Onchocerciasis-associated epilepsy in Maridi, South Sudan: Modelling and exploring the impact of control measures against river blindness.

BACKGROUND: Onchocerciasis, also known as "river blindness", is caused by the bite of infected female blackflies (genus Simuliidae) that transmit the parasite Onchocerca volvulus. A high onchocerciasis microfarial load increases the risk to develop epilepsy in children between the ages of 3 and 18 years. In resource-limited settings in Africa where onchocerciasis has been poorly controlled, high numbers of onchocerciasis-associated epilepsy (OAE) are reported. We use mathematical modeling to predict the impact of onchocerciasis control strategies on the incidence and prevalence of OAE. METHODOLOGY: We developed an OAE model within the well-established mathematical modelling framework ONCHOSIM. Using Latin-Hypercube Sampling (LHS), and grid search technique, we quantified transmission and disease parameters using OAE data from Maridi County, an onchocerciasis endemic area, in southern Republic of South Sudan. Using ONCHOSIM, we predicted the impact of ivermectin mass drug administration (MDA) and vector control on the epidemiology of OAE in Maridi. PRINCIPAL FINDINGS: The model estimated an OAE prevalence of 4.1% in Maridi County, close to the 3.7% OAE prevalence reported in field studies. The OAE incidence is expected to rapidly decrease by >50% within the first five years of implementing annual MDA with good coverage (≥70%). With vector control at a high efficacy level (around 80% reduction of blackfly biting rates) as the sole strategy, the reduction is slower, requiring about 10 years to halve the OAE incidence. Increasing the efficacy levels of vector control, and implementing vector control simultaneously with MDA, yielded better results in preventing new cases of OAE. CONCLUSIONS/SIGNIFICANCES: Our modeling study demonstrates that intensifying onchocerciasis eradication efforts could substantially reduce OAE incidence and prevalence in endemic foci. Our model may be useful for optimizing OAE control strategies.

Eye disease related to onchocerciasis: a clinical study in the Aratha-ú, Yanomami Tribe, Roraima State, Brazil.

The prevalence of ocular lesions due to onchocerciasis was evaluated among residents of the Yanomami Tribe, in the northern Amazon, Brazil, an endemic area for onchocerciasis. 83 natives were submitted to an ocular examination including an external examination, biomicroscopy, intraocular pressure measurement, and a fundus examination. Clinical, parasitological and serological tests were carried out simultaneously. The population demonstrated a high prevalence of eosinophilia, skin microfilaria (55%) and onchocercal subcutaneous nodules (35%). A high prevalence of probable onchocerciasis related eye lesions was detected. Punctate keratitis (41%) and microfilaria in the anterior chamber (39%) were found as well as other probable onchocercotic lesions-chorioretinitis (7.2%) and anterior uveitis (6.0%). Other anterior eye lesions (corneal leucomas, conjunctival injection, lid nodules) occurred in 51% of the individuals. The anterior eye lesions were more prevalent than the posterior lesions. We did not find an association of glaucoma with onchocerciasis. The prevalence of these suggestive ocular lesions strongly correlates with the cutaneous nodules and eosinophilia, suggesting that skin nodules may be an indication for an eye examination. The present study provides evidence that significant infection and eye disease due to onchocerciasis persists in certain regions of Northern South America.

Lymphatic filariasis.

(1) Lymphatic filariasis is a set of parasitic diseases that are endemic in tropical and subtropical regions and can be disabling in the long term. (2) The standard antiparasitic drug for adults is oral diethylcarbamazine. Ivermectin is an alternative, especially for patients with intercurrent onchocercosis or loasis.

Prevalence and causes of blindness and visual impairment in Muyuka: a rural health district in South West Province, Cameroon.

AIM: To estimate the prevalence and causes of blindness and visual impairment in the population aged 40 years and over in Muyuka, a rural district in the South West Province of Cameroon. METHODS: A multistage cluster random sampling methodology was used to select 20 clusters of 100 people each. In each cluster households were randomly selected and all eligible people had their visual acuity (VA) measured by an ophthalmic nurse. Those with VA <6/18 were examined by an ophthalmologist. RESULTS: 1787 people were examined (response rate 89.3%). The prevalence of binocular blindness was 1.6% (95% CI: 0.8% to 2.4%), 2.2% (1.% to 3.1%) for binocular severe visual impairment, and 6.4% (5.0% to 7.8%) for binocular visual impairment. Cataract was the main cause of blindness (62.1%), severe visual impairment (65.0%), and visual impairment (40.0%). Refractive error was an important cause of severe visual impairment (15.0%) and visual impairment (22.5%). The cataract surgical coverage for people was 55% at the <3/60 level and 33% at the <6/60 level. 64.3% of eyes operated for cataract had poor visual outcome (presenting VA<6/60). CONCLUSIONS: Strategies should be developed to make cataract services affordable and accessible to the population in the rural areas. There is an urgent need to improve the outcome of cataract surgery. Refractive error services should be provided at the community level.

Onchocerciasis-related epilepsy? Prospects at a time of uncertainty.

Epilepsy and onchocerciasis (river blindness) constitute serious public health problems in several tropical countries. There are four main mechanisms that might explain a relationship between these two diseases: (i) the presence of Onchocerca volvulus in the central nervous system; (ii) the pathogenicity of various O. volvulus strains; (iii) immunological mechanisms involving cross-reactive immunization or cytokine production during infection; and (iv) the triggering role of insomnia due to itching.

Public-private partnerships in blindness prevention: reaching beyond the eye.

The control of river blindness (onchocerciasis) has been one of the major public health achievements of recent decades. Initially, vector control was used to stop transmission of the parasite Onchocerca volvulus by blackflies (Simulium) but the introduction of ivermectin (Mectizan) as a means of morbidity control enabled new strategies of distribution to be developed based on community directed treatment. The donation of Mectizan by Merck & Co. Inc. for onchocerciasis control in 1987 'as long as needed' was a public health landmark to be followed by a donation from GlaxoSmithKline of albendazole in 1997 for lymphatic filariasis to which Merck also responded by agreeing to extend their donation to include the coadministration of Mectizan and albendazole. Both the drugs, however, have wider impacts than those specific to filarial parasites and are effective against a range of intestinal parasites, whilst ivermectin has an important effect on ectoparasites. The wider benefits of the annual public health intervention-collateral benefits--therefore include deworming, improved nutritional status, increased growth, improved school performance and attendance, and improved haemoglobin status as a result of the impact of albendazole on hookworm, a major cause of anaemia. More recently, studies suggest that worm-free children have a significantly reduced frequency of malaria specific episodes of fever and Ascaris-infected children have a two-fold higher frequency of cerebral or severe malaria than those without Ascaris. These findings suggest that programmes based on annual interventions to control river blindness and lymphatic filariasis can contribute disproportionately more to a range of public health problems than has been hitherto recognized, thereby assisting in attaining the millennium development goal targets.

Onchocerciasis: a potential risk factor for glaucoma.

BACKGROUND: Onchocerciasis is a microfilarial disease that causes ocular disease and blindness. Previous evidence of an association between onchocerciasis and glaucoma has been mixed. This study aims to further investigate the association between onchocerciasis and glaucoma. METHODS: All subjects were patients at the Bishop John Ackon Christian Eye Centre in Ghana, west Africa, undergoing either trabeculectomy for advanced glaucoma or extracapsular extraction for cataracts, who also had a skin snip biopsy for onchocerciasis. A cross sectional case-control study was performed to assess the difference in onchocerciasis prevalence between the two study groups. RESULTS: The prevalence of onchocerciasis was 10.6% in those with glaucoma compared with 2.6% in those with cataracts (OR, 4.45 (95% CI 1.48 to 13.43)). The mean age in the glaucoma group was significantly younger than in the cataract group (59 and 65, respectively). The groups were not significantly different with respect to sex or region of residence. In models adjusted for age, region, and sex, subjects with glaucoma had over three times the odds of testing positive for onchocerciasis (OR, 3.50 (95% CI 1.10 to 11.18)). CONCLUSIONS: This study has shown a positive association between subclinical onchocerciasis and glaucoma. This finding emphasises the importance of eradication of onchocerciasis from west Africa.

Free-floating melanin particles in the anterior chamber: a normal finding in African eyes?

PURPOSE: Pigment dispersion syndrome (PDS) is a well-described entity with Krukenberg's spindle, heavy trabecular pigmentation and retroilluminating iris defects. We have observed a group of patients in mesoendemic onchocercal communities of Kaduna State, Nigeria, with significant amounts of free-floating melanin in the anterior chamber, normal angle pigmentation and absence of iris defects. A pseudo-Krukenberg spindle forms when the patients are asked to maintain a 2 min head-down posture as is often done when examining eyes for the presence of anterior chamber microfilaria. This spindle gradually disappears (tumbles back) after about 2 min of return to the erect posture. This paper describes this finding, which does not appear to fit into accepted notions of pigment dispersion. METHODS: As part of the seventh annual ivermectin dosing exercise during which evidence of optic nerve damage was sought, 455 patients were examined for the presence of microfilaria in the anterior chamber. A total of 352 had been selected for signs of optic nerve disease during an earlier screening exercise, while 103 belonged to a random sample of 5 years and above. Signs of onchocerciasis were sought, while gonioscopy and intraocular pressure measurements were carried out. RESULTS: Of the 455 (11%) individuals examined, 53 demonstrated this phenomenon. Within the random sample, the prevalence was 20%. These tumbling Krukenberg positive (TK+) individuals are significantly younger than TK- individuals and the prevalence, highest in the first decade, dropped steadily to zero levels over the age of 75. Sex distribution was about equal. There was no difference in intraocular pressure, cup-disc ratio and angle pigmentation. Distributions of sclerosing keratitis and chorioretinitis were not statistically different. Optic nerve disease was more common in TK- but this was attributable to the older age distribution. Five TK+ were re-examined after a period of 7 years and had not developed PDS or glaucoma. Four of the five remained TK+. A familial tendency was noted and hereditary factors may be at play, possibly autosomal recessive. The same phenomenon was noted in two of 44 patients in an ophthalmic clinic in Abuja, Nigeria, an urban, non-endemic city south of Kaduna. CONCLUSIONS: This phenomenon does not fit into accepted notions of PDS and may well be a normal finding.

Excess mortality associated with blindness in the onchocerciasis focus of the Mbam Valley, Cameroon.

The association between blindness, mortality and nutritional status was investigated in a retrospective cohort study in villages of central Cameroon where onchocerciasis is hyper-endemic. Overall, 101 blind subjects and 101 non-blind controls matched with the blind for age, sex and (generally) village of residence were followed for 10 years. Blindness gave rise to a significant increase in mortality (relative risk = 2.3; P = 0.012), the life expectancy of the blind adults being reduced by 4 years compared with that of their controls. For a given age, excess mortality was found to be associated with a late onset of blindness. The causes of death were similar for the blind and the controls but blind subjects had relatively low body mass indices, which may lead to relatively early fatal disease outcomes. These results are similar to those obtained in other parts of Africa and emphasise, once more, the demographic impact of blindness in developing countries.

The prevalence of glaucoma in an onchoendemic community in South-Eastern Nigeria.

METHODOLOGY: With the aim of examining all the adults aged 30 years and above a survey was conducted in Alum-Inyi, a mesoendemic Community in South-Eastern Nigeria. The people were subjected to basic ophthalmic tests for the diagnosis of glaucoma namely corrected and uncorrected visual acuity at 6 metres using an illiterate E-chart, with pinhole assessment if visual acuity < 6/18; direct ophthalmoscopy to assess the vertical cup-disc ratio through undilated pupils and Schiotz indentation tonometry. In addition, static visual field analysis using the MK 1 Friedman visual field analyser was carried out in any glaucoma suspect. RESULTS: Of 664 eligible persons examined (out of the estimated total of 946), 14 definite cases of glaucoma were identified, giving a prevalence of 2.10% in the 30 years of age and older population. The mean vertical cup-disc ratio for the non-glaucoma cases were 0.30 (+0.004) and 0.31 (+/- 0.004) and 0.31 (+/- 0.09) in the right and left eyes respective. Among the glaucoma cases, the average vertical cup-disc ratio in the right and left eye were 0.63 (+/- 0.05) and 0.70 (+/- 0.06 respectively. No physiological cup of > or = 0.6 was recorded in our study. The mean iOP in the right and left eyes respectively were 18.54 (+/- 0.15) and 19.42 (+/- 0.14) in the nonglaucomatous cases and 26.39 (+/- 1.75) and 27.46 (+/- 2.59) in the glaucoma cases. CONCLUSION: Despite its limitations, this study confirms that the prevalence of glaucoma varies from one African population or population of African origin to another. It agrees with other reports that the risk of glaucoma increases with age.

Blindness in Africa: present situation and future needs.

AIM: To review the prevalence and causes of blindness in sub-Saharan Africa, the existing services and limitations, and the Vision 2020 goals for the future. METHODS: Methodologically sound population based surveys published in the past 20 years are reviewed and results for prevalence and causes of blindness are tabulated. The current resources and needs according to recent publications and international working groups are described. CONCLUSIONS: Blindness prevalence rates vary widely but the evidence suggests that approximately 1% of Africans are blind. The major cause is cataract; trachoma and glaucoma are also important causes of blindness. The bulk of blindness in the region is preventable or curable. Efforts should focus on eye problems which are universally present and for which there are cost effective remedies, such as cataract and refractive problems and on those problems which occur focally and can be prevented by primary healthcare measures, such as trachoma, onchocerciasis, and vitamin A deficiency. Major development of staffing levels, infrastructure, and community programmes will be necessary to achieve Vision 2020 goals.

Intraocular pressure and gonioscopic findings in rural communities mesoendemic and nonendemic for onchoceriasis, Kaduna State, Nigeria.

PURPOSE: To report on glaucoma-related ocular parameters, namely intraocular pressure and peripheral anterior synechiae, in the presence of onchocercal infection. METHODS: Two computer-generated random samples of individuals were drawn from communities mesoendemic and nonendemic for onchocerciasis respectively. Applanation tonometry and gonioscopy were carried out on these individuals. RESULTS: Four hundred and thirty-six and 319 individuals from the mesoendemic and nonendemic communities were examined respectively. The mean intraocular pressure was 1.58 mmHg lower in the individuals from the mesoendemic communities compared with those from the nonendemic communities (p < 0.001) despite the prevalence of peripheral anterior synechiae being higher in the mesoendemic communities. In these communities, there was strong evidence that the prevalence of peripheral anterior synechiae increased with increasing microfilarial load. CONCLUSIONS: Onchocercal infection produces a low-grade inflammatory process, which may result in a lowering of intraocular pressure despite the formation of peripheral anterior synechiae. Glaucomatous optic nerve damage may therefore not be the primary cause of visual loss in ocular onchocerciasis as this occurs late and is probably preceded by other blinding onchocercal pathology.

Eye lesions and onchocerciasis in a rural farm settlement in Delta State, Nigeria.

Between December 1999 and September 2000, an investigation on 326 inhabitants who voluntarily participated in screening for eye lesions and onchocerciasis in a rural farm settlement in Aniocha North local government area of Delta State, Nigeria was carried out. Microfilariae were reported in the skin tissues of 134 (41.1%) inhabitants. Of these, males had more microfiladermia (49.9%) than their female counterparts (33.3%). The percentage prevalence of the clinical signs of onchocerciasis in the farm settlement was hanging groin 14.1%, onchocercal nodules 25.1%, onchocercal dermatitis 27.6% and scrotal enlargement 3.7%. The percentage prevalence of the eye lesions among the onchocerciasis infected inhabitants was cataract 7.4%, glaucoma 3.7%, optic atrophy 0.6% and uveitis 18 (5.5%). Impaired vision occurred among 80 (24.5%) inhabitants and blindness was reported among 2 (0.6%) inhabitants.

Low vision in persons aged 50 and above in the onchocercal endemic communities of Anambra State, Nigeria.

OBJECTIVE: To determine the prevalence and causes of low vision among persons aged 50 and above in the onchocercal endemic rural areas of Anambra State, Nigeria. MATERIALS AND METHODS: Normal residents of three onchocercal rural villages in 3 local government areas of Anambra State, Nigeria, selected through simple random sampling, were examined using interviewer-administered structured questionnaire. Eye examination included visual acuity test, refraction, tonometry, color vision test and direct ophthalmoscopy. Skin-snips were examined for onchocercal microfilaria. RESULTS: Four hundred and seventy-two persons aged 50 years and above were examined, out of which 8.6% were bilaterally blind; 11.9% were monocularly blind and 23.7% had visual impairment. Cataract caused blindness in nearly two-third of the cases. Other causes of low vision include age-related macular degeneration, glaucoma, onchocerciasis and refractive errors. Of the 56 subjects blinded by cataract in at least one eye, only 16 (28.6%) had undergone cataract surgery. But none had intra-ocular lens implant. Only 2 of these 16 subjects had aphakic eyeglasses. CONCLUSIONS: Blindness rate among the population studied is 6 times the rate in similar aged-matched population in developed countries. Most of the bilaterally blind will have vision restored through cataract surgery. Cataract extraction with intra-ocular lens implant is recommended for better visual rehabilitation.

The causes and profile of visual loss in an onchocerciasis-endemic forest-savanna zone in Nigeria.

In an onchocerciasis-endemic forest-savanna mosaic zone of southeastern Nigeria, blindness was found in 5.4% of 1,217 people who voluntarily attended for examination from a population of 14,000. Apart from cataract, the most important causes of blindness in the area were eye diseases that are known to be associated with onchocerciasis. Refractive error, although a non-onchocerciasis-related eye defect, was the number one cause of visual loss found in the study. The causes of blindness in our examined population are similar to what is found in onchocerciasis-endemic areas of the savanna zone and dissimilar from those found in the forest zone. In this forest-savanna mosaic zone, the prevalence of onchocerciasis was higher in the respondents with poor vision than in those with adequate vision. Similarly, low vision was found to be more common in people with high microfilarial loads, but people with high loads also tended to be older than those with moderate or low microfilarial loads, which might suggest that low vision was only a function of age. Nonetheless, analysis of our data shows evidence of an association between low vision and microfilarial load in adults aged 60 years and above. It is concluded that onchocerciasis in the forest-savanna mosaic zone of Nigeria has the features until recently associated only with savanna onchocerciasis, and that this should be taken into consideration in planning and executing onchocerciasis control programs in the area.

Onchocerciasis: the burden of disease.

The greatest burdens related to human onchocerciasis are the result of the eye and skin lesions and severe itching produced by the microfilariae. Although the major manifestations of the disease do show geographical variation (e.g. onchocercal blindness is not a common complication in all endemic countries), they are often sufficiently severe to prevent human use of the often very fertile land close to the rivers in which the vectors breed. Though for many years thought to be of relatively minor importance compared with onchocercal eye disease, the skin lesions of onchocerciasis have recently been shown to be a major socio-economic burden, in terms of disability-adjusted life-years. The demonstration of an excellent correlation between the prevalence of palpable nodules in a community and the community microfilarial load has led to the development of rapid, safe and non-invasive methods to assess and map the levels of endemicity across whole countries. This has enabled mass treatment with Mectizan (ivermectin, MSD) to be targeted first at hyperendemic communities. Estimates of the burden of onchocerciasis will continue to change as better means of measurement become available. It seems possible, however, that use of Mectizan will eliminate the disease before its true burden can be estimated accurately.

Blue-yellow colour vision in an onchocercal area of northern Nigeria.

AIM: To determine if the City University Tritan Test is a useful addition to visual function assessment in rural communities in northern Nigeria. METHODS: The study was a cross sectional survey. The participants were 8394 people, aged 5 years and over, living in 37 rural communities, mesoendemic and nonendemic for onchocerciasis, in Kaduna State in northern Nigeria. The main outcome measures were the detection of a defect in blue-yellow colour vision by two criteria: (1) failure with the City University tritan screening plates; (2) failure with the City University grading plates to identify severe tritan defects. RESULTS: 91% of those aged 10 years and above could perform the test. Below this age, there were difficulties in comprehension. The test showed good inter- and intraobserver agreement. After adjustment for confounders the odds of failing the screening plates were significantly increased in the presence of optic atrophy or glaucoma (3.55 (2.48-5.08) and 15.9 (4.22-60.2) respectively). There was a greater increase in the adjusted odds of failing the grading plates in the presence of optic atrophy or glaucoma (5.30 (2.97-9.45) and 8.87 (1.61-48.7) respectively). Cataract had a smaller effect on the screening plates, adjusted odds 1.63 (0.95-2.80). CONCLUSION: Blue-yellow colour vision testing is a useful addition to visual function assessment in those aged 10 years and above in rural northern Nigeria, particularly in the detection of optic nerve disease.