Behavioural and clinical predictors for Loiasis

Abstract

BackgroundLoiasis is a vector-borne disease in Central and West Africa. While there is still uncertainty to what extent loiasis is responsible for population morbidity, individuals having both loiasis and onchocerciasis have a high risk of fatal encephalopathy when treatment (ie, ivermectin) for onchocerciasis is given. Therefore it is current policy that communities of high loiasis-burden are excluded from mass drug administration programmes of ivermectin. To address this treatment gap we present diagnostic scores, based on clinical and behavioural predictors that may help to rapidly identify sub-groups with loiasis within high-burden communities.MethodsA cross-sectional survey was performed in the province of la Ngounie, Gabon between December 2015 and Februrary 2016 and 947 participants of all ages were recruited. Clinical parameters and behavioural exposure factors were ascertained by questionnaire-based interviews. Parasitological analysis of blood samples was performed for L. loa detection. Diagnostic scores consisting of clinical and behavioural factors were modelled to predict loiasis in sub-groups residing in endemic regions.ResultsIncreasing sylvan exposure was identified as important risk factor for loiasis with adjusted odds ratios of 5.1 (95% confidence interval CI 2.6-9.9) for occasional forest exposure, 11.1 (95% CI 5.4-22.6) for frequent forest exposure and 25.7 (95% CI 12.5-52.9) for intensive forest exposure. Individuals with loiasis were 7.7 (95% CI 5.4-11.0) times more likely to report recurrent pruritus than those without loiasis. Reporting of regular daily exposure to the deep rain forest and recurrent pruritus was 9-fold (positive likelihood ratio 9.18; 95% CI: 6.39-13.18) more prevalent in individuals with loiasis than in controls. Concordantly, the absence of regular weekly forest exposure was associated with extremely low disease-likelihood (negative likelihood ratio 0.09; 95% CI 0.05-0.16).ConclusionsThese composite scores may serve as a simple tool to rapidly identify both those most and those least at risk of disease and may simplify loiasis control activities as well as screening procedures for studies on loiasis. Further, they may aid policy-makers to tailor the delivery of ivermectin mass drug administration for onchocerciasis control programmes more effectively and safely in regions of high loiasis-burden.

Distinct loiasis infection states and associated clinical and hematological manifestations in patients from Gabon

“…The majority of clinical data in scientific literature stem from reports on travelers and temporary residents of endemic regions [1,[7][8][9][10][11]. Only few studies systematically evaluated the clinical picture of loiasis in long-term residents of endemic regions, not least due to the supposedly benign disease course [4,[12][13][14][15][16][17]. Chronic infection has been associated with unspecific manifestations, such as itching, body pains or fatigue and importantly, individuals with high microfilarial densities are known to be at risk for spontaneous or treatment-related severe manifestations and excess mortality [1,7,12,13,18,19].…”

Low Diagnostic Performance of Thick Blood Smears of 50 µL in Comparison with Blood Direct Examination of 10 µL and Leukoconcentration Techniques among Loiasis-Suspected Patients with Low Microfilaremia in Gabon, Central Africa, using the STARD-BCLM Guidelines

“…The place of residence of the populations in these studies may partly explain the differences in prevalence observed. Indeed, people who live in endemic areas, mainly in rural settlements, are more exposed to Chrysops (loiasis vector) bites than their counterparts living in urban areas [25,28,29]. In the survey performed by Bouyou-Akotet et al, for example, two-thirds of the population came from rural areas, which could explain the higher prevalence observed in that study [1].…”

Diagnostic performance of capillary and venous blood samples in the detection of Loa loa and Mansonella perstans microfilaraemia using light microscopy

“…loa microfilaraemia (i.e. > 20,000 microfilariae/milliliter blood) [ 27 ]. To overcome this treatment gap, a so called ‘Test and not treat’ strategy was developed which is based on withholding mass drug administration from those people with high levels of L .…”

“…In the past, the implementation of ivermectin-based mass drug administration for the control of onchocerciasis or lymphatic filariasis has been impaired because of afore-mentioned serious adverse events in persons with a high L. loa microfilaraemia (i.e. > 20,000 microfilariae/milliliter blood) [27]. To overcome this treatment gap, a so called 'Test and not treat' strategy was developed which is based on withholding mass drug administration from those people with high levels of L. loa microfilariae [28,29].…”