Successful Interruption of Transmission of Onchocerca volvulus in the Escuintla-Guatemala Focus, Guatemala

Abstract

BackgroundElimination of onchocerciasis (river blindness) through mass administration of ivermectin in the six countries in Latin America where it is endemic is considered feasible due to the relatively small size and geographic isolation of endemic foci. We evaluated whether transmission of onchocerciasis has been interrupted in the endemic focus of Escuintla-Guatemala in Guatemala, based on World Health Organization criteria for the certification of elimination of onchocerciasis.Methodology/Principal FindingsWe conducted evaluations of ocular morbidity and past exposure to Onchocerca volvulus in the human population, while potential vectors (Simulium ochraceum) were captured and tested for O. volvulus DNA; all of the evaluations were carried out in potentially endemic communities (PEC; those with a history of actual or suspected transmission or those currently under semiannual mass treatment with ivermectin) within the focus. The prevalence of microfilariae in the anterior segment of the eye in 329 individuals (≥7 years old, resident in the PEC for at least 5 years) was 0% (one-sided 95% confidence interval [CI] 0–0.9%). The prevalence of antibodies to a recombinant O. volvulus antigen (Ov-16) in 6,432 school children (aged 6 to 12 years old) was 0% (one-sided 95% IC 0–0.05%). Out of a total of 14,099 S. ochraceum tested for O. volvulus DNA, none was positive (95% CI 0–0.01%). The seasonal transmission potential was, therefore, 0 infective stage larvae per person per season.Conclusions/SignificanceBased on these evaluations, transmission of onchocerciasis in the Escuintla-Guatemala focus has been successfully interrupted. Although this is the second onchocerciasis focus in Latin America to have demonstrated interruption of transmission, it is the first focus with a well-documented history of intense transmission to have eliminated O. volvulus.

Seventeen Years of Annual Distribution of Ivermectin Has Not Interrupted Onchocerciasis Transmission in North Region, Cameroon

“…7 In field studies in Guatemala, two treatments per year have been shown to both reduce transmission and accelerate the death of adult O. volvulus worms. 33 If transmission interruption becomes a goal for Cameroon, then we strongly recommend that the MOH consider a programmatic alteration to two times per year treatment at least for Touboro (if not throughout North Cameroon), including as yet untreated hypoendemic areas adjacent to these CDTI health districts. 34 One weakness in our entomological study is that molecular testing was not performed to determine if the L3 larvae were O. volvulus or another (animal) Onchocerca species.…”

Polymerase Chain Reaction Pool Screening Used To Compare Prevalence of Infective Black Flies in Two Onchocerciasis Foci in Northern Sudan

“…19 The infected fly rate in Abu Hamed is less than the 1 in 2,000 flies (5/10,000) threshold level used by the Onchocerciasis Control Program as an indicator for interruption of disease transmission. 20,21 This rate reflects a limit of less than 1/1,000 parous flies with a corrected level of less than 1/2,000 flies, assuming a crude parous fly rate of 50% and an infection rate of 1 infective larva per fly ( Table 1 ). 20,21 Thus the black fly infectivity rate in Abu Hamed suggests that transmission of the parasite might be close to the level below which the parasite population is unsustainable.…”

“…20,21 This rate reflects a limit of less than 1/1,000 parous flies with a corrected level of less than 1/2,000 flies, assuming a crude parous fly rate of 50% and an infection rate of 1 infective larva per fly ( Table 1 ). 20,21 Thus the black fly infectivity rate in Abu Hamed suggests that transmission of the parasite might be close to the level below which the parasite population is unsustainable. In contrast, the Galabat focus showed black fly infectivity rate well above the threshold level, indicating continued moderate transmission of the disease in the area ( Table 1 ).…”

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

“…31 In this process, an IVT country visit is undertaken after the submission by a ministry of health of a detailed dossier that provides evidence that all foci in the country have eliminated O. volvulus transmission. In Guatemala, the elimination process has already been completed and published in peer-reviewed journals for three of the four of its onchocerciasis foci: Santa Rosa, 19 Escuintla-Guatemala, 32 and Huehuetenango. 33 Based on the completion of elimination evaluations in the CEZ, as reported herein, Guatemala submitted its dossier to WHO in 2015, along with a request for an IVT visit.…”