A novel antigen biomarker for detection of high-level of Loa loa microfilaremia

Abstract

Background Loiasis is a disease caused by the nematode Loa loa. Serious adverse events sometimes occur in people with heavy L. loa microfilaremia after ivermectin treatment. In regions of Central Africa where loiasis is endemic, this significantly impedes global elimination programs for lymphatic filariasis and onchocerciasis that use mass distribution of ivermectin. Improved diagnostic tests to identify individuals at increased risk of serious adverse events could facilitate efforts to eliminate lymphatic filariasis and onchocerciasis in this region. Methods and findings We previously identified the L. loa protein Ll-Bhp-1 in loiasis patient sera. Here, we further characterize Ll-Bhp-1 and report development of an antigen capture ELISA to detect this antigen. This assay detected Ll-Bhp-1 in 74 of 116 (63.8%) loiasis patient sera. Ll-Bhp-1 levels were significantly correlated with L. loa microfilarial counts, and the sensitivity of the assay was highest for samples from people with high counts, (94% and 100% in people with ≥20,000 and ≥50,000 microfilaria per milliliter of blood, respectively). The antigen was not detected in 112 sera from people with other filarial infections, or in 34 control sera from the USA. Conclusions This Ll-Bhp-1 antigen assay is specific for loiasis, and highly sensitive for identifying people with high L. loa microfilarial counts who are at increased risk for serious adverse events after ivermectin treatment. L. loa antigen detection has the potential to facilitate loiasis mapping efforts and programs to eliminate lymphatic filariasis and onchocerciasis in Central Africa.