title: Positivity of Antigen Tests Used for Diagnosis of Lymphatic Filariasis in Individuals Without Wuchereria bancrofti Infection But with High Loa loa Microfilaremia.
abstract: Since the mid-2000s, the immunochromatographic card test (ICT), a point-of-care test for detecting Wuchereria bancrofti circulating filarial antigens (CFAs), has been the backbone for mapping and monitoring lymphatic filariasis (LF) worldwide. Recently, there have been instances in which CFA positivity has been associated with Loa loa microfilaremia. Here, we examined the association, at both the community and individual levels, between L. loa and CFA using additional diagnostic tools (quantitative polymerase chain reaction [qPCR], Og4C3 enzyme-linked immunosorbent assay, and IgG4 antibodies to Wb123 assays) to demonstrate the relationship between L. loa microfilaremia and ICT positivity. In May 2013, peripheral blood was collected during the day from 1,812 individuals living in southern Cameroon. ICT tests were done on the spot, and positive individuals were resampled at night. Results of qPCR and Wb123 assays concurred proving the absence of W. bancrofti infection. Og4C3 assays indicate a quantitative relationship between the level of L. loa microfilaremia and that of CFA. This was confirmed by epidemiological analyses, which reveal a strong association between L. loa microfilaremia and ICT positivity, with 50% of ICT reacting to L. loa when its microfilarial density exceeds 30,000 microfilariae/mL. At the community level, the proportion of positive ICT would exceed 2% when the prevalence of L. loa microfilaremia in the total population is above 20%. This has significant implications in terms of mapping and control of LF caused by W. bancrofti in Loa-endemic areas. Cross-reactivity of ICT with L. loa has to be considered in the context of both individual and community diagnostics.
authors.affiliation: Centre de Recherche sur les Filarioses et autres Maladies Tropicales, Yaoundé, Cameroon.|Unité Mixte Internationale 233, Institut de Recherche pour le Développement, Université de Montpellier, Institut National de la Santé et de la Recherche Médicale, Montpellier, France.
authors.forename: Sébastien D
authors.initials: SD
authors.lastname: Pion
authors.affiliation: Unité Mixte Internationale 233, Institut de Recherche pour le Développement, Université de Montpellier, Institut National de la Santé et de la Recherche Médicale, Montpellier, France.
authors.forename: Céline
authors.initials: C
authors.lastname: Montavon
authors.affiliation: Unité Mixte Internationale 233, Institut de Recherche pour le Développement, Université de Montpellier, Institut National de la Santé et de la Recherche Médicale, Montpellier, France.
authors.forename: Cédric B
authors.initials: CB
authors.lastname: Chesnais
authors.affiliation: Faculty of Medicine and Biomedical Sciences, University of Yaoundé 1, Yaoundé, Cameroon.|Centre de Recherche sur les Filarioses et autres Maladies Tropicales, Yaoundé, Cameroon.
authors.forename: Joseph
authors.initials: J
authors.lastname: Kamgno
authors.affiliation: Department of Microbiology and Parasitology, University of Buea, Buea, Cameroon.|Research Foundation for Tropical Diseases and Environment, Buea, Cameroon.
authors.forename: Samuel
authors.initials: S
authors.lastname: Wanji
authors.affiliation: National Institutes of Health, Bethesda, Maryland.
authors.forename: Amy D
authors.initials: AD
authors.lastname: Klion
authors.affiliation: National Institutes of Health, Bethesda, Maryland.
authors.forename: Thomas B
authors.initials: TB
authors.lastname: Nutman
authors.affiliation: Unité Mixte Internationale 233, Institut de Recherche pour le Développement, Université de Montpellier, Institut National de la Santé et de la Recherche Médicale, Montpellier, France.
authors.forename: Michel
authors.initials: M
authors.lastname: Boussinesq
mesh_terms: D000293:Adolescent; D000328:Adult; D000818:Animals; D000947:Antigens, Helminth / Q000097:blood*; D002648:Child; D002675:Child, Preschool; D004605:Elephantiasis, Filarial / Q000175:diagnosis* / Q000469:parasitology*; D005260:Female; D006801:Humans; D008117:Loa / Q000302:isolation & purification*; D008297:Male; D008875:Middle Aged; D014958:Wuchereria bancrofti / Q000302:isolation & purification*; D055815:Young Adult
chemical_list: D000947:Antigens, Helminth