title: Cross-Reactivity of Filariais ICT Cards in Areas of Contrasting Endemicity of Loa loa and Mansonella perstans in Cameroon: Implications for Shrinking of the Lymphatic Filariasis Map in the Central African Region.
abstract: BACKGROUND
  Immunochromatographic card test (ICT) is a tool to map the distribution of Wuchereria bancrofti. In areas highly endemic for loaisis in DRC and Cameroon, a relationship has been envisaged between high L. loa microfilaria (Mf) loads and ICT positivity. However, similar associations have not been demonstrated from other areas with contrasting levels of L. loa endemicity. This study investigated the cross-reactivity of ICT when mapping lymphatic filariasis (LF) in areas with contrasting endemicity levels of loiasis and mansonellosis in Cameroon.
  
  
  RESULTS
  A cross-sectional study to assess the prevalence and intensity of W. bancrofti, L. loa and M. perstans was carried out in 42 villages across three regions (East, North-west and South-west) of the Cameroon rainforest domain. Diurnal blood was collected from participants for the detection of circulating filarial antigen (CFA) by ICT and assessment of Mf using a thick blood smear. Clinical manifestations of LF were also assessed. ICT positives and patients clinically diagnosed with lymphoedema were further subjected to night blood collection for the detection of W. bancrofti Mf. Overall, 2190 individuals took part in the study. Overall, 24 individuals residing in 14 communities were tested positive by ICT, with prevalence rates ranging from 0% in the South-west to 2.1% in the North-west. Lymphoedema were diagnosed in 20 individuals with the majority of cases found in the North-west (11/20), and none of them were tested positive by ICT. No Mf of W. bancrofti were found in the night blood of any individual with a positive ICT result or clinical lymphoedema. Positive ICT results were strongly associated with high L. loa Mf intensity with 21 subjects having more than 8,000 L. loa Mf ml/blood (Odds ratio = 15.4; 95%CI: 6.1-39.0; p < 0.001). Similarly, a strong positive association (Spearman's rho = 0.900; p = 0.037) was observed between the prevalence of L. loa and ICT positivity by area: a rate of 1% or more of positive ICT results was found only in areas with an L. loa Mf prevalence above 15%. In contrast, there was no association between ICT positivity and M. perstans prevalence (Spearman's rho = - 0.200; p = 0.747) and Mf density (Odds ratio = 1.8; 95%CI: 0.8-4.2; p = 0.192).
  
  
  CONCLUSIONS
  This study has confirmed the strong association between the ICT positivity and L. loa intensity (Mf/ml of blood) at the individual level. Furthermore, the study has demonstrated that ICT positivity is strongly associated with high L. loa prevalence. These results suggest that the main confounding factor for positive ICT test card results are high levels of L. loa. The findings may indicate that W. bancrofti is much less prevalent in the Central African region where L. loa is highly endemic than previously assumed and accurate re-mapping of the region would be very useful for shrinking of the map of LF distribution.
authors.affiliation: Parasites and Vector Biology research unit (PAVBRU), Department of Microbiology and Parasitology, University of Buea, Buea, Cameroon.|Research Foundation for Tropical Diseases and the Environment (REFOTDE), Buea, Cameroon.
authors.forename: Samuel
authors.initials: S
authors.lastname: Wanji
authors.affiliation: Research Foundation for Tropical Diseases and the Environment (REFOTDE), Buea, Cameroon.|Laboratory of Parasitology and Ecology, Department of Animal Biology and Physiology, University of Yaoundé 1, Yaounde, Cameroon.
authors.forename: Nathalie
authors.initials: N
authors.lastname: Amvongo-Adjia
authors.affiliation: Centre for Neglected Tropical Diseases (incorporating the Lymphatic Filariasis Support Centre), Liverpool School of Tropical Medicine, Liverpool, United Kingdom.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Koudou
authors.affiliation: Parasites and Vector Biology research unit (PAVBRU), Department of Microbiology and Parasitology, University of Buea, Buea, Cameroon.|Research Foundation for Tropical Diseases and the Environment (REFOTDE), Buea, Cameroon.
authors.forename: Abdel Jelil
authors.initials: AJ
authors.lastname: Njouendou
authors.affiliation: Parasites and Vector Biology research unit (PAVBRU), Department of Microbiology and Parasitology, University of Buea, Buea, Cameroon.|Research Foundation for Tropical Diseases and the Environment (REFOTDE), Buea, Cameroon.
authors.forename: Patrick W
authors.initials: PW
authors.lastname: Chounna Ndongmo
authors.affiliation: Parasites and Vector Biology research unit (PAVBRU), Department of Microbiology and Parasitology, University of Buea, Buea, Cameroon.|Research Foundation for Tropical Diseases and the Environment (REFOTDE), Buea, Cameroon.
authors.forename: Jonas A
authors.initials: JA
authors.lastname: Kengne-Ouafo
authors.affiliation: Research Foundation for Tropical Diseases and the Environment (REFOTDE), Buea, Cameroon.
authors.forename: Fabrice R
authors.initials: FR
authors.lastname: Datchoua-Poutcheu
authors.affiliation: Research Foundation for Tropical Diseases and the Environment (REFOTDE), Buea, Cameroon.
authors.forename: Bridget Adzemye
authors.initials: BA
authors.lastname: Fovennso
authors.affiliation: Parasites and Vector Biology research unit (PAVBRU), Department of Microbiology and Parasitology, University of Buea, Buea, Cameroon.|Research Foundation for Tropical Diseases and the Environment (REFOTDE), Buea, Cameroon.
authors.forename: Dizzle Bita
authors.initials: DB
authors.lastname: Tayong
authors.affiliation: Parasites and Vector Biology research unit (PAVBRU), Department of Microbiology and Parasitology, University of Buea, Buea, Cameroon.|Research Foundation for Tropical Diseases and the Environment (REFOTDE), Buea, Cameroon.
authors.forename: Fanny Fri
authors.initials: FF
authors.lastname: Fombad
authors.affiliation: Infectious Diseases Division, Department of Internal Medicine, Washington University School of Medicine, St. Louis, Missouri, United States of America.
authors.forename: Peter U
authors.initials: PU
authors.lastname: Fischer
authors.affiliation: Parasites and Vector Biology research unit (PAVBRU), Department of Microbiology and Parasitology, University of Buea, Buea, Cameroon.|Research Foundation for Tropical Diseases and the Environment (REFOTDE), Buea, Cameroon.
authors.forename: Peter I
authors.initials: PI
authors.lastname: Enyong
authors.affiliation: Centre for Neglected Tropical Diseases (incorporating the Lymphatic Filariasis Support Centre), Liverpool School of Tropical Medicine, Liverpool, United Kingdom.
authors.forename: Moses
authors.initials: M
authors.lastname: Bockarie
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D000947:Antigens, Helminth / Q000097:blood; D002163:Cameroon / Q000453:epidemiology; D002648:Child; D002846:Chromatography, Affinity / Q000379:methods*; D003429:Cross Reactions; D003430:Cross-Sectional Studies; D004605:Elephantiasis, Filarial / Q000175:diagnosis* / Q000453:epidemiology*; D005260:Female; D006801:Humans; D008117:Loa / Q000302:isolation & purification; D008118:Loiasis / Q000453:epidemiology*; D008297:Male; D008368:Mansonelliasis / Q000453:epidemiology*; D008875:Middle Aged; D059208:Parasite Load; D012424:Rural Population; D014958:Wuchereria bancrofti / Q000276:immunology*; D055815:Young Adult
chemical_list: D000947:Antigens, Helminth