The relationship between microfilaraemic and amicrofilaraemic loiasis involving co-infection with Mansonella perstans and clinical symptoms in an exposed population from Gabon

Abstract

The relationship between the frequency of loiasis objective symptoms and microfilaraemic or amicrofilaraemic infection was assessed in 1148 exposed patients also infected, or not, with Mansonella perstans. Filarial infections were detected by direct microscopy, leucoconcentration and serology, with prevalence values of 39.5% Loa loa, 5.6% M. perstans and 3.4% co-infection with both filarial species. Amicrofilaraemic or occult loiasis (OL) predominated among L. loa-infected individuals, with a prevalence of 58.2%. Hypermicrofilaraemia (>8000 microfilariae (mf)/ml) was found in 18.4% of L. loa microfilaraemic patients, with 25.7% of them harbouring more than 30,000 mf/ml. Up to 34% of patients with OL showed evidence of Calabar swelling, compared with 26.3% of microfilaraemic patients (P= 0.03). Overall 5.3% of patients presented with adult worm migration across the eye, representing 16.3% of microfilaraemic individuals and 11.4% of amicrofilaraemic patients (P= 0.13). This symptom was similarly found in patients with more than 30,000 mf/ml (22%), those with microfilaraemia between 8 and 30,000 mf/ml (15.4%) and also in individuals with low or without microfilaraemia (16.1%) (P= 0.7). Five (14.3%) hypermicrofilaraemic patients did not present any L. loa-specific objective symptoms, as well as all the patients with single M. perstans infection. The presence of adult eye worm migration as a strong predictor of high microfilaraemia density would obscure the real burden of L. loa hypermicrofilaraemia in exposed individuals. For epidemiological purposes and control strategies, the mapping of L. loa in endemic areas should also take into account the group of patients with occult loiasis.

Colorimetric and Real-Time Loop-Mediated Isothermal Amplification (LAMP) for Detection of Loa loa DNA in Human Blood Samples

“…43, 45 and 47) resulted positive by real-time LAMP assay. We sincerely believe that those colorimetric LAMP-positive results obtained for Loa loa in both M. perstans microscopy-positive samples and in samples with microscopy-negative findings could be true DNA Loa loa detection, since coinfections with M. perstans in co-endemic areas are very common [6,52], and it is also possible that they may have gone undetected under microscopy due to their wellknown limited sensitivity for Loa loa [53]. Moreover, the higher sensitivity of our in-house LAMP over PCR/nested-PCR could also explain these positive results.…”

A cross-sectional study of the filarial and Leishmania co-endemicity in two ecologically distinct settings in Mali

“…This co-infection was also observed in a neighboring area of Kolokani before any mass drug administration with a high prevalence of 48.3% (69/143) [ 23 ]. A high prevalence of M. perstans infection was also reported in other countries such as Senegal [ 27 ], Nigeria [ 28 ], Ghana [ 29 ], Burkina Faso [ 30 ], Gabon [ 31 ], as well as Cameroon in Central Africa [ 32 ]. Moreover, previous studies reported symptoms such as symptomatic hypereosinophilia related to M. perstans microfilaremia [ 33 ].…”

The impact of Loa loa microfilaraemia on research subject retention during a whole sporozoite malaria vaccine trial in Equatorial Guinea

“… 18 The microfilaricidal effects of ivermectin on L. loa are well established 19 and the prevalence of L. loa microfilaraemia has been shown to decrease markedly in regions where ivermectin mass administration has been employed. 19 , 20 Assessing the prevalence of loiasis is complicated by the fact that many individuals who harbour adult worms are amicrofilaremic 21 and that some care is required to accurately distinguish L. loa from Mansonella perstans microfilariae by microscopy. 22 Of interest, a recent cross-sectional study of 243 residents of Bioko Island found the prevalence of L. loa microfilaraemia to be 0.7% and M. perstans to be 8.8% by qPCR of whole blood.…”

“…It is known that the sensitivity of standard Giemsa-stained TBSs to detect loiasis is low; less than half of individuals who harbour adult worms have detectable microfilaraemia. 21 Antibody tests could be used, but their inability to distinguish past from current infections 30 would be likely to inflate the number of suspected active L. loa cases. Quantitative PCR has been shown to be more sensitive than microscopy for the detection of L. loa microfilariae 16 , 23 and is a technology that is increasingly available in the field.…”