Shrinking the lymphatic filariasis map of Ethiopia: reassessing the population at risk through nationwide mapping

BACKGROUND Mapping of lymphatic filariasis (LF) is essential for the delineation of endemic implementation units and determining the population at risk that will be targeted for mass drug administration (MDA). Prior to the current study, only 116 of the 832 woredas (districts) in Ethiopia had been mapped for LF. The aim of this study was to perform a nationwide mapping exercise to determine the number of people that should be targeted for MDA in 2016 when national coverage was anticipated. METHODOLOGY/PRINCIPAL FINDING A two-stage cluster purposive sampling was used to conduct a community-based cross-sectional survey for an integrated mapping of LF and podoconiosis, in seven regional states and two city administrations. Two communities in each woreda were purposely selected using the World Health Organization (WHO) mapping strategy for LF based on sampling 100 individuals per community and two purposely selected communities per woreda. Overall, 130 166 people were examined in 1315 communities in 658 woredas. In total, 140 people were found to be positive for circulating LF antigen by immunochromatographic card test (ICT) in 89 communities. Based on WHO guidelines, 75 of the 658 woredas surveyed in the nine regions were found to be endemic for LF with a 2016 projected population of 9 267 410 residing in areas of active disease transmission. Combining these results with other data it is estimated that 11 580 010 people in 112 woredas will be exposed to infection in 2016. CONCLUSIONS We have conducted nationwide mapping of LF in Ethiopia and demonstrated that the number of people living in LF endemic areas is 60% lower than current estimates. We also showed that integrated mapping of multiple NTDs is feasible and cost effective and if properly planned, can be quickly achieved at national scale

Elimination of lymphatic filariasis in the Gambia.

BACKGROUND The prevalence of Wuchereria bancrofti, which causes lymphatic filariasis (LF) in The Gambia was among the highest in Africa in the 1950s. However, surveys conducted in 1975 and 1976 revealed a dramatic decline in LF endemicity in the absence of mass drug administration (MDA). The decline in prevalence was partly attributed to a significant reduction in mosquito density through the widespread use of insecticidal nets. Based on findings elsewhere that vector control alone can interrupt LF, we asked the question in 2013 whether the rapid scale up in the use of insecticidal nets in The Gambia had interrupted LF transmission. METHODOLOGY/PRINCIPAL FINDING We present here the results of three independently designed filariasis surveys conducted over a period of 17 years (1997-2013), and involving over 6000 subjects in 21 districts across all administrative divisions in The Gambia. An immunochromatographic (ICT) test was used to detect W. bancrofti antigen during all three surveys. In 2001, tests performed on stored samples collected between 1997 and 2000, in three divisions, failed to show positive individuals from two divisions that were previously highly endemic for LF, suggesting a decline towards extinction in some areas. Results of the second survey conducted in 2003 showed that LF was no longer endemic in 16 of 21 districts surveyed. The 2013 survey used a WHO recommended LF transmission verification tool involving 3180 6-7 year-olds attending 60 schools across the country. We demonstrated that transmission of W. bancrofti has been interrupted in all 21 districts. CONCLUSIONS We conclude that LF transmission may have been interrupted in The Gambia through the extensive use of insecticidal nets for malaria control for decades. The growing evidence for the impact of malaria vector control activities on parasite transmission has been endorsed by WHO through a position statement in 2011 on integrated vector management to control malaria and LF

Diabetes : de sockersjukas tidskrift / utgiven av Föreningen för sockersjuka i Stockholm med omnejd (Årgång 11, N:r 5)

Background Lymphatic filariasis (LF) is targeted for elimination through annual mass drug administration (MDA) for 4–6 years. In 2006, Zanzibar stopped MDA against LF after five rounds of MDA revealed no microfilaraemic individuals during surveys at selected sentinel sites. We asked the question if LF transmission was truly interrupted in 2006 when MDA was stopped. Methodology/Principal Findings In line with ongoing efforts to shrink the LF map, we performed the WHO recommended transmission assessment surveys (TAS) in January 2012 to verify the absence of LF transmission on the main Zanzibar islands of Unguja and Pemba. Altogether, 3275 children were tested on both islands and 89 were found to be CFA positive; 70 in Pemba and 19 in Unguja. The distribution of schools with positive children was heterogeneous with pronounced spatial variation on both islands. Based on the calculated TAS cut-offs of 18 and 20 CFA positive children for Pemba and Unguja respectively, we demonstrated that transmission was still ongoing in Pemba where the cut-off was exceeded. Conclusions Our findings indicated ongoing transmission of LF on Pemba in 2012. Moreover, we presented evidence from previous studies that LF transmission was also active on Unguja shortly after stopping MDA in 2006. Based on these observations the government of Zanzibar decided to resume MDA against LF on both islands in 2013

Spatial distribution and antigen positivity rates of schools selected for TAS surveys on Pemba and Unguja islands in Zanzibar, United Republic of Tanzania.

<p>Spatial distribution and antigen positivity rates of schools selected for TAS surveys on Pemba and Unguja islands in Zanzibar, United Republic of Tanzania.</p

Map of The Gambia showing the location and microfilaria (MF rates in 15 villages surveyed in 1975 and 1976 (adapted from Reference #20) in areas of low transmission (Blue) where MF rates were less than 10% (Upper River and Western Divisions) and high transmission (Red) where MF rates where greater than 18% (Central River Division).

<p>Map of The Gambia showing the location and microfilaria (MF rates in 15 villages surveyed in 1975 and 1976 (adapted from Reference #20) in areas of low transmission (Blue) where MF rates were less than 10% (Upper River and Western Divisions) and high transmission (Red) where MF rates where greater than 18% (Central River Division).</p

The lymphatic filariasis (LF) endemicity map for The Gambia showing locations of villages where at least one of the ~100 individuals tested during the mapping surveys was positive for CFA (Red dot or star) and villages where all ~100 tested individuals were found negative (White dot or star).

<p>The dots and stars represent villages surveyed during 2001 and 2003 respectively.</p

Map of The Gambia showing the location of 60 schools surveyed during the Transmission Assessment Surveys (TAS) carried out in 2013 and revealing no circulating filarial antigen (CFA) positive individuals in all schools indicated by the white dots.

<p>Map of The Gambia showing the location of 60 schools surveyed during the Transmission Assessment Surveys (TAS) carried out in 2013 and revealing no circulating filarial antigen (CFA) positive individuals in all schools indicated by the white dots.</p

The changing pattern of LF infection rates determined by night blood and ICT surveys across the 6 administrative divisions in The Gambia between 1951 and 2013.

<p>The changing pattern of LF infection rates determined by night blood and ICT surveys across the 6 administrative divisions in The Gambia between 1951 and 2013.</p

Map of The Gambia showing the historical boundaries for the six administrative divisions recognised before 2000.

<p>Map of The Gambia showing the historical boundaries for the six administrative divisions recognised before 2000.</p

Current LF endemicity map for Ethiopia for all IUs surveyed to date.

<p>Endemic IUs are shown in red (>1 ICT+) and yellow (1 ICT+) depending on the ICT results. Non-endemic IUs are shown in blue leaving only 58 districts yet to be mapped.</p