Mapping lymphatic filariasis in Loa loa endemic health districts naïve for ivermectin mass administration and situated in the forested zone of Cameroon

Abstract

Background: The control of lymphatic filariasis (LF) caused by Wuchereria bancrofti in the Central African Region has been hampered by the presence of Loa loa due to severe adverse events that arise in the treatment with ivermectin. The immunochromatographic test (ICT) cards used for mapping LF demonstrated cross-reactivity with L. loa and posed the problem of delineating the LF map. To verify LF endemicity in forest areas of Cameroon where mass drug administration (MDA) has not been ongoing, we used the recently developed strategy that combined serology, microscopy and molecular techniques. Methods: This study was carried out in 124 communities in 31 health districts (HDs) where L. loa is present. At least 125 persons per site were screened. Diurnal blood samples were investigated for circulating filarial antigen (CFA) by FTS and for L. loa microfilariae (mf) using TBF. FTS positive individuals were further subjected to night blood collection for detecting W. bancrofti. qPCR was used to detect DNA of the parasites. Results: Overall, 14,446 individuals took part in this study, 233 participants tested positive with FTS in 29 HDs, with positivity rates ranging from 0.0 to 8.2%. No W. bancrofti mf was found in the night blood of any individuals but L. loa mf were found in both day and night blood of participants who were FTS positive. Also, qPCR revealed that no W. bancrofti but L.loa DNA was found with dry bloodspot. Positive FTS results were strongly associated with high L. loa mf load. Similarly, a strong positive association was observed between FTS positivity and L loa prevalence. Conclusions: Using a combination of parasitological and molecular tools, we were unable to find evidence of W. bancrofti presence in the 31 HDs, but L. loa instead. Therefore, LF is not endemic and LF MDA is not required in these districts.

An update on the mosquito fauna and mosquito-borne diseases distribution in Cameroon

“…The disease is on the decline in Cameroon due to the intensification of mass drug administration (MDA) campaigns across the country using the drugs albendazole and ivermectin [ 75 ]. A recent study conducted in 31 health districts of four endemic regions of the south of the country (central, east, south, and littoral) failed to find any cases of W. bancrofti infection [ 77 ]. Due to cross-reaction of the LF diagnostic test (filariasis test strip, FTS) with Loa loa (Spirurida, Filaridae), a microfilaria which is endemic in the southern part of the country, false positives are increasingly reported, and it is obvious that appropriate diagnostic tools avoiding false positive detections are needed to guide disease elimination efforts in the country [ 77 , 78 ].…”

“…A recent study conducted in 31 health districts of four endemic regions of the south of the country (central, east, south, and littoral) failed to find any cases of W. bancrofti infection [ 77 ]. Due to cross-reaction of the LF diagnostic test (filariasis test strip, FTS) with Loa loa (Spirurida, Filaridae), a microfilaria which is endemic in the southern part of the country, false positives are increasingly reported, and it is obvious that appropriate diagnostic tools avoiding false positive detections are needed to guide disease elimination efforts in the country [ 77 , 78 ]. With the intensification of travel and population migrations between East and West Africa and within regions, it is possible that cases could be imported from other endemic settings which will make W. bancrofti filariasis elimination in Cameroon more challenging.…”

Sustainable Surveillance of Neglected Tropical Diseases for the Post-Elimination Era

“…For example, in areas endemic for Wuchereria bancrofti filariasis, WHO recommends the Alere Filariasis Test Strip (FTS), which measures circulating filarial antigen in human blood. However, the FTS is cross-reactive with Loa loa antigens [ 27 ], which limits its utility for post-elimination surveillance in (previously) coendemic settings. STH and schistosomiasis are routinely detected using microscopy-based diagnostic tools that count the number of parasite eggs excreted in urine or stool.…”

Integrated xenosurveillance of Loa loa, Wuchereria bancrofti, Mansonella perstans and Plasmodium falciparum using mosquito carcasses and faeces: A pilot study in Cameroon

“…loa microfilariae have been detected in night blood of infected individuals, L . loa parasite DNA may also be taken up in sufficient quantities by night-biting mosquitoes to be detected through xenosurveillance methods [ 19 , 20 ].…”