Point-of-care quantification of blood-borne filarial parasites with a mobile phone microscope

Parasitic helminths cause debilitating diseases that affect millions of people in primarily low-resource settings. Efforts to eliminate onchocerciasisand lymphatic filariasisin Central Africa through mass drug administrationhave been suspended because of ivermectin-associated serious adverse events, including death, in patients infected with the filarial parasite Loa loa. To safely administer ivermectinfor onchocerciasisor lymphatic filariasisin regions coendemic with L. loa, a strategy termed“ testand (not) treat” has been proposed whereby those with high levels of L. loa microfilariae(>30,000/ml) that put them at risk for life-threatening serious adverse events are identified and excluded from mass drug administration. To enable this, we developed a mobile phone–based video microscope that automatically quantifies L. loa microfilariaein whole bloodloaded directly into a small glass capillary from a fingerprick without the need for conventional sample preparation or staining. This point-of- caredevice automatically captures and analyzes videos of microfilarial motion in whole bloodusing motorized sample scanning and onboard motion detection, minimizing input from health care workers and providing a quantification of microfilariaeper milliliter of whole bloodin under 2 min. To validate performance and usability of the mobile phone microscope, we tested 33 potentially Loa-infected patients in Cameroon and confirmed that automated counts correlated with manual thick smear counts (94% specificity; 100% sensitivity). Use of this technology to exclude patients from ivermectin-based treatment at the pointof carein Loa-endemic regions would allow resumption/expansion of mass drug administrationprograms for onchocerciasisand lymphatic filariasisin Central Africa.