Project Lead(s): Maggy Sikulu
Between 2000 and 2015, malaria incidence rates (new malaria cases) fell by 37% globally, and by 42% in Africa.
Although several factors might have contributed to this sharp decline, vector control, mainly through use of indoor residual spraying (IRS) and the mass distribution of insecticide treated nets (ITNs) have played a major role.
Despite the use of ITNs, there were 214 million new cases of malaria worldwide in 2015, with an estimated 438,000 malaria-related deaths.
Since the disease can only be transmitted by Anopheles mosquitoes that are at least 10 days old, the ability to tell the age and abundance of the vectors is key to identifying transmission hot spots. However, available age and species prediction techniques are time-consuming and costly for resource-limited areas.
The main objective of this study was to use a low-cost near-infrared spectroscopy (NIRS) to estimate age and distinguish morphologically identical major African malaria vectors (Anopheles gambiae and Anopheles arabiensis).
The project team compared the accuracy of a recently developed tool (the NIRS) for prediction of the age of An. gambiae and An arabiensis to the existing gold standards, which involves dissection and observation of the unwinding of ovarial tracheoles to enable a crude determination of whether mosquitoes have previously laid eggs or not.
The ability of NIRS to differentiate morphologically identical An. gambiae from An. arabiensis was compared against the polymerase chain reaction (PCR) technique.
Mosquitoes were collected in four villages from Ulanga district, SE Tanzania, using CDC light traps, three villages in Muleba region North Tanzania using tent traps and three villages on Pemba Island using pit traps.
Female mosquitoes identified as Anopheles gambiae complex were scanned using a LabSpec 5000 NIR spectrometer (ASD Inc, Boulder, CO).
NIRS predicted the age of wild-caught An. arabiensis and An. gambiae s.s with an accuracy rate of 92%. Compared to PCR, NIRS differentiated wild-caught members of the An. gambiae complex s.l. with an average accuracy of 83%.
In one day, NIRS can estimate the age and species of approximately 1,000 mosquitoes.
To date, this is the only tool that has the capacity to predict mosquito age and differentiate cryptic species simultaneously.
In terms of costs, NIRS was over 35 times cheaper and 10 times faster than PCR and dissections.
The models developed during this study require further validation in other jurisdictions and the project team plans to apply for Phase II Transition To Scale funding.
The research team feels the product could be one of the new tools that could be used to effectively detect transmission hotspots to close the gap in controlling residual mosquito-borne disease transmission..