Background Individuals with high microfilarial densities (MFD) of Loa loa are at risk of developing serious adverse events (SAEs) after ivermectin treatment. Pretreatment with drugs progressively reducing Loa MFD below the risk threshold might help prevent these SAEs. We assessed the safety and efficacy of levamisole for this purpose. Methods A double-blind, randomized, placebo-controlled, MFD-ascending trial was conducted in the Republic of the Congo. Participants were treated in 3 cohorts defined by pretreatment MFD and levamisole dose (Cohort 1: 1.0 kg and 1.5 mg/kg, Cohorts 2 and 3: 2.5 mg/kg). Safety outcomes were occurrence of SAE and AE frequency during the first week. The efficacy outcomes were MFD reduction from baseline and proportions of individuals with at least 40% and 80% MFD reduction at day 2 (D2), D7 and D30. Results The two lowest doses (1.0 mg/kg and 1.5 mg/kg) caused no SAE but were ineffective. Compared to placebo, 2.5 mg/kg levamisole caused more mild AEs (10/85 vs. 3/85, P = .018), a higher median reduction from baseline to D2 (-12.9% vs. + 15.5%, P < .001), D7 (-4.9% vs. +18.7%, P < .001) and D30 (-0.5% vs. +13.5%, P = .036) and a higher percentage of participants with >40% MFD reduction at D2 (17.5% vs. 1.2%, P < .001), D7 (11.8% vs. 6.3%, P = .269) and D30 (18.5% vs. 9.6%, P = .107). Conclusions A single 2.5 mg/kg levamisole dose induces a promising transient reduction in Loa loa MFD and should encourage testing different regimens.

Background Individuals with high Loa loa microfilarial densities are at risk of developing severe encephalopathy after administration of antiparasitic drugs. Apart from this finding, loiasis is considered benign with no effect on brain function. However, recent epidemiological data suggest an increased mortality and morbidity in L. loa infected individuals, underscoring the importance of studies on the possible neurological morbidity associated with loiasis. Methodology Using MoCA tests and neurological ultrasounds, we conducted a cross-sectional study to assess cognitive alteration in a population living in a rural area endemic for loiasis in the Republic of Congo. Fifty individuals with high microfilarial densities (MFD) were matched on sex, age and residency with 50 individuals with low MFD and 50 amicrofilaremic subjects. Analyses focused on individuals with MoCA scores indicating an altered cognition (i.e. < 23/30) and on the total MoCA score according to Loa loa MFD, sociodemographic characteristics and neurological ultrasound results. Principal findings MoCA scores were very low in the studied population (mean of 15.6/30). Individuals with more than 15,000 microfilariae per milliliter of blood (mean predicted score:14.0/30) are more than twenty times more likely to have an altered cognition, compared to individuals with no microfilaremia (mean predicted score: 16.3/30). Years of schooling were strongly associated with better MoCA results. Extracranial and intracranial atheroma were not associated with L. loa MFD. Conclusion/significance Loaisis microfilaremia is probably involved in cognitive impairment, especially when the MFD are high. These results highlight the urgent need to better understand loaisis-induced morbidity. Further studies investigating neurological morbidity of loiasis are needed.

Background Loa loa microfilariae circulate in the peripheral blood of human hosts following a diurnal periodicity, with maximal microfilaremia levels generally observed between 10:00 am and 3:00 pm. Few studies have assessed factors potentially associated with this periodicity. Methods Microfilaremia data were collected repeatedly between 9:00 am and 8:00 pm from 13 individuals in the Republic of the Congo. Using local polynomial regression (LOESS), we determined the best models representing the dynamics of microfilaremia over this period. In a second step, using cosinor models, we evaluated the influence of sex, age, and body temperature on the periodicity of L. loa microfilaremia in blood. Results All subjects reached their maximum microfilaremia between 10:00 am and 4:00 pm. Individual microfilaremia showed different patterns between individuals, and some clearly showed multiple peaks within a day. LOESS provided a good fit to the observed data. Without adjustment, the maximum microfilarial density was reached around 11:00 am. Adjustment revealed three distinct modes of microfilaremia, occurring around 10:00 am, 1:00 pm, and 4:00 pm. Cosinor models also provided good fit to our data. After adjustment on body temperature, the L. loa microfilaremia fluctuation amplitude decreased significantly from 1684.8 to 310.6 microfilariae(mf)/ml and the predicted peak was estimated at 12:02 pm. Conclusions We characterized the periodicity of L. loa microfilaremia mathematically with two different approaches: cosinor models and LOESS regression. Both models suggest that body temperature plays a role in the variation in microfilaremia within a day. Further studies are needed to identify individual co-factors affecting microfilaremia. Graphical Abstract

Background: Loa loa microfilariae circulate in the peripheral blood of human hosts following a diurnal periodicity, with maximal microfilaremia levels generally observed between 10:00 am and 3:00 pm. Few studies have assessed factors potentially associated with this periodicity. Methods: Microfilaremia data were collected repeatedly between 9:00 am and 8:00 pm from 13 individuals in the Republic of Congo. Using local polynomial regression (LOESS), we determined the best models representing the dynamics of microfilaremia over this time period. In a second step, using cosinor models we evaluated the influence of sex, age and body temperature on the periodicity of L. loa microfilaraemia in blood.Results: All subjects had their maximum microfilaremia reached between 10:00 am and 4:00 pm. Individual microfilaremia showed different patterns between individuals and some clearly showed multiple peaks within a day. LOESS provided good fit to the observed data. Without adjustment, the maximum microfilarial density was reached around 11:00 am. Adjustment revealed three distinct modes of microfilaremia, occurring around 10:00 am, 1:00 pm and 4:00 pm.Cosinor models also provided good fit to our data. After adjustment on body temperature, the L. loa microfilaremia fluctuation amplitude decreased significantly from 1684.8 to 310.6 mf/mL and the predicted peak was estimated at 12:02 pm. Conclusion: We characterized the periodicity of Loa loa microfilaremia mathematically with 2 different approaches: cosinor models and LOESS regression. Both models suggest that body temperature plays a role in the variation of microfilaremia within a day. Further studies are needed to identify individual cofactors affecting microfilaremia.