Seroprevalence and spatial epidemiology of Lymphatic Filariasis in American Samoa after successful mass drug administration

Colleen L Lau; Kimberly Y Won; Luke Becker; Ricardo J Soares Magalhaes; Saipale Fuimaono; Wayne Melrose; Patrick J Lammie; Patricia M Graves

doi:10.1371/journal.pntd.0003297

Seroprevalence and spatial epidemiology of Lymphatic Filariasis in American Samoa after successful mass drug administration

PLoS Negl Trop Dis. 2014 Nov 13;8(11):e3297. doi: 10.1371/journal.pntd.0003297. eCollection 2014.

Authors

Colleen L Lau¹, Kimberly Y Won², Luke Becker³, Ricardo J Soares Magalhaes⁴, Saipale Fuimaono⁵, Wayne Melrose³, Patrick J Lammie², Patricia M Graves³

Affiliations

¹ WHO Collaborating Centre for Children's Health and Environment, Queensland Children's Medical Research Institute, The University of Queensland, Brisbane, Australia; Research School of Population Health, Australian National University, Canberra, Australia.
² Centers for Disease Control and Prevention, Division of Parasitic Diseases and Malaria, Atlanta, Georgia, United States of America.
³ WHO Collaborating Centre for Lymphatic Filariasis, Soil-Transmitted Helminths, and other Neglected Tropical Diseases, Division of Tropical Health and Medicine, James Cook University, Cairns, Australia.
⁴ WHO Collaborating Centre for Children's Health and Environment, Queensland Children's Medical Research Institute, The University of Queensland, Brisbane, Australia; School of Veterinary Science, The University of Queensland, Gatton, Australia.
⁵ American Samoa Department of Health, Pago Pago, American Samoa.

Abstract

Background: As part of the Global Programme to Eliminate Lymphatic Filariasis (LF), American Samoa conducted mass drug administration (MDA) from 2000-2006, and passed transmission assessment surveys in 2011-2012. We examined the seroprevalence and spatial epidemiology of LF post-MDA to inform strategies for ongoing surveillance and to reduce resurgence risk.

Methods: ELISA for LF antigen (Og4C3) and antibodies (Wb123, Bm14) were performed on a geo-referenced serum bank of 807 adults collected in 2010. Risk factors assessed for association with sero-positivity included age, sex, years lived in American Samoa, and occupation. Geographic clustering of serological indicators was investigated to identify spatial dependence and household-level clustering.

Results: Og4C3 antigen of >128 units (positive) were found in 0.75% (95% CI 0.3-1.6%) of participants, and >32 units (equivocal plus positive) in 3.2% (95% CI 0.6-4.7%). Seroprevalence of Wb123 and Bm14 antibodies were 8.1% (95% CI 6.3-10.2%) and 17.9% (95% CI 15.3-20.7%) respectively. Antigen-positive individuals were identified in all ages, and antibody prevalence higher in older ages. Prevalence was higher in males, and inversely associated with years lived in American Samoa. Spatial distribution of individuals varied significantly with positive and equivocal levels of Og4C3 antigen, but not with antibodies. Using Og4C3 cutoff points of >128 units and >32 units, average cluster sizes were 1,242 m and 1,498 m, and geographical proximity of households explained 85% and 62% of the spatial variation respectively.

Conclusions: High-risk populations for LF in American Samoa include adult males and recent migrants. We identified locations and estimated the size of possible residual foci of antigen-positive adults, demonstrating the value of spatial analysis in post-MDA surveillance. Strategies to monitor cluster residents and high-risk groups are needed to reduce resurgence risk. Further research is required to quantify factors contributing to LF transmission at the last stages of elimination to ensure that programme achievements are sustained.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Adolescent
Adult
Aged
Aged, 80 and over
American Samoa / epidemiology
Animals
Antibodies, Helminth / blood
Antigens, Helminth / blood
Cluster Analysis
Elephantiasis, Filarial / drug therapy
Elephantiasis, Filarial / epidemiology*
Elephantiasis, Filarial / prevention & control
Female
Humans
Male
Middle Aged
Risk
Seroepidemiologic Studies
Spatial Analysis
Surveys and Questionnaires
Wuchereria bancrofti / immunology*
Young Adult

Substances

Antibodies, Helminth
Antigens, Helminth

Grants and funding

We would like to acknowledge James Cook University and GLaxoSmithKline for providing financial support for the WHO Collaborating Centre for Lymphatic Filariasis, Soil-Transmitted Helminths, and Other Neglected Tropical Diseases at James Cook University, Cairns, Australia (LB, WM, PMG). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.