Onchocerciasis (AKA river blindness), caused by the parasitic worm Onchocerca volvulus and spread by the black fly (Figure 1), affects over 17 million people (1). Although pharma giant Merck has committed to donating the antiviral ivermectin until the disease is eliminated, diagnosis remains a big problem. Current testing methods are time-consuming and painful, leading some patients to avoid them altogether. Researchers at the global non-profit organization PATH believe a simple, less invasive alternative is needed to get rid of the debilitating disease for good – so they’ve released one.
Onchocerciasis causes itching, skin lesions, visual impairment and often blindness. The ocular pathology is caused by the worm releasing microfilariae (MF) into the bloodstream of the host; they travel through the scleral and subconjunctival tissues to the cornea, where they die and release bacteria causing inflammation, damage, and eventually blindness. Some patients will have worms visible in their eyes, but not all those infected will present in this manner. The current gold standard diagnostic is a skin snip examined for worms in saline solution, but this test can have poor sensitivity if MF levels in the skin are low, so a negative result will require DNA extraction and PCR analysis. This multi-step method takes time and requires a painful skin biopsy, causing some at-risk individuals or even whole communities to avoid it. Finding a better way to diagnosis the disease could be critical, and PATH believe they have found an answer: their IgG4 rapid test, which requires just a straightforward fingerprick. The sample is run through an immunochromatographic assay, and a result is presented in under 20 minutes.
David Kaslow, PATH vice president of product development, thinks the test could prove to be a game-changer: “The proven technology behind this test makes it a powerful and reliable tool in the multinational collaboration to eliminate river blindness. The availability of a rapid, point-of-care diagnostic is a harbinger of a world free of the suffering caused by this insidious parasite.
“What’s needed now is quick action to add this simple test to control and elimination programs.”
The US Centers for Disease Control and Prevention, however, is less effusive, stating, “These tests cannot distinguish between past and current infections, so they are not as useful in people who live in areas where the parasite exists, but they are useful in visitors to these areas” (2).
It’s not a bug, it’s a feature, say PATH: by detecting unique antibodies to the parasite, it quickly identifies previous exposure (3). Perhaps that’s not the point. Although river blindness has been eliminated from many regions of Africa (4) and scores of people have been successfully treated with ivermectin, many have not. A rapid, reliable method that doesn’t require skin biopsy, should definitely aid screening – and as that’s the first step on the path to eliminating this pernicious disease, it’s certainly a commendable endeavor on the part of PATH.
Newsletters
Receive the latest pathology news, personalities, education, and career development – weekly to your inbox.
References
- World Health Organization, “Neglected Tropical Disease – Onchocerciasis Control,” accessed Dec 08, 2014, http://bit.ly/1BvJ8FJ. Centers for Disease Control and Prevention, “Parasites – Onchocerciasis (also known as River Blindness),” Updated May 21, 2013, accessed Dec 08, 2014, http://1.usa.gov/1wbcUen. PATH, “New Test Will Combat Major Cause of Preventable Blindness in Africa”, November 2, 2014, http://bit.ly/1sf05fg. K.L. Winthrop et al., “River Blindness: An Old Disease on the Brink of Elimination and Control”, J. Glob. Infect. Dis., 3, 151–155 (2011).
