Abstract
BackgroundUnder the Global Programme to Eliminate Lymphatic Filariasis (LF), American Samoa conducted 7 rounds of mass drug administration (MDA) between 2000 and 2006. The territory passed transmission assessment surveys (TASs) in 2011 (TAS-1) and 2015 (TAS-2). In 2016, the territory failed TAS-3, indicating resurgence. This study aims to determine if antibodies (Abs) may have provided a timelier indication of LF resurgence in American Samoa. MethodsWe examined school-level antigen (Ag) and Ab status (presence/absence of Ag- and Ab-positive children) and prevalence of single and combined Ab responses to Wb123, Bm14, and Bm33 Ags at each TAS. Pearson chi-square test and logistic regression were used to examine associations between school-level Ab prevalence in TAS-1 and TAS-2 and school-level Ag status in TAS-3. ResultsSchools with higher prevalence of Wb123 Ab in TAS-2 had higher odds of being Ag-positive in TAS-3 (odds ratio [OR] 24.5, 95% confidence interval [CI] 1.2–512.7). Schools that were Ab-positive for WB123 plus Bm14, Bm33, or both Bm14 and Bm33 in TAS-2 had higher odds of being Ag-positive in TAS-3 (OR 16.0–24.5). ConclusionAbs could provide earlier signals of resurgence and enable a timelier response. The promising role of Abs in surveillance after MDA and decision making should be further investigated in other settings.
Highlights
Lymphatic filariasis (LF) is a parasitic infection caused by three species of the filarial nematodes, Wuchereria bancrofti, Brugia malayi and Brugia timori, that are transmitted between definitive human hosts by multiple mosquito vectors (Culex, Anopheles, Aedes, and Mansonia) (Centers for Disease Control and Prevention (CDC))
In American Samoa, LF is caused by W. bancrofti which are diurnally sub-periodic worms transmitted predominantly by the highly efficient day-biting mosquito Aedes polynesiensis, and night-biting Aedes samoanus as a secondary vector (Schmaedick et al, 2014)
The initial data set consisted of 33 schools and a total of 1,134 elementary school children that participated in Transmission Assessment Surveys (TAS)-1, 864 in TAS-2 and 1,143 in TAS-3
Summary
Lymphatic filariasis (LF) is a parasitic infection caused by three species of the filarial nematodes, Wuchereria bancrofti, Brugia malayi and Brugia timori, that are transmitted between definitive human hosts by multiple mosquito vectors (Culex, Anopheles, Aedes, and Mansonia) (Centers for Disease Control and Prevention (CDC)). Estimates suggest that 4-6 annual rounds of MDA with effective population coverage (>65% of the total population) are required to reduce antigen (Ag) prevalence to below 2% in areas where Anopheles or Culex is the main vector, and 1% where Aedes is the dominant vector (WHO, 2011). TAS is a population-based survey designed to estimate the prevalence of markers of LF infection in children aged 6 to 7 years. TAS is done with rapid Ag tests in W. bancrofti-endemic areas and rapid Ab tests in Brugia endemic areas, since LF rapid Ag tests do not detect Brugia infections. This age group was selected because new incident infections would reflect recent exposure to ongoing transmission (WHO, 2011). According to WHO guidelines, TAS should be repeated at 2-3 and 4-6 years after stopping MDA in each evaluation unit to monitor and identify signals of resurgence (WHO, 2011)
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