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Long Term Evaluation of Etiological Treatment
of Chagas Disease with Benznidazole

J. Romeu Cançado

Departamento de Clínica Médica, Faculdade de Medicina da Universidade Federal de Minas Gerais (UFMG)
Belo Horizonte, MG, Brasil.
Ambulatório de doença de Chagas, GEN-CAD, Hospital das Clínicas, (UFMG)



The aim of this article is to present an investigation of cure rate, after long follow up, of specific chemotherapy with benznidazole in patients both in acute and chronic phase of Chagas disease, applying quantitative conventional serological tests as the basis of the criterion of cure.

Twenty-one patients in acute form and 113 in the various chronic clinical forms of the disease were evaluated, after a follow up period of at least 13 years, the acute, and 6 years, the chronic.

The duration of the acute as well as the chronic disease, a condition that influences in the results of the treatment, was determined.

Quantitative serological reactions of complement fixation, indirect immunofluorescence, indirect hemagglutination, and, occasionally, ELISA, were used.

Cure was found in 76 per cent of the acute patients and only in 8 per cent of those in chronic forms.

Bearing in mind such opposite findings, a discussion is followed on the fundamentals of the etiological therapy of Chagas disease, like the criterion of cure, the pathogenesis and the role of immunosuppression showing tissue parasitism, in support of the concept that post-therapeutic consistently positive serological reactions mean the presence of the parasite in the patient's tissues.

Adverse reactions to the drug were considered.

In relation to the life cycle of T. cruzi in vertebrate host, there are still some obscure and controversial points, but there is no proof of the existence of resistant or latent forms. However, the findings over the last 15 years, that immunosupression brings about the reappearance of acute disease in long stand chronic patients justifies a revision of the matter.


Since 1962, we examined, at the University Hospital and in private practice, in Belo Horizonte, MG, Brasil, 2.405 Chagas disease patients, 47 with the acute form and 2.358 in the various chronic clinical forms5,7. Several academic theses and controlled clinical trials, as well as many research articles, in collaboration with other authors, have already been published, most of them referred to elsewhere 6,7,9.

The objective of this article is to evaluate, after a long follow up period, the results of specific chemotherapy with benznidazole of patients treated, both in the acute and in the chronic phase of the disease, applying conventional quantitative serological tests as the basis of the criterion of cure.8


PATIENTS. Acute form. Table 1 displays data of 21 patients in the acute phase of Chagas disease, treated with benznidazole, from 1974 to 1982.

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Eligible patients included 15 men and 6 women, ranging from two to 60 years old, who fulfilled two basic conditions:

  1. Benznidazole was the only drug used for at least 32 days, consecutively or with short interval
  2. Periodic post-therapeutic examinations were done for a long follow up period of at least 13 years.

The author, in the University Hospital treated all patients.

Chronic form. From among the many hundreds of patients treated in the chronic phase, 113 were selected, by alphabetical order, because they filled up the two following requirements:

  1. Benznidazole was the only drug used for at least 40 consecutive days
  2. Periodic post-therapeutic examinations were done for 6 to 18 years though with different intervals (table 2).

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The author in the Outpatient Clinic treated them; 56 were male, 57, female, the youngest was 9 years old and the oldest, 69. They were in the different chronic clinical forms, as disclosed in table 3.

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Therapeutic schedule. Daily dose of benznidazole varied from 5 to 10 mg/kg/day, given in equal fractions with variable intervals of 6, 8 or 12 hours, consecutively or with a short pause, for different reasons. In 73 patients the treatment was repeated, once, twice or even three times. The duration of the treatment was at least 40 days, while in one patient it reached 94 days.

Duration of the chronic disease. The duration of the chronic disease at the beginning of the treatment was determined. At first sight, it seems impossible, because usually the chronic patient ignores when he was infected, since the acute phase may go unnoticed. Nevertheless, in the majority of the patients the duration may be disclosed, if not exactly at least approximately, by checking at the anamnesis, the time elapsed after the patient moved away from the endemic area to live in the city, where there is no transmission of the disease. Thus it was possible to know the minimal duration of the disease in 88 of the 113 chronic patients and in 45 of them (52%) it was above 20 years when treatment was started.

Inform consent was obtained from adults and from the parents, in case of children.

METHODS. Previously to treatment, the patient was subjected to clinical examination, conventional quantitative serological reactions, parasitological examination (xenodiagnosis or hemoculture), electrocardiogram and x-ray of the thorax, in two positions (postero-anterior and in profile with contrasted esophagus).

Conventional quantitative serological tests were the complement fixation (CF),23,27 indirect immunofluorescence (IF)17, indirect hemagglutination (HA)25 and lately the Enzyme-linked immunosorbent Assay (ELISA)31.

Not every patient made all the above mentioned essays. For instance, in the first years, serology consisted of quantitative CF only, according to the technique of PEDREIRA de FREITAS e ALMEIDA27, in parallel with qualitative technique done in another laboratory. Since 1972, quantitative IF and HA tests were added.

Parasitological examination was the standardized xenodiagnosis12 up to 1983, when it was replaced by hemoculture.19

All laboratory tests were done in research institutions, (Instituto de Ciências Biológicas, UFMG, and Centro de Pesquisas René Rachou) in Belo Horizonte, MG, Brasil by techniques adopted by their investigators. During some time serum was collected at the hospital and sent to the laboratory with a number. In general, the drug was bought in the city drugstores.


The results of the treatment with benznidazole of the 21 patients in the acute phase of Chagas disease, based in the post-therapeutic behavior of quantitative serological reactions of CF, IF, and HA are abridged in table 1.

From 21 treated patients, 16 (76%) presented complete and definitive negative tests in the follow up period of at least 13 years (patient nº 34 died from cancer when follow up was of 9 years). They were considered cured of the infection, while in five patients the serological tests persisted regularly positive and they were taken as failure.

The results of the treatment of 113 patients in different chronic forms of the disease are condensed in table 4. In only 9 patients (8%), post-therapeutic serological tests became completely and consistently negative, indicating cure.

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In 17 patients (15%) the results became oscillating, sometimes negative sometimes positive. So they were considered doubtful cases.

The remainder 87 patients (77%) showed the post-therapeutic serological tests consistently positive, and so they were classified as failure.

The marked difference between results in acute and in chronic cases is discussed ahead.


We discard parasitological tests (xenodiagnosis and hemoculture) as basis of the criterion of cure of American trypanosomiasis because in the long standing chronic disease, negative results obtained with them, even when repeated many times over a long period, by themselves, without taking in account the results of serological tests, do not indicate parasitological cure, as they may reflect only periods of absent or scarce parasitemia6. As pointed out by Villela30, a long time ago, they are aleatory, casual, methods.

On the other hand, serological tests, i.e., the detection of specific serum antibodies against components of Trypanosoma cruzi, are universally accepted for the diagnosis of the disease, since the introduction of the method, in 1913, by Guerreiro and Machado23. New techniques were later developed and nowadays the most common tests which make up conventional serology, in addition to complement fixation (CF), are the indirect immunofluorescence (IF)17, the indirect hemagglutination (HA)25 and the Enzyme-linked Immunosorbent Assay (ELISA)31. These tests use as antigens the parasite extracts of T. cruzi or the whole parasite. As stated by Camargo4, they are safe enough for the screening of blood donors when satisfactorily standardized. Besides being the most sensitive and specific method for the diagnosis of the disease, they are quick, inexpensive, easily done, generally employed and approved as trustworthy, since the discovery of the disease. In our experience8, the sensitivity of CF, IF and HA was 91,5%, 99% and 100%, respectively. Only the complement fixation tests require a more refined technology and reagents, but the other mentioned tests would suffice for the purpose at hand. Positive results conclusively demonstrate the presence of T. cruzi in the patient?s tissues, i.e., Chagas disease. Therefore, we take them as the basis for evaluation of drug efficacy against T. cruzi infection in humans, since the possibility of their becoming negative is the disappearance of the stimulus for specific antibody production: the parasite. Otherwise, it is impossible for a consistent negative conventional serology to coexist with a positive parasitological test, except possibly in the case of immunosuppresion.

As for the results of the treatment, it is obvious in table 1 the high therapeutic efficacy of benznidazole in human acute Chagas disease, cure arriving at 76 per cent of treated patients. This is in accordance with the experience of other authors. Cerisola et al11,13 reported negative serology in 80 per cent of 76 treated children, at the end of one year after treatment. Ferreira15 cured seven from ten treated patients and Rassi et al28 mention 51,6 per cent of cure.

The five patients classified as failure in table 1 showed the three serological tests (CF, IF and HA) uniformly positive all along the follow up period, even after repetition of therapy. Two patients (nº 8 and 41 of table 1) among the five labeled as failure developed cardiomyopathy. As for the titers of the tests, though variable from time to time, they remained in the same pattern of those done before therapy.

The most probable cause of the failure in these five patients is that they were infected by strains of Trypanosoma cruzi naturally resistant to benznidazole, a phenomenon already known2,3,18.

In chronic patients cure was attained in only 8% (table 4), whereas failure achieved 77%.

There is no satisfactory explanation for such marked difference, in comparison with the results of the treatment in acute patients.

Why does chemotherapy cure around three-quarters (76%) of the acute patients and fails in same proportion (77%) of those with long-standing chronic disease?

The first hypothesis that comes to mind is that conventional serology would not be a reliable method to base on the criterion of cure, because it would not change in the long standing chronic disease. Some mechanism have been resorted to explain why CS would continue positive, even in the cured patient: immunological memory, auto-immunity, sequestration of antigens of T. cruzi in cells of the spleen1, presence of determinants of carbohydrates derived from intestinal and pulmonar microflora20 and others.

These hypothesis loose significance by virtue of the demonstration that pathogenesis of American trypanosomiasis depends on the parasite8.

Strongest piece of evidence that the parasite remains in the patient throughout the entire evolutional process of the disease is the reactivation of the infection following heart transplants in cases of terminal chronic chagasic cardiomyopathy29, where the immunosuppressive drugs used results in the reappearance of T. cruzi in blood and tissues. The majority of patients exhibit a return to the acute phase of the disease, with myocarditis in the transplanted heart.

Similarly, non-chagasic patients submitted to immunosuppressive regimes following an organ transplantation (kidney, heart, pancreas, bone marrow) from seropositive donors acquired the infection from the transplanted organ10,14,21.

A further demonstration of the presence of the T. cruzi in chronic patients is the reactivation of the disease in AIDS sufferers, with accompanying meningoencephalitis, myocarditis and other lesions, with high parasite burdens16.

Immunosuppression in chronic Chagas disease patients has revealed reservoirs of amastigotes in quite distinct organs and tissues, such as central nervous system, heart, skin and subcutaneous cellular tissue, esophagus, colon, liver, bone marrow, kidney and others. The parasite, which apparently remained occult, disseminates when the strong and sustained immune response is suppressed8.

Human Chagas disease is a life-long infection. In 45 among 88 chronic treated patients (52%) we ascertained that the duration of the disease was above 20 years. It is well known that a large proportion of chronic chagasic patients lives a normal life and is unaware of their long standing disease. They are taken as healthy persons if a blood test is not done, as it is shown by the many cases of acute disease in non-endemic areas, as Canada and United States, caused by transfusion of blood from Latin America immigrants who lived there sometimes for more than 20 years21,22,24,26.

All the facts strengthen the notion that serological tests are a reliable basis for the criterion of cure in chemotherapy of Chagas disease. So, our finding that 77 per cent our chronic treated patients maintain post-therapy positive serology means that their tissues still harbor the parasite, indeed a therapeutic failure.

In relation to the life cycle of T. cruzi in vertebrate host, there are still some obscure and controversial points. There is no evidence of the existence of resistant or latent forms. However, the finding over the last 15 years, that immunosuppression brings about the reappearance of the acute disease in long standing chronic patients justifies a revision of the matter.

Drug administration. Benznidazole causes various adverse reactions already described in details in previous publications6,7,9.

In practice the most important is a dermatitis from hypersensitivity of the type serum sickness, characterized by skin eruption, generalized edema, fever, lymph nodes enlargement and joints and muscular pains. It appears around the fifth to the tenth day of treatment, usually in the ninth day and is the most relevant adverse reaction to the drug because it is frequent and it hinders the treatment.

Another adverse reaction is a peripheral polineuropathy, which is dose-dependent and therefore preventable.

A third relevant side effect is depression of bone marrow (neutropenia, agranulocitosis and thrombocytopenic purpura). Fortunately, the last two mentioned hematological diseases are extremely rare6,7,9.

Nevertheless, clinical application of benznidazole is a safe procedure, if the physician is aware of the adverse reactions to the drug. Our impression is that this drug, like metronidazole, which causes similar side effects, but even so is largely applied in clinical practice, may be used under close supervision as we have already described7,9.

Finally, though we cannot infer the percentage of cure in the recent disease, two facts show that the duration of the disease have influence on the therapeutical results7,9.

1. Six among the 16 cured acute patients, were cured with the second treatment, one of them five years after the acute phase, therefore in the evident chronic recent phase.
2. Three among the 9 cured chronic patients were adolescents, 9, 10, and 13 years old.



O objetivo deste artigo é verificar o resultado da terapêutica específica com o benznidazole da doença de Chagas aguda e crônica, após prazo longo de seguimento dos pacientes, tomando como base do critério de cura o resultado das reações sorológicas quantitativas.

Foram avaliados 21 pacientes agudos e 113 nas diferentes formas clínicas crônicas, selecionados por terem sido tratados somente com o benznidazole e acompanhados por longo tempo, pelo menos 13 anos os agudos e 6 anos os crônicos.

Anotou-se a duração da doença, tanto aguda como crônica, circunstância que influi no resultado do tratamento.

As reações sorológicas usadas foram a de fixação do complemento, a de imunofluorescência indireta, a de hemaglutinação indireta, e, ocasionalmente, a da ELISA.

Verificou-se a cura em 76 por cento dos pacientes agudos e de apenas 8 por cento dos crônicos.

Tendo em mente esses resultados, discutiram-se pontos duvidosos da terapêutica etiológica da doença de Chagas, como critério de cura, o papel da imunossupressão para o conhecimento da patogenia da doença e as reações adversas ao medicamento.

Com relação ao ciclo vital do Trypanosoma cruzi no hospedeiro vertebrado, há ainda pontos obscuros e controvertidos. Embora não haja prova da existência de formas resistentes ou latentes, a descoberta, ao longo dos últimos 15 anos, de que a imunossupressão desencadeia a doença aguda nos pacientes crônicos de longa duração, justifica revisão do assunto.


To the investigators of the Centro de Pesquisas René Rachou, in the persons of Zigman Brener, Antoniana U. Krettli and Giovanni Gazzinelli, for the permanent collaboration, and to the colleagues of the Hospital das Clínicas da UFMG, especially to Luiz de Paula Castro, for the maintenance of the Ambulatório de Doença de Chagas, the gratitude of the author.



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Correspondence to J. Romeu Cançado, Rua dos Otoni, 927, 6º andar, Belo Horizonte, MG, Brasil CEP: 30.150-270 - Fax: 0(xx)31 3273-4234.
E-mail: Jcançado@terra.com.br
Sponsorship from Fundação Carlos Chagas de Pesquisa Clínica. Belo Horizonte, MG, Brasil.


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