Advances in Preclinical Platforms of Loa loa for Filarial Neglected Tropical Disease Drug and Diagnostics Research

The tropical disease, loiasis, caused by the filarial parasite, Loa loa, has gained prominence in global public health as a cause of excess mortality and a barrier to the elimination of the related prioritized neglected tropical diseases (NTDs), lymphatic filariasis and onchocerciasis, within Central Africa. There are no effective drug cures or vaccines available to treat loiasis safely. Here we review recent advances in loiasis preclinical platform technologies, including novel in vitro culturing systems, animal models and innovations in experimental infections of the L. loa vector, Chrysops, that have facilitated access to all L. loa filarial life-cycle stages. We detail applications of these new model systems in anti-filarial drug screening, diagnostic development, immunology, and pathophysiology research. Finally, we provide an overview of how loiasis preclinical platforms may be further utilized in translational medicine applications to support the development of much needed new interventions against filarial NTDs.

PREVALENC OF LOIASIS, AND ITS DISTRIBUTION IN NDOKWE WEST L.G.A, DELTA STATE

Loa Loa is transmitted to humans by deer vectors, the vectors are bloodsucking and diurnal bites, and are found in rainforest areas in western and central Africa. After infection, a human will mate and produce more microfilariae, assuming the presence of mature male and female worms in the host. Although it has no major complications, the high microfilariae load may cause some neurological symptoms and discomfort in the ocular system may make patients uneasy. Loiasis, also known as African eyeworm, is caused by the parasitic worm Loa-Loa. Infection with this microfilaria worm causes an itchy swelling on the body, also known as Calabar bumps which prefers the rainforest-like environment of western and central Africa. Endemicity is particularly high in Cameroon, Congo, Nigeria, Gabon and the Central African Republic. One area of great concern is the fact that the endemicity of Onchocerciasis with Onchocerciasis as a bulk ivermectin therapy can lead to serious adverse effects in patients with high Loa Loa microfilariae densities and loads. This fact requires the development of more specific diagnostic tests for loa-loa so that areas or individuals at higher risk for neurological outcomes can be identified prior to microfilaricidal therapy. Although diethylcarbamazine, the standard treatment method, gives good results, it can cause serious complications when administered in standard doses to patients with high microfilariae load. A few years later, in 1778, Francois Guyost noticed worms in the eyes of West African slaves on a French ship bound for America and successfully removed the worm from a man's eye. Treatment of loiasis includes chemotherapy, in some cases surgical removal of adult worms, followed by systemic therapy.

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

Background Loa loa and Mansonella perstans–the causative agents of loiasis and mansonellosis—are vector-borne filarial parasites co-endemic in sub-Saharan Africa. Diagnosis of both infections is usually established by microscopic analysis of blood samples. It was recently established that the odds for detecting Plasmodium spp. is higher in capillary (CAP) blood than in venous (VEN) blood. In analogy to this finding this analysis evaluates potential differences in microfilaraemia of L. loa and M. perstans in samples of CAP and VEN blood. Methods Recruitment took place between 2015 and 2019 at the CERMEL in Lambaréné, Gabon and its surrounding villages. Persons of all ages presenting to diagnostic services of the research center around noon were invited to participate in the study. A thick smear of each 10 microliters of CAP and VEN blood was prepared and analysed by a minimum of two independent microscopists. Differences of log2-transformed CAP and VEN microfilaraemia were computed and expressed as percentages. Furthermore, odds ratios for paired data were computed to quantify the odds to detect microfilariae in CAP blood versus in VEN blood. Results A total of 713 participants were recruited among whom 52% were below 30 years of age, 27% between 30–59 years of age and 21% above 60 years of age. Male-female ratio was 0.84. Among 152 participants with microscopically-confirmed L. loa infection median (IQR) microfilaraemia was 3,650 (275–11,100) per milliliter blood in CAP blood and 2,775 (200–8,875) in VEN blood (p<0.0001), while among 102 participants with M. perstans this was 100 (0–200) and 100 (0–200), respectively (p = 0.44). Differences in linear models amount up to an average of +34.5% (95% CI: +11.0 to +63.0) higher L. loa microfilaria quantity in CAP blood versus VEN blood and for M. perstans it was on average higher by +24.8% (95% CI: +0.0 to +60.5). Concordantly, the odds for detection of microfilaraemia in CAP samples versus VEN samples was 1.24 (95% CI: 0.65–2.34) and 1.65 (95% CI: 1.0–2.68) for infections with L. loa and M. perstans, respectively. Conclusion This analysis indicates that average levels of microfilaraemia of L. loa are higher in CAP blood samples than in VEN blood samples. This might have implications for treatment algorithms of onchocerciasis and loiasis, in which exact quantification of L. loa microfilaraemia is of importance. Furthermore, the odds for detection of M. perstans microfilariae was higher in CAP than in VEN blood which may pre-dispose CAP blood for detection of M. perstans infection in large epidemiological studies when sampling of large blood quantities is not feasible. No solid evidence for a higher odds of L. loa microfilariae detection in CAP blood was revealed, which might be explained by generally high levels of L. loa microfilaraemia in CAP and VEN blood above the limit of detection of 100 microfilariae/ml. Yet, it cannot be excluded that the study was underpowered to detect a moderate difference.

Langlebiges Souvenir aus Kamerun – persistierende, massive Hypereosinophilie bei amikrofilarämischer Infektion mit Loa loa

Zusammenfassung Einleitung Die Diagnosestellung einer seltenen polysymptomatischen Parasitose erfordert eine Zusammenarbeit von Internisten, Tropenmedizinern, Parasitologen und Dermatologen. Anamnese Es wird der Krankheitsverlauf einer 66-Jährigen mit regelmäßigen Aufenthalten in Kamerun aufgezeigt, die sich mit massiver Hypereosinophilie und Pruritus bei urtikariellen Schwellungen präsentierte. Untersuchungen und Diagnose Mittels interdisziplinärer Diagnostik wurde anhand Reiseanamnese, klinischen Symptomen und Laborergebnissen die Arbeitsdiagnose einer okkulten, amikrofilarämischen Loa-loa-Infektion mit immunologischer Hyperreaktion gegen das Parasitenantigen, reaktiver Hypereosinophilie und hoher Anti-Filarien-Antikörperkonzentration gestellt. Therapie und Verlauf Die anthelminthische Therapie erfolgte mit Ivermectin und Diethylcarbamazin. Unter Ivermectin kam es zur prompten Symptomregredienz und Abfall der Eosinophilen- und Antikörperwerte. Folgerung Parasitosen wie die L.-loa-Infektion sind in Europa extrem selten, sollten jedoch bei entsprechender Reiseanamnese und klinischem Erscheinungsbild frühzeitig als Differenzialdiagnosen beachtet werden. Es mangelt an standardisierten Therapie- und Nachsorgeempfehlungen. Eine präzise Erfassung aller Neudiagnosen mit Therapieverlauf/-ansprechen in einem internationalen Register sollte etabliert werden.

A Case of Possible Loiasis Contracted in Cameroon and Diagnosed in Milan, Italy, and Review of Cases Published in Dermatological Journals

Loiasis is an infestation of the skin and eyes caused by the nematode <i>Loa loa.</i> We report a case of loiasis in a woman who contracted the infestation in Cameroon. The clinical picture was characterized by Calabar swellings on the upper limbs and axillary lymphadenopathy. Laboratory tests revealed persistent leucocytosis with neutropenia, lymphopenia, and eosinophilia. The search for microfilariae was always negative. The patient was successfully treated with ivermectin and albendazole. Follow-up (5 years) was negative for both clinical manifestations and laboratory tests.

Environmental Factors Associated With Loa loa Microfilaria Prevalence and Intensity in Diverse Bioecological Zones of Cameroon

Loiasis (African Eye Worm) is a filarial infection caused by Loa loa and transmitted by Chrysops vectors, which are confined to the tropical rainforests of Central and West Africa. Loiasis is a major impediment to control and elimination programmes that use the drug ivermectin due to the risk of serious adverse events. There is an urgent need to better refine and map high-risk communities. This study aimed to quantify and predict environmental factors associated with loiasis across five bioecological zones in Cameroon. The L. loa microfilaria (mf) prevalence (%) and intensity (mf number/ml) data from 42 villages within an Equatorial Rainforest and Savannah region were examined in relation to climate, topographic and forest-related data derived from satellite remote sensing sources. Differences between zones and regions were examined using nonparametric tests, and the relationship between L. loa mf prevalence, mf intensity, and the environmental factors using polynomial regression models. Overall, the L. loa mf prevalence was 11.6%, L. loa intensity 927.4 mf/ml, mean annual temperature 23.7°C, annual precipitation 2143.2 mm, elevation 790 m, tree canopy cover 46.7%, and canopy height 19.3m. Significant differences between the Equatorial Rainforest and Savannah region were found. Within the Equatorial Rainforest region, no significant differences were found. However, within the Savannah region, significant differences between the three bioecological zones were found, and the regression models indicated that tree canopy cover and elevation were significant predictors, explaining 85.1% of the L. loa mf prevalence (adjusted R2 = 0.851; p&lt;0.001) and tree cover alone was significant, explaining 58.1% of the mf intensity (adjusted R2 = 0.581; p&lt;0.001). The study highlights that environmental analysis can help delineate risk at different geographical scales, which may be practical for developing larger scale operational plans for mapping and implementing safe effective interventions.