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

Mosquito infection rates (all larval stages) in 10 sentinel villages: baseline and by year (n = 44,668).

<p>Dissections from bimonthly intradomiciliary pyrethrum knockdown collections of mosquitoes showing percent infected with any larval stage (L1–3) determined by dissection. Results reflect only <i>Anopheles</i> sp mosquito dissections. Collections were generally performed in the same household compounds. Baseline data point is explained in <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0001346#pntd-0001346-g006" target="_blank">Figure 6</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-g006" target="_blank">Figure 6</a>). NA = not applicable, not available, or fewer than 100 mosquitoes dissected.</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

Mean sentinel village microfilaremia prevalence by MDA treatment year (n = 10,753).

<p>Nocturnal microfilaremia as determined by 60 ul thick smear. SV results across all four MDA phases have been adjusted to MDA treatment year for comparability. No pretreatment data are available for Gbuwhen, Gwamlar, Lankan, Maiganga and Seri, so earliest available mf data point was used as the baseline figure. Bars show 95% confidence intervals. Chi square for trend for all years was significant (p = 0.035), but was not significant using an analysis between baseline and MDA year 6 (p = 0.187). In addition, the key threshold of <1% microfilaremia was not attained by MDA year 6.</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

Mean mosquito infection (all larval stages) by MDA treatment year in 10 sentinel villages (n = 44,668).

<p>Dissections from bimonthly intradomiciliary pyrethrum knockdown collected mosquitos for all larval stages (L1–3) combined across all SVs and adjusted to MDA treatment year for comparability. Baseline mosquito infection rates are the aggregate values from pretreatment and the first two years of treatment; no baseline data were available for Babale SV. Chi square for trend for all years was highly significant (p = 0.008), but the trend analysis was not significant using data between baseline and MDA year 6 (p = 0.131). Bars show 95% confidence intervals.</p

Annual reported treatment coverage of eligible population of sentinel villages, and 2003 surveyed coverage.

<p>Reported treatment of eligible (aged five and above healthy persons) populations in ten sentinel villages (SVs) based on registers kept by community directed volunteer drug distributors (CDDs). A confirmatory coverage survey undertaken in nine of the ten villages in 2003 showed an overall coverage of 82%, lower than the reported coverage that year of 90%. Gwamlar was not surveyed in 2003 due to insecurity. Babale, in the urban area of Jos North, did not get treated in 2009 due to civil unrest, and had the lowest surveyed coverage in 2003.</p><p>*Antigen >25%.</p><p>NA = Not applicable, in cells corresponding to the years before the MDA program in that SV had been launched.</p

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

Age-specific prevalence for mf or LF antigen in Dokan Tofa and Piapung sentinel villages.

<p>Panel A: Dokan Tofa pretreatment prevalence by age group (n = 418). Panel B: Piapung pretreatment prevalence by age group (n = 400). Panel C: Dokan Tofa prevalence by age group after 6 rounds of MDA (n = 223). Panel D: Piapung prevalence by age group after 6 rounds of MDA (n = 280). Boxes show numbers sampled in each age group. Pretreatment sample for mf is different from <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0001346#pntd-0001346-t002" target="_blank">Table 2</a> because ages were not available on all persons tested. Pretreatment sample for antigen for these SVs are different than baseline figure shown in <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0001346#pntd-0001346-t003" target="_blank">Table 3</a> because 1999/2000 mapping data were added to baseline calculation in <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0001346#pntd-0001346-t003" target="_blank">Table 3</a> (see <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0001346#s2" target="_blank">Methods</a>).</p