Changes in Anti-OV-16 IgG4 Responses to Onchocerciasis after Elimination of Transmission in the Central Endemic Zone of Guatemala.

Current WHO guidelines for onchocerciasis elimination provide requirements for stopping mass drug administration of ivermectin and the verification of elimination of transmission. These guidelines also recommend post-elimination surveillance (PES) based on entomological surveys. Serological markers in humans could complement entomological PES once the longevity of anti-OV-16 antibody responses is better understood. In 2014-2015 we evaluated ELISA anti-OV-16 IgG4 antibody persistence among previously seropositive people from the central endemic zone of Guatemala. The country stopped all onchocerciasis program interventions in 2012 and was verified by WHO as having eliminated transmission of onchocerciasis in 2016. A total of 246 participants with prior OV-16 ELISA results from 2003, 2006, 2007, or 2009 were enrolled in a follow-up study. Of these, 77 people were previously OV-16 seropositive and 169 were previously seronegative. By 2014 and 2015, 56 (72.7%) previously seropositive individuals had sero-reverted, whereas all previous negatives remained seronegative. The progression of antibody responses over time was estimated using a mixed-effects linear regression model, using data from seropositive participants who had sero-reverted. The temporal variation showed a mean activity unit decay of 0.20 per year (95% credible interval [CrI]: 0.17, 0.23), corresponding to an estimated antibody response half-life of 3.3 years (95% CrI: 2.7, 4.1). These findings indicate that the majority of seropositive people will sero-revert over time.