Quantitative detection of PfHRP2 in saliva of malaria patients in the Philippines
1 Department of Electrical Engineering, University of California, Los Angeles, USA
2 Molecular Shared Screening Resources, University of California, Los Angeles, USA
3 Department of Bioengineering, University of California, Los Angeles, USA
4 , Palawan Baptist Hospital, Roxas, Palawan, Philippines
5 Biomedical Engineering IDP, University of California, Los Angeles, USA
6 David Geffen School of Medicine, University of California, Los Angeles, USA
7 Department of Electrical and Computer Engineering, University of Waterloo, Waterloo, Ontario, Canada
Malaria Journal 2012, 11:175 doi:10.1186/1475-2875-11-175Published: 25 May 2012
Malaria is a global health priority with a heavy burden of fatality and morbidity. Improvements in field diagnostics are needed to support the agenda for malaria elimination. Saliva has shown significant potential for use in non-invasive diagnostics, but the development of off-the-shelf saliva diagnostic kits requires best practices for sample preparation and quantitative insight on the availability of biomarkers and the dynamics of immunoassay in saliva. This pilot study measured the levels of the PfHRP2 in patient saliva to inform the development of salivary diagnostic tests for malaria.
Matched samples of blood and saliva were collected between January and May, 2011 from eight patients at Palawan Baptist Hospital in Roxas, Palawan, Philippines. Parasite density was determined from thick-film blood smears. Concentrations of PfHRP2 in saliva of malaria-positive patients were measured using a custom chemiluminescent ELISA in microtitre plates. Sixteen negative-control patients were enrolled at UCLA. A substantive difference between this protocol and previous related studies was that saliva samples were stabilized with protease inhibitors.
Of the eight patients with microscopically confirmed P. falciparum malaria, seven tested positive for PfHRP2 in the blood using rapid diagnostic test kits, and all tested positive for PfHRP2 in saliva. All negative-control samples tested negative for salivary PfHRP2. On a binary-decision basis, the ELISA agreed with microscopy with 100 % sensitivity and 100 % specificity. Salivary levels of PfHRP2 ranged from 17 to 1,167 pg/mL in the malaria-positive group.
Saliva is a promising diagnostic fluid for malaria when protein degradation and matrix effects are mitigated. Systematic quantitation of other malaria biomarkers in saliva would identify those with the best clinical relevance and suitability for off-the-shelf diagnostic kits.