Abstract
In Burkina Faso, onchocerciasis was no longer a public health problem when the WHO Onchocerciasis Control Programme in West Africa closed at the end in 2002. However, epidemiological surveillance carried out from November 2010 to February of 2011, showed a recrudescence of infection in the Cascades Region. This finding was made at a time when ivermectin, a drug recommended for the treatment of both onchocerciasis and lymphatic filariasis, had been distributed in this area since 2004 for the elimination of lymphatic filariasis. It was surprising that ivermectin distributed for treating lymphatic filariasis had not prevented the recrudescence of onchocerciasis. Faced with this situation, the aim of our study was to evaluate the effectiveness of ivermectin on the onchocerciasis parasite. The percentage reduction in microfilarial load after treatment with ivermectin was used as a proxy measure for assessing possible resistance. A cohort study was carried out with 130 individuals who had tested positive for microfilariae of Onchocerca volvulus in 2010 using microscopic examination of skin-snip biopsies from five endemic villages. Subjects were followed from July 2011 to June 2012. The microfilarial load of each individual was enumerated by skin-snip biopsy in 2010, prior to the first ivermectin treatment against onchocerciasis under community guidelines. All individuals received two ivermectin treatments six months apart. In 2012, the microfilarial loads were determined again, six months after the second round of ivermectin and the reductions in parasite loads were calculated to measure the impact of the drug. The percentage reduction of the microfilarial loads ranged from 87% to 98% in the villages. In all villages, there was a statistically significant difference between the average microfilarial loads in 2010 and 2012. The level of reduction of microfilarial loads suggests that ivermectin is effective against the recrudescent population of O. volvulus in Cascades Region of Burkina Faso. Further investigations would be necessary to determine the causes of the recrudescence of onchocerciasis. (For French language abstract, see S1 Alternative Language —Translation of the into French by the authors.)
Highlights
Onchocerciasis, or river blindness, is a severely debilitating vector-borne parasitic disease which has been targeted for elimination by the World Health Organization (WHO) by 2025 [1]
Modern onchocerciasis control is based upon mass drug administration using ivermectin, and biannual distribution of ivermectin was instigated to bring the recrudescence under control
It was by no means certain that this was an appropriate strategy because the area was already under mass drug administration with ivermectin since 2004 to eliminate lymphatic filariasis
Summary
Onchocerciasis, or river blindness, is a severely debilitating vector-borne parasitic disease which has been targeted for elimination by the World Health Organization (WHO) by 2025 [1] It is caused by infection by the filarial nematode worm, Onchocerca volvulus, which is transmitted from person to person by blood-feeding blackflies of the genus Simulium (Diptera: Simuliidae). The reason for the recrudescence is unclear, but it was associated with high levels of vector infectivity [4] and did not appear to be happening in other parts of southern Burkina Faso [5] It was worrying because it happened in an area where ivermectin, had been distributed by Mass Drug Administration (MDA) once a year since 2004 for the elimination of lymphatic filariasis (LF) (i.e. for six consecutive years up to 2010). Ivermectin was registered for use against onchocerciasis in 1987, and remains the only drug recommended for the treatment of onchocerciasis through MDA [6], and biannual MDA with ivermectin was introduced to try to bring the recrudescence under control [3]
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