Excess mortality associated with loiasis: a retrospective population-based cohort study

Evaluation of knowledge, attitude and practice towards loiasis in the rural community of Sindara, in central African Gabon

BACKGROUND

More than 20 million people are infected with L. loa, and around 40 million live in high or intermediate-risk areas in West- and Central Africa. Although loiasis is associated with significant morbidity and excess mortality, little is known about the perception of loiasis by affected communities. This study assessed the knowledge, attitudes, and practices in the rural population of Sindara, Gabon, a region characterized by high loiasis prevalence.

METHODS

A community-based cross-sectional survey was conducted in Gabon between January and June 2022. During systematic door-to-door visits, randomly selected inhabitants were invited to participate in this questionnaire based survey. Venous blood was collected at midday from all participants for microscopic detection of filarial infection and clinical signs of loiasis were assessed.

RESULTS

A total of 150 participants were recruited, of which 66% were infected by L. loa. While almost everyone had some knowledge about L. loa, 72% of the participants understood that L. loa is a parasitic worm. The transmission of L. loa via the deer fly was known to only 21% of participants. The most frequently mentioned clinical symptoms attributed to loiasis were itching (84%), eye worm migration (59%), and conjunctivitis-like symptoms (53%). Participants who experienced migratory loiasis had better knowledge of loiasis and considered it as more serious. Traditional and herbal medicine was reported most often as an available treatment option (72%). While the formal healthcare sector was mentioned as the preferred treatment provider, 60% of the reported infections were treated by traditional medical practitioners.

CONCLUSION

Loiasis is in general well known by this community residing in a region of high L. loa transmission. Important gaps in knowledge were discovered foremost regarding the mode of transmission. The available healthcare system does not seem to provide adequate management for loiasis.

Eosinophils, basophils and myeloid-derived suppressor cells in chronic Loa loa infection and its treatment in an endemic setting

BACKGROUND

Chronic infection by Loa loa remains an unsolved immunological paradox. Despite harboring subcutaneously migrating adult worms and often high densities of microfilariae, most patients experience only relatively mild symptoms, yet microfilaricidal treatment can trigger life-threatening inflammation. Here, we investigated innate cell populations hypothesized to play a role in these two faces of the disease, in an endemic population in Gabon.

METHODOLOGY/PRINCIPAL FINDINGS

We analyzed numbers and activation of eosinophils and basophils, as well as myeloid-derived suppressor cell (MDSC) subsets and associated circulating cytokine levels by flow cytometry in sex- and age-matched L. loa-uninfected (LL-), -amicrofilaraemic (MF-) and -microfilaraemic (MF+) individuals (n = 42), as well as microfilaraemic individuals treated with albendazole (n = 26). The percentage of eosinophils was lower in LL- (3.0%) than in the combined L. loa-infected population, but was similar in MF+ (13.1%) and MF- (12.3%). Upon treatment of MF+, eosinophilia increased from day 0 (17.2%) to day 14 (24.8%) and had decreased below baseline at day 168 (6.3%). Expression of the eosinophil activation marker CD123 followed the same pattern as the percentage of eosinophils, while the inverse was observed for CD193 and to some extent CD125. Circulating IL-5 levels after treatment followed the same pattern as eosinophil dynamics. Basophil numbers did not differ between infection states but increased after treatment of MF+. We did not observe differences in MDSC numbers between infection states or upon treatment.

CONCLUSIONS/SIGNIFICANCE

We demonstrate that both chronic infection and treatment of L. loa microfilaraemia are associated with eosinophil circulation and distinct phenotypical activation markers that might contribute to inflammatory pathways in this setting. In this first ever investigation into MDSC in L. loa infection, we found no evidence for their increased presence in chronic loiasis, suggesting that immunomodulation by L. loa is induced through other pathways.

Low diagnostic performance of thick blood smears of 50 µl in comparison with direct examination of 10 µl blood and the leukoconcentration technique of 5ml blood among loiasis-suspected patients with low microfilaremia in Gabon, Central Africa, using the STARD-BLCM guidelines

BACKGROUND

The aim of this study was to determine performance indicators of thick blood smears of 50 µl (TBS-50), following the Standards for the Reporting of Diagnostic Accuracy Studies-Bayesian Latent Class Model (STARD-BLCM) guidelines. TBS-50 was compared with two common parasitological techniques-direct examination of 10 µl blood and a leukoconcentration of 5 ml-for the diagnosis of microfilaremic loiasis.

METHODS

The study population was recruited among patients of the Department of Parasitology-Mycology-Tropical Medicine over a period of 1 year. Age, sex, symptoms, and eosinophilia variables were recorded from laboratory registers and medical files. Direct examination of 10 µl of blood, TBS-50, and the leukoconcentration technique with 5 ml of blood were performed for each patient. The classical formula and BLCM were used to determine the diagnostic accuracy of the three techniques as well as the prevalence of microfilaremic loiasis. Three models were built within the framework of BLCM-the BLCM model I and alternative models II and III-for sensitivity analysis.

RESULTS

In total, 191 patients consented to be included. The direct blood examination and TBS-50 yielded comparable qualitative and quantitative results. Hence, they are reported together. The prevalence of Loa loa microfilaremia was 9.4% (95% CI 5.7-14.5; n = 18/191) with direct blood examination/TBS-50 and 12.6% [8.2-18.1] (n = 24/191) for leukoconcentration. Comparing TBS-50 with the leukoconcentration method using the classical formula, the sensitivity was 75.0% [53.3-90.2], specificity was 100.0% [97.8-100.0], the positive predictive value was 100.0% [81.5-100.0], and the negative predictive value was 96.5% [92.6-98.7]. The prevalence of microfilaremic loiasis was estimated at 9.7% [6.2-13.7] using BLCM model I. The outputs of BLCM model I showed sensitivity of 78.9% [65.3-90.3], specificity of 100.0% [99.3-100.0], a positive predictive value of 99.1% [87.2-100.0], and a negative predictive value of 93.0% [87.3-97.7] for direct blood examination/TBS-50.

CONCLUSIONS

TBS-50 demonstrates low sensitivity relative to two other techniques. In one in five cases, the result will be falsely declared negative using these methods. However, this method can be deployed with limited funds.

The African eye worm: current understanding of the epidemiology, clinical disease, and treatment of loiasis

Loa loa, the African eye worm, is a filarial pathogen transmitted by blood-sucking flies of the genus Chrysops. Loiasis primarily affects rural populations residing in the forest and adjacent savannah regions of central and west Africa, where more than 20 million patients are chronically infected in medium and high transmission regions. For a long time, loiasis has been regarded as a relatively benign condition. However, morbidity as measured by disability-adjusted life-years lost might be as high as 400 per 100 000 residents, and the population attributable fraction of death is estimated at 14·5% in highly endemic regions, providing unequivocal evidence for the substantial disease burden that loiasis exerts on affected communities. The clinical penetrance of loiasis is variable and might present with the classic signs of eye worm migration or transient Calabar swellings, but might include common, unspecific symptoms or rare but potentially life-threatening complications. Although adult worm migration seems most closely linked to symptomatic disease, high levels of microfilaraemia are associated with clinically important complications and death. Loiasis remains difficult to diagnose, treat, and control due to an absence of reliable point-of-care diagnostic assays, safe and efficacious drugs, and cost-effective prevention strategies. This Review summarises the major advances in our understanding of loiasis made over the past decade and highlights the many gaps that await to be addressed urgently.

Analysis of diagnostic test outcomes in a large loiasis cohort from an endemic region: Serological tests are often false negative in hyper-microfilaremic infections

BACKGROUND

The parasitic disease loiasis is associated with significant morbidity and mortality. Individuals with hyper-microfilaremia (greater than 20,000 microfilariae per mL of blood) may suffer from serious treatment-related or spontaneous adverse events. Diagnosing loiasis remains complex and primarily relies on direct parasite detection. In this study, we analyzed the performance of various diagnostic tests and the influence of parasitological and clinical factors on test outcomes in samples from individuals living in an endemic region.

METHODS

Data and samples were collected from rural Gabon. Loiasis was defined as either detectable microfilaremia, or a positive history of eyeworm as assessed by the RAPLOA questionnaire. Diagnostic testing included a quantitative PCR (qPCR) for detection of Loa loa DNA in blood samples, an in-house crude L. loa antigen IgG ELISA, and a rapid test for antibodies against the Ll-SXP-1 antigen (RDT). Sensitivity and specificity were determined for each test and factors potentially influencing outcomes were evaluated in an exploratory analysis.

RESULTS

ELISA, RDT and qPCR results were available for 99.8%, 78.5%, and 100% of the 1,232 participants, respectively. The ELISA and RDT had only modest diagnostic accuracy. qPCR was specific for L. loa microfilaremia and Cycle threshold values correlated with microfilarial density. Anti-L. loa IgG levels were highest in occult loiasis, and antibody levels correlated inversely with L. loa microfilarial density as did RDT line intensities. Only 84.6% and 16.7% of hyper-microfilaremic individuals tested positive by ELISA (11/13) and RDT (2/12), respectively.

CONCLUSION

None of the tests demonstrated high sensitivity and specificity for loiasis. Indirect diagnostic assays were characterized by low specificity. Additionally, hyper-microfilaremic individuals often tested negative by RDT and ELISA, indicating that these tests are not suitable for individual case management in endemic populations.

Association between arterial stiffness and Loa loa microfilaremia in a rural area of the Republic of Congo: A population-based cross-sectional study (the MorLo project)

BACKGROUND

Loa loa filariasis (loiasis) is still considered a relatively benign disease. However, recent epidemiologic data suggest increased mortality and morbidity in L. loa infected individuals. We aimed to examine whether the density of L. loa microfilariae (mfs) in the blood is associated with cardiovascular disease.

METHODOLOGY

Using a point-of-care device (pOpmètre), we conducted a cross-sectional study to assess arterial stiffness and peripheral arterial disease (PAD) in 991 individuals living in a loiasis-endemic rural area in the Republic of the Congo. Microfilaremic individuals were matched for age, sex and village of residence with 2 amicrofilaremic subjects. We analyzed markers of arterial stiffness (Pulse-Wave Velocity, PWV), PAD (Ankle-Brachial Index, ABI) and cardiovascular health (Pulse Pressure, PP). The analysis considered parasitological results (L. loa microfilarial density [MFD], soil-transmitted helminths infection, asymptomatic malaria and onchocerciasis), sociodemographic characteristics and known cardiovascular risk factors (body mass index, smoking status, creatininemia, blood pressure).

PRINCIPAL FINDINGS

Among the individuals included in the analysis, 192/982 (19.5%) and 137/976 (14.0%) had a PWV or an ABI considered out of range, respectively. Out of range PWV was associated with younger age, high mean arterial pressure and high L. loa MFD. Compared to amicrofilaremic subjects, those with more than 10,000 mfs/mL were 2.17 times more likely to have an out of range PWV (p = 0.00). Factors significantly associated with PAD were older age, low pulse rate, low body mass index, smoking, and L. loa microfilaremia. Factors significantly associated with an elevation of PP were older age, female sex, high average blood pressure, low pulse rate and L. loa microfilaremia.

CONCLUSION

A potential link between high L. loa microfilaremia and cardiovascular health deterioration is suggested. Further studies are required to confirm and explore this association.

Filarial disease in the Brazilian Amazon and emerging opportunities for treatment and control

Following the successful eradication of Wuchereria bancrofti, there are now just three species of conventional microfilaremic human filarial parasites endemic to the Brazilian Amazon region: Mansonella ozzardi, Mansonella perstans and Onchocerca volvulus. The zoonotic filarial parasite Dirofilaria immitis is also found in the Amazon region as are several sylvatic filarial parasites, some of which have been recorded causing zoonoses and some of which have never been recorded outside the region. Onchocerca volvulus is only found in the Amazonia onchocerciasis focus in the Brazilian state of Roraima where it affects the people of the Yanomami tribe living around the densely forested Venezuela border region. Mansonella ozzardi is by far the most common filarial parasite in Brazil and has a broad but patchy distribution throughout the western Amazon region. Recorded in the Brazilian states of Acre, Roraima, Matto Grosso, and within almost every municipality of Amazonas state, it is believed that pollution of the urban stream and river systems prevents the development of the simuliid vectors of M. ozzardi and explains the parasite's reduced distribution within urban areas and an absence of recent reports from the state capital Manaus. Decades of WHO-led periodic ivermectin treatment of Yanomami tribe's people have resulted in the partial suppression of O. volvulus transmission in this focus and has also probably affected the transmission of M. ozzardi in the region. Mansonella perstans, O. volvulus and very probably M. ozzardi infections can all be treated and most likely cured with a 4-6-week treatment course of doxycycline. The Brazilian Ministry of Health does not, however, presently recommend any treatment for mansonellosis infections and thus parasitic infections outside the Amazonia focus are typically left untreated. While the long treatment courses required for doxycycline-based mansonellosis therapies preclude their use in control programmes, new fast-acting filarial drug treatments are likely to soon become available for the treatment of both onchocerciasis and mansonellosis in the Amazon region. Filarial disease management in the Brazilian Amazon is thus likely to become dramatically more viable at a time when the public health importance of these diseases is increasingly being recognized.

Association between blood Loa loa microfilarial density and proteinuria levels in a rural area of the Republic of Congo (the MorLo project): a population-based cross-sectional study

BACKGROUND

Case reports have hypothesised that proteinuria, sometimes with glomerulopathy or nephrotic syndromes, might be associated with loiasis. To our knowledge, no study has been done to assess this association. We aimed to investigate the association between Loa loa microfilariae burden and proteinuria.

METHODS

We did a cross-sectional study between May 16, 2022, and June 11, 2022, to assess the relationship between Loa loa microfilaraemia densities and proteinuria in a rural area of the Republic of Congo. We included all consenting adults living in the target area at study commencement who had L loa microfilarial densities greater than 500 microfilariae per mL during previous screening for a clinical trial in 2019. This study is part of the MorLo project, and used the project's study population of individuals aged 18 years or older who were living near Sibiti. For each microfilaraemic individual, two individuals without L loa microfilarial densities matched on age, sex, and place of residence were included. The association between proteinuria (assessed by dipstick) and L loa microfilarial densities, age, and sex was assessed using an unconstrained ordinal regression model since the parallel-lines assumption was violated for microfilarial densities.

FINDINGS

991 participants were included, of whom 342 (35%) were L loa microfilaraemic. The prevalence of microfilaraemia was 38% (122 of 325) among individuals with trace proteinuria (<300 mg/24 h), 51% (45 of 89) among individuals with light proteinuria (300 mg to 1 g/24 h), and 71% (15 of 21) among individuals with high proteinuria (>1 g/24 h). Individuals with high proteinuria had significantly higher L loa microfilarial densities (p<0·0001): mean microfilariae per mL were 1595 (SD 4960) among individuals with no proteinuria, 2691 (7982) for those with trace proteinuria, 3833 (9878) for those with light proteinuria, and 13 541 (20 118) for those with high proteinuria. Individuals with 5000-14 999 microfilariae per mL and individuals with 15 000 microfilariae per mL or greater were, respectively, 5·39 and 20·49 times more likely to have a high proteinuria than individuals with no microfilaraemia.

INTERPRETATION

The risk of proteinuria increases with L loa microfilaraemia. Further studies are needed to identify renal disorders (eg, tubulopathies, glomerulopathies, or nephrotic syndromes) responsible for loiasis-related proteinuria.

FUNDING

European Research Council, MorLo project.

TRANSLATION

For the French translation of the abstract see Supplementary Materials section.

The search for better treatment strategies for mansonellosis: an expert perspective

INTRODUCTION

Four species of the Mansonella genus infect millions of people across sub-Saharan Africa and Central and South America. Most infections are asymptomatic, but mansonellosis can be associated with nonspecific clinical manifestations such as fever, headache, arthralgia, and ocular lesions (M. ozzardi); pruritus, arthralgia, abdominal pain, angioedema, skin rash, and fatigue (M. perstans and perhaps Mansonella sp. 'DEUX'); and pruritic dermatitis and chronic lymphadenitis (M. perstans).

AREAS COVERED

We searched the PubMed and SciELO databases for publications on mansonelliasis in English, Spanish, Portuguese, or French that appeared until 1 May 2023. Literature data show that anthelmintics - single-dose ivermectin for M. ozzardi, repeated doses of mebendazole alone or in combination with diethylcarbamazine (DEC) for M. perstans, and DEC alone for M. streptocerca - are effective against microfilariae. Antibiotics that target Wolbachia endosymbionts, such as doxycycline, are likely to kill adult worms of most, if not all, Mansonella species, but the currently recommended 6-week regimen is relatively impractical. New anthelmintics and shorter antibiotic regimens (e.g. with rifampin) have shown promise in experimental filarial infections and may proceed to clinical trials.

EXPERT OPINION

We recommend that human infections with Mansonella species be treated, regardless of any apparent clinical manifestations. We argue that mansonellosis, despite being widely considered a benign infection, may represent a direct or indirect cause of significant morbidity that remains poorly characterized at present.

Association between altered cognition and Loa loa microfilaremia: First evidence from a cross-sectional study in a rural area of the Republic of Congo

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.

Cases of Loiasis Among a Congolese Family: Screening for Loiasis Among Newly Arrived Refugees From Endemic Areas

Loiasis is a parasitic infection caused by the filarial nematode Loa loa within endemic regions of West and Central Africa. These regions include areas co-endemic for other nematode infections. Although loiasis is rarely seen in the United States (US), primary care providers who regularly see refugees from endemic areas should be aware of its clinical presentation, diagnostic work-up, and initial management. Given the challenges of diagnosing loiasis, especially in low prevalence settings, we present cases of four family members, two of whom were diagnosed with loiasis, and discuss an approach to screening populations from endemic regions during their initial Refugee Health Examination upon arrival to the US.

Development and validation of small animal models for onchocerciasis and loiasis microfilaricide discovery

BACKGROUND

Onchocerciasis (river blindness) caused by the filarial worm Onchocerca volvulus is a neglected tropical disease that affects the skin and eyes of humans. Mass drug administration with ivermectin (IVM) to control the disease often suffers from severe adverse events in individuals co-injected with high loads of Loa loa microfilariae (mf). Thus loiasis animal models for counter-screening of compounds effective against onchocerciasis are needed, as are the corresponding onchocerciasis screening models. The repertoire of such models is highly limiting. Therefore, this study was aimed at developing and validating mf immunocompetent small animal models to increase tools for onchocerciasis drug discovery.

METHODOLOGY/PRINCIPAL FINDINGS

O. ochengi mf from cattle skin and L. loa mf from human blood were used to infect BALB/c mice and Mongolian gerbils, and IVM was used for model validation. O. ochengi mf were given subcutaneously to both rodents while L. loa mf were administered intravenously to mice and intraperitoneally to gerbils. IVM was given orally. In an 8-day model of O. ochengi mf in BALB/c mice, treatment with IVM depleted all mf in the mice, unlike the controls. Also, in a 2.5-day model of L. loa mf in BALB/c, IVM significantly reduced mf in treated mice compared to the untreated. Furthermore, the gerbils were very susceptible to O. ochengi mf and IVM eradicated all mf in the treated animals. In the peritoneal L. loa mf gerbil model, IVM reduced mf motility in treated animals compared to the controls. In a 30-day gerbil co-injection model, IVM treatment cleared all O. ochengi mf and reduced motility of L. loa mf. Both mf survived for up to 50 days in a gerbil co-injection model.

CONCLUSIONS/SIGNIFICANCE

We have developed two immunocompetent small animal models for onchocerciasis and loiasis that can be used for microfilaricide discovery and to counter-screen onchocerciasis macrofilarides.

Loiasis – Eine extrem vernachlässigte Tropenerkrankung

Rund 10–15 Mio. Menschen in Zentral- und Westafrika sind mit der Filarie Loa loa infiziert. Obwohl die assoziierte Krankheitslast vergleichbar mit wichtigen Tropenkrankheiten wie der Schistosomiasis ist, gilt die Loaisis bisher als extrem vernachlässigte Tropenerkrankung. Parasitologisch wird differenziert zwischen der mikrofilariämen Loiasis, bei der die Mikrofilarien mittels Mikroskopie im Blutausstrich nachgewiesen werden, und der okkulten Loiasis, die nur bei entsprechender Exposition durch typische Symptome diagnostiziert werden kann. Pathognomonische Symptome sind die Wanderung des adulten Wurms in der Konjunktiva („afrikanischer Augenwurm“) sowie die transiente Calabar-Schwellung. Die Therapie der Loaisis stellt vor allem in Endemiegebieten oft eine große Herausforderung dar. Potenziell schwere Nebenwirkungen der verfügbaren Medikamente sowie das hohe Risiko einer Reinfektion führen meist dazu, dass L. loa-Patient*innen in den Endemiegebieten keine Therapie erhalten.

Profile of loiasis infection through clinical and laboratory diagnostics: the importance of biomarkers

Background

Detection of Loa loa microfilariae in peripheral blood is insensitive given only 30% of individuals are microfilaraemic while 70% are amicrofilaraemic with a variety of clinical signs. Biomarkers may improve the diagnosis of loiasis.

Methods

A total of 545 individuals exposed to L. loa were analysed using clinical data collected through a questionnaire (requesting information on eye worm, Calabar swelling, pruritis) and detection of microfilariae, immunoglobulin G4 (IgG4), DNA and antigens using microscopy, enzyme-linked immunosorbent assay (ELISA), quantitative polymerase chain reaction (qPCR) and Western blot, respectively.

Results

The results revealed that the rates of detection of L. loa microfilariae in the blood, of DNA by qPCR, of IgG4 by ELISA and of antigen by Western blot were 4.7%, 5.5%, 15.60% and 10.09%, respectively.

Conclusions

This study showed that clinical signs based on a questionnaire are highly subjective. Therefore it is imperative to use IgG4 and DNA biomarkers as well as antigens detected by Western blot to identify individuals infected with L. loa.

A large case series of travel-related Mansonella perstans (vector-borne filarial nematode): a TropNet study in Europe

BACKGROUND

Infection with Mansonella perstans is a neglected filariasis, widely distributed in sub-Saharan Africa, characterized by an elusive clinical picture; treatment for mansonellosis is not standardized. This retrospective study aimed to describe the clinical features, treatment schemes and evolution, of a large cohort of imported cases of M. perstans infection seen in four European centres for tropical diseases.

METHODS

Mansonella perstans infections, diagnosed by identification of blood microfilariae in migrants, expatriates and travellers, collected between 1994 and 2018, were retrospectively analysed. Data concerning demographics, clinical history and laboratory examinations at diagnosis and at follow-up time points were retrieved.

RESULTS

A total of 392 patients were included in the study. Of the 281 patients for whom information on symptoms could be retrieved, 150 (53.4%) reported symptoms, abdominal pain and itching being the most frequent. Positive serology and eosinophilia were present in 84.4% and 66.1%, respectively, of those patients for whom these data were available. Concomitant parasitic infections were reported in 23.5% of patients. Treatment, administered to 325 patients (82.9%), was extremely heterogeneous between and within centres; the most commonly used regimen was mebendazole 100 mg twice a day for 1 month. A total of 256 (65.3%) patients attended a first follow-up, median 3 months (interquartile range 2-12) after the first visit; 83.1% of patients having received treatment based on mebendazole and/or doxycycline, targeting Wolbachia, became amicrofilaremic, 41.1-78.4% of whom within 12 months from single treatment.

CONCLUSIONS

Lack of specific symptoms, together with the inconstant positivity of parasitological and antibody-based assays in the infected population, makes the clinical suspicion and screening for mansonellosis particularly difficult. Prospective studies evaluating prevalence of infection in migrants from endemic areas, infection-specific morbidity, presence of Wolbachia endosymbionts in M. perstans populations from different geographical areas and efficacy of treatment regimens are absolutely needed to optimize the clinical management of infection.

Prevalence and risk factors for blood filariasis among HIV-infected adults in Gabon, Central Africa: a pilot study

BACKGROUND

The level of blood filariasis parasitaemia as well as the frequency of and the relationship between cotrimoxazole prophylaxis (CTX-P), antiretroviral therapy (ART) intake and CD4 cell count among people living with human immunodeficiency virus (PLHIV) in rural areas of Gabon were being studied.

METHODS

Sociodemographic data and recent biological tests of PLHIV and HIV-negative participants were collected. Loa loa and Mansonella perstans microfilaria were detected by direct microscopy examination and leucoconcentration.

RESULTS

Overall, 209 HIV-positive and 148 HIV-negative subjects were enrolled. The overall prevalence of microfilaria was comparable between PLHIV (19.9% [n=41/206]) and HIV-negative participants (14.8% [n=22/148]) (p=0.2). The L. loa infection rate was comparable between HIV-positive (9.2%) and HIV-negative participants (6.8%) (p=0.2), while the M. perstans infection rate was 14-fold higher among PLHIV (p<0.01). L. loa parasitaemia was 6-fold lower in PLHIV receiving CTX-P (median 150 mf/mL [interquartile range {IQR} 125-350]) than in patients without (900 [550-2225]) (p<0.01). Among subjects with a CD4 cell count <200 cells/μL, the prevalence of M. perstans was 7-fold higher than that of L. loa (20.6% vs 2.9%).

CONCLUSIONS

This study suggests a similar exposure to L. loa infection of PLHIV and HIV-negative patients while M. perstans is more frequently found in HIV-positive individuals, notably those with a CD4 count <200 cells/μL.

A call for loiasis to be added to the WHO list of neglected tropical diseases

Loiasis, also called African eye worm, is not currently on WHO's list of priority neglected tropical diseases, even though the risk that individuals with high Loa loa microfilarial densities will develop potentially fatal encephalopathy when they take ivermectin has complicated efforts to use mass drug administration for onchocerciasis (river blindness) and lymphatic filariasis control in co-endemic areas. At least 10 million residents of central and west Africa are thought to have loiasis, which causes painful and itchy subcutaneous oedema, arthralgia, and discomfort when adult helminths that are 3-7 cm in length are present under the conjunctiva of the eye. High levels of microfilaraemia are associated with renal, cardiac, neurological, and other sequelae, and an increased risk of death. The public health burden of loiasis could be greatly reduced with expanded use of diagnostic tests, anthelmintic treatment, and control of the Chrysops spp (tabanid flies) vectors that transmit the parasite. Loiasis should be added to the next revision of the WHO neglected tropical disease priority list, not merely because its inclusion will support the elimination of other skin and subcutaneous neglected tropical diseases, but also because of the complications caused by loiasis itself.

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

Background

Loiasis–a filarial disease endemic in Central and West Africa–is increasingly recognized as significant individual and public health concern. While the understanding of the disease characteristics remains limited, significant morbidity and excess mortality have been demonstrated. Here, we characterize clinical and hematological findings in a large cohort from Gabon.

Methods

Loiasis-related clinical manifestations and microfilaremia, hemoglobin and differential blood counts were recorded prospectively during a cross-sectional survey. For analysis, participants were categorized into distinct infection states by the diagnostic criteria of eye worm history and microfilaremia.

Results

Analysis of data from 1,232 individuals showed that occurrence of clinical and hematological findings differed significantly between the infection states. Eye worm positivity was associated with a wide range of clinical manifestations while microfilaremia by itself was not. Loa loa infection was associated with presence of eosinophilia and absolute eosinophil counts were associated with extent of microfilaremia (p-adj. = 0.012, ß-estimate:0.17[0.04–0.31]).

Conclusions

Loiasis is a complex disease, causing different disease manifestations in patients from endemic regions. The consequences for the affected individuals or populations as well as the pathophysiological consequences of correlating eosinophilia are largely unknown. High-quality research on loiasis should be fostered to improve patient care and understanding of the disease.

Loiasis is a parasitic disease, endemic in parts of Western and Central Africa. While the disease has traditionally been considered to be benign, only recently significant disease morbidity and mortality have been shown. Most of the knowledge about loiasis, however, stems from reports on returning travelers, while comprehensive data from patients living in endemic areas are missing. Blood microfilaremia and reported eye worm are important diagnostic manifestations of the disease, but they can occur independent of each other in affected individuals. We analyzed hematological and clinical findings according to loiasis infection states, comprising reported eye worm and microfilaremia positivity, in a large group of individuals from a highly endemic area.

While we found that all loiasis infection states were significantly associated with absolute blood eosinophilia, the eosinophilia was more pronounced in microfilaremic loiasis. Further, there was an association between the extent of microfilaremia and absolute eosinophilia. Analyzing the frequency of clinical disease manifestations, we found that eye worm positive loiasis was associated with a range of symptoms, but microfilaremic loiasis was not. Summarizing, even in highly endemic populations different loiasis infection states are associated with distinct disease manifestations, underlining that loiasis is a versatile and indeed relevant disease.

The Human Filaria Loa loa: Update on Diagnostics and Immune Response

Loa loa loiasis was considered an anecdotal disease 30 years ago. Its spread in Equatorial Africa and the side effects associated with mass drug administration programs against filariasis in co-endemic areas have drawn the attention of the international research community. Progress in research conducted to date has provided insight into the immunobiology of this parasite. An interesting finding reported in several studies is that 70% of individuals with loiasis do not carry microfilariae in their blood, and 30% are microfilaremic, suggesting the involvement of several immunological mechanisms, as shown by elevated specific IgG4 and IgE levels signifying a potential cross-linking mechanism between the two isotypes via L. loa antigen to prevent allergy. A mechanism of anergy in the appearance of microfilariae in the peripheral blood results in immunological unresponsiveness in individuals with microfilariae. There is an interaction between other pathogens (parasites, bacteria, viruses) in individuals co-infected with L. loa. The strong antigen cross-reactivity between L. loa and lymphatic filarial worms warrants a re-evaluation of the distribution of the latter in co-endemic regions. The mechanism of concomitant immunity observed in the elimination of microfilariae or infective larvae (third-stage larvae, L3) may be used for the conception of an immunoprophylactic strategy.

Historical overview and geographical distribution of neglected tropical diseases amenable to preventive chemotherapy in the Republic of the Congo: A systematic review

Background

Neglected Tropical Diseases amenable to Preventive Chemotherapy (PC-NTDs) affect the poorest populations around the world, especially in Africa. Scientific information on the distribution and level of endemicity of these diseases in the Republic of the Congo (RoC) is scarce in the published literature. We sought to collect all available epidemiological data on PC-NTDs in the RoC to document the historical and current situation and identify challenges in reaching the elimination of NTDs.

Methods

We searched Medline and Horizon databases for studies published until to July 4^th, 2019, on onchocerciasis, lymphatic filariasis, soil-transmitted helminth infections, schistosomiasis, and trachoma in the RoC. Unpublished reports were also reviewed. We included all epidemiological studies containing community data and excluded case reports. Location, prevalence data, and dates of the studies were extracted.

Principal findings

We identified 933 records, of which 56 met the inclusion criteria. The articles published before 1960 mainly concerned onchocerciasis and schistosomiasis. Despite a low number over the studied period, since 2005 there has been a steady increase in the number of publications. Most of the studies were cross-sectional and conducted in the general population. Trachoma is endemic in the Sangha and Likouala departments (prevalence of trachomatous inflammation-follicular > 5% in some villages), and further mapping is essential to properly assess the burden of this disease in the country. While the prevalence of soil-transmitted helminths is still high (over 20%) in a large part of Congo, cases of lymphatic filariasis (based on Wuchereria bancrofti antigenaemia and/or microfilaraemia) and onchocerciasis are becoming rare and very focused. To achieve the elimination of PC-NTDs, further intervention is required.

Conclusions

Except for trachoma, whose epidemiological situation should be better evaluated, PC-NTDs are endemic in the RoC, and actions to control them have been taken by health authorities. To eliminate PC-NTDs, which are still present in some locations, new mapping surveys are needed, and increased investment in scientific research should be encouraged in the country.

For many years, the Republic of the Congo has implemented control programs to combat neglected tropical diseases that cause severe disabilities. By tracing the past and recent distribution of these diseases through the analysis of epidemiological studies, we show that most remaining NTDs are located in defined foci of infection, maintained depending on ecology and lifestyle habits. However, the small number of recent studies limits the production of new knowledge, which would be useful for a better understanding of epidemiological patterns and to accelerate NTD elimination.

Spleen nodules in Loa loa infection: re-emerging knowledge and future perspectives

Loiasis, the infection with the vector-borne filarial nematode Loa loa, is widely distributed in central and west Africa. Long considered a rather benign infection, recently loiasis with high microfilarial burden was associated with increased mortality risk. Eyeworm and Calabar swelling are pathognomonic signs of the infection, but other atypical, non-specific manifestations can also occur. For instance, splenic nodules have been seldom reported. In this Grand Round, we report two cases of loiasis in migrants who presented with spleen nodules, which could be followed up over time (up to 27 months) with multiple imaging techniques until their resolution. We comment on the clinical implications of these observations, including differential diagnosis with similar imaging findings, and critically review the evidence of spleen involvement in loiasis and other filarial infections.

Loiasis is endemic in the Ndikinimeki Health District (Centre Region, Cameroon) but does not represent a hindrance to onchocerciasis elimination

Community-Directed Treatment with Ivermectin (CDTI) is the strategy of choice to fight onchocerciasis in Africa. In areas where loiasis is endemic, onchocerciasis control and/or elimination is hindered by severe adverse events (SAEs) occurring after ivermectin mass treatments. This study aimed at (i) investigating the impact of two decades of CDTI on L. loa clinical and parasitological indicators in the Ndikinimeki Health District, and (ii) assessing the risk of SAEs after this long-term preventive chemotherapy. A cluster-based cross-sectional survey was conducted in the six Health Areas of the Ndikinimeki Health District. All volunteers underwent day-time calibrated thick blood smears to search for L. loa microfilariae, as well as an interview to assess the history of migration of eye worm and Calabar swelling. The overall prevalence of L. loa microfilaraemia was 2.2 % (95% CI: 1.3-3.7%), and the proportions of individuals who had already experienced eye worm and/or Calabar swelling were 1.0% and 0.5%, respectively. The mean microfilarial density was 63.55 (SD: 559.17; maximum: 9220.0) mf/mL. These findings indicate that (i) the long-term ivermectin-based preventive chemotherapy against onchocerciasis significantly reduced L. loa clinical and parasitological indicators, and (ii) the risk of developing neurologic and potentially fatal SAE after ivermectin mass treatment is zero in the Ndikinimeki Health District.

OUP accepted manuscript

Loa loa microfilariae were found on thick blood smears (TBSs) from 8 of 300 (2.7%) residents of Bioko Island, Equatorial Guinea, during a Plasmodium falciparum sporozoite malaria vaccine clinical trial. Only one subject was found to have microfilaraemia on his first exam; parasites were not discovered in the other seven until subsequent TBSs were performed, at times many weeks into the study. All infected individuals were asymptomatic, and were offered treatment with diethylcarbamazine, per national guidelines. L. loa microfilaraemia complicated the enrolment or continued participation of these eight trial subjects, and only one was able to complete all study procedures. If ruling out loiasis is deemed to be important during clinical trials, tests that are more sensitive than TBSs should be performed.

Human filariasis-contributions of the Litomosoides sigmodontis and Acanthocheilonema viteae animal model

Filariae are vector-borne parasitic nematodes that are endemic worldwide, in tropical and subtropical regions. Important human filariae spp. include Onchocerca volvulus, Wuchereria bancrofti and Brugia spp., and Loa loa and Mansonella spp. causing onchocerciasis (river blindness), lymphatic filariasis (lymphedema and hydrocele), loiasis (eye worm), and mansonelliasis, respectively. It is estimated that over 1 billion individuals live in endemic regions where filarial diseases are a public health concern contributing to significant disability adjusted life years (DALYs). Thus, efforts to control and eliminate filarial diseases were already launched by the WHO in the 1970s, especially against lymphatic filariasis and onchocerciasis, and are mainly based on mass drug administration (MDA) of microfilaricidal drugs (ivermectin, diethylcarbamazine, albendazole) to filarial endemic areas accompanied with vector control strategies with the goal to reduce the transmission. With the United Nations Sustainable Development Goals (SDGs), it was decided to eliminate transmission of onchocerciasis and stop lymphatic filariasis as a public health problem by 2030. It was also requested that novel drugs and treatment strategies be developed. Mouse models provide an important platform for anti-filarial drug research in a preclinical setting. This review presents an overview about the Litomosoides sigmodontis and Acanthocheilonema viteae filarial mouse models and their role in immunological research as well as preclinical studies about novel anti-filarial drugs and treatment strategies.

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, 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.

Natural Products Are a Promising Source for Anthelmintic Drug Discovery

Parasitic nematodes infect almost all forms of life. In the human context, parasites are one of the major causative factors for physical and intellectual growth retardation in the developing world. In the agricultural setting, parasites have a great economic impact through a reduction in livestock performance or control cost. The main method of controlling these devastating conditions is the use of anthelmintic drugs. Unfortunately, there are only a few anthelmintic drug classes available in the market and significant resistance has developed in most of the parasitic species of livestock. Therefore, development of new anthelmintics with different modes of action is critical for sustainable parasitic control in the future. The drug development pipeline is broadly limited to two types of molecules, namely synthetic compounds and natural plant products. Compared to synthetic compounds, natural products are highly diverse, and many have historically proven valuable in folk medicine to treat various gastrointestinal ailments. This review focus on the use of traditional knowledge-based plant extracts in the development of new therapeutic leads, the approaches used as screening techniques, and common bottlenecks and opportunities in plant-based anthelmintic drug discovery.

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.

Projected Number of People With Onchocerciasis-Loiasis Coinfection in Africa, 1995 to 2025

BACKGROUND

Onchocerciasis elimination through mass drug administration (MDA) is hampered by coendemicity of Loa loa, as people with high L. loa microfilariae (mf) density can develop serious adverse events (SAEs) after ivermectin treatment. We assessed the geographical overlap of onchocerciasis and loiasis prevalence and estimated the number of coinfected individuals at risk of post-ivermectin SAEs in West and Central Africa from 1995 to 2025.

METHODS

Focusing on regions with suspected loiasis transmission in 14 countries, we overlaid precontrol maps of loiasis and onchocerciasis prevalence to calculate precontrol prevalence of coinfection by 5 km2 × 5 km2 pixel, distinguishing different categories of L. loa mf intensity. Using statistical and mathematical models, we predicted prevalence of both infections and coinfection for 2015 and 2025, accounting for the impact of MDA with ivermectin.

RESULTS

The number of people infected with onchocerciasis was predicted to decline from almost 19 million in 1995 to 4 million in 2025. Of these, 137 000 people were estimated to also have L. loa hypermicrofilaremia (≥20 000 L. loa mf/mL) in 1995, declining to 31 000 in 2025. In 2025, 92.8% of coinfected cases with loiasis hypermicrofilaremia are predicted to live in hypoendemic areas currently not targeted for MDA.

CONCLUSIONS

Loiasis coinfection is a major concern for onchocerciasis elimination in Africa. We predict that under current strategies, at least 31 000 coinfected people still require treatment for onchocerciasis in 2025 while being at risk of SAEs, justifying continued efforts in research and development for safer drugs and control strategies.

Collateral Impact of Community-Directed Treatment with Ivermectin (CDTI) for Onchocerciasis on Parasitological Indicators of Loa loa Infection

Ivermectin (IVM) is a broad spectrum endectocide whose initial indication was onchocerciasis. Although loiasis is not among its indications, IVM also exhibits antiparasitic activity against Loa loa. IVM-based preventive chemotherapies (PCs), so-called community-directed treatment with ivermectin (CDTI), have led to the interruption of transmission of onchocerciasis in some foci. A cross-sectional study was conducted in the Yabassi Health District where CDTI have been implemented since 20 years to fight onchocerciasis. All volunteers aged ≥ 5 years underwent daytime calibrated thick blood smears to search for L. loa microfilariae (mf). The prevalence of loiasis was 3.7% (95% CI: 2.2-6.2), significantly lower than its baseline prevalence (12.4%; 95% CI: 10.1-15.2; Chi-Square = 21.4; df = 1; p < 0.0001). Similarly, the microfilarial density was significantly low (mean = 1.8 mf/mL; SD = 13.6; max = 73,600) compared to baseline microfilarial density (mean = 839.3 mf/mL; SD = 6447.1; max = 130,840; Wilcoxon W = 179,904.5; p < 0.0001). This study revealed that the endemicity level of loiasis was significantly low compared to its baseline value, indicating a significant impact of IVM-based PC on this filarial disease. However, transmission is still ongoing, and heavily infected individuals are still found in communities, supporting why some individuals are still experiencing severe adverse events despite > 2 decades of CDTI in this Health District.

Slithering Through the Bone Marrow: Loiasis in a Patient With Human T-Cell Leukemia Virus-1-Associated Adult T-Cell Lymphoma

Loiasis is a filarial disease endemic to areas of Central and West Africa. We present a case of Loa loa microfilaremia in a patient with HTLV-1-related adult T-cell lymphoma. This case may suggest the possible role of cellular immunity in controlling microfilaria burden.

Assessing Hypoendemic Onchocerciasis in Loa loa Endemic Areas of Southeast Nigeria

Nigeria changed its goal for onchocerciasis from control to transmission elimination. Under the control program, ivermectin mass drug administration (MDA) focused only on hyper/meso-endemic local government areas (LGAs) identified by Rapid Epidemiological Mapping of Onchocerciasis as having ≥ 20% nodule rates. Because transmission is likely in some LGAs where nodule rates are < 20%, the new elimination paradigm requires MDA expansion. Determining which hypoendemic areas require MDA, termed onchocerciasis elimination mapping, is a major challenge. In 2016, we studied 19 ivermectin-naive hypoendemic LGAs in southern Nigeria that bordered LGAs under MDA. Fifty adults and 50 children (aged 5–10 years) were tested in 110 villages for onchocerciasis IgG4 antibody using an Ov16 rapid diagnostic test (RDT). A 10% subset of subjects provided a blood spot for confirmatory Ov16 ELISA. The mean prevalence of RDT positives was 0.5% in the 5,276 children tested (village range, 0.0–4.0%) versus 3.3% in 5,302 adults (village range, 0.0–58.0%). There was 99.3% agreement between the Ov16 RDT and ELISA. Six different MDA launch thresholds were applied to the RDT results based on different recommendations by the Nigeria Onchocerciasis Elimination Committee and the Onchocerciasis Technical Advisory Subgroup of the WHO. Mass drug administration targets for the same area varied tenfold by threshold chosen, from one LGA (population to be treated 221,935) to 13 LGAs (population 2,426,987). Because the Ov16 threshold selected will have considerable cost and resource implications, the decision to initiate MDA should incorporate entomological data demonstrating onchocerciasis transmission.

Burden of disease in Gabon caused by loiasis: a cross-sectional survey

BACKGROUND

Loiasis is a highly prevalent helminth infection found in distinct regions of sub-Saharan Africa. The disease has been considered to be of minor clinical significance, but this belief is being increasingly challenged by recent evidence. We aimed to prospectively quantify the overall burden of disease caused by loiasis in an endemic region of Gabon, using disability-adjusted life years (DALYs).

METHODS

We did a cross-sectional survey during 2017 and 2018 in rural Gabon. Volunteers underwent diagnostic tests for loiasis and were given a standardised questionnaire on symptoms. Participants reporting eye worm migration or harbouring Loa loa microfilariae were defined as loiasis positive. Morbidity-based DALYs associated with loiasis were estimated for the rural population of Gabon.

FINDINGS

Between Sept 1, 2017 and May 31, 2018, 1235 participants residing in 38 villages in the Gabonese departments of Tsamba-Magotsi and Ogooué et des Lacs were screened. 626 (50·8%) of 1232 eligible participants had loiasis. 520 (42·2%) of 1232 participants reported eye worm migration. 478 (93·9%) of 509 individuals with eye worm migration also reported associated pain, and 397 (78·6%) of 505 reported vision disturbances. After correcting for age and sex, loiasis was significantly associated with a variety of symptoms, including transient painful oedema (adjusted odds ratio 1·76 [95% CI 1·37-2·26]) and arthralgia (1·30 [1·01-1·69]). Application of attributable fractions of correlating symptoms resulted in 412·9 (95% CI 273·9-567·7) morbidity-based DALYs per 100 000 people in rural Gabon.

INTERPRETATION

Loiasis, with the pathognomonic sign of eye worm migration, appears to not be benign, but severely impeding to affected individuals. Furthermore, loiasis is associated with substantial morbidity, comparable to that of other neglected tropical parasitic diseases. These findings call for reconsideration of L loa as a relevant pathogen in affected populations, with a need for more concerted research and control of these infections.

FUNDING

Federal Ministry of Science, Research and Economy of Austria, and the European Union.

Performance of two serodiagnostic tests for loiasis in a Non-Endemic area

Loiasis, caused by the filarial nematode Loa loa, is endemic in Central and West Africa where about 10 million people are infected. There is a scarcity of convenient, commercial diagnostics for L. loa. Microscopy requires trained personnel and has low sensitivity, while the serodiagnosis is currently not standardized. Individual case management is also important in non-endemic countries to treat migrants, expatriates and tourists. We retrospectively compared the performance of a Loa Antibody Rapid Test (RDT) and a commercial ELISA pan-filarial test on 170 patients, 65 with loiasis [8 with eyeworm, 29 with positive microfilaremia, 28 with neither microfilaremia nor history of eyeworm but eosinophilia and history of Calabar swelling (probable loiasis)], 95 with other common parasitic infections and no previous exposure to L. loa (37 with M. perstans, 1 with Brugia sp., 18 with strongyloidiasis, 20 with schistosomiasis, 5 with hookworm, 4 with Ascaris lumbricoides infection, 10 with hyper-reactive malarial splenomegaly), and 10 uninfected controls. The sensitivity of the RDT and of the ELISA were 93.8% (61/65) and 90.8% (59/65), respectively. For the RDT, most of the cross-reactions were observed in patients with M. perstans: 7/37 (18.9%), followed by 1/10 (10%) with hyper-reactive malarial splenomegaly and 1/20 (5%) with schistosomiasis. None of the 27 subjects infected with intestinal nematodes was found positive at this test. The ELISA is meant to be a pan-filarial assay, and reacted extensively with cases of M. perstans (95%), as expected, and also in 11/18 (61.1%) patients with strongyloidiasis and in 3/5 (60%) with hookworm infection. The RDT and the ELISA are both highly sensitive for the diagnosis of loiasis. The main difference lies in the extent of cross-reactivity with other parasites. Considering that the RDT is specifically meant for Loa loa infection, and its high sensitivity, this test could be a useful tool for the diagnosis of occult loiasis.

Loa loa is a filarial worm which infects millions of people living in the forested areas of central Africa. The infection is rarely diagnosed outside Africa, but individual case management is also important in non-endemic countries to treat migrants, tourists and expatriates. Aim of this study was to describe the performance of a Rapid Test and an ELISA pan filarial test for the diagnosis of Loa loa infection. Both tests demonstrated good performance for the detection of cases of loiasis. In case of infection with other parasites, the RDT gave less false positive results.

Loiasis in sub-Saharan migrants living in Spain with emphasis of cases from Equatorial Guinea

Background

Loiasis is an uncommon and poorly understood parasitic disease outside endemic areas of Africa. The aim of this study was to describe the clinical and biological patterns and treatment of imported loiasis by sub-Saharan migrants diagnosed in Madrid, Spain.

Methods

A retrospective study was conducted with sub-Saharan immigrants seen at the Tropical Medicine Unit of the Carlos III Hospital in Madrid, Spain, a reference center, over 19 years. Categorical variables were expressed as frequency counts and percentages. Continuous variables were expressed as the mean and standard deviation (SD) or median and interquartile range (IQR: Q3–Q1). Chi-square tests were used to assess the association between categorical variables. The measured outcomes were expressed as the odds ratio (OR) with a 95% confidential interval. Continuous variables were compared by Student’s t-tests or Mann-Whitney U tests. Binary logistic regression models were used. P <  0.05 was considered a statistically significant difference.

Results

One hundred thirty-one migrants from tropical and subtropical areas with loiasis were identified. Forty-nine patients were male (37.4%). The migrants’ mean age (±SD) was 42.3 ± 17.3 years, and 124 (94.7%) were from Equatorial Guinea. The median time (IQR) between arrival in Spain and the first consultation was 2 (1–7) months. One hundred fifteen migrants had eosinophilia, and one hundred thirteen had hyper-IgE syndrome. Fifty-seven patients had pruritus (43.5%), and thirty patients had Calabar swelling (22.9%). Seventy-three patients had coinfections with other filarial nematodes (54.2%), and 58 migrants had only Loa loa infections (45.8%). One hundred two patients (77.9%) were treated; 45.1% (46/102) patients were treated with one drug, and 54.9% (56/102) patients were treated with combined therapy. Adverse reactions were described in 14 (10.7%) migrants.

Conclusions

Our patients presented early clinical manifestations and few atypical features. Thus, physicians should systematically consider loiasis in migrants with a typical presentation. However, considering that 72.5% of the patients had only positive microfilaremia without any symptoms, we suggest searching for microfilaremia in every migrant from endemic countries for loiasis presenting with eosinophilia.

Efficacy of High-Dose Albendazole with Ivermectin for Treating Imported Loiasis, Italy

We describe the outcomes of 16 cases of imported loiasis in Italy. Patients had microfilaremia <20,000/mL and were treated with high-dose albendazole for 28 days and a single dose of ivermectin. This combination might be an effective treatment option in nonendemic areas, when diethylcarbamazine, the drug of choice, is not available.

Encephalopathy in a patient with loiasis treated with albendazole: A case report

BACKGROUND

Loiasis is a vector-borne parasitic infection endemic across many areas of Central and West Africa. Its treatment is tricky due to the risk of serious neurologic adverse events occurring after the administration of microfilaricidal drugs, like diethylcarbamazine or ivermectin, in subjects with high pre-treatment microfilarial load. Albendazole is currently recommended to slowly reduce microfilaremia before curative regimen is prescribed.

CASE PRESENTATION

We report the case of a 25-year-old man from Guinea-Conakry who was incidentally diagnosed with highly microfilaremic Loa loa infection. A three weeks regimen of albendazole was prescribed. Minor neurologic side effects occurred after two weeks of administration, while serious encephalopathy developed one week later. Clinical and electroencephalographic features of the patient resembled those of an immune-mediated encephalitis. After exclusion of other causes of encephalopathy, treatment-related Loa loa encephalopathy induced by albendazole was suspected. Corticosteroid treatment was administered and the patient recovered.

DISCUSSION

Our case confirms that Loa loa treatment-related encephalopathy may occur even during albendazole treatment. The clinical and electroencephalographic similarities between Loa loa albendazole-related encephalopathy and immune-mediated encephalitis suggest the possibility of an underlying inflammation-based pathogenesis. Although corticosteroid administration is not recommended in Loa loa ivermectin-induced encephalopathy, in this case of Loa loa albendazole-induced encephalopathy it may have played a therapeutic role.

Atypical Clinical Manifestations of Loiasis and Their Relevance for Endemic Populations

Background

Loiasis is mostly considered a relatively benign infection when compared with other filarial and parasitic diseases, with Calabar swellings and eyeworm being the most common signs. Yet, there are numerous reports in the literature of more serious sequelae. Establishing the relationship between infection and disease is a crucial first step toward estimating the burden of loiasis.

Methods

We conducted a systematic review of case reports containing 329 individuals and detailing clinical manifestations of loiasis with a focus on nonclassical, atypical presentations.

Results

Results indicate a high proportion (47%) of atypical presentations in the case reports identified, encompassing a wide range of cardiac, respiratory, gastrointestinal, renal, neurological, ophthalmological, and dermatological pathologies. Individuals with high microfilarial densities and residing in an endemic country were at greater risk of suffering from atypical manifestations.

Conclusions

Our findings have important implications for understanding the clinical spectrum of conditions associated with Loa loa infection, which extends well beyond the classical eyeworm and Calabar swellings. As case reports may overestimate the true rate of atypical manifestations in endemic populations, large-scale, longitudinal clinico-epidemiological studies will be required to refine our estimates and demonstrate causality between loiasis and the breadth of clinical manifestations reported. Even if the rates of atypical presentations were found to be lower, given that residents of loiasis-endemic areas are both numerous and the group most at risk of severe atypical manifestations, our conclusions support the recognition of loiasis as a significant public health burden across Central Africa.

Case Report: Monoclonal Gammopathy of Undetermined Significance is Associated with Loa loa Infection

A 63-year-old woman who migrated from Nigeria to the United States was found to have an elevated total serum protein, anemia, and eosinophilia. Serum protein electrophoresis (SPEP) and serum protein immunofixation electrophoresis (SPIFE) demonstrated monoclonal immunoglobulin G (IgG) κ restricted bands (IgG 3,820 mg/dL; κ/λ ratio 4.47), indicative of monoclonal gammopathy of unknown significance (MGUS). A rapid diagnostic test (RDT) for malaria was positive for Plasmodium falciparum (BinaxNOW^®; Alere Scarborough Inc., Scarborough, ME). Giemsa-stained blood smears were negative for malarial parasites, however, Loa loa microfilariae were identified. Reverse transcription polymerase chain reaction for P. falciparum, Plasmodium ovale, Plasmodium malariae, and Plasmodium vivax yielded a negative result. She was treated for loiasis with diethylcarbamazine and received no malaria medication. Treatment resulted in a resolution of the microfilaremia and eosinophilia, a negative RDT for malaria, and marked reduction in the monoclonal gammopathy. This is the first reported human case of MGUS associated with loiasis and its resolution after antiparasitic treatment.

New promising method to assess microfilarial Loa loa load on the peripheral blood

Loiasis is a vector-borne parasitic disease caused by the filarial Loa loa (L. loa). Definitive diagnosis can be done by identifying and counting microfilariae in the peripheral blood by microscopy and with L.loa-specific PCR. An additional diagnostic method is the detection of L.loa-specific antibodies. Accurate methods are needed to automate quantification of microfilaria (mf) in peripheral blood. Indeed, the treatment procedure depends on the microfilarial L. loa load in blood. We report the first documented use of flow cytometry as a new method to count microfilaraemia in peripheral blood from a patient with L. loa infection. The diagnosis of loiasis was strongly suspected based on clinical presentation and rapidly confirmed by identifying typical features of L. loa in the peripheral blood. This diagnosis was achieved by flow cytometry using a specific fluorescence pattern for microfilaraemia count. The current report highlights the potential of flow cytometry to assess microfilarial L. loa load from a patient with loiasis infection.

Laboratory Parameters after Treatment for Loa loa and Mansonella perstans: The Experience of a Single Referral Center for Tropical Diseases in a Non-Endemic Area

Infections due to Loa loa and Mansonella perstans are common yet elusive neglected filariases. Parasitological cure after treatment is very difficult to assess, as adult parasites are not accessible. Therefore, outside transmission areas, patients require a long follow-up period to ascertain the therapeutic outcome, which is impractical for non-sedentary populations such as migrants. We studied the change over time of microfilaremia, eosinophil counts, and antifilarial antibodies tested with a commercial ELISA test (Bordier Affinity Products, Crissier, Switzerland), in a retrospective cohort of patients with confirmed L. loa and M. perstans infections, to evaluate the role of serology in clinical practice. After treatment, all 22 eligible patients diagnosed in our center between 2015 and 2017 reached amicrofilaremia, with microfilarial counts decreasing sharply within 2 months. Paralleling eosinophil counts, antibodies decreased in all patients, 36% of whom reached sero-reversion or near-sero-reversion in < 20 months. These findings suggest that positive serology is not just residual from a past infection, and may be used for diagnosis even when microfilaremia is negative or cannot be performed. Interestingly, antibodies and eosinophil counts increased following some, but not all, re-treatment courses. If the rise in these parameters reflects death of macrofilariae, caution is required in interpreting high eosinophil counts and antibody titers shortly after treatment, as these may reflect no need for further treatment. To optimize patients' management, it is now pivotal to ascertain the interval between treatment and macrofilarial death and therefore whether re-treatments are required for complete clearance of parasites.

Mouse models of Loa loa

Elimination of the helminth disease, river blindness, remains challenging due to ivermectin treatment-associated adverse reactions in loiasis co-infected patients. Here, we address a deficit in preclinical research tools for filarial translational research by developing Loa loa mouse infection models. We demonstrate that adult Loa loa worms in subcutaneous tissues, circulating microfilariae (mf) and presence of filarial biomarkers in sera occur following experimental infections of lymphopenic mice deficient in interleukin (IL)-2/7 gamma-chain signaling. A microfilaraemic infection model is also achievable, utilizing immune-competent or -deficient mice infused with purified Loa mf. Ivermectin but not benzimidazole treatments induce rapid decline (>90%) in parasitaemias in microfilaraemic mice. We identify up-regulation of inflammatory markers associated with allergic type-2 immune responses and eosinophilia post-ivermectin treatment. Thus, we provide validation of murine research models to identify loiasis biomarkers, to counter-screen candidate river blindness cures and to interrogate the inflammatory etiology of loiasis ivermectin-associated adverse reactions.

Here, the authors develop a mouse model of Loa loa that reflects human infections, including eosinophilia, and determine effects of ivermectin treatment.

Prevalence and intensity of Loa loa infection over twenty-three years in three communities of the Mbalmayo health district (Central Cameroon)

BACKGROUND

Loiasis is a vector-borne parasitic disease due to Loa loa and transmitted to humans by tabanids of the genus Chrysops. Loiasis has been historically considered as the second or third most common reason for medical consultation after malaria, and a recent study has reported an excess mortality associated with the infection. However, the clinical impact of this filarial disease is yet to be elucidated, and it is still considered a benign disease eliciting very little attention. As a consequence of post-treatment severe adverse events occurring in individuals harboring very high Loa microfilarial loads, ivermectin is not recommended in onchocerciasis hypo-endemic areas that are co-endemic for loiasis. Without treatment, it is likely that the transmission of the disease and the morbidity associated with the infection will increase over time. This study aimed at investigating the long-term trends in prevalence and intensity of Loa loa infection in an area where no mass anti-filarial treatment has ever been distributed.

METHODS

A cross-sectional survey was conducted in three communities of the Mbalmayo health district (Central Cameroon). All volunteers, males and females aged five years and above, underwent daytime calibrated thick blood smears (CTBS) to search for L. loa microfilariae (mf). A structured questionnaire was administered to assess the history of both loiasis related clinical signs and migration of enrollees.

RESULTS

The prevalence of loiasis was 27.3% (95% CI: 22.3-32.9) in the three surveyed communities, with a mean mf density of 1922.7 (sd: 6623.2) mf/mL. Loa loa infection rate was higher amongst females than in males (p = 0.0001) and was positively associated with age of (OR = 1.018; p = 0.007). The intensity of infection was higher among males than in females (p < 0.0001), and displayed a convex in form trends with age groups. The follow up over 23 years revealed that both the rate and intensity of infection were similar to baseline.

CONCLUSIONS

The prevalence and intensity of Loa loa infection 23 years on is stable over time, indicating that this filarial disease might be noncumulative as regarded till now.

Environmental factors associated with the distribution of Loa loa vectors Chrysops spp. in Central and West Africa: seeing the forest for the trees

Background

Loiasis is caused by the filarial parasite Loa loa, which is widespread through Central and West Africa and largely confined the tropical equatorial rainforests. The tabanid flies Chrysops silacea and Chrysops dimidiata are the main vectors driving transmission. This study aimed to better define the spatial distribution and ecological niche of the two vectors to help define spatial-temporal risk and target appropriate, timely intervention strategies for filariasis control and elimination programmes.

Methods

Chrysops spp. distributions were determined by collating information from the published literature into a database, detailing the year, country, locality, latitude/longitude and species collected. Environmental factors including climate, elevation and tree canopy characteristics were summarised for each vector from data obtained from satellite modelled data or imagery, which were also used to identify areas with overt landcover changes. The presence of each Chrysops vector was predicted using a maximum entropy species distribution modelling (MaxEnt) method.

Results

A total of 313 location-specific data points from 59 published articles were identified across seven loiasis endemic countries. Of these, 186 sites were included in the climate and elevation analysis, and due to overt landcover changes, 83 sites included in tree canopy analysis and MaxEnt model. Overall, C. silacea and C. dimidiata were found to have similar ranges; annual mean temperature (24.6 °C and 24.1 °C, respectively), annual precipitation (1848.6 mm and 1868.8 mm), elevation (368.8 m and 400.6 m), tree canopy cover (61.4% and 66.9%) and tree canopy height (22.4 m and 25.1 m). MaxEnt models found tree canopy coverage was a significant environmental variable for both vectors.

Conclusions

The Chrysops spp. database and large-scale environmental analysis provides insights into the spatial and ecological parameters of the L. loa vectors driving transmission. These may be used to further delineate loiasis risk, which will be important for implementing filariasis control and elimination programmes in the equatorial rainforest region of Central and West Africa.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3327-9) contains supplementary material, which is available to authorized users.

Effect of a Single Standard Dose (150-200 μg/kg) of Ivermectin on Loa loa Microfilaremia: Systematic Review and Meta-analysis

Background

In central Africa, millions of individuals infected with Loa loa have received the anthelminthic drug ivermectin (IVM) as part of mass drug administration (MDA) campaigns targeting onchocerciasis control or elimination. Nonetheless, the parasitological surveys that are occasionally conducted to evaluate the impact of IVM treatments on Onchocerca volvulus do not include an assessment of the extra benefits of those MDA campaigns on L. loa.

Methods

We conducted a systematic review of trials on the effect of a single standard (150–200 μg/kg) dose of IVM on L. loa microfilarial density (MFD). The dynamics of MFD over 365 days of treatment were described using multilevel regression and latent class modeling.

Results

IVM brings about a rapid, dramatic, and sustained decrease, with reduction rates of 60%, 75%, 85%, and 90% on day 1 (D1), D2, D7, and D365, respectively. At D365, no participants (0/238) with an initial MFD of <20 000 microfilariae (mf)/mL were at risk of postivermectin severe adverse events, and only 1/57 individuals with an initial MFD of ≥20 000 mf/mL presented with an MFD above this value. The main predictor of post-treatment MFD was the pretreatment value, but this post-treatment value varied little between D8 and D365 regardless of the pretreatment level.

Conclusions

A single dose of IVM is very effective at substantially reducing L. loa MFD for at least a year, irrespective of the initial level of parasitemia. Individuals treated with IVM are probably not any more at risk of severe adverse events when retreated 1 year later.

Removal of adult subconjunctival Loa loa amongst urban dwellers in Nigeria

Loiasis is a neglected tropical disease caused by infection with the filarial parasite Loa loa. It is a disease considered by many to be benign. Several reports of trans border importation of the Loa loa worm amongst immigrants and visitors from endemic regions of the world exist. In most cases an adult subconjunctival worm is removed from the patient. An interventional case series is reported and examines the practice of removal of subconjunctival adult Loa loa worms amongst urban dwellers in Nigeria. Four cases of ocular loiasis seen amongst urban dwellers in Nigeria exemplify the different presentations and removal methods of the subconjunctival adult worm. There were 2 males and 2 females aged 35years, 23years, 25years and 30years respectively. Each patient gave a history of having been raised in a rural community in childhood years, during which they were exposed to streams and muddy farm land; and then migrated to the urban community in later years. They all present with the finding of a subconjunctival adult worm, which was successfully removed and identified to be Loa loa. There are more urban dwellers in Nigeria who present with symptoms of foreign body sensation that may be related to the manifestation of a subconjunctival worm and are not recognized. This is because the emphasis on this disease has erstwhile been on the rural, village dwellers and not on urban dwellers. Eye care practitioners working in urban centers need to be aware of the possibility of this presentation, and be ready to remove any subconjunctival worm when it presents.

Subconjunctival adult Loa loa is one of the ocular manifestations of paraisitosis by Loa loa, which is categorized as a neglected benign disease. Loa loa transmission has predominantly been amongst inhabitants in rural communities in Nigeria, one of the countries in the endemic belt of Africa. However we report a case series of 4 patients presenting with subconjunctival Loa loa who in childhood lived in rural communities but later migrated from rural to urban cities where they presented. The varied presentation of the patients in this series and the technique of worm removal are reported.