Onchocerca Volvulus Microfilariae Research Articles

Onchocerca volvulus microfilariae in the anterior chambers of the eye and ocular adverse events after a single dose of 8 mg moxidectin or 150 µg/kg ivermectin: results of a randomized double-blind Phase 3 trial in the Democratic Republic of the Congo, Ghana and Liberia

BackgroundAfter ivermectin became available, diethylcarbamazine (DEC) use was discontinued because of severe adverse reactions, including ocular reactions, in individuals with high Onchocerca volvulus microfilaridermia (microfilariae/mg skin, SmfD). Assuming long-term ivermectin use led to < 5 SmfD with little or no eye involvement, DEC + ivermectin + albendazole treatment a few months after ivermectin was proposed. In 2018, the US FDA approved moxidectin for treatment of O. volvulus infection. The Phase 3 study evaluated SmfD, microfilariae in the anterior chamber (mfAC) and adverse events (AEs) in ivermectin-naïve individuals with ≥ 10 SmfD after 8 mg moxidectin (n = 978) or 150 µg/kg ivermectin (n = 494) treatment.MethodsWe analyzed the data from 1463 participants with both eyes evaluated using six (0, 1–5, 6–10, 11–20, 21–40, > 40) mfAC and three pre-treatment (< 20, 20 to < 50, ≥ 50) and post-treatment (0, > 0–5, > 5) SmfD categories. A linear mixed model evaluated factors and covariates impacting mfAC levels. Ocular AEs were summarized by type and start post-treatment. Logistic models evaluated factors and covariates impacting the risk for ocular AEs.ResultsMoxidectin and ivermectin had the same effect on mfAC levels. These increased from pre-treatment to Day 4 and Month 1 in 20% and 16% of participants, respectively. Six and 12 months post-treatment, mfAC were detected in ≈5% and ≈3% of participants, respectively. Ocular Mazzotti reactions occurred in 12.4% of moxidectin- and 10.2% of ivermectin-treated participants without difference in type or severity. The risk for ≥ 1 ocular Mazzotti reaction increased for women (OR 1.537, 95% CI 1.096–2.157) and with mfAC levels pre- and 4 days post-treatment (OR 0: > 10 mfAC 2.704, 95% CI 1.27–5.749 and 1.619, 95% CI 0.80–3.280, respectively).ConclusionsThe impact of SmfD and mfAC levels before and early after treatment on ocular AEs needs to be better understood before making decisions on the risk-benefit of strategies including DEC. Such decisions should take into account interindividual variability in SmfD, mfAC levels and treatment response and risks to even a small percentage of individuals.Graphical

Procedure for Handling and Storage of Onchocerca volvulus Microfilariae Obtained from Skin Snips for Downstream Genetic Work.

WHO and endemic countries target elimination of transmission of Onchocerca volvulus, the parasite causing onchocerciasis. Population genetic analysis of O. volvulus may provide data to improve the evidence base for decisions on when, where, and for how long to deploy which interventions and post-intervention surveillance to achieve elimination. Development of necessary methods and tools requires parasites suitable for genetic analysis. Based on our experience with microfilariae obtained from different collaborators, we developed a microfilariae transfer procedure for large-scale studies in the Democratic Republic of Congo (DRC) comparing safety and efficacy of ivermectin, the mainstay of current onchocerciasis elimination strategies, and moxidectin, a new drug. This procedure is designed to increase the percentage of microfilariae in skin snips suitable for genetic analysis, improve assignment to metadata, and minimize time and materials needed by the researchers collecting the microfilariae. Among 664 microfilariae from South Sudan, 35.7% and 39.5% failed the mitochondrial and nuclear qPCR assay. Among the 576 microfilariae from DRC, 16.0% and 16.7% failed these assays, respectively. This difference may not only be related to the microfilariae transfer procedure but also to other factors, notably the ethanol concentration in the tubes in which microfilariae were stored (64% vs. ≥75%).

Ivermectin treatment response in two rural villages with a high prevalence of onchocerciasis and epilepsy, Mahenge Tanzania.

Despite 20 years of ivermectin mass distribution in the Mahenge area, Tanzania, the prevalence of onchocerciasis and epilepsy has remained high in rural villages. We investigated the efficacy of ivermectin in reducing Onchocerca volvulus microfilariae and predictors for parasitic load following ivermectin treatment in persons with (PWE) and without epilepsy (PWOE). Between April and September 2019, 50 PWE and 160 randomly selected PWOE from Msogezi and Mdindo villages participated in a follow-up study. Skin snips were obtained pre (baseline) and three months post-ivermectin treatment. The overall prevalence of O. volvulus positive skin snips at baseline was 49% (103/210), with no significant difference between PWE (58.0%) and PWOE (46.3%); p=0.197. The overall mean microfilarial density was significantly higher at baseline 1.45(95%CI:0.98-2.04)) than three-month post-ivermectin treatment (0.23(95%CI:0.11-0.37), p<0.001. Three months after ivermectin, the microfilarial density had decreased by ≥80% in 54 (81.8%, 95%CI: 72.3-91.4) of the 66 individuals with positive skin snips at baseline. High microfilarial density at baseline was the only significant predictor associated with higher microfilarial density in the post-ivermectin skin snips. Our study reports a decrease in microfilarial density following ivermectin treatment in most individuals. Optimizing ivermectin coverage will address the ongoing onchocerciasis transmission in Mahenge.

Pathological Impact and Disease Burden of Human Onchocerciasis in Endemic Areas of Delta State, Nigeria

Background to the Study/Aim: The context of onchocerciasis being one of the neglected tropical diseases (NTDs) in Nigeria; and the predicted increase in the rate of spread of tropical diseases and vectors to higher altitude, as a result of climate change and global warming, underscores the need for more studies on the disease. Thus, this research was conducted to examine the pathological impact and disease burden of human onchocerciasis on the infected in endemic communities in three local government areas of Delta State, Nigeria.&#x0D; Materials and Methods: The study was carried out in two phases. The first phase involved four stages. Stage one was visual acuity test on those who volunteered to take part in the research. Stage two was the physical examination of individuals for characteristic onchocercal lesions. The third stage was the collection of skin snips from individuals while the fourth stage was microscopic examination of the skin snips for microfilariae of Onchocerca volvulus. The second phase examined the impact of the disease and was carried out with the aid of a structured questionnaire.&#x0D; Results: The results showed that human onchocerciasis existed in the study area. Out of the 1,201 persons, comprising of 826 (68.8%) males and 375 (31.2%) females examined, 138 were positive for the onchocercal parasite. The infected, consisted of 101 (12.2%) males and 37 (9.9%) females. Generally, infected persons had manifestations ranging from ocular defects, visual problems to skins disfiguration.&#x0D; Conclusion: In addition to the administration of ivermectin and vector control, psychosocial and economic needs of the infected should be addressed through counseling and offering of palliating assistance to reduce their economic problems and give them feeling of independence.

Knowledge, attitude and perception of people infected with human onchocerciasis in endemic areas of Delta State, Nigeria

Onchocerciasis is one of the Neglected Tropical Diseases (NTDs) in Nigeria. The rate of spread of tropical diseases to higher altitudes is on the increase, due to climate change and global warming. This is why this research was conducted to determine knowledge, attitude and perception of those suffering from human onchocerciasis in reported endemic communities of Delta State, Nigeria. The study was carried out in two phases. The first phase involved the collection and examination of samples using standard parasitological protocols. Those who volunteered to participate were included in the study. The second phase examined the knowledge, attitude and perception of the infected and was carried out with the aid of a structured questionnaire. The results showed that out of the 1,201 persons, comprising of 826 (68.8%) males and 375 (31.2%) females examined, 138 were positive for the microfilaria of Onchocerca volvulus. The infected consisted of 101 (12.2%) males and 37 (9.9%) females. Most of the infected persons neither knew the name of the disease nor its vector. Rather, they associated the disease to low income and self-esteem. Comprehensive epidemiological surveys of onchocerciasis in remote areas should be carried out and all the affected population treated by the application of a holistic medical approach. People need to be more informed about the biology and local autecology of the vector and parasite of onchocerciasis. This requires proper health education in the public and schools to minimize the risk of disease transmission in the study area.

ONCHOCERCIASIS: KNOWLEDGE, ATTITUDE AND PRACTICE TO DISEASE INTERVENTION AMONG RESIDENTS IN AN ENDEMIC VILLAGE IN ONDO STATE, SOUTHWEST NIGERIA

The study of Onchocerciasis was undertaken in Imeri, an endemic community in Ondo State, Nigeria. The skin snip method was employed in the examination of the nodules that characterize the disease followed by application of structured questionnaires on knowledge attitude and practice (KAP) of the disease. Of the 194 respondents interviewed and screened for onchocerciasis, 62 (32%) respondents, were positive for microfilariae of Onchocerca volvulus. 150(77.3%) respondents claimed ignorance of the aetiology of the disease while 44(22.7%) showed appreciable knowledge of the disease. 184(94.8%) respondents received ivermectin but 156 (80.4%) actually took the drug during the study and 10(5.2%) showed apathy to the drug. 60 (30.9%) of the respondents complained of side effects but the side effects were more among the infected persons (25.8%) than the uninfected persons (5.1%). The study showed good attitude towards reception and use of ivermectin, however there was a dearth of knowledge about the aetiology and transmission of the disease in the community despite its endemicity. Routine enlightenment programmes in native tongue may be necessary for effective and lasting intervention

A Reevaluation of the Tolerability and Effects of Single-Dose Ivermectin Treatment on Onchocerca volvulus Microfilariae in the Skin and Eyes in Eastern Ghana.

ABSTRACT.Mass administration of ivermectin (IVM) has significantly reduced onchocerciasis prevalence, intensity, and morbidity in most endemic areas. Most IVM clinical trials were performed long ago in persons with high-intensity infections that are uncommon in West Africa today. This cohort treatment study recruited participants from a hypoendemic area in eastern Ghana to reevaluate the efficacy and tolerability of IVM with a special focus on the kinetics of microfilaria (Mf) clearance. Mf in the skin and anterior chambers (AC) were assessed by skin snip and slit lamp examinations at baseline and at 3 and 6 months after treatment with IVM 150 μg/kg. Most participants (184–231, 79.7%) enrolled were treatment-naïve. The baseline geometric mean skin Mf count was 12.67/mg (range 3–86). Although persons with MfAC at baseline (64/231, 27%) had significantly higher skin Mf counts than people without MfAC, 7 of 39 (15%) of persons with skin Mf counts in the range of 3–5 Mf/mg had MfAC. Skin Mf were detected in 14% (31/218) and 45% (96/216) of participants 3 and 6 months after IVM treatment, respectively. MfAC were detected in 12 of 212 (5.7%) study participants at 6 months. 81% (187 of 231) of participants experienced 439 adverse events within 7 days after treatment; all adverse events were mild (96.1%) or moderate. This study has provided new data on the kinetics of Mf in the skin and eyes after IVM treatment of persons with light to moderate intensity Onchocerca volvulus infections that are common in Africa at this time.

Unusual Localization of Blood-Borne Loa loa Microfilariae in the Skin Depends on Microfilarial Density in the Blood: Implications for Onchocerciasis Diagnosis in Coendemic Areas.

BackgroundThe diagnostic gold standard for onchocerciasis relies on identification and enumeration of (skin-dwelling) Onchocerca volvulus microfilariae (mf) using the skin snip technique (SST). In a recent study, blood-borne Loa loa mf were found by SST in individuals heavily infected with L. loa, and microscopically misidentified as O. volvulus due to their superficially similar morphology. This study investigates the relationship between L. loa microfilarial density (Loa MFD) and the probability of testing SST positive.MethodsA total of 1053 participants from the (onchocerciasis and loiasis coendemic) East Region in Cameroon were tested for (1) Loa MFD in blood samples, (2) O. volvulus presence by SST, and (3) Immunoglobulin (Ig) G4 antibody positivity to Ov16 by rapid diagnostic test (RDT). A Classification and Regression Tree (CART) model was used to perform a supervised classification of SST status and identify a Loa MFD threshold above which it is highly likely to find L. loa mf in skin snips.ResultsOf 1011 Ov16-negative individuals, 28 (2.8%) tested SST positive and 150 (14.8%) were L. loa positive. The range of Loa MFD was 0–85 200 mf/mL. The CART model subdivided the sample into 2 Loa MFD classes with a discrimination threshold of 4080 (95% CI, 2180–12 240) mf/mL. The probability of being SST positive exceeded 27% when Loa MFD was >4080 mf/mL.ConclusionsThe probability of finding L. loa mf by SST increases significantly with Loa MFD. Skin-snip polymerase chain reaction would be useful when monitoring onchocerciasis prevalence by SST in onchocerciasis–loiasis coendemic areas.

The impact of ivermectin on onchocerciasis in villages co-endemic for lymphatic filariasis in an area of onchocerciasis recrudescence in Burkina Faso.

In Burkina Faso, onchocerciasis was no longer a public health problem when the WHO Onchocerciasis Control Programme in West Africa closed at the end in 2002. However, epidemiological surveillance carried out from November 2010 to February of 2011, showed a recrudescence of infection in the Cascades Region. This finding was made at a time when ivermectin, a drug recommended for the treatment of both onchocerciasis and lymphatic filariasis, had been distributed in this area since 2004 for the elimination of lymphatic filariasis. It was surprising that ivermectin distributed for treating lymphatic filariasis had not prevented the recrudescence of onchocerciasis. Faced with this situation, the aim of our study was to evaluate the effectiveness of ivermectin on the onchocerciasis parasite. The percentage reduction in microfilarial load after treatment with ivermectin was used as a proxy measure for assessing possible resistance. A cohort study was carried out with 130 individuals who had tested positive for microfilariae of Onchocerca volvulus in 2010 using microscopic examination of skin-snip biopsies from five endemic villages. Subjects were followed from July 2011 to June 2012. The microfilarial load of each individual was enumerated by skin-snip biopsy in 2010, prior to the first ivermectin treatment against onchocerciasis under community guidelines. All individuals received two ivermectin treatments six months apart. In 2012, the microfilarial loads were determined again, six months after the second round of ivermectin and the reductions in parasite loads were calculated to measure the impact of the drug. The percentage reduction of the microfilarial loads ranged from 87% to 98% in the villages. In all villages, there was a statistically significant difference between the average microfilarial loads in 2010 and 2012. The level of reduction of microfilarial loads suggests that ivermectin is effective against the recrudescent population of O. volvulus in Cascades Region of Burkina Faso. Further investigations would be necessary to determine the causes of the recrudescence of onchocerciasis. (For French language abstract, see S1 Alternative Language —Translation of the into French by the authors.)

Differential susceptibility of Onchocerca volvulus microfilaria to ivermectin in two areas of contrasting history of mass drug administration in Cameroon: relevance of microscopy and molecular techniques for the monitoring of skin microfilarial repopulation within six months of direct observed treatment

BackgroundIvermectin is an excellent microfilaricide against Onchocerca volvulus. However, in some regions, long term use of ivermectin has resulted in sub-optimal responses to the treatment. More data to properly document the phenomenon in various contexts of ivermectin mass drug administration (IVM-MDA) is needed. Also, there is a need to accurately monitor a possible repopulation of skin by microfilariae following treatment. Skin snip microscopy is known to have a low sensitivity in individuals with light infections, which can be the case following treatment. This study was designed with two complementary objectives: (i) to assess the susceptibility of O. volvulus microfilariae to ivermectin in two areas undergoing IVM-MDA for different lengths of time, and (ii) to document the repopulation of skin by the O. volvulus microfilariae following treatment, using 3 independent diagnostic techniques.MethodIdentified microfilaridermic individuals were treated with ivermectin and re-examined after 1, 3, and 6 months using microscopy, actin real-time PCR (actin-qPCR) and O-150 LAMP assays. Susceptibility to ivermectin and trends in detecting reappearance of skin microfilariae were determined using three techniques. Microscopy was used as an imperfect gold standard to determine the performance of actin-qPCR and LAMP.ResultsIn Bafia with over 20 years of IVM-MDA, 11/51 (21.6%) direct observe treated microfilaridemic participants were still positive for skin microfilariae after 1 month. In Melong, with 10 years of IVM-MDA, 2/29 (6.9%) treated participants were still positive. The microfilarial density reduction per skin biopsy within one month following treatment was significantly lower in participants from Bafia.In both study sites, the molecular techniques detected higher proportions of infected individuals than microscopy at all monitoring time points. LAMP demonstrated the highest levels of sensitivity and real-time PCR was found to have the highest specificity.ConclusionPatterns in skin mirofilariae clearance and repopulation were established. O. volvulus worms from Bafia with higher number of annual MDA displayed a lower clearance and higher repopulation rate after treatment with ivermectin. Molecular assays displayed higher sensitivity in monitoring O. volvulus microfilaridemia within six months following treatment.

Oxfendazole mediates macrofilaricidal efficacy against the filarial nematode Litomosoides sigmodontis in vivo and inhibits Onchocerca spec. motility in vitro.

A major impediment to eliminate lymphatic filariasis and onchocerciasis is the lack of effective short-course macrofilaricidal drugs or regimens that are proven to be safe for both infections. In this study we tested oxfendazole, an anthelmintic shown to be well tolerated in phase 1 clinical trials. In vitro, oxfendazole exhibited modest to marginal motility inhibition of adult worms of Onchocerca gutturosa, pre-adult worms of Onchocerca volvulus and Onchocerca lienalis microfilariae. In vivo, five days of oral treatments provided sterile cure with up to 100% macrofilaricidal efficacy in the murine Litomosoides sigmodontis model of filariasis. In addition, 10 days of oral treatments with oxfendazole inhibited filarial embryogenesis in patent L. sigmodontis-infected jirds and subsequently led to a protracted but complete clearance of microfilaremia. The macrofilaricidal effect observed in vivo was selective, as treatment with oxfendazole of microfilariae-injected naïve mice was ineffective. Based on pharmacokinetic analysis, the driver of efficacy is the maintenance of a minimal efficacious concentration of approximately 100 ng/ml (based on subcutaneous treatment at 25 mg/kg in mice). From animal models, the human efficacious dose is predicted to range from 1.5 to 4.1 mg/kg. Such a dose has already been proven to be safe in phase 1 clinical trials. Oxfendazole therefore has potential to be efficacious for treatment of human filariasis without causing adverse reactions due to drug-induced microfilariae killing.

Onchocerca volvulus is not detected in the cerebrospinal fluid of persons with onchocerciasis-associated epilepsy

ObjectivesEpidemiological evidence links onchocerciasis with the development of epilepsy. The aim of this study was to detect Onchocerca volvulus microfilariae or its bacterial endosymbiont, Wolbachia, in the cerebrospinal fluid (CSF) of persons with onchocerciasis-associated epilepsy (OAE). MethodsThirteen persons with OAE and O. volvulus skin snip densities of >80 microfilariae were recruited in Maridi County (South Sudan) and their CSF obtained. Cytospin centrifuged preparations of CSF were examined by light microscopy for the presence of O. volvulus microfilariae. DNA was extracted from CSF to detect O. volvulus (O–150 repeat) by quantitative real-time PCR, and Wolbachia (FtsZ gene) by standard PCR. To further investigate whether CSF from onchocerciasis-infected participants could induce seizures, 3- and 7-day old zebrafish larvae were injected with the CSF intracardially and intraperitoneally, respectively. For other zebrafish larvae, CSF was added directly to the larval medium. ResultsNo microfilariae, parasite DNA, or Wolbachia DNA were detected in any of the CSF samples by light microscopy or PCR. All zebrafish survived the procedures and none developed seizures. ConclusionsThe absence of O. volvulus in the CSF suggests that OAE is likely not caused by direct parasite invasion into the central nervous system, but by another phenomenon triggered by O. volvulus infection.

Filaricidal properties of Lantana camara and Tamarindus indica extracts, and Lantadene A from L. camara against Onchocerca ochengi and Loa loa.

BackgroundIvermectin is the only drug currently recommended for the treatment of onchocerciasis, the second leading infectious cause of blindness in the world. This drug kills only the first stage larvae—microfilariae (mf) of Onchocerca volvulus and is to be used cautiously in areas where Loa loa is prevalent because of severe adverse events observed with coinfected patients.Methodology/Principal findingsThis study investigated the anti-filarial activities of two Cameroonian medicinal plants, Lantana camara and Tamarindus indica locally used to treat onchocerciasis. Twelve (12) extracts were prepared and tested in vitro on the bovine model parasite, O. ochengi as well as L. loa mf. Both mf and adult male worm viabilities were assessed by motility scoring, while adult female worm viability was determined biochemically by standard MTT/formazan colorimetry. Cytotoxicity and acute toxicity were determined respectively, in monkey kidney epithelial cells and in BALB/c mice. Pure compounds were isolated by LC/MS using a bio-assay guided strategy. All the extracts showed 100% activity at 500 μg/mL against O. ochengi adult worms and mf. The highest activity against O. ochengi was observed with the hexane extract of L. camara leaves (LCLhex), with IC50 of 35.1 μg/mL for adult females and 3.8 μg/mL for the mf. Interestingly, this extract was more active against O. ochengi mf than L. loa mf. Further studies on the extracts led to the isolation of lantadene A from the methylene chloride extract of L. camara leaves, with IC50s of 7.85 μg/mL for adult males, 10.38 μg/mL for adult females, 10.84 μg/mL for O. ochengi mf and 20.13 μg/mL for L. loa mf.Conclusions/SignificanceWe report for the first time the anti-onchocercal activities of these locally consumed medicinal plants and lantadene A, a potential lead for further development as an onchocerciasis cure.

Single dose moxidectin versus ivermectin for Onchocerca volvulus infection in Ghana, Liberia, and the Democratic Republic of the Congo: a randomised, controlled, double-blind phase 3 trial

SummaryBackgroundThe morbidity and socioeconomic effects of onchocerciasis, a parasitic disease that is primarily endemic in sub-Saharan Africa, have motivated large morbidity and transmission control programmes. Annual community-directed ivermectin treatment has substantially reduced prevalence. Elimination requires intensified efforts, including more efficacious treatments. We compared parasitological efficacy and safety of moxidectin and ivermectin.MethodsThis double-blind, parallel group, superiority trial was done in four sites in Ghana, Liberia, and the Democratic Republic of the Congo. We enrolled participants (aged ≥12 years) with at least 10 Onchocerca volvulus microfilariae per mg skin who were not co-infected with Loa loa or lymphatic filariasis microfilaraemic. Participants were randomly allocated, stratified by sex and level of infection, to receive a single oral dose of 8 mg moxidectin or 150 μg/kg ivermectin as overencapsulated oral tablets. The primary efficacy outcome was skin microfilariae density 12 months post treatment. We used a mixed-effects model to test the hypothesis that the primary efficacy outcome in the moxidectin group was 50% or less than that in the ivermectin group. The primary efficacy analysis population were all participants who received the study drug and completed 12-month follow-up (modified intention to treat). This study is registered with ClinicalTrials.gov, number NCT00790998.FindingsBetween April 22, 2009, and Jan 23, 2011, we enrolled and allocated 998 participants to moxidectin and 501 participants to ivermectin. 978 received moxidectin and 494 ivermectin, of which 947 and 480 were included in primary efficacy outcome analyses. At 12 months, skin microfilarial density (microfilariae per mg of skin) was lower in the moxidectin group (adjusted geometric mean 0·6 [95% CI 0·3–1·0]) than in the ivermectin group (4·5 [3·5–5·9]; difference 3·9 [3·2–4·9], p<0·0001; treatment difference 86%). Mazzotti (ie, efficacy-related) reactions occurred in 967 (99%) of 978 moxidectin-treated participants and in 478 (97%) of 494 ivermectin-treated participants, including ocular reactions (moxidectin 113 [12%] participants and ivermectin 47 [10%] participants), laboratory reactions (788 [81%] and 415 [84%]), and clinical reactions (944 [97%] and 446 [90%]). No serious adverse events were considered to be related to treatment.InterpretationSkin microfilarial loads (ie, parasite transmission reservoir) are lower after moxidectin treatment than after ivermectin treatment. Moxidectin would therefore be expected to reduce parasite transmission between treatment rounds more than ivermectin could, thus accelerating progress towards elimination.FundingUNICEF/UNDP/World Bank/WHO Special Programme for Research and Training in Tropical Diseases.

Analysis of age-dependent trends in Ov16 IgG4 seroprevalence to onchocerciasis.

BackgroundDiagnostics provide a means to measure progress toward disease elimination. Many countries in Africa are approaching elimination of onchocerciasis after successful implementation of mass drug administration programs as well as vector control. An understanding of how markers for infection such as skin snip microfilaria and Onchocerca volvulus-specific seroconversion perform in near-elimination settings informs how to best use these markers.MethodsAll-age participants from 35 villages in Togo were surveyed in 2013 and 2014 for skin snip Onchocerca volvulus microfilaria and IgG4 antibody response by enzyme-linked immunosorbent assay (ELISA) to the Onchocerca volvulus-specific antigen Ov16. A Gaussian mixture model applying the expectation-maximization (EM) algorithm was used to determine seropositivity from Ov16 ELISA data. For a subset of participants (n = 434), polymerase chain reaction (PCR) was performed on the skin snips taken during surveillance.ResultsWithin the 2,005 participants for which there was Ov16 ELISA data, O. volvulus microfilaremia prevalence and Ov16 seroprevalence were, 2.5 and 19.7 %, respectively, in the total population, and 1.6 and 3.6 % in children under 11. In the subset of 434 specimens for which ELISA, PCR, and microscopy data were generated, it was found that in children under 11 years of age, the anti-Ov16 IgG4 antibody response demonstrate a sensitivity and specificity of 80 and 97 %, respectively, against active infections as determined by combined PCR and microscopy on skin snips. Further analysis was performed in 34 of the 35 villages surveyed. These villages were stratified by all-age seroprevalence into three clusters: < 15 %; 15–20 %; and > 20 %. Age-dependence of seroprevalence for each cluster was best reflected by a two-phase force-of-infection (FOI) catalytic model. In all clusters, the lower of the two phases of FOI was associated with a younger age group, as reflected by the seroconversion rates for each phase. The age at which transition from lower to higher seroconversion, between the two phases of FOI, was found to be highest (older) for the cluster of villages with < 15 % seroprevalence and lowest (younger) for the cluster with the highest all-age seroprevalence.ConclusionsThe anti-Ov16 IgG4 antibody response is an accurate marker for active infection in children under 11 years of age in this population. Applying Ov16 surveillance to a broader age range provides additional valuable information for understanding progression toward elimination and can inform where targeted augmented interventions may be needed. Clustering of villages by all-age sero-surveillance allowed application of a biphasic FOI model to differentiate seroconversion rates for different age groups within the village cluster categories.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-016-1623-1) contains supplementary material, which is available to authorized users.

Detection of Onchocerca volvulus in Skin Snips by Microscopy and Real-Time Polymerase Chain Reaction: Implications for Monitoring and Evaluation Activities.

Microscopic evaluation of skin biopsies is the monitoring and evaluation (M and E) method currently used by multiple onchocerciasis elimination programs in Africa. However, as repeated mass drug administration suppresses microfilarial loads, the sensitivity and programmatic utility of skin snip microscopy is expected to decrease. Using a pan-filarial real-time polymerase chain reaction with melt curve analysis (qPCR-MCA), we evaluated 1) the use of a single-step molecular assay for detecting and identifying Onchocerca volvulus microfilariae in residual skin snips and 2) the sensitivity of skin snip microscopy relative to qPCR-MCA. Skin snips were collected and examined with routine microscopy in hyperendemic regions of Uganda and Ethiopia (N= 500 each) and "residual" skin snips (tissue remaining after induced microfilarial emergence) were tested with qPCR-MCA. qPCR-MCA detected Onchocerca DNA in 223 residual snips: 139 of 147 microscopy(+) and 84 among microscopy(-) snips, suggesting overall sensitivity of microscopy was 62.3% (139/223) relative to qPCR-MCA (75.6% in Uganda and 28.6% in Ethiopia). These findings demonstrate the insufficient sensitivity of skin snip microscopy for reliable programmatic monitoring. Molecular tools such as qPCR-MCA can augment sensitivity and provide diagnostic confirmation of skin biopsies and will be useful for evaluation or validation of new onchocerciasis M and E tools.

Nodding syndrome—a new hypothesis and new direction for research

Nodding syndrome (NS) is an unexplained neurological illness that mainly affects children aged between 5 and 15 years. NS has so far been reported from South Sudan, northern Uganda, and Tanzania, but in spite of extensive investigations, the aetiology remains unknown. We hypothesize that blackflies (Diptera: Simuliidae) infected with Onchocerca volvulus microfilariae may also transmit another pathogen. This may be a novel neurotropic virus or an endosymbiont of the microfilariae, which causes not only NS, but also epilepsy without nodding. This hypothesis addresses many of the questions about NS that researchers have previously been unable to answer. An argument in favour of the hypothesis is the fact that in Uganda, the number of new NS cases decreased (with no new cases reported since 2013) after ivermectin coverage was increased and with the implementation of a programme of aerial spraying and larviciding of the large rivers where blackflies were breeding. If confirmed, our hypothesis will enable new strategies to control NS outbreaks.

The Prevalence and Distribution of Human Onchocerciasis in Two Senatorial Districts in Ebonyi State, Nigeria

Background: There has been a recent increase in the number of human Onchocerciasis cases in hospitals in Ebonyi Central. This study therefore sets out to determine the prevalence of the disease in Ebonyi North and Central Senatorial Zones of Ebonyi State as well as determine the age groups and sex most affected. Methods: This study was carried out in Ebonyi North and Central Senatorial Zones of Ebonyi State between January 2011 and April 2012, among subjects of 20-59 years. Diagnosis was by skin examination for onchocercal lesions, ocular examination for ocular lesion and parasitological examination for the presence of microfilariae of Onchocerca volvulus in skin biopsies and adult filariae in excised nodules. Results: Out of the 250 persons randomly examined in each zone, 82 (32.8%) persons in Ebonyi Central zone comprising of 60 (38.7%) males and 22 (23.1%) females were found positive for Onchocerca volvulus while 73 (29.2%) persons in Ebonyi North Zone comprising 48 (32.0%) males and 25 (25.0%) females. Chi-square test shows that male subjects had significantly higher diseases prevalence (p < 0.05) than their female counterparts in the two zones but combined prevalence among male and female do not differ significantly in the two zones. The age group most affected was 50-59 years with the prevalence of 40.0% in Ebonyi Central and 38.6% in Ebonyi North Zones. Out of the 155 (30.8%) persons infected in the two zones, 28 (5.6%) males and 14 (2.8%) females had Onchocercal skin lesions, 57 (11.4%) males and 22 (4.4%) females had low vision. Partial blindness was observed in 16 (3.2%) males and 8 (1.6%) females. However, 7 (1.4%) males and 3 (0.6%) females had complete blindness. Farmers were mostly affected than any other occupational group. Conclusion: The findings obtained from this work suggested that Ebonyi Central and North Senatorial Zones are Onchocerciasis hypo-endemic Zones having the prevalence rate of 32.8% and 29.2% respectively. Sex, age and occupation are related to Onchocerciasis infections in both Zones. Males are more infected than females. Massive distribution of insecticides to destroy the vector Simulium damnosum (black fly), provision of adequate antiflarial drugs - ivermectin and mass health education targeted on preventive measures are highly recommended.

Reproductive status of Onchocerca volvulus after ivermectin treatment in an ivermectin-naïve and a frequently treated population from Cameroon.

BackgroundFor two decades, onchocerciasis control has been based on mass treatment with ivermectin (IVM), repeated annually or six-monthly. This drug kills Onchocerca volvulus microfilariae (mf) present in the skin and the eyes (microfilaricidal effect) and prevents for 3–4 months the release of new mf by adult female worms (embryostatic effect). In some Ghanaian communities, the long-term use of IVM was associated with a more rapid than expected skin repopulation by mf after treatment. Here, we assessed whether the embryostatic effect of IVM on O. volvulus has been altered following frequent treatment in Cameroonian patients.MethodologyOnchocercal nodules were surgically removed just before (D0) and 80 days (D80) after a standard dose of IVM in two cohorts with different treatment histories: a group who had received repeated doses of IVM over 13 years, and a control group with no history of large-scale treatments. Excised nodules were digested with collagenase to isolate adult worms. Embryograms were prepared with females for the evaluation of their reproductive capacities.Principal FindingsOocyte production was not affected by IVM. The mean number of intermediate embryos (morulae and coiled mf) decreased similarly in the two groups between D0 and D80. In contrast, an accumulation of stretched mf, either viable or degenerating, was observed at D80. However, it was observed that the increase in number of degenerating mf between D0 and D80 was much lower in the frequently treated group than in the control one (Incidence Rate Ratio: 0.25; 95% CI: 0.10–0.63; p = 0.003), which may indicate a reduced sequestration of mf in the worms from the frequently treated group.Conclusion/SignificanceIVM still had an embryostatic effect on O. volvulus, but the effect was reduced in the frequently treated cohort compared with the control population.

Editorial: Nodding Disease or syndrome: What is the way forward?

Nodding disease or syndrome is one of those conditions that recently appeared to be of public health concern in some countries in Africa. The disease has been reported to occur in South Sudan, Tanzania, northern Uganda and Liberia. In South Sudan the disease is mainly concentrated along Yei River1, 2. Nodding syndrome is a mentally and physically disabling disease that affects children3, typically between the ages of 5 and 15. The disease is characterized by episodes of repetitive nodding of the head, with progression to generalized tonic-clonic seizures, mental deterioration and physical incapacity1, 3. During seizures the children lose consciousness and they may fall into fire or hurt themselves. They usually drop out of school because of deterioration in cognitive function and inability to cope with the school environment. A disease similar to nodding syndrome was first reported in Uganda by Raper 4 in 1950. This disease was called ‘nakalanga’ because of the pathological dwarfism and the affected persons were incapable of procreation. It occurred among the dwellers of Mabira forest near the source of the Nile in Uganda. The forest was heavily infested by the black fly. The disease occurred among any of the tribes living in the area provided they had lived in the forested area for a sufficient number of years. The children born by uneventful pregnancies became thin, weak and listless around the time of weaning with progressive mental and physical retardation with maximal severity occurring around 8 to 15 years. The local inhabitants, who had long recognized the disease, had incriminated the bites of the black fly. Similarly, a high number of patients with epilepsy and retarded growth was reported in an endemic area for onchocerciasis in western Uganda5. However, a study that evaluated the role of Onchocerca volvulus in the development of epilepsy in rural Tanzania reported no difference in microfilaria density between participants with epilepsy and those without6. Since 2009, about 4000 cases of nodding disease have been reported in northern Uganda. For over 20 years northern Uganda was a conflict area and most people lived in camps for the internally displaced. Following a cease-fire in 2006, most of the people have returned to their villages and this period has coincided with increased numbers of nodding disease, with some families reporting more than two cases7. In this issue of African Health Sciences, Tumwine and others8 report clinical and epidemiological characteristics of nodding syndrome in Mundri county, South Sudan. The study was carried out in poor rural communities that had been characterised by several displacements between 1994 and 1997. The prevalence of Nodding Syndrome in the study areas was 2.1% and 4.6% in the endemic communities. Similar to the epidemic in northern Uganda, some families have more than one affected child. The ratio of male to female cases was 1.2. The age at onset of suspected cases ranged from 2 to 18 years, with a median of 12 years, and the mean duration of illness had been reported to be 3.0 years. Previous case-control studies had shown a positive association between cases and infestation with Onchocerca volvulus microfilaria, evidenced by positive skin snips. The nodding was reported to be worse during meals or upon walking up in the morning, and on the traditional carbohydrate based diet compared to the western style diet. For some children, head nodding did not disrupt eating or the ability to follow commands. Episodes of abnormal behaviour associated with shouting, screaming or running were reported. Physical examination revealed stunting of growth, dwarfism, mental retardation, and poor development of secondary sexual characteristics. Electroencephalographic examination was consistent with progressive epileptic encephalopathy. The authors concluded that Nodding Syndrome was strongly associated with Onchocerca volvulus. There was no evidence to suggest an environmental pollutant, chemical agent, or other toxic factor. The authors recommend larger studies to elucidate the etiology and optimal treatment for these children. It has been proven that symptomatic treatment with anticonvulsants and other supportive measures such as nutrition rehabilitation improves the quality of life, though not a cure. On going studies in northern Uganda speculate that the disease is associated with vitamin B6 deficiency and probably high doses of vitamin B6 may be beneficial to these children. The disease seems to be more prevalent in the poor communities. Improved social economic status, environmental control measures for microfilaria will go along way to reduce morbidity due to nodding syndrome.