An international clinical trial, coordinated by the Tropical Medicine and International Health Unit at Vall d'Hebron University Hospital, has proposed a new treatment approach for Chagas disease. The aim of the study, published in Lancet Infectious Diseases, is not to change the medication given, but to modify the administration strategy to achieve a treatment that is just as effective, but which causes fewer side effects and dropouts.

The World Health Organisation estimates that six to seven million people worldwide are currently affected by the disease. Although about one third of untreated patients may develop life-threatening conditions, less than one per cent of those affected have access to treatment. This low coverage is due to multiple causes, one of them being the complexity of providing and maintaining a two-month course of treatment with a high rate of side effects in remote regions where most patients are located.

The study tested three different dosing schemes for Benznidazole, an antiprotozoal that is one of the most widely used drugs in the treatment of Chagas disease. One third of the patients were given the standard regimen, a dose of 300 mg every 24 hours for 60 days; the second group had the dose halved (150 mg), but the duration of treatment was maintained; the last group received more medication (400 mg dose) but only for 15 days. All three interventions had similar efficacy rates, around 60%, a success measured by a sustained absence of parasites in the blood. The difference was seen in the dropout rate due to side effects: in the short treatment it was only 2%, much lower than the 9% in the half-dose group and the 14% in the standard treatment.

Dr Israel Molina, head of the Tropical Medicine and International Health Unit at Vall d'Hebron and head of the infectious diseases group at Vall d'Hebron Institute of Research (VHIR), explains that 'having a much shorter treatment with the same efficacy and lower toxicity means increasing its accessibility to many more patients, as well as decreasing the cost to health systems'. However, he points out that a phase three clinical trial is needed to confirm that the treatment is equally effective.

The Brazilian variant may be more resistant to treatment

One of the other variables analysed in the trial was whether the place where the disease was contracted had an effect on the response to treatment. Chagas disease is caused by infection by the Trypanosoma cruzi parasite, which is found in some kinds of bedbugs in South America. The parasite has different regional variants, which could theoretically affect its response to the drug.

To analyse this variable, patients were recruited in different countries, Colombia, Argentina, Brazil and Spain (with Bolivian population). In general, the Brazilian population group performed worse than the other groups, with an efficacy between 5 and 15%, while the rest were around 70%. Although there is no clear answer to explain this phenomenon, it is hypothesised that some kind of genetic variation in the parasites in that region makes them more resistant to the drug. Further studies will be needed to confirm this hypothesis and to discover the exact causes of this reduced efficacy of the treatment.