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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.

Wanji S, Amvongo-Adjia N, Koudou B, Njouendou AJ, Chounna Ndongmo PW, Kengne-Ouafo JA, Datchoua-Poutcheu FR, Fovennso BA, Tayong DB, Fombad FF, Fischer PU, Enyong PI, Bockarie M - PLoS Negl Trop Dis (2015)

Bottom Line: No Mf of W. bancrofti were found in the night blood of any individual with a positive ICT result or clinical lymphoedema.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%.These results suggest that the main confounding factor for positive ICT test card results are high levels of L. loa.

View Article: PubMed Central - PubMed

Affiliation: Parasites and Vector Biology research unit (PAVBRU), Department of Microbiology and Parasitology, University of Buea, Buea, Cameroon.

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.

Methodology/principal findings: 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/significance: 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.

No MeSH data available.


Related in: MedlinePlus

Map of the study area.
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pntd.0004184.g001: Map of the study area.

Mentions: Data were collected between March and September 2013 in 42 villages across seven health districts (HDs) in the East (two HDs), North-west (one HD) and South-west (four HDs) regions, located in the Cameroon rainforest belt (Fig 1). The pre-control LF survey data in these study sites showed LF prevalence of 1% and above. These villages are situated in areas of contrasting endemicity of loiasis and mansonellosis. In the East region, Messamena and Batouri HDs are areas of high endemicity for both L. loa and M. perstan. The Nwa HD in the North-west is highly endemic for loiasis with very low endemicity for M. perstans. In the South-west region, four health districts with different profiles of endemicities for loiasis and mansonellosis endemicities were chosen: Kumba-Konye HDs, with low endemicity for both L. loa and M. perstans and the Mamfe-Eyumodjock HDs with low endemicity for loaisis and intermediate to high endemicity level for mansonellosis. Except Batouri, which is a naïve HD to ivermectin MDA, the remaining six HDs are under ivermectin MDA for onchocercasis elimination, and the most recent ivermectin MDA took place one to two months before the survey. The ivermectin treatment history in the study area is documented in S1 Table. Ivermectin clears L. loa Mf and W. bancrofti Mf at similar rates and it is likely that Individuals with high L. loa Mf counts did not participate in MDA.


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.

Wanji S, Amvongo-Adjia N, Koudou B, Njouendou AJ, Chounna Ndongmo PW, Kengne-Ouafo JA, Datchoua-Poutcheu FR, Fovennso BA, Tayong DB, Fombad FF, Fischer PU, Enyong PI, Bockarie M - PLoS Negl Trop Dis (2015)

Map of the study area.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4636288&req=5

pntd.0004184.g001: Map of the study area.
Mentions: Data were collected between March and September 2013 in 42 villages across seven health districts (HDs) in the East (two HDs), North-west (one HD) and South-west (four HDs) regions, located in the Cameroon rainforest belt (Fig 1). The pre-control LF survey data in these study sites showed LF prevalence of 1% and above. These villages are situated in areas of contrasting endemicity of loiasis and mansonellosis. In the East region, Messamena and Batouri HDs are areas of high endemicity for both L. loa and M. perstan. The Nwa HD in the North-west is highly endemic for loiasis with very low endemicity for M. perstans. In the South-west region, four health districts with different profiles of endemicities for loiasis and mansonellosis endemicities were chosen: Kumba-Konye HDs, with low endemicity for both L. loa and M. perstans and the Mamfe-Eyumodjock HDs with low endemicity for loaisis and intermediate to high endemicity level for mansonellosis. Except Batouri, which is a naïve HD to ivermectin MDA, the remaining six HDs are under ivermectin MDA for onchocercasis elimination, and the most recent ivermectin MDA took place one to two months before the survey. The ivermectin treatment history in the study area is documented in S1 Table. Ivermectin clears L. loa Mf and W. bancrofti Mf at similar rates and it is likely that Individuals with high L. loa Mf counts did not participate in MDA.

Bottom Line: No Mf of W. bancrofti were found in the night blood of any individual with a positive ICT result or clinical lymphoedema.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%.These results suggest that the main confounding factor for positive ICT test card results are high levels of L. loa.

View Article: PubMed Central - PubMed

Affiliation: Parasites and Vector Biology research unit (PAVBRU), Department of Microbiology and Parasitology, University of Buea, Buea, Cameroon.

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.

Methodology/principal findings: 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/significance: 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.

No MeSH data available.


Related in: MedlinePlus