Image: Photomicrograph of the protozoan parasite Trypanosoma cruzi in a thin blood smear (Photo courtesy of the CDC - Centers for Disease Control and Prevention).
Two molecular tests have been evaluated for the diagnosis of American trypanosomiasis or Chagas disease, caused by the etiological agent Trypanosoma cruzi.
Accurate diagnosis of Chagas disease is challenging due to the latent character of the infection, while the parasite load in the blood of acute phase patients is generally high enough to be detected by microscopic analysis of blood smears or buffy coat in microhaematocrit capillaries. However, only 1% to 2% of all infected individuals are actually diagnosed during this phase.
Scientists at the Institute of Tropical Medicine (Antwerp, Belgium) performed a prospective study with participants classified as healthy endemic controls or Chagas disease patients based on the results of the reference tests. They developed a new prototype test based on kinetoplast DNA (kDNA) detection. The evaluated this test and another satellite DNA test in a multi-cohort study with 187 chronic Chagas patients and 88 healthy endemic controls recruited in Argentina, Chile, and Spain and 26 diseased non-endemic controls from the Democratic Republic of Congo and the Sudan. The participants were recruited between 2009 and 2012.
The following tests were evaluated in the study: the T. cruzi satDNA OligoC-TesT kit (Coris BioConcept; Gembloux, Belgium) which contains all the components needed for performing the polymerase chain reaction (PCR) and the product analysis is by dipstick; and the Coris BioConcept’s T. cruzi
kDNA OligoC-Test, which is almost identical to the satDNA OligoC-TesT except that the primers target the conserved region of the T. cruzi
The investigators found that that the T. cruzi kDNA OligoC-TesT, detected between 0.4 and 40 parasites/mL which corresponds with 0.02 to 2 fg DNA per µL, had a higher analytical sensitivity than the T. cruzi satDNA OligoC-TesT. Specificities of the two T. cruzi OligoC-TesT prototypes were high on non-endemic and endemic controls. Sensitivities were moderate, but statistically significantly higher for the kDNA OligoC-TesT compared to the satDNA OligoC-TesT.
The authors concluded that in the next phase, the kDNA OligoC-TesT should be evaluated in specific niches where standard serological tools have their limitations, for example, diagnosing newborns and human immunodeficiency virus (HIV) co-infected patients and follow-up after treatment. The study was published on January 2, 2014, in the journal Public Library of Science Neglected Tropical Diseases.
Institute of Tropical Medicine