Evolution of knowledge on the etiological diagnosis of chagasic infection.

Abstract

Very early after the publication of Chagas, in1909, methods for the parasitological diagnosis (xe-nodiagnosis, Brumpt 1914) and serological diag-nosis (Guerreiro & Machado 1913) were alreadyavailable. More interesting, both methods are stillbeeing used, 85 years later. The same method useduntil now for parasitological diagnosis of the acutephase, was performed by Chagas (wet blood smear,as well as animal inoculation). Of course, in themeantime, other techniques became available foretiological diagnosis. We may divide theimprovments in diagnosis in several periods: onthe first, until 1960, diagnosis was performed ba-sically with the same tools, i.e. xenodiagnosis forthe parasitological and complement fixation for theserological diagnosis of the chronic phase. Thesecond period may be delimitated between 1960and 1975, in which major advances were per-formed. For the acute phase, a major advance wasthe Strout method for hemoflagellates (1962), andafter, the microhematocrit, mainly for newbornsand children. Camargo et al. (1974) described theIgM-IFI as a secure method for acute (includingtransfusionally acquired) phase. For the chronicphase, parasitological diagnosis include nowhemoculture (Chiari et al. 1966), disputing sensi-tivity with xenodiagnosis, in a fight that runs untiltoday. Serological diagnosis was firmly established,first with the standardization of the complementfixation reaction (CFR) by Almeida and Fife (1974)and also with the introduction of indirect hemag-glutination (Cerisola et al. 1962) and indirect im-munofluorescence (Camargo et al. 1966), tech-niques that are prefered today to the CFR. The thirdperiod, of, again, major improvments, was from1975 until today. Parasitological diagnosis re-ceived a great help with the PCR amplificationtechniques (Sturm et al. 1989, Moser et al. 1989).Results obtained with hemocultures were improvedafter substancial modifications (Chiari et al. 1989,Luz et al. 1994). Serological diagnosis includedELISA after Voller description (1975), and sev-eral purified antigens started to be used, asGP90kD, GP72kDa, GP25kDa, and shortly after,recombinant antigens and synthetic peptides wereused and evaluated in several multicentric trials(Moncayo & Luquetti 1990, Levin et al. 1991).Easier diagnosis encouraged scientists to monitorchanges after treatment. Recognition that antibodylevels could came down after successful etiologi-cal treatment during the acute phase, and even theirabscence after a period of time, led to search thesame phenomena in recently acquired chronicphase children, with the same results, i.e. abscenceof antibodies against Trypanosoma cruzi after someyears of follow up (Andrade et al. 1996, Sosa et al1998). Today, the same holds for succesfully treatedchronic phase adults, but the follow up should ex-tent to some decades [review in Rev Pat Trop 27(Supl.) 1998]. This is a clear example of theusefullness of laboratory tests in Chagas disease,appart from diagnosis. In this period, other toolsstarted to be used, as the chemiluminescent assay(Almeida et al. 1994) and the fluorescent activatedcell sorter (Martins-Filho et al. 1995).Nowadays, high technology applied on sero-logical techniques allow to use few steps withshorter incubation time, which permit to run anELISA test in less than 1 hr, instead of 8 hr when itwas described. Other assays involve the use of re-combinant antigens in strips, in a single step, withresults in few minutes, as one developed byCYTED-BT (Bialy 1998). Nevertheless, perform-ing two paralel assays is still necessary, since welack of an universal antigen, recognized by all in-fected individuals. Responsability for true resultshas been increasing, avoiding both false positivesor false negatives. Even if parasites are scarce, thetendency to look for circulating antigens with dif-ferent methods, including PCR, will give in the nearfuture, more basis for a true diagnosis.