Differential immune response to Onchocerca volvulus: IgG4 antibody responses differ in onchocerciasis patients from Guatemala and Ghana

Onchocerca volvulus-neurotransmitter tyramine is a biomarker for river blindness

Onchocerciasis, also known as "river blindness", is a neglected tropical disease infecting millions of people mainly in Africa and the Middle East but also in South America and Central America. Disease infectivity initiates from the filarial parasitic nematode Onchocerca volvulus, which is transmitted by the blackfly vector Simulium sp. carrying infectious third-stage larvae. Ivermectin has controlled transmission of microfilariae, with an African Program elimination target date of 2025. However, there is currently no point-of-care diagnostic that can distinguish the burden of infection--including active and/or past infection--and enable the elimination program to be effectively monitored. Here, we describe how liquid chromatography-MS-based urine metabolome analysis can be exploited for the identification of a unique biomarker, N-acetyltyramine-O,β-glucuronide (NATOG), a neurotransmitter-derived secretion metabolite from O. volvulus. The regulation of this tyramine neurotransmitter was found to be linked to patient disease infection, including the controversial antibiotic doxycycline treatment that has been shown to both sterilize and kill adult female worms. Further clues to its regulation have been elucidated through biosynthetic pathway determination within the nematode and its human host. Our results demonstrate that NATOG tracks O. volvulus metabolism in both worms and humans, and thus can be considered a host-specific biomarker for onchocerciasis progression. Liquid chromatography-MS-based urine metabolome analysis discovery of NATOG not only has broad implications for a noninvasive host-specific onchocerciasis diagnostic but provides a basis for the metabolome mining of other neglected tropical diseases for the discovery of distinct biomarkers and monitoring of disease progression.

Prevalence of antibodies to onchocerca volvulus in residents of Oaxaca, Mexico, treated for 10 years with ivermectin

Studies to determine the prevalence of antibodies to Onchocerca volvulus, prior to and after actions carried out to interrupt transmission, are scarce in Mexico. Here we report the prevalence of immunoglobulin G (IgG) and IgG4 antibodies in an enzyme-linked immunosorbent assay (ELISA) against a crude extract of O. volvulus adult worm in serum samples from persons under noninterrupted biannual treatment with ivermectin in areas of onchocercosis endemicity in Mexico. To perform the prevalence studies, the ELISA procedures were first evaluated. Serological studies were performed with serum samples from skin microfilaria carriers from Guatemala and from people microfilariodermic negative living in the same area as the Guatemalan patients. Sensitivity values for IgG or IgG4 detection were 71 and 86%, while specificities were 92 and 100%, respectively. No anti-O. volvulus antibodies were found in samples from nonendemic controls from Mexico, but 3 of 71 samples from residents in the onchocercosis area of Oaxaca, Mexico, and who have been under ivermectin treatment during the last 10 years were only positive to IgG. Notwithstanding that the IgG4 isotype was not detected and a low (4.2%) anti-O. volvulus IgG antibody prevalence was found, a seroepidemiological follow-up must be performed in order to confirm interruption of onchocercosis transmission in the area of Oaxaca, Mexico, in which onchocercosis is endemic.

Comparison between the skin snip test and simple dot blot assay as potential rapid assessment tools for Onchocerciasis in the postcontrol era in Ghana

Successful control of onchocerciasis through mass distribution of ivermectin needs to be coupled with reliable, sensitive, specific, yet affordable diagnostic methods to monitor and ensure the efficacy of such measures. The effort put into the development of diagnostic methods for onchocerciasis that can substitute for or work in combination with the present "gold standard," the skin snip test, has resulted in the discovery of a number of immunogenic proteins with potential use as diagnostic tools in the postcontrol era. Most of these proteins have now been produced through recombinant DNA techniques. However, when costs are not a trivial issue, none of them have yet found their way into the areas where the disease still exists. In the present study, we have evaluated the performance of a simple dot blot assay which uses a mixture of native proteins designated PakF as a serious contender in the quest for a less invasive and more sensitive method to detect Onchocerca volvulus infection in areas with diverse endemicities. Our results indicate that the assay we propose is more sensitive than the skin snip test and shows high specificity, both characteristics required for a suitable tool for the monitoring of onchocerciasis in the postcontrol era.