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The burden of Onchocerca volvulus in Sudan
Abstract
Onchocerciasis has been reported in Sudan since 1908 and now prevails in three endemic regions known as the southern, northern and eastern foci. The southern focus is the largest, with nodule and blindness rates exceeding 80% and 12%, respectively, in certain villages. Onchocercal infection in this region causes only a mild skin reaction although microfilarial loads in the skin are high. In contrast, those with onchocerciasis in the northern focus, located between the fourth and fifth Nile cataracts, present with limited but severe skin reactions, low nodule rates (16%), low microfilarial loads in the skin and no ocular involvement. The characteristics of patients from the eastern focus, close to the border with Ethiopian border are similar to those in the north, although most onchocercal skin disease in this area comprises the severe localized pruritus known as sowda.
... The skin changes in ROD are most commonly localized to a single limb or area of the body, and a darkening of the affected area almost always occurs, hence the name 'sowda', an Arabic word meaning 'looks dark or black' (Connor et al., 1983;Fawdry, 1957). ROD cases are seen in both males and females; most cases encountered in the present and other previous studies are young, mostly in their teen years (Ghalib et al., 1987;Mukhtar et al., 1998). The finding that one focus (hypo-endemic) is interestingly characterized by a high prevalence of ROD could partially be due the very short transmission (maximum of 4 weeks per year or every other ...
... Our findings also underline the significance of including clinical evaluation in epidemiological mapping for the disease prevalence rather than solely depending on parasitological tools in an agreement with the pertinent recommendations raised earlier (Ghalib et al., 1987;Mukhtar et al., 1998). ...
... Because neither O. volvulus nor W. bancrofti can be cultured in the laboratory, this work requires correlations to be determined from worms collected from infected people and phenotyped for a trait (e.g., disease manifestation, variation in drug response) and then subsequently genotyped. For example, onchocerciasis disease severity and manifestations vary widely across Africa, with onchocerciasis-associated blindness more common in savannah regions (Remme et al., 1989;Dadzie et al., 1990), and severe onchodermatitis (Sowda, hyperreactive onchocerciasis) prevalent in Yemen and in one focus in Sudan (Mukhtar et al., 1998), but rare in other endemic areas (Al-Kubati et al., 2018). Similarly, the extent to which the level of skin microfilariae decreases after ivermectin treatment and the timing and extent of subsequent increases in skin microfilariae levels varies between individuals even in ivermectin-naive areas (Awadzi et al., 2014;Opoku et al., 2018). ...
Onchocerciasis and lymphatic filariasis are targeted for elimination, primarily using mass drug administration at the country and community levels. Elimination of transmission is the onchocerciasis target and global elimination as a public health problem is the end point for lymphatic filariasis. Where program duration, treatment coverage, and compliance are sufficiently high, elimination is achievable for both parasites within defined geographic areas. However, transmission has re-emerged after apparent elimination in some areas, and in others has continued despite years of mass drug treatment. A critical question is whether this re-emergence and/or persistence of transmission is due to persistence of local parasites—i.e., the result of insufficient duration or drug coverage, poor parasite response to the drugs, or inadequate methods of assessment and/or criteria for determining when to stop treatment—or due to re-introduction of parasites via human or vector movement from another endemic area. We review recent genetics-based research exploring these questions in Onchocerca volvulus, the filarial nematode that causes onchocerciasis, and Wuchereria bancrofti, the major pathogen for lymphatic filariasis. We focus in particular on the combination of genomic epidemiology and genome-wide associations to delineate transmission zones and distinguish between local and introduced parasites as the source of resurgence or continuing transmission, and to identify genetic markers associated with parasite response to chemotherapy. Our ultimate goal is to assist elimination efforts by developing easy-to-use tools that incorporate genetic information about transmission and drug response for more effective mass drug distribution, surveillance strategies, and decisions on when to stop interventions to improve sustainability of elimination.
... The World Health Organization estimated that more than two million persons are infected with Onchocerca volvulus in Sudan, 1 and the largest endemic focus in south-southwestern Sudan is among the most highly disease-endemic areas in the world. [2][3][4][5] Patients in this area have severe onchocerciasis, which includes blinding disease. Two additional main disease foci in Sudan are in Abu Hamed on Nile River in northern Sudan 6 and the Galabat area in eastern Sudan near the border with Ethiopia. ...
Onchocerciasis remains an important debilitating disease in many areas of Africa, including Sudan. The
status of infection transmission in 2007 was assessed in the vectors of two disease foci in Sudan: Abu Hamed in northern
Sudan, which has received at least 10 years of annual treatment and Galabat focus in eastern Sudan, where only minor,
largely undocumented treatment activity has occurred. Assessment of more than 30,000 black flies for Onchocerca volvulus
infectious stage L3 larvae by using an O-150 polymerase chain reaction protocol showed that black fly infectivity rates
were 0.84 (95% confidence interval = 0.0497–1.88) per 10,000 flies for Abu Hamed and 6.9 (95% confidence interval =
1.1–16.4) infective flies per 10,000 for Galabat. These results provide entomologic evidence for suppressed Onchocerca
volvulus transmission in the Abu Hamed focus and a moderate transmission rate of the parasite in the Galabat focus.
... As recent studies in endemic countries suggests that onchocercal skin symptom is just as damaging as ocular disease, being responsible for poor school performance as well as a high dropout rate. [11][12][13] Since troublesome itching is a self-reported symptom, there is no gold standard to measure its prevalence. Thus, we employed the proportion of those having troublesome itching among total infected from several multi-country studies to estimate the prevalence of troublesome itching. ...
Onchocerciasis is caused by infection with the nematode Onchocerca volvulus for which man is the only known reservoir. The parasite is transmitted by blackflies which ingest microfilariae during a bloodmeal on a human being. The adult worms are usually found in subcutaneous nodules and have an average longevity of around 9-11 years. The adult female worm produces millions of microfilariae
... Strong associations have been found between the prevalence of skin lesions and troublesome itching and onchocercal endemicity (World Health Organization 1995). Despite that, O. volvulus loads are not linearly associated with disease severity, and low and high parasite intensities can result in skin reactions (Ghalib et al. 1987;Mukhtar et al. 1998;Makunde et al. 2000). ...
The Onchocerciasis Control Program (OCP), one of the most successful vertical disease control programs in the history of public health, came to an end in 2003 with devolvement of responsibilities for control program activities passed to the countries affected. Fortunately, 15 years ago the Mectizan Distribution Program (MDP) was founded to provide a complementary approach to controlling the disabling consequences of this parasitic infection. With over 250 million doses of ivermectin distributed over the past 15 years, the MDP is well on its way to both solidifying the progress made by the OCP and extending program reach well beyond the boundaries of the OCP. Through the extensive clinical testing protocols implemented in a variety of countries in Aftica, ivermectin has been proven to be a safe and highly effective treatment for onchocerciasis. Regular distribution to populations living in endemic areas has demonstrated significant reductions in blinding ocular complications, transmission, and disability caused by onchocercal skin disease. As yet undocumented, are the likely significant impact regular population dosing with ivermectin has on intestinal helminth infections, lymphatic filariasis, and human scabies infection. While there are significant barriers to continued program success, focussed attention on expanding and improving community-directed ivermectin distribution is likely to lead to further progress against this resilient infection.
Musculoskeletal parasites (MSKP) are usually encountered in tropical areas. However, there have recently been reports from
western countries, e.g., Germany (Kienast et al. 2007), France (Ansart et al. 2007; Bouchaud et al. 2000), and Canada (Ancelle
et al. 2005; Davies et al. 1993). The relation of the musculoskeletal system (MSK) to parasites has its own peculiarity. The
large surface area of the overlying skin is an open entrance gate, particularly during swimming in polluted ponds and swamps.
The exposure of farmers to parasites is compulsory in agricultural irrigation canals. Sleeping on the bare ground provides
a fast track into the human body. Soil-transmitted parasites are a major health problem in many countries, particularly in
children (Xu et al. 1995). Temporarily, the subcutaneous tissues provide a medium for local wandering movement as in cutaneous
larva migrans (Jelinek et al. 1994). The MSK may act as a graveyard for those parasites that do not complete their life cycle
and finally lodge in muscles or bones. Unlike the gastrointestinal tract (GIT), there is no continuous supply of soluble nourishment
and no room for delivery of offspring or reproduction because of bone tissue compactness, muscle movements, and contractions.
Onchocerciasis remains an important debilitating disease in many areas of Africa, including Sudan. The status of infection transmission in 2007 was assessed in the vectors of two disease foci in Sudan: Abu Hamed in northern Sudan, which has received at least 10 years of annual treatment and Galabat focus in eastern Sudan, where only minor, largely undocumented treatment activity has occurred. Assessment of more than 30,000 black flies for Onchocerca volvulus infectious stage L3 larvae by using an O-150 polymerase chain reaction protocol showed that black fly infectivity rates were 0.84 (95% confidence interval = 0.0497-1.88) per 10,000 flies for Abu Hamed and 6.9 (95% confidence interval = 1.1-16.4) infective flies per 10,000 for Galabat. These results provide entomologic evidence for suppressed Onchocerca volvulus transmission in the Abu Hamed focus and a moderate transmission rate of the parasite in the Galabat focus.
Southern Sudan has been ravaged by decades of conflict and is thought to have one of the highest burdens of neglected tropical diseases (NTDs) in the world. Health care delivery, including efforts to control or eliminate NTDs, is severely hampered by a lack of infrastructure and health systems. However, the post-conflict environment and Southern Sudan's emerging health sector provide the unprecedented opportunity to build new, innovative programmes to target NTDs. This article describes the current status of NTDs and their control in Southern Sudan and outlines the opportunities for the development of evidence-based, innovative implementation of NTD control.
A new focus of onchocerciasis is reported from Upper Atbara River area in the Sudan. This river is a known seasonal breeding place of Simulium damnosum. The area was sparsely populated in the past but now, following agricultural development, is inhibited mainly by immigrants from Northern Nigeria and Chad. Clinically the common features are skin changes of the legs, thighs buttocks, arms and trunk. Other features are corneal opacities and small often deeply placed subcutaneous nodules. Choroido-retinal degeneration, genital elephantiasis and hydrocoele, commonly associated with onchocerciasis in other parts of the Sudan, are absent.
The prevalence, intensity and clinical manifestations of onchocerciasis were investigated in three village communities along the Bahr El Arab and its tributaries in Southern Darfur, Western Sudan. Onchocerca volvulus has not been reported from this region before. Over 300 people were examined and the selection of patients was aimed at obtaining a cross-sectional view of the disease at all ages and in both sexes. Prevalence rates were high (67.5%, 28.6% and 32% in Titribi, Radom and Kafia Kingi, respectively). The intensity of infection in young adults was generally about 30 mf/mg, but ranged up to 100 mf/mg. Infections were detected in subjects as young as two years old; about one quarter of those sampled in Titribi had nodules, mostly in the pelvic region. Clinical signs of acute and chronic dermal changes were especially marked in Titribi. This village was located closest to the breeding sites, which appear in the rainy season only. More than a third of those samples had severe pruritus and showed many self-inflicted excoriations. Both anterior and posterior eye segment changes were detected in each community, and cases of onchocercal blindness were attributed to sclerosing keratitis and to optic and chorioretinal atrophy. One case typical of intensely localized disease was seen, where the affliction was unilateral and severe with oedema and pigment changes, but very few microfilariae present. Onchocerciasis appears to be well established in this region and has apparently caused abandonment of some settlements in recent years.(ABSTRACT TRUNCATED AT 250 WORDS)
Cases of onchocerciasis were treated with three drugs, Antrypol, Pentostam and Hetrazan. Antrypol proved undoubtedly effective, producing disappearance of the microfilariae and onchocercal nodules, and improvement in cases of defective vision with anterior ocular manifestations, but little or no improvement in cases with well-defined posterior manifestations. The severe toxic effects of the drug, however, are sometimes fatal, and therefore preclude its use. Pentostam, although non-toxic, did not prove effective in the doses tried; it may be of some use in very large doses. Hetrazan was given to three cases only, in all of which it produced very rapid disappearance of the microfilariae, but this was accompanied by some allergic reactions and there was no other indication of improvement. Moreover, one month after treatment, microfilariae reappeared in one case. It seems that the more actively filaricidal a drug is, the more toxic it will be, and this is likely to be a serious limitation in the chemotherapy of onchocerciasis until some method of avoiding the allergic reactions can be devised.