Mapping the Geographical Distribution of Lymphatic Filariasis in Zambia

Abstract

BackgroundPast case reports have indicated that lymphatic filariasis (LF) occurs in Zambia, but knowledge about its geographical distribution and prevalence pattern, and the underlying potential environmental drivers, has been limited. As a background for planning and implementation of control, a country-wide mapping survey was undertaken between 2003 and 2011. Here the mapping activities are outlined, the findings across the numerous survey sites are presented, and the ecological requirements of the LF distribution are explored.Methodology/Principal findingsApproximately 10,000 adult volunteers from 108 geo-referenced survey sites across Zambia were examined for circulating filarial antigens (CFA) with rapid format ICT cards, and a map indicating the distribution of CFA prevalences in Zambia was prepared. 78% of survey sites had CFA positive cases, with prevalences ranging between 1% and 54%. Most positive survey sites had low prevalence, but six foci with more than 15% prevalence were identified. The observed geographical variation in prevalence pattern was examined in more detail using a species distribution modeling approach to explore environmental requirements for parasite presence, and to predict potential suitable habitats over unsurveyed areas. Of note, areas associated with human modification of the landscape appeared to play an important role for the general presence of LF, whereas temperature (measured as averaged seasonal land surface temperature) seemed to be an important determinant of medium-high prevalence levels.Conclusions/significanceLF was found to be surprisingly widespread in Zambia, although in most places with low prevalence. The produced maps and the identified environmental correlates of LF infection will provide useful guidance for planning and start-up of geographically targeted and cost-effective LF control in Zambia.

Modelling the distribution and transmission intensity of lymphatic filariasis in sub-Saharan Africa prior to scaling up interventions: integrated use of geostatistical and mathematical modelling

“…For example, the Slater and Michael model predict mf prevalences above 75 % in Sudan and South Sudan-Ethiopia border, whereas our predicted prevalence <10 % and recent surveys using ICTs found low levels of antigenaemia [ 55 – 57 ]. Our predicted distribution of antigenaemia is also consistent with previous country-level models [ 8 , 58 – 60 ]. Uncertainty in predictions based on mf prevalence data is greatest for central Africa, primarily driven by a scarcity of mf surveys conducted since 1990.…”

Significant decline in lymphatic filariasis associated with nationwide scale-up of insecticide-treated nets in Zambia

“…gambiae with LF transmission, however, transmission was not directly confirmed ( Shawa et al, 2013 ). Overall LF prevalence was found to be low (8.6%) and indicated a marked decline from prevalence measured in 2003 (33.3%) ( Mwase et al, 2014 ), which the authors attribute to the concurrent scale up of vector control in the area.…”

“…Endemicity mapping 2003–2011: Initial information on the geographical distribution of LF was based on two phases of mapping surveys conducted across Zambia by the Ministry of Health (MoH) Lymphatic Filariasis Control Programme (2003–2005) and the Programme for Integrated Control of Neglected Tropical Diseases (2009–2011). Community prevalence information was based on data collected from 10,193 individuals from 108 survey sites ( Mwase et al, 2014 ), with the majority of data collected between 2003 and 2010, and only one site in early 2011. These surveys were conducted in accordance with the standard guidelines from the World Health Organization ( WHO, 2000 ), which included adult individuals (> 15 years of age) tested for the presence of CFA from finger-prick blood using the rapid BinaxNOW ICT card.…”

“…The ICT card was read after 10 min as per manufacture instructions to avoid the possibility of false-positives if the tests are read too late. Details of the survey, methodology and locations have been described previously ( Mwase et al, 2014 ).…”

“…Lymphatic filariasis (LF) is a mosquito-borne disease, which is widely endemic in Zambia. Overall prevalence rates were estimated at 7.4% in 2011 from > 10,000 sampled individuals across 108 sites in all regions of the country by rapid circulating filarial antigen (CFA; a marker of the Wuchereria bancrofti adult worm infection) BinaxNOW Filariasis immunochromatographic test (ICT) card ( Mwase et al, 2014 ). The initial mapping started in 2003 and 2005 at 42 sites across 14 districts thought to be endemic for LF.…”