Clinical and epidemiological features of imported loiasis in Beijing: a report from patients returned from Africa.

BACKGROUND: Loiasis is one of the significant filarial diseases for people living in West and Central Africa with wide endemic area but is not seen in China. As economy booms and international traveling increase, China faces more and more imported parasitic diseases that are not endemic locally. Loiasis is one of the parasitic diseases that enter China by travelers infected in Africa. The better understanding of the clinical and laboratory features of loa loa infection will facilitate the diagnosis and treatment of loiasis in China. METHODS: The study targeted travelers who were infected with L. loa in endemic Africa regions and returned to Beijing between 2014 and 2023. Epidemiological, clinical, and biological data as well as treatment of these patients were collected. RESULTS: Total 21 cases were identified as L. loa infection based on their typical clinical manifestations and parasite finding. All cases had a history of travel to Africa for more than 6 months, most of them are the construction workers dispatched to West Africa with outdoor activities. Calabar swelling (n = 19; 90.5%) and pruritus (n = 11; 52.4%) were among the most common clinical symptoms followed by muscle pain (n = 7; 33.3%) and skin rash (n = 2; 9.5%). The adult worms were observed in the eyelid or subconjunctiva (n = 2; 9.5%) and subcutaneous tissues (n = 2; 9.5%). Although all patients presented with a high eosinophil count (> 0.52 × 109/L), only two cases displayed microfilariae in fresh venous blood and positive for filarial antigen. A cut section of adult worm was observed through biopsy on a skin nodule surrounded by lymphocytes, plasma cells and eosinophils. All subjects were positive in PCR targeting L. loa ITS-1. The constructed phylogenetic tree based on the amplified ITS-1 sequences identified their genetical relation to the L. Loa from Africa. All patients treated with albendazole and diethylcarbamazine were recovered without relapse. CONCLUSION: This study provides useful information and guideline for physicians and researchers in non-endemic countries to diagnose and treat loiasis and L. loa infections acquired from endemic regions.

A Novel, Highly Sensitive Nucleic Acid Amplification Test Assay for the Diagnosis of Loiasis and its Use for Detection of Circulating Cell-Free DNA.

Mass drug administration programs targeting filarial infections depend on diagnostic tools that are sensitive and specific. The coendemicity of Loa loa with other filarial species often hampers the control programs. LL2634 was identified as the most promising target among several highly repeated targets, with sensitivity between 500 ag and 1 fg of genomic DNA. Using DNA from infected individuals, LL2643 quantitative polymerase chain reaction (qPCR) was positive in all individuals. LL2643 was detected in plasma-derived circulating cell-free DNA (ccfDNA) from 48 of 53 microfilariae-positive patients. Detection of ccfDNA in urine was possible, but it occurred rarely among those tested. Importantly, LL2643 ccfDNA became undetectable within 1 month following diethylcarbamazine (DEC) treatment and remained negative for at least a year. LL2643 offers a more sensitive and specific target for detection of L. loa infection and would be easily configurable to a point-of-contact assay. Clinical Trials Registration. NCT00001230 and NCT00090662.

Safety and Efficacy of Levamisole in Loiasis: A Randomized, Placebo-controlled, Double-blind Clinical Trial.

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

IL-10 and Its Related Superfamily Members IL-19 and IL-24 Provide Parallel/Redundant Immune-Modulation in Loa loa Infection.

BACKGROUND: Interleukin-10 (IL-10) has been implicated as the major cytokine responsible for the modulation of parasite-specific responses in filarial infections; however, the role of other IL-10 superfamily members in filarial infection is less well studied. METHODS: Peripheral blood mononuclear cells from loiasis patients were stimulated with or without filarial antigen. Cytokine production was quantified using a Luminex platform and T-cell expression patterns were assessed by flow cytometry. RESULTS: All patients produced significant levels of IL-10, IL-13, IL-5, IL-4, and IL-9 in response to filarial antigen, indicating a common infection-driven response. When comparing microfilaria (mf)-positive and mf-negative patients, there were no significant differences in spontaneous cytokine nor in parasite-driven IL-10, IL-22, or IL-28a production. In marked contrast, mf-positive individuals had significantly increased filarial antigen-driven IL-24 and IL-19 compared to mf-negative subjects. mf-positive patients also demonstrated significantly higher frequencies of T cells producing IL-19 in comparison to mf-negative patients. T-cell expression of IL-19 and IL-24 was positively regulated by IL-10 and IL-1ß. IL-24 production was also regulated by IL-37. CONCLUSION: These data provide an important link between IL-10 and its related family members IL-19 and IL-24 in the modulation of the immune response in human filarial infections. CLINICAL TRIALS REGISTRATION: NCT00001230.

Imported loiasis in France: a retrospective analysis of 167 cases with comparison between sub-Saharan and non sub-Saharan African patients.

BACKGROUND: Imported loiasis is a rare cause of consultation at the return of stay in central Africa, which often poses difficult diagnostic and therapeutic questions to practitioners especially those who are unaccustomed to tropical medicine. These difficulties can lead to risks for the patients especially if inappropriate treatment is given. Large series of imported loiasis are scarce. METHODS: We retrospectively studied the data including outcome in patients diagnosed with imported loiasis between 1993 and 2013 in the Paris area on the basis of a parasitological diagnosis (microfilaremia > 1/ml and/or serologic tests). We compared sub-Saharan and non sub-Saharan African patients. RESULTS: Of the 177 identified cases, 167 could be analysed. Sex ratio was 1, mean age 41 years and 83% were sub-Saharan Africans. Cameroon was the main country of exposure (62%). Incubation time may be long (up to 18 months). Of the 167 cases, 57% presented with characteristic symptoms (Calabar swellings, creeping dermatitis, eyeworm) whereas 43% were diagnosed fortuitously. Microfilaremia was evidenced in 105 patients (63%), and specific antibodies in 53%. Compared to sub-Saharan Africans, other patients were presenting less frequently with eyeworm migration and microfilaremia whereas they had higher eosinophilia and positive serology. Prevalence of Calabar swellings was not significantly different between the two groups. Cure rates were 52% with ivermectin alone, and 77% with ivermectin followed by diethylcarbamazine. No severe adverse event was reported. CONCLUSIONS: Presentation of imported loiasis varies according to ethnicity. A systematic screening should be recommended in patients with potential exposure in endemic country. Treatment with ivermectin followed by diethylcarbamazine could be a valuable option.

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.

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.

Loiasis in US Traveler Returning from Bioko Island, Equatorial Guinea, 2016.

The filarial parasite Loa loa overlaps geographically with Onchocera volvulus and Wuchereria bancrofti filariae in central Africa. Accurate information regarding this overlap is critical to elimination programs targeting O. volvulus and W. bancrofti. We describe a case of loiasis in a traveler returning from Bioko Island, Equatorial Guinea, a location heretofore unknown for L. loa transmission.

The Golden Age of parasitology-1875-1925: the Scottish contributions.

The period 1875-1925 was remarkable in the history of parasitology partly because of the number of significant discoveries made, especially the elucidation of important life cycles, and partly because of the achievements of the clinicians and scientists who made these discoveries. What is remarkable is that so many of these individuals were Scots. Preeminent in this pantheon was Patrick Manson, who not only discovered the mosquito transmission of filarial worms but was instrumental in directly encouraging others to make significant discoveries in the fields of malaria, Guinea worm disease (dracunculiasis), onchocerciasis, loiasis and schistosomiasis and, indirectly, sleeping sickness and leishmaniasis. This chapter describes and discusses the contributions made by Douglas Argyll-Robertson, Donald Blacklock, David Bruce, David Cunningham, Robert Leiper, William Leishman, George Low, Patrick Manson, Muriel Robertson and Ronald Ross together with short biographical notes.

Eosinophil-associated processes underlie differences in clinical presentation of loiasis between temporary residents and those indigenous to Loa-endemic areas.

BACKGROUND: Loa loa has emerged as an important public health problem due to the occurrence of immune-mediated severe posttreatment reactions following ivermectin distribution. Also thought to be immune-mediated are the dramatic differences seen in clinical presentation between infected temporary residents (TR) and individuals native to endemic regions (END). METHODS: All patients diagnosed with loiasis at the National Institutes of Health between 1976 and 2012 were included. Patients enrolled in the study underwent a baseline clinical and laboratory evaluation and had serum collected and stored. Stored pretreatment serum was used to measure filaria-specific antibody responses, eosinophil-related cytokines, and eosinophil granule proteins. RESULTS: Loa loa infection in TR was characterized by the presence of Calabar swelling (in 82% of subjects), markedly elevated eosinophil counts, and increased filaria-specific immunoglobulin G (IgG) levels; these findings were thought to reflect an unmodulated immune response. In contrast, END showed strong evidence for immune tolerance to the parasite, with high levels of circulating microfilariae, few clinical symptoms, and diminished filaria-specific IgG. The striking elevation in eosinophil counts among the TR group was accompanied by increased eosinophil granule protein levels (associated with eosinophil activation and degranulation) as well as elevated levels of eosinophil-associated cytokines. CONCLUSIONS: These data support the hypothesis that differing eosinophil-associated responses to the parasite may be responsible for the marked differences in clinical presentations between TR and END populations with loiasis.

Safety and Short-term Efficacy of a Single Dose of 2†mg Moxidectin in Loa loa-Infected Individuals: A Double-Blind, Randomized Ivermectin-Controlled Trial With Ascending Microfilarial Densities.

Background: In 2018, the US Food and Drug Administration approved the macrocylic lactone moxidectin (MOX) at 8 mg dosage for onchocerciasis treatment in individuals aged ≥12 years. Severe adverse reactions have occurred after ivermectin (IVM), also a macrocyclic lactone, in individuals with high Loa microfilarial density (MFD). This study compared the safety and efficacy of a 2 mg MOX dose and the standard 150 µg/kg IVM dose in individuals with low L loa MFD. Methods: A double-blind, randomized, ivermectin-controlled trial of a 2 mg moxidectin dose was conducted in Cameroon between May and July 2022. It enrolled 72 adult men with L loa MFD between 5 and 1000 microfilariae/mL. Outcomes were occurrence of adverse events (AEs) and L loa MFD reduction rate during the first month off treatment. Results: No serious or severe AEs occurred among the 36 MOX- or the 36 IVM-treated individuals. Forty-nine AEs occurred in the MOX arm versus 59 AEs in the IVM arm. Grade 2 AE incidence was higher among IVM- than MOX-treated participants (38.5% and 14.3%, respectively, P = .043). Median MFD reduction rates were significantly higher after IVM than MOX at day 3 (70.2% vs 48.5%), day 7 (76.4% vs 50.0%), and day 30 (79.8% vs 48.1%). Conclusions: A single 2 mg MOX dose is as safe as 150 µg/kg IVM in patients with low L loa MFD. Further studies with higher MOX doses and in patients with higher MFD are warranted. Clinical Trials Registration: NCT04049851.

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.

Excess Mortality Associated With Loiasis: Confirmation by a New Retrospective Cohort Study Conducted in the Republic of Congo.

Background: Loiasis (Loa loa filariasis) is considered a benign disease and is currently not included in the World Health Organization's (WHO's) list of Neglected Tropical Diseases, despite mounting evidence suggesting significant disease burden in endemic areas. We conducted a retrospective cohort study to assess the mortality associated with L. loa microfilaremia in the Southwestern Republic of Congo. Methods: The cohort included 3329 individuals from 53 villages screened for loiasis in 2004. We compared mortality rates in 2021 for individuals initially diagnosed as with or without L. loa microfilariae 17 years earlier. Data were analyzed at the community level to calculate crude mortality rates. Survival models were used to estimate the effect of L. loa microfilaremia on mortality in the population. Results: At baseline, prevalence of microfilaremia was 16.2%. During 17.62 years of cohort follow-up, 751 deaths were recorded, representing a crude mortality rate of 15.36 (95% CI, 14.28-16.50) per 1000 person-years. Median survival time was 58.5 (95% CI, 49.7-67.3) years and 39.2 (95% CI, 32.6-45.8) years for amicrofilaremic and microfilaremic indiviudals, respectively. Conclusions: A significant reduction in life expectancy was associated with L. loa microfilaremia, confirming previous observations from Cameroon. This adds to the evidence that loiasis is not a benign disease and deserves to be included in the WHO's list of Neglected Tropical Diseases.

Unexpected Loa loa Finding in an Asymptomatic Patient From The Gambia: A Case Report.

A 17-year-old asymptomatic male from The Gambia presented for a routine health examination after migration to Spain. Laboratory diagnosis confirmed the presence of Loa loa microfilariae. This unusual finding emphasizes the importance of screening in newly arrived migrants and the need of an extended anamnesis including migratory route and previous travels.

Longitudinal study of cross-reactive antigenemia in individuals with high Loa loa microfilarial density reveals promising biomarkers for distinguishing lymphatic filariasis from loiasis.

Background and methods: Circulating Loa loa antigens are often detected in individuals with heavy L. loa infections by diagnostic tests for lymphatic filariasis (LF) caused by Wuchereria bancrofti. This is a major challenge to LF mapping and elimination efforts in loiasis co-endemic areas. However, it also provides an opportunity to identify antigen biomarkers for loiasis. To determine which L. loa antigens might be promising biomarkers for distinguishing true LF from loiasis, we screened for L. loa antigens in a group of individuals with heavy L. loa infections living in the Okola Health District of Cameroon. In this longitudinal study, participants were tested for cross-reactive antigenemia by filariasis test strip (FTS), ELISA, and western blot, and were monitored for FTS status at 6, 9, 12, and 15 months post-enrollment. We then identified specific circulating L. loa antigens by liquid chromatography-tandem mass spectrometry (LC-MS/MS) from baseline and 15-month plasma samples. Principal findings and conclusions: Among 73 FTS-positive (FTS+) and 13 FTS-negative (FTS-) participants with high L. loa microfilarial loads, 83% maintained their FTS status over the course of the study, while 17% experienced at least one FTS conversion event (from FTS+ to FTS- or vice versa). Cross-reactive antigens were detected in both FTS+ and FTS- sera by western blot, and there was poor agreement in antigen detection by FTS, western blot, and ELISA methods. One protein family, a group of Nas-14 metalloproteases, was detected by LC MS/MS in >80% of tested samples, including FTS- samples. These data identify Nas-14 as a promising loiasis biomarker potentially capable of distinguishing loiasis from lymphatic filariasis.

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.

Vector control and entomological capacity for onchocerciasis elimination.

Mass drug administration (MDA) of ivermectin is currently the main strategy to achieve elimination of transmission (EoT) of onchocerciasis. Modelling suggests that EoT may not be reached in all endemic foci using annual MDA alone. Onchocerciasis and loiasis are coendemic in forest areas of Central Africa where ivermectin treatment can lead to severe adverse events in individuals with heavy loiasis load, rendering MDA inappropriate. Vector control has been proposed as a complementary intervention strategy. Here, we discuss (i) achievements and pitfalls of previous interventions; (ii) epidemiological impact, feasibility, and combination with MDA to accelerate and/or protect EoT; (iii) role of modelling; (iv) opportunities for innovative methods of vector monitoring and control; and (v) strengthening entomological capacity in endemic countries.

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

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.