Onchocerciasis in Sudan: the Abu Hamed focus

Abstract

The current status of onchocerciasis in Abu Hamed, Northern Province, Sudan, was studied. Of 208 persons attending out-patient clinics in villages in this region, 71 were microfilariae-positive on skin snips or had palpable nodules. Microfilariae and worms in nodules were identified as Onchocerca volvulus. No microfilariae were seen in peripheral blood. Most nodules and microfilariae were found in the pelvic region, but the intensity of infection was uniformly low (av. less than 3 mf/mg). Despite this, signs of onchocercal dermatitis were common and severe, especially over the buttocks. Papular eruptions and scarring often appeared to lead to black-grey hyperpigmentation, but no cases were seen of the unilateral, hyper-reactive 'sowda' described in Arabs in Yemen. No microfilariae were detected in the eyes of any of the patients who had positive outer canthus snips. Serum retinol concentrations were normal but mildly elevated concentrations of serum IgG, IgM and IgA were detected in many patients. Immunoglobulin E values in a sample of 20 microfilariae-positive patients were markedly higher than normal, with most in the 4,000 to 15,000 U/ml range. Eosinophil levels in differential counts of peripheral blood from the 208 villagers were markedly elevated. In skin snip surveys of over 400 villagers and school pupils, sample prevalence rates of 2 to 17.5% were recorded. Simulium biting was seasonal (November to May) and peaked in March. Over-all, the results indicate that O. volvulus infection persists in the Abu Hamed region as a serious cause of skin disease in the absence of other complicating filariases.

Interruption of Onchocerca volvulus Transmission in the Abu Hamed Focus, Sudan

“…In addition, we reported low levels of transmission based on the presence of L3 larvae in black flies that same year. 18 These reports indicated that the annual treatment regimen had achieved a high degree of onchocerciasis control in the area, with a considerable reduction in prevalence of dermal mf from the 34% to 37% reported in the mid-1980s, 7,27 but had not yet interrupted transmission. It is important to note, however, that coverage during the years where annual treatment was offered was inadequate (less than 65%).…”

“…17 Historic parasitological data evaluating the status of the disease in the Abu Hamed focus were reported in 1985. 7 In 2007, additional entomological, parasitological, and serological data were collected, concurrent with the onset of semiannual treatments. Entomological analysis revealed that low levels of disease transmission existed before the shift to semiannual treatment activities in the area.…”

“…In 2011, we were able to reach the required sample size ( 3,000) by sampling school children from 40 communities, including 29 communities within the focus, 7 communities close to but beyond the focus southern limits, and 4 displaced communities in and around the focus (Figure 1 Parasitologic studies. Sentinel villages in this study included the three communities (Kiji, ElBagair, and ElGeraif) originally reported in the mid 1980s 7,27 as having the highest endemicity in the focus. These were reinvestigated in 2007 and 2011 for the prevalence of O. volvulus skin microfilariae (mf), palpable nodules, and signs of the skin disease (onchodermatitis).…”

“…Palpable nodules and onchodermatitis were used as additional indicators of infection, because the Abu Hamed focus is historically known for low infection intensity (average of 3 mf/mg skin). 7,27 In 2011, four additional communities in and around the Abu Hamed focus were assessed for parasitological indicators of the disease. These communities included three communities (Sharrari, Elfida, and Mukabrab) displaced by the Merowe Dam and relocated within and outside the focus together and another community (Alfiraikha) located about 33 km outside the southern limit of the known onchocerciasis focus that had not been covered by CDTI activities (Figure 1).…”

“…6 The disease here is also non-blinding and associated with severe skin manifestations. Skin microfilaria rates were originally described to reach 37%, 7 ranking the Abu Hamed focus as mesoendemic based on World Health Organization (WHO) criteria. 8 Molecular studies showed that the parasites from this focus differed from all of the O. volvulus isolates examined.…”