Swiss Tropical Institute

Basel, Switzerland

Swiss Tropical Institute

Basel, Switzerland
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Orhan I.,Gazi University | Sener B.,Gazi University | Kaiser M.,Swiss Tropical Institute | Brun R.,Swiss Tropical Institute | Tasdemir D.,University of London
Marine Drugs | Year: 2010

In this study, thirteen sponge-derived terpenoids, including five linear furanoterpenes: furospinulosin-1 (1), furospinulosin-2 (2), furospongin-1 (3), furospongin-4 (4), and demethylfurospongin-4 (5); four linear meroterpenes: 2-(hexaprenylmethyl)-2-methylchromenol (6), 4-hydroxy-3-octaprenylbenzoic acid (7), 4-hydroxy-3-tetraprenylphenylacetic acid (8), and heptaprenyl-p-quinol (9); a linear triterpene, squalene (10); two spongian-type diterpenes dorisenone D (11) and 11β-acetoxyspongi-12-en-16-one (12); a scalarane-type sesterterpene; 12-epi-deoxoscalarin (13), as well as an indole alkaloid, tryptophol (14) were screened for their in vitro activity against four parasitic protozoa; Trypanosoma brucei rhodesiense, Trypanosoma cruzi, Leishmania donovani and Plasmodium falciparum. Cytotoxic potential of the compounds on mammalian cells was also assessed. All compounds were active against T. brucei rhodesiense, with compound 8 being the most potent (IC 50 0.60 μg/mL), whereas 9 and 12 were the most active compounds against T. cruzi, with IC 50 values around 4 μg/mL. Compound 12 showed the strongest leishmanicidal activity (IC 50 0.75 μg/mL), which was comparable to that of miltefosine (IC 50 0.20 μg/mL). The best antiplasmodial effect was exerted by compound 11 (IC 50 0.43 μg/mL), followed by compounds 7, 10, and 12 with IC 50 values around 1 μg/mL. Compounds 9, 11 and 12 exhibited, besides their antiprotozoal activity, also some cytotoxicity, whereas all other compounds had low or no cytotoxicity towards the mammalian cell line. This is the first report of antiprotozoal activity of marine metabolites 1-14, and points out the potential of marine sponges in discovery of new antiprotozoal lead compounds. © 2010 by the authors; licensee Molecular Diversity Preservation International.

Brun R.,Swiss Tropical Institute | Blum J.,Swiss Tropical Institute | Chappuis F.,University of Geneva | Chappuis F.,Médecins Sans Frontières | Burri C.,Swiss Tropical Institute
The Lancet | Year: 2010

Human African trypanosomiasis (sleeping sickness) occurs in sub-Saharan Africa. It is caused by the protozoan parasite Trypanosoma brucei, transmitted by tsetse flies. Almost all cases are due to Trypanosoma brucei gambiense, which is indigenous to west and central Africa. Prevalence is strongly dependent on control measures, which are often neglected during periods of political instability, thus leading to resurgence. With fewer than 12 000 cases of this disabling and fatal disease reported per year, trypanosomiasis belongs to the most neglected tropical diseases. The clinical presentation is complex, and diagnosis and treatment difficult. The available drugs are old, complicated to administer, and can cause severe adverse reactions. New diagnostic methods and safe and effective drugs are urgently needed. Vector control, to reduce the number of flies in existing foci, needs to be organised on a pan-African basis. WHO has stated that if national control programmes, international organisations, research institutes, and philanthropic partners engage in concerted action, elimination of this disease might even be possible. © 2010 Elsevier Ltd. All rights reserved.

Bousema T.,London School of Hygiene and Tropical Medicine | Okell L.,Radboud University Nijmegen | Felger I.,Imperial College London | Drakeley C.,Swiss Tropical Institute
Nature Reviews Microbiology | Year: 2014

Most Plasmodium falciparum infections that are detected in community surveys are characterized by low-density parasitaemia and the absence of clinical symptoms. Molecular diagnostics have shown that this asymptomatic parasitic reservoir is more widespread than previously thought, even in low-endemic areas. In this Opinion article, we describe the detectability of asymptomatic malaria infections and the relevance of submicroscopic infections for parasite transmission to mosquitoes and for community interventions that aim at reducing transmission. We argue that wider deployment of molecular diagnostic tools is needed to provide adequate insight into the epidemiology of malaria and infection dynamics to aid elimination efforts. © 2014 Macmillan Publishers Limited. All rights reserved.

Lamelas A.,University of Valencia | Lamelas A.,Swiss Tropical Institute | Gosalbes M.J.,University of Valencia | Manzano-Marin A.,University of Valencia | And 3 more authors.
PLoS Genetics | Year: 2011

The genome sequencing of Buchnera aphidicola BCc from the aphid Cinara cedri, which is the smallest known Buchnera genome, revealed that this bacterium had lost its symbiotic role, as it was not able to synthesize tryptophan and riboflavin. Moreover, the biosynthesis of tryptophan is shared with the endosymbiont Serratia symbiotica SCc, which coexists with B. aphidicola in this aphid. The whole-genome sequencing of S. symbiotica SCc reveals an endosymbiont in a stage of genome reduction that is closer to an obligate endosymbiont, such as B. aphidicola from Acyrthosiphon pisum, than to another S. symbiotica, which is a facultative endosymbiont in this aphid, and presents much less gene decay. The comparison between both S. symbiotica enables us to propose an evolutionary scenario of the transition from facultative to obligate endosymbiont. Metabolic inferences of B. aphidicola BCc and S. symbiotica SCc reveal that most of the functions carried out by B. aphidicola in A. pisum are now either conserved in B. aphidicola BCc or taken over by S. symbiotica. In addition, there are several cases of metabolic complementation giving functional stability to the whole consortium and evolutionary preservation of the actors involved. © 2011 Lamelas et al.

Kuster T.,University of Bern | Stadelmann B.,University of Bern | Stadelmann B.,Uppsala University | Hermann C.,University of Bern | And 3 more authors.
Antimicrobial Agents and Chemotherapy | Year: 2011

Alveolar echinococcosis (AE) is caused by the metacestode stage of the fox tapeworm Echinococcus multilocularis and causes severe disease in the human liver, and occasionally in other organs, that is fatal when treatment is unsuccessful. The present chemotherapy against AE is based on mebendazole and albendazole. Albendazole treatment has been found to be ineffective in some instances, is parasitostatic rather than parasiticidal, and usually involves the lifelong uptake of large doses of drugs. Thus, new treatment options are urgently needed. In this study we investigated the in vitro and in vivo efficacy of mefloquine against E. multilocularis metacestodes. Treatment using mefloquine (20 μM) against in vitro cultures of metacestodes resulted in rapid and complete detachment of large parts of the germinal layer from the inner surface of the laminated layer within a few hours. The in vitro activity of mefloquine was dependent on the dosage. In vitro culture of metacestodes in the presence of 24 μM mefloquine for a period of 10 days was parasiticidal, as determined by murine bioassays, while treatment with 12 μM was not. Oral application of mefloquine (25 mg/kg of body weight administered twice a week for a period of 8 weeks) in E. multilocularis-infected mice was ineffective in achieving any reduction of parasite weight, whereas treatment with albendazole (200 mg/kg/day) was highly effective. However, when the same mefloquine dosage was applied intraperitoneally, the reduction in parasite weight was similar to the reduction seen with oral albendazole application. Combined application of both drugs did not increase the treatment efficacy. In conclusion, mefloquine represents an interesting drug candidate for the treatment of AE, and these results should be followed up in appropriate in vivo studies. Copyright © 2011, American Society for Microbiology. All Rights Reserved.

Keiser J.,Swiss Tropical Institute | Vargas M.,Swiss Tropical Institute | Doenhoff M.J.,University of Nottingham
American Journal of Tropical Medicine and Hygiene | Year: 2010

Immune effector mechanisms can enhance the activity of antischistosomal drugs. We examined the in vivo effect of single oral doses of the antimalarials artemether (400 mg/kg) and mefloquine (200 mg/kg), recently described to have promising antischistosomal properties, against juvenile and adult Schistosoma mansoni in T cell-deficient and in comparably infected age- and sex-matched immunologically intact control mice. Artemether and mefloquine are equally effective in athymic and immunocompetent mice. Artemether treatment resulted in total and female worm burden reductions ranging between 71.1% and 85.3%, whereas mefloquine achieved total and female worm burden reductions of 80.4-97.8%. In conclusion, artemether and mefloquine act T-cell independently and no synergistic interaction with the immune response was involved. Copyright © 2010 by The American Society of Tropical Medicine and Hygiene.

Fugi M.A.,Swiss Tropical Institute | Wittlin S.,Swiss Tropical Institute | Dong Y.,University of Nebraska Medical Center | Vennerstrom J.L.,University of Nebraska Medical Center
Antimicrobial Agents and Chemotherapy | Year: 2010

Peroxidic antimalarials such as the semisynthetic artemisinins are critically important in the treatment of drug-resistant malaria. Nevertheless, their peroxide bond-dependent mode of action is still not well understood. Using combination experiments with cultured Plasmodium falciparum cells, we investigated the interactions of the nitroxide radical spin trap, 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO), and four of its analogs with artemisinin and the ozonide drug development candidate OZ277. The antagonism observed for combinations of artemisinin or OZ277 with the TEMPO analogs supports the hypothesis that the formation of carbon-centered radicals is critical for the activity of these two antimalarial peroxides. The TEMPO analogs showed a trend toward greater antagonism with artemisinin than they did with OZ277, an observation that can be explained by the greater tendency of artemisinin-derived carbon-centered radicals to undergo internal self-quenching reactions, resulting in a lower proportion of radicals available for subsequent chemical reactions such as the alkylation of heme and parasite proteins. In a further mechanistic experiment, we tested both artemisinin and OZ277 in combination with their nonperoxidic analogs. The latter had no effect on the antimalarial activities of the former. These data indicate that the antimalarial properties of peroxides do not derive from reversible interactions with parasite targets. Copyright © 2010, American Society for Microbiology. All Rights Reserved.

Manneck T.,Swiss Tropical Institute | Haggenmuller Y.,Swiss Tropical Institute | Keiser J.,Swiss Tropical Institute
Parasitology | Year: 2010

There is a pressing need to develop novel anti-schistosomal drugs, as current treatment relies largely on praziquantel (PZQ). To further strengthen current evidence of the anti-schistosomal properties of mefloquine (MQ), we studied the temporal effect of this compound in vitro and in vivo, and examined alterations on the tegumental surface of schistosomula and adults of S. mansoni by means of scanning electron microscopy (SEM). Schistosomula and adults were each incubated in vitro using MQ over a wide concentration range (1100 g/ml). In addition, mice infected with adult S. mansoni were treated with a single oral dose of 400 mg/kg MQ, and worms were recovered 24, 48, 72, 96 and 120 h following treatment. MQ showed a rapid onset of action on schistosomula in vitro; 100 and 75 μg/ml of MQ killed schistosomula immediately; the minimal lethal and effective concentrations of MQ on schistosomula after 1 h were 25 and 5 μg/ml, respectively. Adult worms incubated with 100 and 10 μg/ml of MQ were dead after 1 h and 24 h of incubation, respectively. A hepatic shift of adult schistosomes was observed in mice already 24 h after treatment, and 120 h following treatment >98% of all worms had translocated to the liver. SEM observations revealed extensive tegumental destruction, including blebbing, shrinking and sloughing, particularly following in vitro incubation and on the tegument of female worms. © 2009 Cambridge University Press.

Keiser J.,Swiss Tropical Institute
Parasitology | Year: 2010

Schistosomiasis and food-borne trematodiases are chronic parasitic diseases affecting millions of people mostly in the developing world. Additional drugs should be developed as only few drugs are available for treatment and drug resistance might emerge. In vitro and in vivo whole parasite screens represent essential components of the trematodicidal drug discovery cascade. This review describes the current state-of-the-art of in vitro and in vivo screening systems of the blood fluke Schistosoma mansoni, the liver fluke Fasciola hepatica and the intestinal fluke Echinostoma caproni. Examples of in vitro and in vivo evaluation of compounds for activity are presented. To boost the discovery pipeline for these diseases there is a need to develop validated, robust high-throughput in vitro systems with simple readouts. © 2009 Cambridge University Press.

Gosoniu L.,Swiss Tropical Institute | Veta A.M.,Consultoria de Servicos | Vounatsou P.,Swiss Tropical Institute
PLoS ONE | Year: 2010

The 2006-2007 Angola Malaria Indicator Survey (AMIS) is the first nationally representative household survey in the country assessing coverage of the key malaria control interventions and measuring malaria-related burden among children under 5 years of age. In this paper, the Angolan MIS data were analyzed to produce the first smooth map of parasitaemia prevalence based on contemporary nationwide empirical data in the country. Bayesian geostatistical models were fitted to assess the effect of interventions after adjusting for environmental, climatic and socio-economic factors. Non-linear relationships between parasitaemia risk and environmental predictors were modeled by categorizing the covariates and by employing two non-parametric approaches, the B-splines and the P-splines. The results of the model validation showed that the categorical model was able to better capture the relationship between parasitaemia prevalence and the environmental factors. Model fit and prediction were handled within a Bayesian framework using Markov chain Monte Carlo (MCMC) simulations. Combining estimates of parasitaemia prevalence with the number of children under 5 we obtained estimates of the number of infected children in the country. The population-adjusted prevalence ranges from 3:76% in Namibe province to 32:65% in Malanje province. The odds of parasitaemia in children living in a household with at least 0:2 ITNs per person was by 41% lower (CI: 14%, 60%) than in those with fewer ITNs. The estimates of the number of parasitaemic children produced in this paper are important for planning and implementing malaria control interventions and for monitoring the impact of prevention and control activities. © 2010 Gosoniu et al.

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