New mobile microscopy and software technology may replace slow and tedious manual examinations for Loa loa parasites
The African eye worm, Loa loa, is widely distributed across the rainforests of west and central Africa. Unfortunately, so are other parasites like the Onchocerca volvulus worm, which causes river blindness. And while the loiasis-causing worm is often asymptomatic or causes only mild irritation, many of the other parasites require treatment with drugs like ivermectin to prevent permanent or life-threatening symptoms.
But there is a serious problem: when Loa loa hosts take ivermectin, they can suffer severe adverse effects including encephalopathy, coma and even death (1) – but, until now, there has been no easy way to detect carriers of the parasite. The worms are tiny, and the traditional screening method involves manually counting the number of worms in a blood sample in order to determine if their density is great enough to prompt an adverse reaction to ivermectin treatment. It’s a process so long and tedious that it would be impossible to implement on a large scale. One study determined that sites at the greatest risk of adverse events were those with 20 to 40 percent loiasis prevalence, which are not normally considered high-risk populations because of the small number of people estimated to have high Loa loa densities (2). It’s clear that the relationship between worm densities and adverse risk isn’t fully understood – so one group of scientists from the University of California, Berkeley (CA, USA) decided to eliminate the problem at its source with a rapid screening test to detect the Loa loa worm in blood. Researchers from Daniel Fletcher’s bioengineering group used their own iPhone-based microscopy platform, CellScope, to view magnified blood samples on slides. In conjunction with the CellScope device, they wrote a software program that would detect Loa loa in the blood by analyzing wiggling motions, caused by the shifting of blood cells as worms move between them, during a five-second video. Dubbed CellScope Loa, the technology successfully estimated worm densities in 33 patients, providing similar results to those from the manual test – but with significant advantages. For one, the test can be completed in under two minutes; for another, the result can be tagged with a set of GPS coordinates as well, providing a detailed and accessible geographic record of Loa loa infections. CellScope Loa could greatly improve life for millions of Africans seeking anti-parasite treatment – but only if Fletcher and his group can overcome one obstacle: scaling. At the moment, each device is assembled by hand in their laboratory, so before they can provide the number of devices needed for widespread Loa loa testing, they’ll need to find an industry collaborator interested in taking on the challenge.
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References
- J Gardon, et al., “Serious reactions after mass treatment of onchocerciasis with ivermectin in an area endemic for Loa loa infection”, Lancet, 350, 18–22 (1997). PMID: 9217715. LA Kelly-Hope, et al., “Innovative tools for assessing risks for severe adverse events in areas of overlapping Loa loa and other filarial distributions: the application of micro-stratification mapping”, Parasit Vectors, 7, 307 (2014). PMID: 24992829.
