By Corrado Minetti
On my way back from Ghana, where we have been testing the molecular protocols for the detection of filarial parasites in mosquitoes, in the laboratory of Mike Osei-Atweneboana at the Council for Scientific and Industrial Research (CSIR) in Accra; I had some thoughts about how far molecular diagnostics has come but also questioned how can we make it a sustainable reality to assist effectively in disease control and elimination.
DNA extraction from pooled mosquitoes for the detection of filarial worms (on the left) and an example of amplification of parasite DNA (+) with the LAMP method (on the right) (Photo: Corrado Minetti)
In order to achieve the goals of the London Declaration on Neglected Tropical Diseases for the effective and sustainable control and long term elimination of Lymphatic Filariasis, onchocerciasis, soil-transmitted helminthiasis and schistosomiasis; the deployment of appropriate diagnostic tools is crucial at every stage of these disease control and elimination programmes from initial mapping to post-elimination surveillance. With the rapidly changing epidemiological scenario of these diseases due to the scaling up of mass drug administration, and the push towards more sustainable and cost-effective multi-disease interventions, the implementation of more sensitive and cost-effective diagnostic tools is a priority well recognized and advocated by the World Health organization.
Molecular diagnostics tools, including (multiplex) real-time polymerase chain reaction and more recent isothermal amplification assays such as loop-mediated isothermal amplification and recombinase polymerase amplification do offer increased sensitivity compared to traditional approaches but they are yet to be used in control and elimination programmes due to their cost and technical requirements. There are various gaps that need to be highlighted and solved in order to allow these approaches to become potentially embedded into disease control programmes & policies, and to inform decision-making.
In order to identify these much-needed gaps, we have recently published a review paper where we compared the features of published real-time PCR and isothermal amplification assays for the detection of Lymphatic Filariasis, onchocerciasis, soil-transmitted helminthiasis and schistosomiasis in clinical and vector/intermediate host samples. Despite the availability of a wide range of assays for both patient diagnosis and xenomonitoring (parasite detection in insect vectors or snails), little or no research has been devoted to estimate the real costs and logistics of implementing these approaches on a wider scale for control and elimination. We highlight the need for a major focus on the implementation aspects of these tools in developing countries, and how barriers for their full adoption in resource-poor settings could be overcome. Key issues are the technical requirements and the related need for capacity building, the abatement of costs and the economic sustainability of molecular screening over time. For example, diagnosing multiple parasites from the same clinical sample can heavily reduce the number of samples that a community may need to provide, resulting in a far less invasive procedure for the communities, as well as reducing significantly the cost of processing. A multi-disease approach to diagnostics will certainly benefit the health system as well, both logistically and economically.
Writing this review paper has been extremely valuable to get a clearer picture of the progress in the field so far and to identify the best and most cost-effective diagnostic approaches for our project. In a broader sense and within the COUNTDOWN research consortium, we hope this review could serve as a starting point of discussion in the NTDs control and elimination community, leading to a more comprehensive analysis of what molecular diagnostics can offer and how we can make sure these tools can finally get out from the laboratory becoming embedded into policy, to strengthen disease control and elimination programmes and the health system itself.