A Chagas urine nanoparticle test (Chunap) has been developed to concentrate, preserve and detect Trypanosoma cruzi antigens in urine for early, noninvasive diagnosis of congenital Chagas disease.

The conventional diagnosis of congenital Chagas disease is based on microscopy at birth and serology at nine months; however microscopy misses many infections and many at-risk infants fail to complete serology at six to nine months.

A team of international scientists led by those at Johns Hopkins University (Baltimore, MD, USA) collected 74 urine samples from Bolivian infants without congenital infection and 23 specimens from infants with congenital infection whose urine collection occurred prior to initiation of antitrypanosomal treatment. Urine samples from 12 seronegative infants from Lima (Peru) were collected as non-endemic negative controls. Blood samples from infants obtained at birth and one month were evaluated by the micromethod, using a microscope, and polymerase chain reaction (PCR).

The screening specimens were tested by two rapid diagnostic tests (RDTs): an indirect hemagglutination test (IHA), and Chagas Detect, an immunochromatographic strip assay (InBios International; Seattle, WA, USA). The team evaluated the ability of the Poly N-isopropylacrylamide nanoparticles functionalized with trypan blue and synthesized by precipitation polymerization and characterized with photon correlation spectroscopy, to capture, concentrate and preserve T. cruzi antigens.

Urine samples from congenitally infected and uninfected infants were then concentrated using these nanoparticles. The antigens were eluted and detected by Western Blot using a monoclonal antibody against T. cruzi lipophosphoglycan. Visualization of antigenic bands was done using an enhanced chemiluminescence system (Supersignal West Dura, Thermo Fisher Scientific; Rockford, IL, USA). The Chunap test was carried out by a laboratory biologist who was also blinded to the Chagas status of the patient.

The nanoparticles concentrated T. cruzi antigens by 100 fold with the western blot detection limit decreased from 50 ng/mL to 0.5 ng/mL. The sensitivity of Chunap in a single specimen at one month of age was 91.3% (21/23) comparable to PCR in two specimens at birth and one month and significantly higher than microscopy in two specimens. Chunap specificity was 96.5%, 71/74 for endemic, 12/12 for non-endemic specimens. The cumulative sensitivity of micromethod and PCR was 34.8% (8/23) and 91.3% (21/23), respectively. Particle-sequestered T. cruzi antigens were protected from trypsin digestion.

The authors concluded that Chunap has the potential to enable early point-of-care diagnosis of congenital Chagas disease in peripheral health facilities. Further steps will be necessary to apply this nanotechnology in developing countries. The team is currently optimizing a novel separation method based on magnetic labeling of capturing nanoparticles to enable particle separation from urine without the need for a high speed centrifuge. Although used in this study for Chagas disease, this method could be adapted for detection of other parasitic infections in urine and other body fluids. The study was published on October 2, 2014 in the journal Public Library of Science Neglected Tropical Diseases.

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Johns Hopkins University 
InBios International
Thermo Fisher Scientific