Xenodiagnostico, hemocultura e teste de lise mediada pelo complemento, como critérios de seleção de pacientes chagásicos crônicos para quimioterapia

Abstract

RESUMOO tratamento etiológico da doença de Chagas é iniciado geralmente apenas quando se dispõe de um diagnóstico parasitológico positivo. Na tentativa de aumentar o número de candidatos assim selecionados para o tratamento específico, estuda¬ mos 36 pacientes chagásicos crônicos associando o xenodiagnóstico, a hemocultura e o teste de lise mediada pelo complemento, em duas séries sucessivas, intercaladas de um mínimo de 60 dias. A sensibilidade do xenodiagnóstico e da hemocultura foi respectivamente de 30,5% e de 8,3% na primeira série e de 36,1% e de 19,4% nas duas séries. Em pacientes com infecção chagásica aguda, a comprovação da parasitemia é feita por métodos diretos de relativa simplicidade, pois o número de parasitas quase sempre é elevado.

Xenodiagnosis

“…These contributions have stressed on different aspects of it: (a) generalities (Dias 1934a, Mazza 1938, Talice 1944, Schenone et al 1968a, Salgado 1969, Cerisola et al 1974, Neal & Miles 1977, Pereira VL et al 1989); (b) quality and number of XD kits and species, instar and number of insects to be used: according to the best of available information there have been neither uniform criteria for quality and number of kits nor for the instars and number of bugs to be used and duration of its application. Thus, a XD unit, considered as routine or natural XD, in summary, has consisted in one kit (one unit), commonly a cylindric pot of varied material, holding 5-10 nymphs of laboratory reared local triatomine species, applied on the skin surface of the individual for about 30 min.…”

“…To each of 109 children 0-10 yearold, with positive serology for T. cruzi infection who were going to receive specific treatment, a pair of XD kits was applied resulting 65 (59.6%) positive, figures that increased to 82 (75.2%) when an additional pair of kits was applied to those who had resulted negative (Schenone 1998). Several authors consider that one XD consists in the simultaneous application of 40 triatomine nymphs distributed into four containers with batches of 10 insects each, method with a good yield, but for us, consisting in the use of four XD kits simultaneously (Pereira JB et al 1989, 1996, Pereira VL et al 1989, Coura et al 1991, Menezes et al 1992, Medeiros et al 1994. In some instance, authors have referred to one XD with 90 insects and one XD with 120 insects (Bronfen & Alvarenga 1991); (c) blood ingestion and mortality of insects utilized in XD: it is necessary to consider that not all the nymphs used in the XD are going to produce suitable material for the microscopical detection of T. cruzi because a proportion of them does not suck blood when are applied on the skin of patients, and another proportion dies during the laboratory maintenance periods before examinations, proportions that, in average, reach to 20.5 and 7.3% respectively (Bronfen & Alvarenga 1991).…”

“…According to Santos et al (1995), it has a higher positivity than routine or natural method. Particularly interesting is the post mortem artificial XD performed in blood collected from corpses during autopsy, with a preliminary 30% positivity in individuals whose serological tests for Chagas disease -performed previously to XD -were positive (Lopes et al 1986); (e) technique for obtaining the substratum to be examined: abdominal compression (Schenone et al 1968a, 1969, 1974, Pereira JB et al 1989, Pereira VL et al 1989, Coura et al 1991; intestine dissection, grinding and homogenization (Perlowagora-Szumlewicz et al 1982, Bronfen et al 1989, Bronfen & Alvarenga 1991, Menezes, 1992; liquefaction of the whole insect, filtration of resultant material through cotton, and centrifugalization (Maekelt, 1964, Rohwedder et al 1970, Cedillos et al 1982a); examination of contents:individual (Cedillos et al 1982a, Pereira JB et al 1989, Bronfen & Alvarenga 1991, Coura et al 1991, Menezes et al 1992) and pooled (Schenone et al 1968a, Bronfen et al 1989); (f) apparently sensitivity of XD can be improved by the so-called xenoculture which consists in sowing the intestinal contents of the triatomine nymphs used in it in a modified LIT medium (Bronfen et al 1989); (g) reading: must be done by well trained and skilled personnel. It is highly advisable to have in mind the eventual finding of T. rangeli and/ or Blastocrithidia triatomae in the intestinal contents of triatomines (Cerisola et al 1971a, Cedillos et al 1982a); (h) interpretation of results: a positive XD in a suspected individual (clinical picture, positive serology and/or epidemiological antecedents) means T. cruzi infection and may confirm a chagasic etiology, but a negative XD no necessarily indicates abscence of the parasite and the need of repeating the exam (Freitas 1952, Castro et...…”

“…Since the 70s XD has systematically been used as a relaible tool for the selection and evaluation of patients who have received specific chemotherapy for Chagas disease (Schenone et al 1970, Cançado et al 1973, Cerisola et al 1977, Pereira VL et al 1989, Schenone 1998.…”

Serological diagnosis of Chagas disease with purified and defined Trypanosoma cruzi antigens

“…So far, the unique test described to control the parasitological cure of treated chagasic patients is the lysis of bloodstream trypomastigotes mediated by complement (Krettli et al 1982). However, several groups point many methodological difficulties for the inclusion of that test in the routine of clinical laboratories (Pereira et al 1989). For this reason, the search of specific antigens and/ or alternative tests remains important for the follow up of the chagasic patients after drug treatment (Almeida et al 1991, Norris et al 1994, Krautz et al 1994, Levy et al 1996.…”