Decrease in adverse reactions after repeated ivermectin treatment in onchocerciasis

Elimination of onchocerciasis in Africa by 2025: the need for a broad perspective

Background

In response to the recent publication “Is onchocerciasis elimination in Africa feasible by 2025: a perspective based on lessons learnt from the African control programmes” by Dadzie et al., it is important to clarify and highlight the positive and unequivocal research and operational contributions from the American experience towards the worldwide elimination of human onchocerciasis (river blindness).

Main text

The strategies of twice or more rounds of mass drug administration (MDA) of ivermectin per year, as well as the use of OV-16 serology have allowed four American countries to be verified by World Health Organization to have eliminated transmission of Onchocerca volvulus, the etiological agent. These advances were also implemented in Sudan and Uganda; currently, both are the only African countries where ivermectin MDA was safely stopped in several transmission zones.

Conclusions

Programmatic treatment and evaluation approaches, pioneered in the Americas, are the most efficient among the existing tools for elimination, and their broader use could catalyze the successful elimination of this disease in Africa.

Electronic supplementary material

The online version of this article (10.1186/s40249-019-0557-1) contains supplementary material, which is available to authorized users.

Thirty-month follow-up of sub-optimal responders to multiple treatments with ivermectin, in two onchocerciasis-endemic foci in Ghana

The pathogenesis of the sub-optimal response of Onchocerca volvulus to ivermectin was investigated in a 30-month follow-up of 28 individuals who, in a previous study, had been found to show a sub-optimal (N = 15) or adequate response (N = 13) to multiple treatments with the drug. Verbal informed consent was obtained before each subject was given a general clinical and ocular examination. Skin snips were taken from both iliac crests and both calves. Seventeen nodule carriers were hospitalized for nodulectomy. Adult worms were harvested, embryogrammes were constructed and all developmental stages were counted; degenerate, stretched microfilariae were noted separately. All the subjects were in good general health and all except one had received at least one additional treatment with ivermectin since the earlier study. A large proportion of the adult female worms in 10 out of the 11 sub-optimal responders who were nodule carriers were in full embryonic production but most of the stretched microfilariae they carried were degenerate. This picture is similar to that found in adult worms exposed to the first dose of ivermectin. In one subject who had no viable worms in his nodules, the existence of occult but actively reproductive worms was inferred from the high level of microfilaridermia observed less than 12 months after treatment. These observations confirm the existence of populations of adult female O. volvulus that respond poorly to repeated doses of ivermectin. The use of suramin in the treatment of the sub-optimal responders is discussed.

Comparison of the sensitivity of different geographical isolates of Onchocerca volvulus microfilariae to ivermectin: effects of exposure to drug on development in the blackfly Simulium ornatum

Four geographical isolates (Ghana forest, Ghana savannah, Cameroon forest, Guatemala) of Onchocerca volvulus microfilariae (mf) and O. lienalis mf (UK) were examined for their sensitivity to ivermectin by incubation in vitro in drug followed by assessing their ability to develop in the blackfly Simulium ornatum after intrathoracic injection. Parasites were incubated for 30 min in ivermectin (10(-6) to 10(-9) M), which resulted in a concentration dependent decrease in the numbers of parasites surviving and developing in the insect; there were significant reductions in parasite recoveries from all isolates in the 10(-6) M to 5 x 10(-8) M ivermectin groups, but no significant effect was seen following incubation in concentrations of 10(-8) M and below. Experiments consistently demonstrated that the 4 isolates of O. volvulus were similarly sensitive to ivermectin (in the 10(-7) M ivermectin groups there was a reduction of 76.3% to 85.1% in numbers of infective larvae, and 60.9% to 85.5% in numbers of all larval stages, compared to controls); O. lienalis mf were significantly more sensitive (100% reduction in infective larvae, 98.7% reduction in all larval stages). This baseline information on drug sensitivity and techniques should prove useful for examining populations of O. volvulus for possible development of drug resistance in the future.

Effects of repeated ivermectin treatment in onchocerciasis

A group of 87 onchocerciasis patients from a hyperendemic area without vector control was treated with a single dose of 150 micrograms/kg ivermectin. A second, third and fourth dose was administered 5, 12 and 17 months later to 44, 35 and 25 patients. Skin snip loads reduced substantially following each consecutive dose. However, after three doses 44% of the patients remained skin snip positive. Side-effects decreased from 32.2% requiring medical treatment at the first dose to none after the fourth dose. From this study it was concluded that a complete eradication of microfilariae in skin snips in severely infected persons living in a hyperendemic area without vector control is probably not feasible. Medical supervision for the observation of side-effects after the third dose can be limited.