Epidemiological and Entomological Evaluations after Six Years or More of Mass Drug Administration for Lymphatic Filariasis Elimination in Nigeria

The current strategy for interrupting transmission of lymphatic filariasis (LF) is annual mass drug administration (MDA), at good coverage, for 6 or more years. We describe our programmatic experience delivering the MDA combination of ivermectin and albendazole in Plateau and Nasarawa states in central Nigeria, where LF is caused by anopheline transmitted Wuchereria bancrofti. Baseline LF mapping using rapid blood antigen detection tests showed mean local government area (LGA) prevalence of 23% (range 4–62%). MDA was launched in 2000 and by 2003 had been scaled up to full geographic coverage in all 30 LGAs in the two states; over 26 million cumulative directly observed treatments were provided by community drug distributors over the intervention period. Reported treatment coverage for each round was ≥85% of the treatment eligible population of 3.7 million, although a population-based coverage survey in 2003 showed lower coverage (72.2%; 95% CI 65.5–79.0%). To determine impact on transmission, we monitored three LF infection parameters (microfilaremia, antigenemia, and mosquito infection) in 10 sentinel villages (SVs) serially. The last monitoring was done in 2009, when SVs had been treated for 7–10 years. Microfilaremia in 2009 decreased by 83% from baseline (from 4.9% to 0.8%); antigenemia by 67% (from 21.6% to 7.2%); mosquito infection rate (all larval stages) by 86% (from 3.1% to 0.4%); and mosquito infectivity rate (L3 stages) by 76% (from 1.3% to 0.3%). All changes were statistically significant. Results suggest that LF transmission has been interrupted in 5 of the 10 SVs, based on 2009 finding of microfilaremia ≥1% and/or L3 stages in mosquitoes. Four of the five SVs where transmission persists had baseline antigenemia prevalence of >25%. Longer or additional interventions (e.g., more frequent MDA treatments, insecticidal bed nets) should be considered for ‘hot spots’ where transmission is ongoing

Long-Lasting Insecticidal Nets Are Synergistic with Mass Drug Administration for Interruption of Lymphatic Filariasis Transmission in Nigeria

<div><p>In central Nigeria <i>Anopheles</i> mosquitoes transmit malaria and lymphatic filariasis (LF). The strategy used for interrupting LF transmission in this area is annual mass drug administration (MDA) with albendazole and ivermectin, but after 8 years of MDA, entomological evaluations in sentinel villages showed continued low-grade mosquito infection rates of 0.32%. After long-lasting insecticidal net (LLIN) distribution by the national malaria program in late 2010, however, we were no longer able to detect infected vectors over a 24-month period. This is evidence that LLINs are synergistic with MDA in interrupting LF transmission.</p></div

Mosquito lymphatic filariasis infection rates (all larval stages) in Plateau and Nasarawa state sentinel sites.

<p>Mosquito lymphatic filariasis infection rates (all larval stages) in Plateau and Nasarawa state sentinel sites.</p

13 years of mass drug administration for LF in Plateau and Nasarawa states, Nigeria, 2000–2012 (n = 36,119,921).

<p>13 years of mass drug administration for LF in Plateau and Nasarawa states, Nigeria, 2000–2012 (n = 36,119,921).</p

Community-wide distribution of long-lasting insecticidal nets can halt transmission of lymphatic filariasis in southeastern Nigeria

Lymphatic filariasis (LF) in rural southeastern Nigeria is transmitted mainly by Anopheles spp. mosquitoes. Potential coinfection with Loa loa in this area has prevented use of ivermectin in the mass drug administration (MDA) strategy for LF elimination because of potential severe adverse L. loa-related reactions. This study determined if long-lasting insecticidal net (LLIN) distribution programs for malaria would interrupt LF transmission in such areas, without need for MDA. Monthly entomologic monitoring was conducted in sentinel villages before and after LLIN distribution to all households and all age groups (full coverage) in two districts, and to pregnant women and children less than five years of age in the other two districts. No change in human LF microfilaremia prevalence was observed, but mosquito studies showed a statistically significant decrease in LF infection and infectivity with full-coverage LLIN distribution. We conclude that LF transmission can be halted in southeastern Nigeria by full-coverage LLIN distribution, without MDA

Mean sentinel village antigen prevalence by MDA treatment year (n = 9,394).

<p>Filarial antigenemia as determined by ICT testing. SV results across all four MDA phases have been adjusted to MDA treatment year for comparability. Data for the baseline antigen for five villages (Gbuwhen, Gwamlar, Lankan, Maiganga, and Seri) were from 1999–2000 mapping surveys. Baseline for the remaining villages (Akwete, Anzara, Babale, Dokan Tofa, Piapung) combined values from the community wide nocturnal pre-treatment surveys conducted in 2003 with pre-treatment data from the 1999–2000 mapping surveys. Chi square for trend not significant (p = 0.06 for all MDA years and p = 0.271 for baseline through MDA year 6). Bars show 95% confidence intervals.</p

MF prevalence in 10 sentinel villages: baseline and by year (n = 10,753).

<p>Nocturnal microfilaremia as determined by 60 ul thick smear. The total n value in the table is also reflected in the related graph (<a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0001346#pntd-0001346-g004" target="_blank">Figure 4</a>). Baseline data point is explained in <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0001346#pntd-0001346-g004" target="_blank">Figure 4</a> legend. NA = not applicable or not available.</p><p>°Started treatment in 2000.</p><p>*Started treatment in 2001.</p><p>**Started treatment in 2002.</p><p>***Started treatment in 2003.</p

LF antigen prevalence in 10 sentinel villages: baseline and by year (n = 9,394).

<p>Filarial antigenemia as determined by ICT test. Baseline data point is explained in <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0001346#pntd-0001346-g005" target="_blank">Figure 5</a> legend. The total n value in the table is also reflected in the related graph (<a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0001346#pntd-0001346-g005" target="_blank">Figure 5</a>). NA = not applicable or not available.</p><p>°Started treatment in 2000.</p><p>*Started treatment in 2001.</p><p>**Started treatment in 2002.</p><p>***Started treatment in 2003.</p