel-resistant or -susceptible, all the laboratory-selected isolates gave similar results in B. glabrata. However, the snails infected with any of three field-collected isolates from Senegal, each of which has been shown to be praziquantel-resistant, shed fewer cercariae and survived longer than the snails infected with the drug-susceptible or laboratory-selected, drug-resistant isolates. There were no differences between isolates in terms of their infectivity to mice. However, mice infected with any of four of the five drug-resistant isolates shed more eggs in their faeces than mice carrying the drug-susceptible parasites, and mice infected with any of the resistant isolates also had larger numbers of eggs in their tissues. Although granuloma sizes were generally similar for all isolates, the praziquantel-resistant isolates may be more pathogenic in mice than the susceptible ones because of their relatively high egg productions.

Impact of the South-to-North Water Diversion Project on the transmission of Schistosoma japonicum in China

Abstract The South-to-North Water Diversion Project (SNWDP) is currently the key, national, water-conservation project in China, designed to optimise the use of water resources and relieve the water shortages in the north of the country. As one of the main water intakes for the project, that of the Eastern Route Scheme (ERS), is a breeding site for Oncomelania hupensis (the intermediate host of Schistosoma japonicum), there is concern that the snail may be carried far to the north, in the water passing through the project. To see if they could survive and breed to the north of their current range in China, O. hupensis were collected in marshland near Nanjing City and transferred to cages, on the banks of fish ponds, in the cities of Zhenjiang (in Jiangsu province, at 32°10′N), Xuzhou (in the same province but at a latitude of 34°23′N) and Jining (in Shandong province, at 35°23′N). Except over the first 6 months in Xuzhou, the snails moved north of their natural distribution did not survive and reproduce as well as those in Zhenjiang, and all those transferred to Jining died out within 1 year. Although the snail populations in Xuzhou survived for 7–8 years and retained their infectivity to S. japonicum, histological and histochemical studies revealed abnormalities in the reproductive organs of these snails. It is concluded that, unless global warming significantly increases the minimum winter temperatures in northern China, the SNWDP is unlikely to result in the northward spread of schistosomiasis japonica.

In‐vivo activity of dihydroartemisinin against Schistosoma japonicum

Schistosomiasis japonica, caused by Schistosoma japonicum, is still a major public-health concern in China, afflicting thousands of people (Zhou et al., 2007; Li et al., 2009). Since 1992, when the World Bank Loan Project for Schistosomiasis Control was initiated in China, praziquantel-based chemotherapy has been used to control the disease (Chen, 2005). Unfortunately, in the long term, repeated praziquantel treatment may lead to resistance to the drug in some Schistosoma species (Fallon et al., 1995; Ismail et al., 1996; Wang et al., 2010), and the development of new schistosomicidal drugs, as alternatives to praziquantel, is therefore a priority.

Toxicity of a novel suspension concentrate of niclosamide against Biomphalaria glabrata

As a new suspension concentrate of niclosamide (SCN) was more effective in controlling Oncomelania snails than a wettable powder of the same drug, it was tested against Biomphalaria glabrata. There were no differences in the effect of the suspension concentrate, the wettable powder of niclosamide and ball-milled pure niclosamide against the adult snails, but at after 48h 0.125mg/l SCN killed 100% of eggs compared with 84.3% for WPN and 17.7% for pure niclosamide. Because of the improved handling characteristics of SCN over the other formulations, further field tests on Biompharia and Bulinus species are warranted.

Dihydroartemisinin-praziquantel combinations and multiple doses of dihydroartemisinin in the treatment of Schistosoma japonicum in experimentally infected mice.

Currently, praziquantel is virtually the only drug used for the treatment of human schistosomiases (WHO, 2002). Although there is little direct evidence of the existence of praziquantel resistance in field isolates of schistosomes, decreased sensitivity to the drug has been reported in some Schistosoma species from several endemic areas (Tchuem–Tchuente et al., 2001; Alonso et al., 2006; Melman et al., 2009). The screening and development of novel antischistosomal drugs, as alternatives to praziquantel, therefore need to be given high priority. One derivative of artemisinin, dihydroartemisinin, shows activity against many parasites and, when administered orally to mammals, is rapidly absorbed, widely distributed and promptly excreted and metabolised (Tu, 2009). Single oral doses of dihydroartemisinin have recently been found effective against the 7-day-old schistosomula and 35-day-old adult worms of Schistosoma japonicum (Li et al., 2011). The aim of the present study was to explore the effects of multiple doses of dihydroartemisinin and of combined treatments with dihydroartemisinin and praziquantel against S. japonicum in experimentally infected mice, mainly to see if such treatments led to increased efficacy.