Evaluation of the xenodiagnosis of chronic Chagas patients infected ten years or over in an area where transmission has been interrupted - Iguatama and Pains, west Minas Gerais State, Brazil

Abstract

To evaluate the results of xenodiagnosis in chronic Chagas patients infected for ten years or over in an area where transmission has been stemmed as well as the performance of these tests applied one or more times to determine the presence of the parasite in serum-positive patients for Trypanosoma cruzi infection, 570 xenodiagnosis were performed in 246 patients by exposing each patient to 40 Triatoma infestans nymphs of 3rd/4th stage once, twice or three times, at 30 days intervals. The 570 xenodiagnosis showed overall positive results in 50.7% with a peak 78% in patients under 20 years of age, and 60.5% in those over 60. Of the 158 patients who underwent three xenodiagnosis, 51 (32.3%) had three positive tests, 48 (30.3%) had all negative results, and the remainder had alternating positive and negative findings. There was no difference in number of positive results between the 1st, 2nd and 3rd tests; however, the 1st and 2nd trials added up to 53.2% and the sum total of all three trials was 57.7%.

Xenodiagnosis

“…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...…”

“…By the use of XD as a tool, interesting studies have been carried out (Dias 1935, Neghme & Schenone 1962, Schenone et al 1968b, Coura et al 1991.…”

Changes in the hemoculture methodology improve the test positivity

“…Due to low levels of circulating parasites in the chronic phase of the disease, xenodiagnosis and hemoculture are more commonly used. These indirect methods are highly specific, but in general their sensitivities are rather low (Schenone et al 1974, Coura et al 1991, Chiari 1992. The Table summarizes some hemoculture and xenodiagnosis results as described in literature.…”

Diagnosis of Trypanosoma cruzi chronic infections in humans: usefulness of the complement regulatory protein antigens and lytic antibodies in the control of cure

“…Its drawn back is the invasiveness represented by the need of hundreds of bites when the vector feeds on the patient, and injects saliva, resulting in local allergies. Although such problem is easy to overcome by artificial feeding through membranes an additional problem is the use of serial xenodiagnosis, proven to increase the test positivity from 30-40% in one test (Schenone et al 1974) to about 70% in three tests (Coura et al 1991).…”