The impact of five years of annual ivermectin treatment on skin microfilarial loads in the onchocerciasis focus of Asubende, Ghana

Abstract

Following the registration of ivermectin (Mectizan) for human use in the treatment of onchocerciasis, in 1987 the Onchocerciasis Control Programme in West Africa (OCP) begun a series of trials in order to determine the safety of the drug when used on a large scale and its potential for morbidity control. This paper reports the changes in skin microfilarial loads during the first 5 years of annual treatment in the holoendemic focus of Asubende in Ghana, which was the largest trial area and which also had the longest series of follow-up surveys. The general observed pattern was a marked reduction of microfilarial loads shortly after each treatment followed by a steady repopulation of the skin until a subsequent treatment round. The overall reduction of microfilarial loads observed between the base line survey and one year after the last treatment was 90% for the total population examined and over 93% for a cohort which received the drug at all 5 treatment rounds. In contrast, there was only a very gradual decrease in the prevalence of infection in the population after subsequent treatments. The study further emphasizes that even a single treatment with ivermectin has a significant medium-term impact on microfilarial loads. Microfilarial counts barely increased after 14-16 months of treatment and stabilized around 55% of pre-treatment counts 2-4 years after a single treatment.

Rates of microfilarial production by Onchocerca volvulus are not cumulatively reduced by multiple ivermectin treatments

“…Although their modelling approach is different from ours, and the frequency of treatment in Asubende, Ghana (Alley et al 1994) was annual rather than 6-monthly as in Guatemala, the results of both studies are compatible and also comparable to those obtained by Basáñ ez et al (2008), who modelled the effect of a single ivermectin dose. However, Plaisier et al (1995) found that a progressive reduction of microfilarial production with each dose would be the scenario most consistent with the data.…”

A community trial of ivermectin for onchocerciasis in Sierra Leone: compliance and parasitological profiles after three and a half years of intervention

“…These figures are in contrast to the findings of Schulz-Key et al (1989) in Togo, and Lariviere et al (1989) in Ivory Coast, who found that microfilarial loads remained a t less than 30-40% of pretreatment levels for a t least z years after a single dose of ivermectin. However, they are compatible with the findings of Alley et al (1994) in Ghana who found that microfilariae continued to repopulate the skin for z years after a single dose of ivermectin, combined with continuing vector control, before stabilizing at about 5 5 % of pretreatment levels.…”

“…1993). It has been suggested that skin microfilarial loads d o not return to pretreatment levels after even a single dose, but stabilize at a lower density (Schulz-Key et al 1989;Lariviere et al 1989;Alley et al 1994). Whether these effects accumulate with every dose of ivermectin or whether a maximum effect is reached is not known.…”

Nodding syndrome in Mundri county, South Sudan: Environmental, nutritional and infectious factors

“…[96][97] Consequently single treatments with ivermectin do not change the infection status of treated subjects, and the effect of ivermectin mass treatment on infection prevalence is primarily due to reduction in transmission. [98][99][100][101][102][103] Between 1987 and 2011, the Mectizan Donation programme approved 139,265,010 ivermectin treatments for Africa. 104 Adverse reactions to ivermectin treatment of O. volvulus infection constitute the body's reaction to the microfilaria killed and include primarily itching, rash, gland pain and tenderness, joint and muscle pain, fever and headache, pulse and blood pressure changes, all of which disappear within a few days.…”