New Study Shows Unexpected Benefits of Integrated Mass Drug Administration in Sierra Leone

June 25th, 2013

A new study published in the June 2013 issue of the online journal PLOS Neglected Tropical Diseases, reports quicker-than-anticipated reductions in the number of lymphatic filariasis (LF) cases in Sierra Leone following just three rounds of mass drug administration (MDA) with ivermectin and albendazole.

The study, titled “Impact of Three Rounds of Mass Drug Administration on Lymphatic Filariasis in Areas Previously Treated for Onchocerciasis in Sierra Leone,” showed that LF microfilaria were present in the blood of less than 1% of the population that was sampled in 11 of the country’s 12 health districts (HD) reporting previous disease prevalence, after just 3 rounds of MDA. Microfilaria are immature worms that migrate through the bloodstream and live in the lymph nodes of their human hosts, once people are bitten by disease-carrying mosquitoes.

School children in Sierra Leone Photo: Helen Keller International

School children in Sierra Leone
Photo: Helen Keller International

According to current World Health Organization procedures for treating LF endemic communities, six annual doses of the drugs are typically required to bring prevalence down to <1% of residents in a given HD. So, how is it possible that disease prevalence would drop to <1% of residents after just three rounds of MDA in Sierra Leone?

The likely answer was that the HDs that were being treated for LF were also endemic for another neglected tropical disease known as onchocerciasis, which is also treated with ivermectin–one of the same drugs used to treat LF. Communities in 12 HDs in Sierra Leone have consistently been doing annual community-based MDA with ivermectin to prevent and treat residents for onchocerciasis since 2003.

Thus, researchers decided to undertake a study to test the hypothesis that areas previously exposed to ivermectin treatment for onchocerciasis control may need fewer rounds of annual MDA to eliminate LF (i.e. reduce microfilaremia (mf) prevalence to <1%). And as it turns out, they were onto something.

Results of the midterm evaluation study, conducted after just three rounds of MDA with ivermectin and albendazole, showed very significant and rapid reductions in mf prevalence and density. In fact, 11 out of the 12 districts reported having mf prevalence <1%.

Given the results of the study, the researchers felt confident in concluding that relatively low LF baseline prevalence and effective integrated MDA for onchocerciasis and LF led to rapid reduction in LF prevalence.

Details of the study are available in the abstract below; or by accessing the full research article on the PLOS Neglected Tropical Diseases journal website.


Background: Studies conducted across Sierra Leone between 1974-2005 provided data on onchocerciasis endemicity in 12 of 14 health districts (HDs); and baseline studies between 2005-2008 provided data on lymphatic filariasis (LF) endemicity in all 14 HDs. 3 integrated annual mass drug administration (MDA) were conducted in the 12 co-endemic districts 2008-2010 with good geographic, programme  and drug coverage. Midterm assessment was conducted 2011 to determine impact of these MDAs on LF in these districts.

Methodology/Principal Findings: The mf prevalence and intensity in the 12 districts were determined using the thick blood film method and results compared with baseline data from 2007-2008. Overall mf prevalence fell from 2.6% (95% CI: 2.3%–3.0%) to 0.3% (95% CI: 0.19%-0.47%), a decrease of 88.5% (p=0.000); prevalence was 0.0% (100.0% decrease) in 4 districts: Bo, Moyamba, Kenema and Kono (p=0.001, 0.025, 0.085 and 0.000 respectively); and 7 districts had reductions in mf prevalence of between 70.0% and 95.0% (p=0.000, 0.060, 0.001, 0.014, 0.000, 0.000 and 0.002 for Bombali, Bonthe, Kailahun, Kambia, Koinadugu, Port Loko and Tonkolili districts respectively). Pujehun had baseline mf prevalence of 0.0%, which was maintained. Only Bombali still had an mf prevalence ≥1.0% (1.58%, 95% CI: 0.80%-3.09%)), and this is the district that had the highest baseline mf prevalence: 6.9% (95% CI: 5.3%-8.8%). Overall arithmetic mean mf density after 3 MDAs was 17.59 mf/ml (95% CI: 15.64 mf/ml-19.55 mf/ml) among mf positive individuals (65.4% decrease from baseline of 50.9 mf/ml (95% CI: 40.25 mf/ml-61.62 mf/ml; p=0.001) and 0.05 mf/ml (95% CI: 0.03 mf/ml-0.08 mf/ml) for the entire population examined (96.2% decrease from baseline of 1.32 mf/ml (95% CI: 1.00 mf/ml-1.65 mf/ml; p=0.000)).

Conclusions/Significance: The results show that mf prevalence decreased to <1.0% in all but 1 of the 12 districts after 3 MDAs. Overall mf density reduced by 65.0% among mf-positive individuals, and 95.8% for the entire population.