Traditional testing for river blindness, a neglected tropical disease that World Health Organization aims to eradicate, is not as sensitive as it could be.
Onchocerciasis, also known as river blindness, is a parasitic disease endemic in Africa and parts of Latin America. It is caused by infection with the parasitic worm Onchocera volvulus, which occurs after a black fly bite (black flies breed near fast-moving bodies of water, hence the name), and it can cause loss of vision in those most severely affected.
Onchocerciasis is 1 of 13 neglected tropical diseases that the World Health Organization (WHO) has targeted for elimination. Roughly 17 million people are currently infected in Africa and parts of the Middle East and Latin America, and more than 205 million people in sub-Saharan Africa alone are at risk of infection. There is no vaccine, although several are in development.
Diagnosis of onchocerciasis typically involves assessing the antibody response to the parasitic antigen OV-16. However, the sensitivity of tests measuring the antibody response to OV-16 hovers around 60% to 80%, meaning a substantial number of people who are infected are not properly diagnosed. With this in mind, a team of investigators based out of the National Institutes of Allergy and Infectious Diseases’ Laboratory of Parasitic Diseases in Bethesda, Maryland, conducted a study that tested a multitude of novel proteins potentially improving blood testing for onchocerciasis. The study, which was published in The Journal of Infectious Diseases, revealed 2 new diagnostic tools that are particularly promising—assays known as OVOC10469 and OVOC3261.
The investigators used human serum samples from subjects infected with onchocerciasis and other parasitic diseases, along with uninfected individuals acting as controls, to test the efficacy of various proteins. Combining OV-16 with either OVOC10469 or OVOC3261 resulted in sensitivity of 88%, while using both novel assays in conjunction with OV-16 raised the sensitivity to 94%.
Because the focus on onchocerciasis has shifted from control to elimination, it’s crucial that the scientific community come up with more accurate tests that can determine exactly who is infected so they can be started on treatment. It’s also important that diagnostic tools be useful for long-term surveillance so previously infected subjects can definitively be declared parasite-free after treatment.
Quality assurance and control also need to be taken into account, according to Charles Mackenzie, PhD, a pathologist with expertise in tropical disease at the Neglected Tropical Diseases Support Center in Decatur, Georgia, who authored a commentary on the study noting that any new diagnostic tools will be tested “against a range of different parasitological conditions.”
“[We need] a reliable, easily used, point-of-care, heat-stable, rapid diagnostic test,” Mackenzie told Contagion®, adding that cost would also be a factor.
Mackenzie expressed optimism about new rapid diagnostic tools (RDTs) helping to eliminate the disease in areas currently affected. “This is 1 of the first demonstrations towards a more sensitive RDT and thus more accurate diagnosis, and is an improvement on a test where at least 20% of people are biologically excluded (ie, are missed in terms of detection),” he said.