A newly identified chemical could help to monitor the treatment of a tropical disease that afflicts tens of millions of people.

Onchocerciasis, commonly known as river blindness, is caused by the parasitic worm Onchocerca volvulus. The worm can persist in the body in nodules, even after treatment.

Kim Janda at the Scripps Research Institute in La Jolla, California, and his colleagues studied urine from people with the disease, aiming to find a marker of active infection. The team found a previously unknown molecule called N-acetyltyramine-O,β-glucuronide by using liquid chromatography–mass spectrometry. The molecule — which is derived from one of the worm's neurotransmitters — was present at high levels in the urine of infected people, but at much lower levels in healthy people and patients who were receiving antibiotic treatment.

The authors suggest that a similar approach could be used to find biomarkers for other tropical diseases.

Proc. Natl Acad. Sci. USA http://dx.doi.org/10.1073/pnas.1221969110 (2013)