One Hundred Years After Its Discovery in Guatemala by Rodolfo Robles, Onchocerca volvulus Transmission Has Been Eliminated from the Central Endemic Zone

Abstract

We report the elimination of Onchocerca volvulus transmission from the Central Endemic Zone (CEZ) of onchocerciasis in Guatemala, the largest focus of this disease in the Americas and the first to be discovered in this hemisphere by Rodolfo Robles Valverde in 1915. Mass drug administration (MDA) with ivermectin was launched in 1988, with semiannual MDA coverage reaching at least 85% of the eligible population in > 95% of treatment rounds during the 12-year period, 2000-2011. Serial parasitological testing to monitor MDA impact in sentinel villages showed a decrease in microfilaria skin prevalence from 70% to 0%, and polymerase chain reaction (PCR)-based entomological assessments of the principal vector Simulium ochraceum s.l. showed transmission interruption by 2007. These assessments, together with a 2010 serological survey in children 9-69 months of age that showed Ov16 IgG4 antibody prevalence to be < 0.1%, meeting World Health Organization (WHO) guidelines for stopping MDA, and treatment was halted after 2011. After 3 years an entomological assessment showed no evidence of vector infection or recrudescence of transmission. In 2015, 100 years after the discovery of its presence, the Ministry of Health of Guatemala declared onchocerciasis transmission as having been eliminated from the CEZ.

Figure 1.

This map of Guatemala shows the three provinces (Sololá, Suchitepéquez, and Chimaltenango) that contribute to the Central Endemic Zone (CEZ) for onchocerciasis in Guatemala. The CEZ (dark polygon) indicates the contiguous parts of the provinces where onchocerciasis transmission took place, just south of Lake Atítlan, in the highlands at elevations from 500 to 1500 m.

Figure 2.

The top panel shows the Central Endemic Zone (CEZ) treatment percent coverage of the eligible population during the years 1988–2011, by treatment round (dark bars first round, light bars second round). The horizontal line indicates the coverage goal of ≥ 85% per round. The bottom panel shows single bars representing the total treatments provided by year (the bars represent the sum of treatments given during the year in those years when two rounds were given). Mass drug administration (MDA) was halted in 2012 after over 2.9 million cumulative treatments had been delivered over the period.

Figure 3.

The top panel shows the results from 47 sentinel village (SV) visits between 1981 and 2010 for skin snip evaluations to determine microfilariae (mf) prevalence in the nine SVs of the Central Endemic Zone (CEZ). Each village was visited between four and six times (mean: 5.2 assessments per SV). The graphic only shows positive results. Zero skin mf prevalence was first observed in 2007 and occurred in Buena Vista, Costa Rica, Los Andes, and Tarrales. In 2010, mf prevalence was zero in El Brote, Buena Vista, La Estrellita, Monte Carlo, Santa Isabel, Tarrales, and Vesubio. The bottom panel shows similar data for fewer (19) SV visits for ophthalmological evaluations to determine mf prevalence in the anterior chamber (MfAC); note that Monte Carlo and El Brote baseline are mf in cornea, not MfAC. Each of the nine SVs of the CEZ was visited at least twice (range 2–3). Zero values MfAC was recorded in 2007 in El Brote, Buena Vista, Costa Rica, La Estrellita, Los Andes, and Monte Carlo. In 2009, MfAC was zero in Santa Isabel and Vesubio. One individual (0.5%) was positive in Tarrales in 2009. See text and Table 2 for additional SV information.

Figure 4.

The two graphs show the upper 95% confidence intervals for vector infectivity and for annual transmission potential in sentinel villages as calculated by PoolScreen. Horizontal lines indicate the breakpoint thresholds (< 1/2,000 cutoff for vector infectivity and < 20 for seasonal transmission potential [STP]) below which onchocerciasis transmission is not possible. Data are based on the examination of 328,575 vectors in 4,616 polymerase chain reaction (PCR) reactions (pools): 46,160 vectors in 835 pools in 2002, 67,808 flies in 1,260 pools in 2007, 95,306 flies in 1,836 pools in 2010–2011, and 119,301 flies in 685 pools in 2014.