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

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) using successive drug treatments of Biomphalaria glabrata snails infected with S. mansoni. Infected B. glabrata were treated three times with 100 mg/kg PZQ for five consecutive days with a one-week interval between them. After the treatment, the cercariae (LE-PZQ) produced from these snails and the LE strains (susceptible) were used to infect mice. Forty-five days after infection, mice were treated with 200, 400 or 800 mg/kg PZQ. Thirty days post-treatment, we observed that the mean number of worms recovered by perfusion was significantly higher in the group of mice infected with the LE-PZQ isolate treated with 200 and 400 mg/kg in comparison to the LE strain with the same treatment. Moreover, there was a significant difference between the ED50 (effective dose required to kill 50% of the worms) of the LE-PZQ isolate (362 mg/kg) and the LE strain (68 mg/kg). In the in vitro assays, the worms of the LE-PZQ isolate were also less susceptible to PZQ. Thus, the use of infected snails as an experimental model for development of resistance to S. mansoni is effective, fast, simple and cheap.

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

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) using successive drug treatments of Biomphalaria glabrata snails infected with S. mansoni. Infected B. glabrata were treated three times with 100 mg/kg PZQ for five consecutive days with a one-week interval between them. After the treatment, the cercariae (LE-PZQ) produced from these snails and the LE strains (susceptible) were used to infect mice. Forty-five days after infection, mice were treated with 200, 400 or 800 mg/kg PZQ. Thirty days post-treatment, we observed that the mean number of worms recovered by perfusion was significantly higher in the group of mice infected with the LE-PZQ isolate treated with 200 and 400 mg/kg in comparison to the LE strain with the same treatment. Moreover, there was a significant difference between the ED50 (effective dose required to kill 50 percent of the worms) of the LE-PZQ isolate (362 mg/kg) and the LE strain (68 mg/kg). In the in vitro assays, the worms of the LE-PZQ isolate were also less susceptible to PZQ. Thus, the use of infected snails as an experimental model for development of resistance to S. mansoni is effective, fast, simple and cheap.

The schistosome excretory system: a key to regulation of metabolism, drug excretion and host interaction.

There is a gulf between the enormous information content of the various genome projects and the understanding of the life of the parasite in the host. In vitro studies with adult Schistosoma mansoni using several substrates suggest that the excretory system contains both P-glycoproteins and multiresistance proteins. If both these families of protein were active in vivo, they could regulate parasite metabolism and be responsible for the excretion of drugs. During skin penetration, membrane-impermeant molecules of a wide range of molecular weights can be taken into the cercaria and schistosomulum through the nephridiopore, through the surface membrane or through both. We speculate that this uptake process might stimulate novel signalling pathways involved in growth and development.

Schistosoma mansoni: expression of Fes-like tyrosine kinase SmFes in the tegument and terebratorium suggests its involvement in host penetration.

Protein Tyrosine Kinases (PTKs) are important molecules in intra- and inter-cellular communication, playing a major role in signal transduction processes. We have previously identified and characterized the molecular structure of a new PTK in Schistosoma mansoni, SmFes. SmFes exhibits the characteristic features of Fes/Fps protein tyrosine kinase subfamily of which it is the first member described in helminths. Herein, we show that genes orthologous to SmFes are also present in other Schistosoma species and the transcript is detected in Schistosoma japonicum. The SmFes protein was detected at all the main life-cycle stages and was most abundant in cercariae and newly-transformed schistosomula. However, no protein was detected in schistosomula maintained in vitro for 7 days. By immunolocalization assays we showed that SmFes is particularly concentrated at the terebratorium of miracidia and tegument of cercaria and schistosomula skin-stage. These findings suggest that SmFes may play a role in signal transduction pathways involved in larval transformation after penetration into intermediate and definitive hosts.

Schistosoma japonicum migration through mouse skin compared histologically and immunologically with S. mansoni.

The migration of Schistosoma japonicum and S. mansoni through mouse skin epidermis and dermis was compared by immunofluorescence techniques from 4 to 22 h after infection. At all times, the percentage of parasites detected in the dermis was significantly higher for S. japonicum than for S. mansoni. Thus, S. japonicum migrates more rapidly very early after infection. This agrees with the quicker migration observed previously by this species for later times. Both species expressed antigens related to the cercarial glycocalyx on the parasite body and antigenically detectable elastase in the acetabular glands, at least until 22 h after infection. Bot sets of antigens were also left as "traces" in cercarial migration channels in the skin as well as in skin tissue in the absence of detectable worms or migration channels. The data further substantiate differences between schistosome species in the speed of migration, and suggest that glycocalyx-related antigens and cercarial elastase continue to be expressed for at least 1 day after infection.

Schistosomiasis control: keep taking the tablets.

Despite the limited reports of praziquantel resistance, the relative success of chemotherapy-based control programmes for schistosomiasis has prompted overdue efforts to expand the use of cheap, generic, praziquantel in sub-Saharan Africa. The likely impact of such programmes on the development and spread of praziquantel resistance is uncertain, but this possibility reinforces the need for monitoring the spectrum of praziquantel sensitivity of schistosome populations and for an improved knowledge of the precise targets for the action of the drug. The search for alternatives to praziquantel and other tools for control of schistosomiasis must continue.

In vitro effect of cyclosporine A on juvenile Schistosoma mansoni labeled by AF18 (5-N-octadecanoyl aminofluorescein).

OBJECTIVE: To explore the in vitro effect of cyclosporine A on the tegument of juvenile Schistosoma mansoni labeled by AF18 and investigate the effect of cyclosporine A on schistosomula surface membrane fluidity. METHODS: Preparation of transformed schistosomula, adding cyclosporine A into tubes containing schistosomula and labeling of transformed schistosomula with AF18, then observe schistosomula under fluorescence microscope. RESULTS: Schistosomula of different groups labeled by AF18 were damaged by cyclosporine A in vitro. CONCLUSION: Cyclosporine A increases the uptake of AF18 by schistosomula in vitro which is dose-dependent, and decreases the parasite surface membrane fluidity.

The uptake of Texas Red-BSA in the excretory system of schistosomes and its colocalisation with ER60 promoter-induced GFP in transiently transformed adult males.

The excretory system of schistosomes has focused some attention during the last years since accumulating evidence suggests that it plays an important role in the host-parasite interaction. Signalling molecules such as phosphatases, but also proteases have been localised in the excretory system. To some extent, however, localisation studies are limited by the fact that sections of fixed specimens are used. In this study, we tested the fluorescent molecules FITC-dextran and Texas Red-BSA for their ability to enter the excretory system of living Schistosoma mansoni males. It is demonstrated that the dyes selectively stain the excretory tubules which are widely distributed along the worm body. This finding was used to investigate whether the staining of worms with Texas Red-BSA can help to localise transgene activity in worms which were transiently transformed by particle bombardment. A vector was used for transformation which contained the green fluorescent protein gene, under the control of the regulatory elements of the cysteine protease ER60 gene. After transformation and staining, confocal laser scanning microscopy revealed that ER60-induced green fluorescent protein activity colocalises with Texas Red-BSA in the excretory tubules. The results suggest a role for ER60 during the host-parasite interaction. Furthermore, the colocalisation approach introduced here opens further perspectives to characterise gene-expression profiles in this parasite.

Resistance of Schistosoma mansoni to praziquantel: is there a problem?

Evidence for resistance to praziquantel (PZQ) in Schistosoma mansoni has been sought in parasites taken from treated, but uncured human patients, and in a laboratory isolate of S. mansoni subjected to successive passages under drug pressure. Patients from villages in Egypt and Senegal have yielded isolates that can tolerate higher dosages of PZQ than other ostensible control isolates when passaged and subjected to drug treatment in mice. In vitro tests on these and the laboratory-selected isolate support the conclusion that a degree of resistance to PZQ can occur in S. mansoni, but the levels of drug resistance found so far are low. Preliminary studies have begun on these isolates to identify genetic, physiological and morphological characteristics associated with PZQ resistance and some of these may find use as markers for monitoring whether or not resistance is developing in endemic areas where the drug is used. More intensive application of PZQ can be expected in future, particularly in other parts of Africa, and vigilance will be needed to ensure that it continues to be useful as a drug for treatment of schistosomiasis. Further work is needed to elucidate the mode of action of PZQ and there is already a need for alternative drugs to treat PZQ-resistant schistosomiasis, such as already exists in northern Senegal.