Project Lead(s): Palmer Netongo
Issue
Despite intensified control efforts, an estimated 438,000 people died of malaria in 2015, with 90% of these deaths occurring in Sub-Saharan Africa. Worldwide, the number of new episodes of clinical malaria in 2015 was estimated to be around 214 million.
Tracking cases and attacking the parasite reservoir among “asymptomatic” individuals is critical for elimination of malaria in areas where the disease is endemic.
Surveillance is particularly difficult because diagnosis currently relies on identifying malaria parasites by microscopy and detecting soluble parasite antigens using Rapid Diagnostic Tests (RDT). These techniques do not detect low-level, sub-clinical malaria infections, and are inherently hazardous and invasive.
Solution
The object of this project was to develop a homemade, non-invasive, thermos-stable, saliva-based, field-adaptable molecular method for nation-wide surveillance of malaria in Cameroon and Senegal.
The approach involved developing a method of collecting and stabilizing plasmodium DNA from saliva, coupled with a molecular method for parasite detection using Loop mediated Isothermal DNA Amplification (LAMP) which can be conducted in resource-limited laboratories.
The homemade, saliva-based LAMP test was compared to conventional PCR on saliva collected in commercial saliva kits produced by Canada’s DNA Genotek Inc. Sensitivity of the saliva-based detection of the malaria parasite DNA was also compared to blood, using standard molecular methodology with 624 blood and saliva samples.
Outcome
The team successfully demonstrated that it is possible to detect sub-clinical malaria (parasites that cannot be detected using a microscope) in saliva using homemade LAMP technology, with results comparable to those from commercially available molecular kits.
Of the 624 participants tested in Cameroon, PCR on saliva collected in the Genotek kits was able to detect 33 of the 44 sub-microscopic infections detected by blood PCR. This constituted 75% of all sub-microscopic infections.
When homemade or field-adapted LAMP on saliva samples was compared to standard saliva PCR, the observed agreement was 69%, against an expected agreement of 60.2%.
The sensitivity of the test was 70.3%, with a positive predictive value of 90.8% and a specificity of 62.5%, with a negative predictive value of 28.5%.
The project team also surveyed 764 patients on the use of saliva to test malaria and found 98% of them preferred this approach to taking blood samples.
Results of the research was presented in a policy brief, with team members also attending the International Network of Research Management Societies (INORMS) conference in Melbourne, Australia, and the 8th European & Developing Countries Clinical Trials Partnership (EDCTP) Forum in Lusaka, Zambia.