RESUMO
Skin biopsies (Skin snips) have historically been the gold standard for the diagnosis of onchocerciasis. However, in low prevalence areas and in areas with successful ivermectin mass drug administration (MDA) programs, skin snips are not sensitive enough to decide when to stop MDA; thus, serological diagnostic tools have been recommended for this purpose. This study assessed the sensitivity and specificity of the Ov16 Rapid Diagnostic Test (SD BIOLINE Onchocerciasis RDT) compared to skin snip in endemic areas undergoing ivermectin mass distribution using Community Directed Treatment with Ivermectin (CDTI) strategy. A cross-sectional study was conducted between September and November 2016 in five endemic villages in the Cascades region in Burkina Faso. Children aged 2 to 9-years were examined during the impact epidemiological survey using both the skin snip and Ov16 Rapid Diagnostic Test. The Ov16 Rapid Diagnostic Test sensitivity and specificity were determined with reference to the skin biopsy. Skin snip positivity was 1.25% in this population, while seroprevalence was 6.5%. When compared to the skin snip as the gold standard, the sensitivity of the Ov16 Rapid Diagnostic Test was 60% and the specificity 94%. When the Ov16 Rapid Diagnostic Test was considered as the gold standard, the skin snip exhibited a sensitivity of 11.5% and a specificity of 99.5%. These results are similar to other studies comparing the performance of the Ov16 ELISA to skin snips, suggesting that the Ov16 RDT may be a useful tool for ivermectin STOP MDA and post transmission surveys, assuming that the prevalence of infection is low or close to zero, and the Ov16 RDT detected also pre patent infections.
RESUMO
BACKGROUND: The Sud-Ouest region of Burkina Faso (especially the Bougouriba valley) has been historically problematic with respect to onchocerciasis control, with a recrudescence of infections after vector control carried out the WHO Onchocerciasis Control Programme was halted in 1989. After 1996, mass drug administration of ivermectin was instigated to control the recrudescence so that it would no longer constitute a public health problem. However, in 2010 WHO changed its recommended policy from control to elimination, and in 2013 biannual Community-Directed Treatment with Ivermectin (CDTI) was instigated. Epidemiological surveys were carried-out in 2011 and 2018 to determine whether CDTI was producing a decline in infection levels and progress towards elimination. METHODOLOGY/PRINCIPAL FINDINGS: A cross-sectional study was conducted across 20 villages in four health districts in 2011 and 29 villages in 2018. Individuals aged five years and above were examined by skin-snip, and the prevalence and microfilarial load was determined for each village. In 2011, 75% of villages had some infections and 20% had prevalences >5%, with a mean prevalence across all villages of 2.63% (range 0.0-9.7%), and community microfilarial load ranging from 0 to 0.25 microfilariae per biopsy. In 2018, nine villages (= 31% of total) had some infections, with prevalences ranging from 0.41% to 3.54%, and a mean prevalence across all villages of 0.37%. Community microfilarial load ranged from 0 to 0.1. Amongst those people found to be microfilarial positive, 87% had a history of migration. CONCLUSIONS/SIGNIFICANCE: The endemicity of onchocerciasis infection in the Sud-Ouest region has declined to low levels and seems to be progressing towards elimination. Our findings indicated that biannual CDTI is having good effect, but it should continue for a number of years to ensure elimination of transmission. However, progress towards elimination has a troublesome history in this region, and it would be advisable to select more sentinel villages to have confidence in any future epidemiological and entomological surveys, especially Stop-MDA surveys. With positive individuals migrating between countries, cross-border collaboration needs more attention to ensure effective treatment for onchocerciasis elimination.
