Laboratory diagnosis of Chagas’ disease in immunocompromised patients is based on the same methods used in the immunocompetent population. Diagnostic methods include serological tests and the direct detection of the parasite (Fig. 30.4). However, the knowledge of the natural history of Chagas’ disease is important to determine the stage and to interpret the laboratory findings (Fig. 30.1). The reactivation of Chagas’ disease in an AIDS patient with chronic infection due to T. cruzi includes the following laboratory findings: (1) serological tests to detect specific antibodies to T. cruzi; (2) detection of the parasite in fresh blood by QBC, Strout method, or microhematocrit45; (3) in patients with meningoencephalitis the detection of the parasite by microscopic examination of CSF with Giemsa smear; and (4) the detection of T. cruzi amastigotes with an acute and necrotic inflammatory infiltration in tissue by biopsies obtained in patients with chagomas or myocarditis.46
Reactivation of Chagas’ disease in AIDS patients are usually associated with the detection of T. cruzi trypomastigote forms by direct microscopic examination of
Figure 30.4 Diagnosis algorithm of focal brain lesions in AIDS patients.
blood. High levels of T. cruzi parasitemia can precede the clinical manifestations or may be found later, during the reactivation. The dynamics of T. cruzi parasitemia in HIV-coinfected patients may play an important role in the reactivation of the disease. T. cruzi parasitemia was detected more frequently in HIV-seropositive patients with chronic Chagas’ disease than in HIV-negative individuals. HIV-coinfected patients also had higher levels of parasitemia.47 According to the number of triato- mines fed, Sartori et al.47 classified the parasitemia level in three categories: (1) very high parasitemia; (2) high parasitemia; and (3) low parasitemia when trypomastigotes of T. cruzi were detected by direct examination of blood or CSF.
More recently, different studies have reported a higher sensitivity of polymerase chain reaction (PCR) to detect the DNA of T. cruzi in laboratory samples. PCR appears to be a specific and highly sensitive laboratory method to inform the number of DNA copies present in the sample examination.20,48 In order to investigate the reactivation of T. cruzi infection in immunosupressed patients, in 2005, the Brazil Consensus of Chagas’ disease proposed that PCR should be performed directly from the patient’s fresh blood.49
In patients with AIDS, the differential diagnosis between acute encephalitis due to T. gondii and T. cruzi may be difficult; in this context, PCR in peripheral blood and brain tissue obtained by stereotactic biopsy, provided a rapid differential and sensitive diagnosis method of T. cruzi reactivation, allowing the prompt administration of specific therapy which can modify the poor prognosis of this kind of patients.50
Qualitative parasitological techniques, such as xenodiagnosis and hemoculture (the gold standard of laboratory Chagas’ disease diagnosis), have a low value in AIDS patients with suspected Chagas’ disease reactivation (Fig. 30.5).51
Figure 30.5 Laboratory diagnosis of suspected Chagas’ disease reactivation in AIDS patients.
Source: Taken from Almeida Braz, LM, Amato Neto V, Okay TS. Reactivation of Trypanosoma cruzi infection in immunosupressed patients: contributions for the laboratorial diagnosis standardization. Rev Inst Med trop S Paulo 2008;50:65-6.52