Does onchocerciasis transmission take place in hypoendemic areas? a study from the North Region of Cameroon.

OBJECTIVE: Community-directed treatment with ivermectin (CDTI) for onchocerciasis control is targeted to meso and hyperendemic areas in Africa. Below the threshold, communities are considered hypoendemic and, mass treatment is not recommended. As policy begins to shift from control to elimination, the role of hypoendemic areas in maintaining Onchocerca volvulus needs to be re-examined. The study determined whether independent transmission occurs in a hypoendemic area in the North region of Cameroon. METHODS: Ten 'high risk' communities along the River Mayo Douka system in Ngong Health District, at least 20 km from the nearest CDTI program were studied. Six hundred and forty-nine adults (over 20 years of age) and 561 children (under 10 years) were examined for nodules and microfilaria. A subsample of 334 adults was examined for onchocercal ocular morbidity. Simulium flies from 4 collection points were captured over 3 months annually for 2 years and dissected for larval stages of O. volvulus. RESULTS: Nodule and microfilariae (mf) prevalence among adults was 12.20% and 2.91%, and 9.2% and 0.48% among children, respectively. Blindness because of onchocerciasis was insignificant, although low rates of chronic onchocercal ocular disease (<2%) were observed. Four (0.16 percent) of 255 flies collected in 2008 were infected with L3 larval stage, and 1 black fly of 39 collected in 2009 had two L2 larval stage morphologically consistent with O. volvulus. CONCLUSION: Ngong is a 'hypoendemic' focus with likely low grade indigenous transmission in isolation from meso/hyperendemic areas. Consequently, transmission from hypoendemic areas could contribute to rapid disease recrudescence in the post-treatment phase of adjacent former meso and hyperendemic areas.

Data-driven modelling and spatial complexity supports heterogeneity-based integrative management for eliminating Simulium neavei-transmitted river blindness.

Concern is emerging regarding the challenges posed by spatial complexity for modelling and managing the area-wide elimination of parasitic infections. While this has led to calls for applying heterogeneity-based approaches for addressing this complexity, questions related to spatial scale, the discovery of locally-relevant models, and its interaction with options for interrupting parasite transmission remain to be resolved. We used a data-driven modelling framework applied to infection data gathered from different monitoring sites to investigate these questions in the context of understanding the transmission dynamics and efforts to eliminate Simulium neavei- transmitted onchocerciasis, a macroparasitic disease that causes river blindness in Western Uganda and other regions of Africa. We demonstrate that our Bayesian-based data-model assimilation technique is able to discover onchocerciasis models that reflect local transmission conditions reliably. Key management variables such as infection breakpoints and required durations of drug interventions for achieving elimination varied spatially due to site-specific parameter constraining; however, this spatial effect was found to operate at the larger focus level, although intriguingly including vector control overcame this variability. These results show that data-driven modelling based on spatial datasets and model-data fusing methodologies will be critical to identifying both the scale-dependent models and heterogeneity-based options required for supporting the successful elimination of S. neavei-borne onchocerciasis.

Historical Elimination of Onchocerciasis from Victoria Nile Focus in Central Uganda Verified Using WHO Criteria.

Uganda has verified elimination of seven onchocerciasis foci since 2007 when the nationwide onchocerciasis elimination policy was launched. However, the Victoria Nile focus (which was eliminated in the early 1970s) had not been verified. The objective of this study was to verify this focus to the WHO verification guidelines and bring it in line with recently eliminated foci. Vector control with dichlorodiphenyltrichloroethane was the main intervention used at the Victoria Nile from the 1950s to the 1970s. Historical fly collection sites along River Nile were identified for recent fly collection. Relevant health workers near the sites were trained to supervise fly collection activity. With support from communities, fly collectors were identified, trained, and equipped to collect Simulium flies for at least a year. A total of 854 Simulium flies were collected and analyzed by polymerase chain reaction to detect Onchocerca volvulus DNA. The communities and their leaders provided consent for the collection of dry blood spots (DBS) from children younger than 10 years for investigation of recent exposure to the disease. A total of 2,953 DBS were collected and analyzed by OV16 ELISA to detect the presence of IgG4 antibodies recognizing the OV16 antigen. The results showed that none of the flies carried O. volvulus DNA. Similarly, all the children were OV16 negative, showing no exposure to onchocerciasis. All the flies collected were identified as Simulium adersi, which is not a known vector for O. volvulus. The results confirmed that onchocerciasis and its vector Simulium damnosum had been eliminated in the Victoria Nile focus.

Elimination of Simulium neavei-Transmitted Onchocerciasis in Wambabya-Rwamarongo Focus of Western Uganda.

Wambabya-Rwamarongo onchocerciasis focus is one of the eight foci Uganda verified using the WHO verification guidelines. The approach for elimination was twice yearly treatment with ivermectin for every round, treating at least 90% of all the eligible population. This was in combination with vector elimination using Abate® (BASF SE, Limburgerhof, Germany) since elimination nationwide policy was launched. From 2008 to 2013, the program distributed ivermectin with a mean treatment coverage of the ultimate treatment goal (UTG) or eligible population of 91.2%, with a range of 85-96%. In 2009, vector elimination based on ground larviciding had a dramatic impact on the Simulium vectors, as the last fly was observed in October 2009. No more Simulium vectors were observed during a period of at least 7 years, including the 3-year posttreatment surveillance (PTS) until the focus was reclassified as eliminated in August 2017. During the PTS period, none of the 10,578 trapped crabs were found infested with the aquatic stages of the vector. The last infested crab was observed in March 2010, and for at least 7 years, no infested crabs were observed. Serological surveys showed that of 2,978 young children examined in 2013, only one was OV16 positive (0.0%; 95% CI: 0-0.21). In 2017, after the PTS period, all 3,079 young children examined were negative for OV16 (95% CI: 0-0.16). Therefore, entomological and serological results provided evidence that resulted in the reclassification of Wambabya-Rwamarongo focus from "transmission interrupted" to "transmission eliminated" with no possibility of recrudescence.

The Galabat-Metema cross-border onchocerciasis focus: The first coordinated interruption of onchocerciasis transmission in Africa.

BACKGROUND: Onchocerciasis transmission across international borders is not uncommon, yet a coordinated cross border stops mass drug administration (MDA) decision has not been documented. METHODS/PRINCIPLE FINDINGS: The Galabat-Metema focus involves neighboring districts on the border between Sudan and Ethiopia. Mass drug administration (MDA) was provided once and subsequently twice per year in this focus, with twice-per-year beginning in Ethiopia's Metema subfocus in 2016 and in the Sudan's Galabat subfocus in 2008. Ov16 ELISA-based serosurveys were conducted in 6072 children under 10 years of age in the Metema subfocus in 2014, and 3931 in the Galabat in 2015. Between 2014 and 2016, a total of 27,583 vector Simulium damnosum flies from Metema and 9,148 flies from Galabat were tested by pool screen PCR for Onchocerca volvulus O-150 DNA. Only 8 children were Ov16 seropositive (all in the Metema subfocus); all were negative by skin snip PCR. The upper limit of the 95% confidence interval (UCL) for Ov16 seropositive was <0.1% for the overall focus and 0.14 positive fly heads per 2000 (UCL = 0.39/2000). However, an entomological 'hotspot' was detected on the Wudi Gemzu river in Metema district. The hotspot was confirmed when 4 more positive fly pools were found on repeat testing in 2017 (1.04 L3/2000 flies (UCL = 2.26/2000). Information exchange between the two countries led to stopping MDA in a coordinated fashion in 2018, with the exception of the hotspot at Wudi Gemzu, where MDA with ivermectin was increased to every three months to hasten interruption of transmission. CONCLUSION: Coordinated stop MDA decisions were made by Sudan and Ethiopia based on data satisfying the World Health Organization's criteria for interruption of onchocerciasis transmission. Definitions of entomological 'hotspots' and buffer zones around the focus are proposed.

Accelerating river blindness elimination by supplementing MDA with a vegetation "slash and clear" vector control strategy: a data-driven modeling analysis.

Attention is increasingly focusing on how best to accelerate progress toward meeting the WHO's 2030 goals for neglected tropical diseases (NTDs). For river blindness, a major NTD targeted for elimination, there is a long history of using vector control to suppress transmission, but traditional larvicide-based approaches are limited in their utility. One innovative and sustainable approach, "slash and clear", involves clearing vegetation from breeding areas, and recent field trials indicate that this technique very effectively reduces the biting density of Simulium damnosum s.s. In this study, we use a Bayesian data-driven mathematical modeling approach to investigate the potential impact of this intervention on human onchocerciasis infection. We developed a novel "slash and clear" model describing the effect of the intervention on seasonal black fly biting rates and coupled this with our population dynamics model of Onchocerca volvulus transmission. Our results indicate that supplementing annual drug treatments with "slash and clear" can significantly accelerate the achievement of onchocerciasis elimination. The efficacy of the intervention is not very sensitive to the timing of implementation, and the impact is meaningful even if vegetation is cleared only once per year. As such, this community-driven technique will represent an important option for achieving and sustaining O. volvulus elimination.

Comparison of Reported and Survey-Based Coverage in Onchocerciasis Programs over a Period of 8 Years in Cameroon and Uganda.

Mass drug administration (MDA) with ivermectin must reach a high treatment coverage (90% of the eligible population) if onchocerciasis is to be eliminated. Questions have been raised as to whether reported treatment figures reaching such high coverage are reliable. Sample surveys are proposed as the method of choice for "validating" reported coverage figures. The purpose of this study was to compare the district-level MDA coverage reported by programs with contemporaneous surveys of randomly selected respondents living in those same districts. Over an 8-year period, 19,219 households were selected using multistage random sampling; 38,433 adult male and female heads of those households were asked about their recent ivermectin MDA treatment experience. District coverage reports were considered "accurate" if they fell within the 95% CIs determined by the corresponding district's survey. Ninety-eight treatment rounds were evaluated over an 8-year period. Overall, the reported coverage of 96.5% (range: 68-100%) was significantly higher than the 92.5% surveyed coverage (range: 62.1-99.6%, 95% CI: 91.9-93.2%). However, only 20% of districts reported significantly higher coverage than surveys, 68% of district program reports were judged as accurate, and 12% of districts reported significantly lower coverage figures than their corresponding surveys. Eighty-eight percent of districts reported coverage ≥ 90% threshold for success, compared with 97% of surveys that included 90% in their 95% CIs. We conclude that when analyzed statistically at the district level, most surveys verified the reported coverage.

After 70 years of fighting an age-old scourge, onchocerciasis in Uganda, the end is in sight.

Onchocerciasis causes severe itching, serious skin disease and ocular damage leading to visual impairment or permanent blindness. It is associated with hanging groin, epilepsy, Nakalanga dwarfism and, most recently, nodding disease. This disease affected communities in 17 transmission foci in 37 districts of Uganda, where about 6.7 million people are once at risk. The efforts against onchocerciasis in Uganda commenced in the late 1940s, when vector control was launched using dichlorodiphenyltrichloroethane; by 1973, Simulium damnosum had been eliminated in the Victoria focus. Success outside of the Victoria focus was short-lived due to changes in government priorities and the political upheavals of the 1970s and 1980s. With the return of political stability, annual treatment with ivermectin through mass drug administration was launched in the early 1990s. Control of the disease has been successful, but there has been failure in interrupting transmission after more than 15 years. In 2007 Uganda launched a nationwide transmission elimination policy based on twice-per-year treatment and vector control/elimination, with a goal of eliminating river blindness nationwide by 2020. By 2017, 1 157 303 people from six foci had been freed from river blindness. This is the largest population ever declared free under World Health Organization elimination guidelines, providing evidence that elimination of river blindness in Africa is possible.

Substantiating freedom from parasitic infection by combining transmission model predictions with disease surveys.

Stopping interventions is a critical decision for parasite elimination programmes. Quantifying the probability that elimination has occurred due to interventions can be facilitated by combining infection status information from parasitological surveys with extinction thresholds predicted by parasite transmission models. Here we demonstrate how the integrated use of these two pieces of information derived from infection monitoring data can be used to develop an analytic framework for guiding the making of defensible decisions to stop interventions. We present a computational tool to perform these probability calculations and demonstrate its practical utility for supporting intervention cessation decisions by applying the framework to infection data from programmes aiming to eliminate onchocerciasis and lymphatic filariasis in Uganda and Nigeria, respectively. We highlight a possible method for validating the results in the field, and discuss further refinements and extensions required to deploy this predictive tool for guiding decision making by programme managers.

Author Correction: Substantiating freedom from parasitic infection by combining transmission model predictions with disease surveys.

The original version of this Article contained an error in the spelling of Emily Griswold, which was incorrectly given as Emily Grisworld. This error has now been corrected in both the PDF and HTML versions of the Article.

Molecular Identification of Onchocerca spp. Larvae in Simulium damnosum sensu lato Collected in Northern Uganda.

Previous studies have demonstrated that the presence of larvae of other filarial species in Simulium damnosum sensu lato can distort estimates of transmission potential for Onchocerca volvulus in West Africa. However, studies conducted in foci of onchocerciasis in West Central Uganda indicated that larvae other than O. volvulus were not common in vectors collected there. Recent data collected in Northern Uganda revealed a striking discordance between estimates of the prevalence of flies carrying O. volvulus infective larvae obtained from molecular pool screening and dissection methods. To resolve this discrepancy, sequences from three mitochondrially encoded genes were analyzed from the larvae collected by dissection. All larvae analyzed were Onchocerca ochengi v. Siisa, a parasite of cattle, or Onchocerca ramachandrini, a parasite of warthogs. These results suggest that nonhuman parasite larvae are common in vectors in Northern Uganda, underscoring the necessity for molecular identification methods to accurately estimate O. volvulus transmission.

Community-directed interventions are practical and effective in low-resource communities: experience of ivermectin treatment for onchocerciasis control in Cameroon and Uganda, 2004-2010.

BACKGROUND: The community-directed intervention (CDI) approach has improved treatment coverage in onchocerciasis-affected communities. However, there is still a lot to learn. This study assessed its performance and highlighted the lessons learnt so far. METHODS: Representative samples of households were selected from Cameroon and Uganda program areas through multi-stage random sampling. An adult male and female from every selected household were interviewed separately on their involvement in CDI activities every year between 2004 and 2010. Community health workers (CHWs) were interviewed and treatment records reviewed to determine whether 90% treatment coverage was attained within 2 weeks. Records related to training of CHWs and their supervisors were analyzed. RESULTS: Decision making decreased for community leaders and health workers, while it increased for community members. The proportion of CHWs attaining 90% treatment coverage within 2 weeks improved as their demand for monetary incentives, and number of persons they served, reduced. The number of CHWs supervised by a community supervisor remained low, but increased for the health workers. The cost of training a CHW and a community supervisor reduced to about US$1 and US$4.8, respectively. CONCLUSIONS: The CDI approach was effective, culturally appropriate and probably less costly in delivering health services in low-resource communities.

The Imaramagambo Onchocerciasis Focus in Southwestern Uganda: Interruption of Transmission After Disappearance of the Vector Simulium neavei and Its Associated Freshwater Crabs.

It was not until early 1990s that, when the Imaramagambo focus of southwest Uganda was mapped, mass treatment with a single annual dose of ivermectin for onchocerciaisis control commenced. However, comprehensive investigations on its transmission were launched after a nationwide policy for onchocerciasis elimination in 2007. Entomological surveys throughout the focus from 2007 to 2015 have yielded few or no freshwater crabs (Potamonautes aloysiisabaudiae), which serve as the obligate phoretic host of the larvae and pupae of the vector Simulium neavei No S. neavei flies have been observed or collected since 2007. Skin snips (microscopy) from 294 individuals in 2008 were negative for skin microfilariae, and of the 462 persons analyzed by polymerase chain reaction skin snip poolscreen in 2009, only five (1.08%) persons were indicated as infected with onchocerciasis. All five of the positive persons were at least 40 years old. Serosurvey results showed negative exposure among 3,332 children in 2012 and 3,108 children in 2015. Both were within the upper bound of the 95% confidence interval of the prevalence estimate of 0.06%, which confirmed the elimination of onchocerciasis. Treatment coverage in Imaramagambo was generally poor, and transmission interruption of onchocerciasis could not be attributed solely to annual mass treatment with ivermectin. There was sufficient evidence to believe that the possible disappearance of the S. neavei flies, presumed to have been the main vector, may have hastened the demise of onchocerciasis in this focus.

Presence of Wuchereria bancrofti microfilaremia despite 7 years of annual ivermectin monotherapy mass drug administration for onchocerciasis control: a study in north-west Ethiopia.

BACKGROUND: There is considerable interest in determining whether mass drug administration (MDA) with ivermectin for onchocerciasis control will eliminate coendemic lymphatic filariasis (LF). The objective of this study was to determine the prevalence of LF microfilaremia in onchocerciasis endemic districts that had received 7 years of MDA with ivermectin. METHOD: Three villages with a 2010 LF circulating antigenaemia prevalence (determined in a mapping exercise using immunochromatography tests) ranging from 23 to 56% were surveyed for the presence of Wuchereria bancrofti microfilaria (mf) in 2012. These villages had been treated with ivermectin MDA for onchocerciasis with reported total population coverage of ≥65%. A total of 774 residents aged 2 years and above, of both genders, provided 60 µl nocturnal blood samples between 10 pm and 2 am. Standard thick smears were prepared and examined microscopically after Giemsa staining for the presence of W. bancrofti mf. RESULTS: The mean mf prevalence was 4.7% (village range 1.1-11.0%). The mean mf density was 9.8 mf/60 µl (village range 9-13.1) among the positive individuals. Children in the 2-4-year-old and 5-9-year-old age groups were infected suggesting transmission occurred during the MDA period. A village level review of MDA treatment coverage records showed an average total population coverage of 66.4% over a 7-year period, but with a considerable range of annual coverage (43.0-89.9%). In addition, village level treatment coverage data were missing from the village with the highest mf prevalence (11%) for 2 of the 7 years. CONCLUSION: 7 years of annual mass treatment with ivermectin monotherapy for onchocerciasis did not interrupt LF transmission. In expanding the onchocerciasis ivermectin MDA programme to include LF, albendazole should be added and treatment coverage improved.

Involvement and performance of women in community-directed treatment with ivermectin for onchocerciasis control in Rukungiri District, Uganda.

The present study aimed: (1) to assess and improve the level of women's involvement in a strategy to control onchocerciasis by community-directed treatment with ivermectin (CDTI) in three parishes of Rukungiri District, Uganda; (2) to measure the performance of female community-directed health workers (CDHWs) in comparison with males; and (3) to identify culturally acceptable means of enhancing women's involvement in community-directed healthcare. Health education sessions were used to instruct community members to select female CDHWs in Masya Parish and to stress their potential importance in Karangara Parish; this subject was not raised in Mukono Parish. In all, 403 mature women who were randomly selected from the three parishes were interviewed as to their: (1) knowledge of the classes of people not eligible to take ivermectin; (2) knowledge and beliefs about the benefits of ivermectin; (3) participation in decision-making; and (4) attitudes on the performance of female CDHWs. For analysis, the respondees were divided into: (1) those who had or had not taken ivermectin treatment during the previous year; and (2) those who had or had not attended health education sessions. During the period when face-to-face interviews with women in randomly selected households were being carried out, participatory evaluation meetings (PEMs) were conducted in selected communities from the same parishes in order to reach a consensus on issues which could not easily be included in individual face-to-face interviews. Participant observations were also made regarding: how communities selected their CDHWs; how the CDHWs organised the distribution exercise and treated community members; and how the CDHWs kept records in order to understand issues which were deliberately hidden from the researchers during face-to-face interviews and PEMs. Significantly, the women who had been treated or health educated in Masya Parish were: (1) more knowledgeable on the groups which were not supposed to be treated; (2) aware of women's involvement in mobilisation of other community members; (3) involved in CDTI decision-making; and (4) had a better attitude towards female CDHWs' performance compared with males when compared with those from Karangara and Mukono parishes. There were no differences between the attitude of women in Karangara and Mukono parishes towards performance of female CDHWs. Face-to-face interviews and records from all parishes indicated that female CDHWs achieved as good a coverage as their male counterparts, and sometimes better, in about the same time. Health education increased the number of female CDHWs from nine to 52 in Masya Parish, from 7 to 22 in Karangara Parish and from 6 to 20 in Mukono Parish. Health education improved the attitude of women towards female CDHWs, but the actual experience of having and observing female CDHWs in action in Masya Parish had a more significant positive impact on the womenfolk, as well as on the rest of the community members, and created an impetus for more of them to become actively involved in actual ivermectin distribution. The present authors conclude that recruiting more female CDHWs and supervisors would reduce the current male domination of the health delivery services, greatly strengthening the activities of CDTI programmes.

Transmission of Onchocerca volvulus continues in Nyagak-Bondo focus of northwestern Uganda after 18 years of a single dose of annual treatment with ivermectin.

The objective of the study was to determine whether annual ivermectin treatment in the Nyagak-Bondo onchocerciasis focus could safely be withdrawn. Baseline skin snip microfilariae (mf) and nodule prevalence data from six communities were compared with data collected in the 2011 follow-up in seven communities. Follow-up mf data in 607 adults and 145 children were compared with baseline (300 adults and 58 children). Flies collected in 2011 were dissected, and poolscreen analysis was applied to ascertain transmission. Nodule prevalence in adults dropped from 81.7% to 11.0% (P < 0.0001), and mf prevalence dropped from 97.0% to 23.2% (P < 0.0001). In children, mf prevalence decreased from 79.3% to 14.1% (P < 0.0001). Parous and infection rates of 401 flies that were dissected were 52.9% and 1.5%, respectively, whereas the infective rate on flies examination by polymerase chain reaction (PCR) was 1.92% and annual transmission potential was 26.9. Stopping ivermectin treatment may result in onchocerciasis recrudescence.

Validation of a remote sensing model to identify Simulium damnosum s.l. breeding sites in Sub-Saharan Africa.

BACKGROUND: Recently, most onchocerciasis control programs have begun to focus on elimination. Developing an effective elimination strategy relies upon accurately mapping the extent of endemic foci. In areas of Africa that suffer from a lack of infrastructure and/or political instability, developing such accurate maps has been difficult. Onchocerciasis foci are localized near breeding sites for the black fly vectors of the infection. The goal of this study was to conduct ground validation studies to evaluate the sensitivity and specificity of a remote sensing model developed to predict S. damnosum s.l. breeding sites. METHODOLOGY/PRINCIPAL FINDINGS: Remote sensing images from Togo were analyzed to identify areas containing signature characteristics of S. damnosum s.l. breeding habitat. All 30 sites with the spectral signature were found to contain S. damnosum larvae, while 0/52 other sites judged as likely to contain larvae were found to contain larvae. The model was then used to predict breeding sites in Northern Uganda. This area is hyper-endemic for onchocerciasis, but political instability had precluded mass distribution of ivermectin until 2009. Ground validation revealed that 23/25 sites with the signature contained S. damnosum larvae, while 8/10 sites examined lacking the signature were larvae free. Sites predicted to have larvae contained significantly more larvae than those that lacked the signature. CONCLUSIONS/SIGNIFICANCE: This study suggests that a signature extracted from remote sensing images may be used to predict the location of S. damnosum s.l. breeding sites with a high degree of accuracy. This method should be of assistance in predicting communities at risk for onchocerciasis in areas of Africa where ground-based epidemiological surveys are difficult to implement.

Fifteen years of annual mass treatment of onchocerciasis with ivermectin have not interrupted transmission in the west region of cameroon.

We followed up the 1996 baseline parasitological and entomological studies on onchocerciasis transmission in eleven health districts in West Region, Cameroon. Annual mass ivermectin treatment had been provided for 15 years. Follow-up assessments which took place in 2005, 2006, and 2011 consisted of skin snips for microfilariae (mf) and palpation examinations for nodules. Follow-up Simulium vector dissections for larval infection rates were done from 2011 to 2012. mf prevalence in adults dropped from 68.7% to 11.4%, and nodule prevalence dropped from 65.9% to 12.1%. The decrease of mf prevalence in children from 29.2% to 8.9% was evidence that transmission was still continuing. mf rates in the follow-up assessments among adults and in children levelled out after a sharp reduction from baseline levels. Only three health districts out of 11 were close to interruption of transmission. Evidence of continuing transmission was also observed in two out of three fly collection sites that had infective rates of 0.19% and 0.18% and ATP of 70 (Foumbot) and 300 (Massangam), respectively. Therefore, halting of annual mass treatment with ivermectin cannot be done after 15 years as it might escalate the risk of transmission recrudescence.

Transmission of onchocerciasis in wadelai focus of northwestern Uganda has been interrupted and the disease eliminated.

Wadelai, an isolated focus for onchocerciasis in northwest Uganda, was selected for piloting an onchocerciasis elimination strategy that was ultimately the precursor for countrywide onchocerciasis elimination policy. The Wadelai focus strategy was to increase ivermectin treatments from annual to semiannual frequency and expand geographic area in order to include communities with nodule rate of less than 20%. These communities had not been covered by the previous policy that sought to control onchocerciasis only as a public health problem. From 2006 to 2010, Wadelai program successfully attained ultimate treatment goal (UTG), treatment coverage of ≥90%, despite expanding from 19 to 34 communities and from 5,600 annual treatments to over 29,000 semiannual treatments. Evaluations in 2009 showed no microfilaria in skin snips of over 500 persons examined, and only 1 of 3011 children was IgG4 antibody positive to the OV16 recombinant antigen. No Simulium vectors were found, and their disappearance could have sped up interruption of transmission. Although twice-per-year treatment had an unclear role in interruption of transmission, the experience demonstrated that twice-per-year treatment is feasible in the Ugandan setting. The monitoring data support the conclusion that onchocerciasis has been eliminated from the Wadelai focus of Uganda.

Seventeen years of annual distribution of ivermectin has not interrupted onchocerciasis transmission in North Region, Cameroon.

We studied onchocerciasis transmission and impact on ocular morbidity in three health districts in North Region, Cameroon, where annual mass ivermectin treatment has been provided for 12-17 years. The studies, which took place from 2008 to 2010, consisted of skin snips for microfilariae (mf), palpation examinations for nodules, slit lamp examinations for mf in the eye, and Simulium vector dissections for larval infection rates. Adults had mf and nodule rates of 4.8% and 13.5%, respectively, and 5.5% had mf in the anterior chamber of the eye. Strong evidence of ongoing transmission was found in one health district, where despite 17 years of annual treatments, the annual transmission potential was 543 L3/person per year; additionally, children under 10 years of age had a 2.6% mf prevalence. Halting ivermectin treatments in North Cameroon now might risk recrudescence of transmission and ocular disease.