Studies on onchocerciasis in the United Cameroon Republic. II. Comparison of onchocerciasis in rain-forest and Sudan-savanna

A community trial of ivermectin for onchocerciasis in Sierra Leone: clinical and parasitological responses to the initial dose

A double-blind placebo-controlled trial of ivermectin was started in 1987 in 6 villages in southern Sierra Leone. 1625 villagers, 93% of the total population, were surveyed before treatment and allocated at random to the trial. Onchocerciasis was hyperendemic and of moderate intensity in the area. Typical onchocerciasis skin lesions were seen in most cases; the blindness rate was 1.5% and a further 4.3% had visual impairment. Six months after treatment 988 subjects (80%) were reassessed and microfilarial loads in the ivermectin group were found to be 10% of control levels. Additionally, blood eosinophil concentrations were reduced by one-quarter. The severity, but not the prevalence, of skin lesions was significantly reduced in the ivermectin group, with a particularly marked effect on papular eruptions. There had been no reduction in the prevalence of itching, nor had markers of general health shown improvement after ivermectin. Ivermectin is an effective microfilaricidal agent and may improve Onchocerca-related skin lesions after a single dose. However, the lack of obvious benefit to a target population after the first dose of ivermectin may reduce compliance with subsequent doses. This has implications for planned mass treatment initiatives in onchocerciasis endemic regions.

Longitudinal study of lesions of the posterior segment in onchocerciasis

Onchocerciasis is a major cause of blindness, and much of the blindness due to onchocerciasis is caused by chorioretinitis. Little is known about the progression of lesions in the posterior segment in either untreated or treated disease. The authors studied the progression of onchocercal chorioretinitis in 57 patients from 1 to 3 years. Changes were documented from detailed ocular examinations, fundus photographs, and fluorescein angiograms, and included live intraretinal microfilariae, intraretinal hemorrhages, cotton-wool opacities, intraretinal pigment, white and shiny intraretinal deposits, retinal pigment epithelial window defects, and atrophy. Depigmentation at the edge of chorioretinal scarring progressed at a rate of up to 200 microns per year. Ivermectin or mebendazole treatment did not appear to alter the progress of depigmentation at the edge of chorioretinal scars. These observations suggest that onchocercal chorioretinitis is associated with early changes in the retina and retinal pigment epithelium, and that disease in the posterior segment may progress rapidly.

Onchocerciasis in Sierra Leone.2: A comparison of forest and savanna villages

Very little of the original primary forest remains in Sierra Leone and the savanna is mainly woodland or a forest-savanna mosaic. The prevalence of microfilariae of Onchocerca volvulus, nodules and moderate or severe skin lesions was higher in forest than savanna villages. In forest villages the prevalence of microfilariae was 71.8% at the iliac crest, 36.6% (outer canthus), 12.8% (cornea) and 34.1% in the anterior chamber of the eye. Corresponding figures for the savanna villages were 51.9%, 20.5%, 5.6% and 21.8%. The overall prevalence of nodules in the forest and savanna was 70.5% and 53.2% respectively, while the prevalence of head and upper body nodules was 14.8% (forest) and 11.0% (savanna). The prevalence of moderate or severe skin lesions was 17.7% in forest and 13.0% in savanna villages. Lesions of the groin and scrotum were few in both zones. In persons aged 30 years or more the prevalence rates of severe eye lesions--sclerosing keratitis, iritis, optic atrophy and choroidoretinitis--were 4.3%, 16.1%, 13.9% and 14.8% respectively in forest villages. Corresponding figures for the savanna villages were 3.7%, 8.7%, 14.2% and 11.3%. Males were more commonly affected than females. At least one of these lesions was found in 32% persons in forest and 24% in savanna villages.

Onchocerciasis in Sierra Leone 3: Relationships between eye lesions and microfilarial prevalence and intensity

The relationship between severe onchocercal eye lesions (iritis, sclerosing keratitis, optic atrophy and choroidoretinitis) and (i) the prevalence and intensity of microfilariae (mf) of Onchocerca volvulus in skin snips from the iliac crest and outer canthus, and (ii) the prevalence of mf in the cornea and anterior chamber of the eye, was studied in 1414 persons from forest and savanna villages and 312 attenders at eye clinics. Ecologically the savanna of Sierra Leone more closely resembles the forest than the dry Sudan-savanna areas of West Africa, and in persons aged 30 years or more the combined prevalence of anterior segment lesions (iritis and sclerosing keratitis) was higher in the forest villages (20.6%) than in the savanna (12.7%). The higher loads of mf found in the forest compared to savanna villages could explain these results. Prevalence rates for posterior segment lesions (optic atrophy and choroidoretinitis) were 28.1% and 22.6% in the forest and savanna respectively. Although in villages from both zones there was a close association between mf in the anterior chamber and optic atrophy, other associations between posterior segment lesions and mf were either not significant or weak. In contrast, there was a strong association between anterior segment lesions and mf in the eye and the concentration of mf at the outer canthus. This association was stronger for iritis than for sclerosing keratitis.

Onchocerciasis in the Blue Nile Valley of western Ethiopia

In a survey among 477 inhabitants of the Blue Nile Valley of western Ethiopia 182 (38%) were positive by skin snip investigation for microfilariae of Onchocerca volvulus. Of these only 23% had typical clinical signs and symptoms of onchocerciasis. The highest prevalence rate of microfilariae (84%) was found among Nilotics in the lowlands, where 50% of the children above 10 years, and 90% of adults above 30 years of age, were infected. The mean microfilarial density per skin snip was significantly higher in the high prevalence areas (14) than in the low prevalence areas (3). Positive skin snips from both hip and shoulder were found in 24% of the population, whereas 3% had microfilariae only in the shoulder and 11% only in the hip region. The mean microfilarial density in the hips (16) was double that in the shoulders (8). Ophthalmological evaluation, including slit lamp examination, was possible in 77 of the 182 cases with positive skin snips. Severe eye damage due to onchocerciasis was not observed. However, one 35 year old female had live microfilariae in the anterior chambers of both eyes.

Characterization of an Onchocerca-specific DNA clone from Onchocerca volvulus

A genomic library of a savanna isolate of Onchocerca volvulus was screened to detect recombinant plasmids containing highly repeated DNA sequences of this parasite. Four recombinant plasmids were identified which hybridized specifically to Onchocerca DNA, but not to DNA from humans, black flies, Brugia malayi, B. pahangi, or Wuchereria bancrofti. The recombinant plasmids had a low level of homology to Dirofilaria immitis. All recombinant plasmids contain related DNA sequences based on Southern hybridization analysis. Sequences related to these recombinant plasmids are present in different geographic isolates of O. volvulus and O. ochengi, an animal parasite. Two of the recombinant plasmids contain sequences also found in O. lienalis. One recombinant plasmid, puOvs3, has been characterized in detail, including DNA sequence determination. Radiolabeled puOvs3 is able to detect 100 pg of genomic DNA isolated from O. volvulus worms from both savanna and forest regions. It can differentiate O. volvulus from O. ochengi by Southern blot analysis.

A DNA sequence specific for forest form Onchocerca volvulus

Onchocerciasis, or river blindness, is caused by infection with Onchocerca volvulus, a filarial parasite which infects about 40 million people in Africa and Latin America. Epidemiological, clinical, entomological and serological studies of African onchocerciasis led to the hypothesis that Onchocerca volvulus exists in different forms in the forest and savannah. It is uncertain if these differences are due to genetic differences within O. volvulus itself, or to epigenetic factors, such as differences in the host populations. To date no basic biochemical differences between the forest and savannah populations of O. volvulus has been found, although isoenzyme studies have shown that differences in allele frequency between forest and savannah populations exist. Here we describe the isolation of a DNA sequence that seems to be specific for the forest form of O. volvulus, the first indication of a basic genetic difference between the savannah and forest forms.

A comparison of the surface and secretions of Trichinella pseudospiralis and T. spiralis

Intact, viable adults, infective and newborn larvae of Trichinella pseudospiralis were surface labelled with 125I by the chloramine T method and labelled proteins were compared with those obtained from equivalent stages of T. spiralis. Electron-microscope autoradiography determined that labelled proteins were restricted to the cuticle for all stages of both isolates. Comparative polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate (SDS-PAGE), using thin gradient gel slabs, of proteins obtained from each stage, demonstrated that the profile of surface-labelled proteins of T. pseudospiralis were restricted in number, stage specific, and similar to equivalent proteins of T. spiralis both in size and in their organization into aggregates. The stage-specific profiles of surface-labelled proteins derived from newborn larvae were indistinguishable, but differences were noted between adults and infective larvae of the two isolates. These differences in protein structure were confirmed by two dimensional mapping of tryptic peptides. Stage-specific profiles were also obtained when [35S]methionine biosynthetically labelled secretions of the 3 stages of T. pseudospiralis were compared by SDS-PAGE. Comparison of the profiles obtained with secretions for respective stages of T. spiralis again failed to distinguish newborn larvae, but adults and infective larvae of T. spiralis and T. pseudospiralis displayed a mixture of common and species-specific proteins. These findings are discussed in relation to the different pathology associated with infection with two isolates.

Schoolchildren and ocular onchocerciasis in the rain-forest of Cameroon

The results of surveys among 188 primary school children in two hyperendemic rain-forest villages in South-West Cameroon are reported. The children were examined for their nutritional state and for lesions due to onchocerciasis, with emphasis on eye pathology. Clinical manifestations in the two villages hyperendemic for onchocerciasis were compared with those found in a hypo-endemic coastal village. The primary school age appeared to be the period with the highest increase in ocular, notably corneal, involvement in onchocerciasis. The prevalence of ocular involvement showed an increase from 42.8% in the 6-year age group to 100% in the 12-year age group. 17.5% of the children were considered to be at risk of developing serious ocular onchocerciasis. Significant correlation between nutritional state and severity of infection could not be demonstrated. Sex differences in onchocercal symptomatology appeared not to be significant. The importance of microfilarial concentration in the skin snip near the eye is stressed as a simple but important indicator of danger to the eye. Prognosis and therapy are discussed.

Onchocerca volvulus: enzyme polymorphism in relation to the differentiation of forest and savannah strains of this parasite

Isozyme analysis was carried out on Onchocerca volvulus worms collected from Liberia, Ivory Coast, Burkina Faso and Sudan to see whether this technique could detect differences between forest and savannah populations of this parasite. A total of 243 forest and 189 savannah individual female worms were electrophoresed and stained for seven enzymes. Four showed some polymorphism, LDH, MDH, PGM and MPI and the other three, GAPDH, PEP and GPI were invariant. Statistical analysis of the results showed that the relative proportions of genotypes from within the different countries conformed to Hardy-Weinberg expectations. Pairwise comparisons of allele frequencies between countries showed that populations from Liberia and Ivory Coast had a very similar composition; there was some divergence between all the other pairs of populations and the genetic distance was calculated to summarize the degree of divergence. The number of loci examined was small and the genetic distances were within the range expected for separate geographical populations of the same species. The usefulness of this technique in worm identification is discussed.

Onchocerciasis in Sierra Leone. I. Studies on the prevalence and transmission at Gbaiima village

A longitudinal survey--parasitological, clinical, immunological and entomological--of onchocerciasis is being conducted in Gbaiima village in Sierra Leone. The estimated Annual Transmission Potential (ATP) is 5863. More than 80% of the annual transmission occurs between October and December. Four species of the Simulium damnosum complex are known to breed in a nearby river. The relative role of these species as vectors has yet to be determined. The total population (598 persons) aged one year and over were examined. Based on microfilarial and nodular rates the prevalence of onchocerciasis was 68.6%. In persons above 15 years of age this prevalence was 88.9%. Microfilarial and nodular rates were related to age. Severe skin lesions occurred in 1.0% of persons. 24 adults (7.5%) were blind (but the cause of the blindness was not determined).

The incidence of eye lesions and visual impairment in onchocerciasis in relationship to the intensity of infection

Data from follow-up surveys of onchocerciasis, conducted in the rain-forest and savanna areas of the United Cameroon Republic, are used to fit equations relating the incidence of eye lesions and visual impairment to microfilaria concentration in skin-snips. The incidence of lesions in those aged under 45 appears to be directly proportional to concentration, though the association is less clear in females over 25 in the savanna. The incidence of visual impairment appears also to be directly proportional to concentration among those under 45, but only in the savanna. Predictions of changes in incidence rates under transmission control are made, using hypothetical values for the rate of decline of infection. They are compared with reported incidence of lesions from the Onchocerciasis Control Programme: they are in good agreement for those aged under 30 years, but they understate the observed decline in older subjects.

Onchocerciasis in Ecuador. III. Clinical manifestations of the disease in the province of Esmeraldas

Considerable variation in the frequency of the clinical manifestations of onchocerciasis was seen in the individual endemic foci of the disease in province of Esmeraldas, Ecuador. In hypoendemic areas, 84.6% of all microfilaria-positive inhabitants were found to be free of any clinical manifestations of the disease, whereas in the hyperendemic area clinical manifestations were present in 57.9% of those infected. Ocular keratitis, macular papular rash of the skin and subcutaneous onchocercal nodules of varying frequency were the major clinical variants. Long-standing onchodermatitis and hypertrophy of the skin were rarely seen. Clinical evidence of prolonged ocular and skin invasion by microfilariae was seen only in the hyperendemic area. Of the 26.1% of the microfilaria-positive inhabitants who had onchocercal nodules, 91.7% lived in the hyperendemic area. 41.1% of all nodules occurred in the region of the iliac crest. Clinical conditions associated with high microfilarial density, i.e., elephantiasis of the legs and scrotum, lymphadenopathy, hanging groin, hydrocele and inguinal hernia were seen only in the hyperendemic area. The clinical features were similar to those seen in Africa, but the low incidence of the clinical presentation and severity of the disease suggested a recent infestation of the province.

Ocular onchocerciasis with living microfilariae in the anterior chamber in two Dutch boys

In 2 Dutch boys, 15 and 12-year-old brothers, living microfilariae were observed in the anterior chamber. Both boys had returned 4 years before from a hyperendemic onchocerciasis region where they had lived for 5 years. The pathogenesis and treatment of onchocerciasis are discussed.

Further observations on the relationship between ocular onchocerciasis and the head nodule, and on the possible benefit of nodulectomy

From the examination of 197 patients who presented with one or more head nodules in the Sudan savanna in Cameroon, and from previous examinations of patients with ocular onchoceriasis, it concluded that in this part of Africa the formation of a head nodule is often preceded by the development of ocular lesions. Head nodulectomy is therefore of limited prophylactic value. Head nodules were removed from 107 of these patients, of whom 17 also received diethyl-carbamazine citrate (DEC), and 20 received both DEC and suramin. Fifteen other patients received DEC as the only treatment, and 4 suramin alone, while 5 received both DEC and suramin. From the follow-up examinations at 9, 12, and 24 months after treatment it was concluded that removal of the head nodule was of some benefit to lesions of the anterior segment, but that the procedure should be combined with efficient micro- and macrofilaricidal therapy in patients at risk of developing ocular pathology, that is, those with 15 or more microfilariae per skin snip near the outer canthus. This index can be measured by paramedical personnel and is therefore of great public health importance in the early detection of "at risk" patients.

Variation in delayed hypersensitivity in onchocerciasis

Soluble antigen preparations were made from Onchocerca volvulus adults recovered from subcutaneous nodules, and from Necator americanus third-stage larvae. Intradermal skin tests were carried out on a total of 100 individuals clinically classified as having either the generalized form of onchocerciasis (86 cases, or the localized sowda form (14 cases). 91 of the people studied produced immediate reactions to the onchocercal antigen, but only those with sowda showed delayed reactions, though one person with generalized disease showed a doubtful delayed reaction. Reactions to N. americanus antigen, both immediate and delayed, were seen in both forms of the disease. The lack of delayed skin reaction in the generalized form of onchocerciasis is discussed, and a comparison is made with other diseases. Preliminary evidence for the existence of a true spectrum of clinical and immunological forms of onchocerciasis is suggested by one case in this study.

Droplet degeneration of the cornea in North Cameroon. Prevalence and clinical appearances

The prevalence of droplet degeneration of the cornea in a defined population of 517 persons in north Cameroon was similar in males and females, but severe changes were commoner in elderly men. Most cases showed only mild changes of granularity and droplet formation in Bowman's zone, but they were sometimes widespread. More severe changes were seen in only nine patients. The clinical appearances are compared with those described from other parts of the world. In support of the aetiological role of direct sunlight, droplet degeneration was much more prevalent in the savanna than in the rain-forest in Cameroon. The condition ranges in severity from very mild to very severe, but difficulties in differential diagnosis, particularly in advanced cases, make it doubtful whether the same basic condition is being described in all cases. These doubts will be resolved only by properly conducted epidemiological studies in different parts of the world.

Studies on onchocerciasis in the United Cameroon Republic. III. A four year follow-up of 6 rain-forest and 6 Sudan-savanna villages

After an interval of four years the same observers used the same standardized techniques to re-examine 1,016 people in 12 heavily infected rain-forest and savanna villages in Cameroon. The changes in the number of nodules and in the concentration of microfilariae in the skin and eye are described. These latter changes are correlated with the development and/or deterioration of eye lesions and visual impairment. In both the rainforest and the savanna there was a strong association between the development of eye lesions and a high concentration of microfilariae, not only in the eye but also in the skin, and more so at the shoulder than at the buttock. The importance of these findings for the prevention of blindness is discussed.