Urban-rural differences in the gene expression profiles of Ghanaian children.

Recent studies indicate that urbanization is having a pronounced effect on disease patterns in developing countries. To understand the immunological basis of this, we examined mRNA expression in whole blood of genes involved in immune activation and regulation in 151 children aged 5-13 years attending rural, urban low socioeconomic status (SES) and urban high-SES schools in Ghana. Samples were also collected to detect helminth and malaria infections. Marked differences in gene expression were observed between the rural and urban areas as well as within the urban area. The expression of both interleukin (IL)-10 and programmed cell death protein 1 increased significantly across the schools from urban high SES to urban low SES to rural (P-trend <0.001). Although IL-10 gene expression was significantly elevated in the rural compared with the urban schools (P<0.001), this was not associated with parasitic infection. Significant differences in the expression of toll-like receptors (TLRs) and their signaling genes were seen between the two urban schools. Genetic differences could not fully account for the gene expression profiles in the different groups as shown by analysis of IL-10, TLR-2 and TLR-4 gene polymorphisms. Immune gene expression patterns are strongly influenced by environmental determinants and may underlie the effects of urbanization seen on health outcomes.

Schistosome infection is negatively associated with mite atopy, but not wheeze and asthma in Ghanaian schoolchildren.

BACKGROUND: Epidemiological evidence suggests that helminth infection and rural living are inversely associated with allergic disorders. OBJECTIVE: The aim of the study was to investigate the effect of helminth infections and urban versus rural residence on allergy in schoolchildren from Ghana. METHODS: In a cross-sectional study of 1385 children from urban-high socio-economic status (SES), urban-low SES and rural schools, associations between body mass index (BMI), allergen-specific IgE (sIgE), parasitic infections and allergy outcomes were analysed. Allergy outcomes were skin prick test (SPT) reactivity, reported current wheeze and asthma. RESULTS: Helminth infections were found predominantly among rural subjects, and the most common were hookworm (9.9%) and Schistosoma spp (9.5%). Being overweight was highest among urban-high SES (14.6%) compared to urban-low SES (5.5%) and rural children (8.6%). The prevalence of SPT reactivity to any allergen was 18.3%, and this was highest among rural children (21.4%) followed by urban-high SES (20.2%) and urban-low SES (10.5%) children. Overall, SPT reactivity to mite (12%) was most common. Wheeze and asthma were reported by 7.9% and 8.3%, respectively. In multivariate analyses, factors associated with mite SPT were BMI (aOR 2.43, 95% CI 1.28-4.60, P = 0.007), schistosome infection (aOR 0.15, 95% CI 0.05-0.41) and mite sIgE (aOR 7.40, 95% CI 5.62-9.73, P < 0.001) but not area. However, the association between mite IgE and SPT differed by area and was strongest among urban-high SES children (aOR = 15.58, 95% CI 7.05-34.43, P < 0.001). Compared to rural, urban-low SES area was negatively associated with current wheeze (aOR 0.41, 95% CI 0.20-0.83, P = 0.013). Both mite sIgE and mite SPT were significantly associated with current wheeze and asthma. CONCLUSION AND CLINICAL RELEVANCE: Infection with schistosomes appeared to protect against mite SPT reactivity. This needs to be confirmed in future studies, preferably in a longitudinal design where schistosome infections are treated and allergic reactions reassessed.

Efficacy of DEET and non-DEET-based insect repellents against bites of Simulium damnosum vectors of onchocerciasis.

Coping strategies including smoke screens are used against nuisance bites of Simulium damnosum Theobald (Diptera:Simuliidae) in onchocerciasis endemic communities. To find more effective alternatives, the efficacy of commercially available N,N-diethyl-3-methylbenzamide (DEET) products with active concentrations of 9.5, 13, 25, 50 and 98.1-100% and 'NO MAS,' (active component: para-menthane-3,8-diol and lemon grass oil) were tested at Bui-Agblekame, Ghana. A Latin square study design was implemented using eight groups of two vector collectors each, who used repellents (treatment), mineral oil or nothing each day until the end of the study. Flies were caught and their numbers each hour recorded using the standard methods for onchocerciasis transmission studies. T-tests were used to compare the mean duration of protection and a one-way analysis of variance controlling for catchers and repellents was performed. Tukey's test was used to compare protection by repellents and mineral oil. The highest percentage protection was 80.8% by NO MAS and the least 42.5% by the 13% DEET product. The period of absolute protection was 5 h by NO MAS and 1 h by 50% DEET product. No significant increase in protection was offered beyond 25% active DEET products and no significance was observed in terms of catcher × repellent effect (F = 1.731, d.f. = 48, P = 0.209).

Point and period prevalences of eczema in rural and urban schoolchildren in Ghana, Gabon and Rwanda.

BACKGROUND: Eczema is a growing problem in Africa, particularly amongst children. OBJECTIVES: To investigate the point-prevalences of eczema by physical examination in schoolchildren living in rural and urban areas and with different socioeconomic backgrounds in Ghana, Gabon and Rwanda. In Ghana period-prevalences were also estimated by questionnaire and compared with the point-prevalences. METHODS: In total, 4839 schoolchildren in Ghana, Gabon and Rwanda were seen by at least one dermatologist. The point-prevalences of eczema were estimated on the basis of physical examination. Period-prevalences were measured in Ghana with questionnaire based-interviews adapted from the International Study of Asthma and Allergies in Childhood (ISAAC). RESULTS: The point-prevalences were 1.5% and 1.6% in the two Ghanaian studies; 4% in Gabon and 0.8% in Rwanda. The period-prevalences were 2.6% and 4.4% in the two Ghanaian studies. The prevalences of eczema were not significantly different when comparing the urban and rural groups as well as the different socioeconomic levels. The sensitivity and positive predictive value to identify eczema cases based on the questionnaires compared to the diagnoses by physical examination were only 33% and 22% in the first Ghanaian study and 10% and 4% in the second Ghanaian study respectively. CONCLUSIONS: The point-prevalences of eczema in the three African countries studied were low compared with industrialized countries. Physical examination by a dermatologist is still the gold standard to identify eczema cases because the sensitivity and the positive predictive value to identify eczema cases with questionnaires were low in the two Ghanaian studies.

Deforestation and the spatio-temporal distribution of savannah and forest members of the Simulium damnosum complex in southern Ghana and south-western Togo.

Spatio-temporal data on cytotaxonomic identifications of larvae of different members of the Simulium damnosum complex collected from rivers in southern Ghana and south-western Togo from 1975 until 1997 were analysed. When the data were combined, the percentages of savannah blackflies (S. damnosum sensu stricto and S. sirbanum) in the samples were shown to have been progressively increasing since 1975. The increases were statistically significant (P < 0.001), but the rates of increase were not linear. Further analyses were conducted according to the collection seasons and locations of the samples, to account for possible biases such as savannah flies occurring further south in the dry season or a preponderance of later samples from northern rivers having more savannah flies. These analyses showed that the increasing trend was statistically significant (P < 0.0001) only during the periods April to June and October to December. The presence of adult savannah flies carrying infective larvae (L3) indistinguishable from those of Onchocerca volvulus in the study zone was confirmed by examinations of captured flies. The percentages of savannah flies amongst the human-biting populations and the percentages with L3s in the head were higher during dry seasons than wet seasons and the savannah species were found furthest south (5 degrees 25'N) in the dry season. Comparisons of satellite images taken in 1973 and 1990 over a study area in south-western Ghana encompassing stretches of the Tano and Bia rivers demonstrated that there have been substantial increases in urban and savannah areas, at the expense of forest. This was so not only for the whole images but also for subsamples of the images taken at 1, 2, 4, 8 and 16 km distant from sites alongside the River Tano. At every distance from the river, the percentages of pixels classified as urban or savannah have increased in 1990 compared with 1973, while those classified as degraded or dense forest have decreased. The possibility that the proportionate increases in savannah forms of the vectors of onchocerciasis, and hence in the likelihood of the transmission of savannah strains of the disease in formerly forested areas, were related to the decreases in forest cover is discussed.

Evidence of multiple mating and hybridization in Simulium damnosum s.l. (Diptera: Simuliidae) in nature.

Beakers with aeration were used to rear individual (single) egg batches of Simulium damnosum (Theobald) s.l. to larvae and adults. Chromosomal analysis of the progeny of individual females indicated that multiple mating occurred within the S. damnosum complex and that hybridization occurred between S. damnosum s.s. and S. sirbanum (Vajime & Dunbar) in nature. These results indicate that possibly more extensive hybridization may be taking place in some areas of the Onchocerciasis Control Program than previously reported. Dramatic changes in the rates of hybridization among members of the S. damnosum complex possibly may lead to the formation of new cytotypes.

Cytotaxonomic and molecular analysis of Simulium (Edwardsellum) damnosum sensu lato (Diptera: Simuliidae) from Abu Hamed, Sudan.

The northernmost focus for Onchocerca volvulus Leuckhart (Nematoda: Onchocercidae), the causative agent of human onchocerciasis, is found along the Nile near the town of Abu Hamed in Sudan. The vector for O. volvulus at this focus is a single monomorphic population of Simulium (Edwardsellum) damnosum Theobald. This black fly population is limited to a small area between the fourth and fifth cataracts of the Nile River that is isolated geographically from all other populations of S. damnosum sensu lato. Phylogenies produced from cytological analyses and sequence data derived from the NADH dehydrogenase subunit 4 and 16S rRNA genes indicate that Abu Hamed black flies are similar to, but distinct from, the savanna-dwelling sibling species of S. damnosum s.l., Simulium (Edwardsellum) damnosum sensu strictu Theobald, and S. (Edwardsellum) sirbanum Vajime & Dunbar. The DNA sequence and the cytological data support the hypothesis that the black fly population present in Abu Hamed may represent a new sibling species of S. damnosum s.l. We propose that this population be informally designated as the hamedense form of the Simulium damnosum complex.

Temporary small-scale colonization of the Beffa form of the Simulium damnosum theobald complex (Diptera: Simuliidae) in Africa.

Two populations of the Beffa form of Simulium damnosum s.l. were colonized on a small scale for the first time in Africa. The colonies survived for three and five generations, respectively. Information gained led to improvements in adult handling techniques which proved adequate for colony maintenance despite the small numbers reared. Nevertheless, large scale rearings are required to avoid inbreeding and to produce sufficient numbers for experimental purposes.

A review of epidemiological studies of asthma in Ghana.

CONTEXT/BACKGROUND: The last few decades have witnessed a rise in the global prevalence of asthma with a number of risk factors being linked to this increase. Although there is insufficient data on the prevalence of asthma in Ghana, a few studies conducted in this country have shed light on the disease aetiology and associated risk factors. EVIDENCE ACQUISITION: The purpose of this review is to explore the literature on epidemiological studies on asthma carried out in Ghana and how these findings fit into the wider context of observations from other countries. RESULTS: Asthma research in Ghana has focused mainly on children between the ages of 5-16 years with one published study that included adults. Different markers for the disease have been used such as clinician-diagnosed asthma, exercise-induced bronchospasm (EIB) as well as questionnaire-derived symptoms of asthma. Factors found to be associated with asthma in Ghana include atopic sensitisation to environmental allergens, inner-city residence and socioeconomic differences. Other implicated factors are family history of asthma, sib-ship position, breast-feeding duration and helminth infections. CONCLUSIONS: Future research in Ghana must establish the burden of disease among all age-groups as well as clearly differentiate between allergic and non-allergic asthma. Studies are also needed to examine the role of environmental air pollutants on the disease's pathogenesis.

In the case of transmission of Mycobacterium ulcerans in buruli ulcer disease Acanthamoeba species stand accused.

Buruli ulcer disease caused by Mycobacterium ulcerans results in extensive destruction of skin and soft tissue and long-term functional disabilities that ultimately require surgery and rehabilitation. The disease is associated with aquatic and swampy environments with the mycobacterium occurring in biofilms, soil, aquatic insects, fish and wildlife however, the mode of transmission to humans remains an enigma. Current transmission ideas including bites from predatory water bugs and mosquitoes, do not explain satisfactorily the spasmodic disease distribution in human populations. Here we argue that Acanthamoeba species are the natural hosts of M. ulcerans and are mainly responsible for disease transmission because; (i) Acanthamoebae are known natural hosts of several microbial pathogens including M. marinum, M. avium and Legionella pneumophila, (ii) culture of slow-to-grow microbial pathogens hosted in nature by Acanthamoeba spp is enhanced when the media is seeded with the protozoa, (iii) acanthamoebae and M. ulcerans share similar bio-ecological and epidemiological settings, (iv) documented evidence that prior growth of L. pneumophila and M. avium in acanthamoebae influences entry mechanisms, intracellular growth and virulence in human monocytes, (v) Acanthamoeba spp also infect humans and cause diseases via routes of openings including broken skin and sites of trauma similar to M. ulcerans and (vi) M. ulcerans is rather a fastidious intracellular organism as recent analysis of the genome indicate. We argue further that temperature plays a significant role in transmission determining the fate of either the intracellular microbe or the host cells. Also, Acanthamoeba-pathogen association has a long evolutionary history because the same set of bacterial genes and gene products e.g. in L. pneumophila are required for survival in both mammalian and protozoan host cells. We suggest that the involvement of Acanthamoeba in the transmission of M. ulcerans to humans better explains the disease's epidemiology.

Application of a circulating-cathodic-antigen (CCA) strip test and real-time PCR, in comparison with microscopy, for the detection of Schistosoma haematobium in urine samples from Ghana.

In the detection of parasitic infection, the traditional methods based on microscopy often have low sensitivity and/or specificity compared with the newer, molecular tests. An assay based on real-time PCR and a reagent strip test for detecting circulating cathodic antigen (CCA) have both now been compared with urine filtration and microscopy, in the detection of Schistosoma haematobium infections. Urine samples, obtained from 74 'cases' in areas of Ghana with endemic S. haematobium and 79 'controls' from non-endemic areas, were each checked using the three methods. With the results of the filtration and microscopy taken as the 'gold standard', real-time PCR was found to be 100% specific and 89% sensitive whereas the CCA strips were 91% specific and 41% sensitive. With the samples found to contain > or =50 eggs/10 ml (indicating relatively intense infections), the sensitivities of the PCR and CCA were higher, at 100% and 62%, respectively. As expected, egg counts were negatively correlated with the number of amplification cycles needed, in the PCR, to give a signal that exceeded the background (r=-0.38; P<0.01). Although the real-time PCR and CCA strip tests are very different, both show promise in the detection of S. haematobium infections. The PCR has optimal specificity and high sensitivity but the specificity of the CCA strips and the sensitivity of both tools could still be improved. A more thorough re-evaluation of the sensitivity and specificity of microscopy and these newer diagnostic methods, with an estimation of the cost-effectiveness of each technique, is recommended.

A review of leishmaniasis in west Africa.

The DiseaseLeishmaniasis is vector-borne disease caused by blood and tissue dwelling protozoan parasite species belonging to the genus Leishmania. It is basically a disease of animals that gets into the human population when man, flies and the animal reservoirs coexist in the same environment. In man, infections with Leishmania parasites results in a broad range of clinical manifestations involving the skin, mucous membranes and visceral organs with devastating consequences. Two main forms of leishmaniasis have been reported in humans. These are Cutaneous Leishmaniasis, which is a less severe for of the disease with usually self-healing ulcers and Visceral Leishmaniasis, the most severe form of the disease which can result in 100% mortality of infected patients if not treated1. A third form, muco-cutaneous leishmaniasis, results in extensive disfiguring lesions of the nose, mouth and throat mucous membranes. The diverse clinical manifestations of the disease result from a reaction between the virulence of the parasite species and the host's immune response.

Cytotaxonomic description of Simulium kaffaense, a new member of the S. damnosum complex (Diptera: Simuliidae) from south-western Ethiopia.

Although Ethiopia is one of the countries worst affected by human onchocerciasis, the exact taxonomic identity of the blackflies acting as the main vectors in the endemic areas has never been determined. A cytotaxonomic analysis of Simulium damnosum s.l. collected from three endemic sites in south-western Ethiopia has now revealed the existence of the 'Kisiwani' form (a non-anthropophilic cytoform that is common in East Africa) and a newly recognized species, Simulium kaffaense. Simulium kaffaense sp. nov. is differentiated from other members of the S. damnosum complex by six fixed inversions and dozens of 'new' floating inversions. The rearing of egg batches from some of the biting adult females, to larvae or adults, indicated that the human-biting blackflies were all S. kaffaense. As S. kaffaense is not only highly anthropophilic but also, apparently, the only anthropophilic member of the S. damnosum complex present, it is likely to be the main (if not the only) vector of Onchocerca volvulus in the study area. The presence of inversion 1S-1 and a complex inversion possibly involving 1L-3 indicates that S. kaffaense either belongs or is close to the 'Nile' phylogenetic group of S. damnosum s. l. The karyotype frequencies of the inversions in the collections from the three study sites indicate that at least two forms of S. kaffaense, here designated 'Bebeka' and 'Jimma', were caught. The taxonomy and medical importance of S. kaffaense are discussed.

Field and laboratory studies on water conditions affecting the potency of VectoBac (Bacillus thuringiensis serotype H-14) against larvae of the blackfly, Simulium damnosum.

River water conditions that might influence the efficacy of VectoBac, a formulation of the microbial insecticide Bacillus thuringiensis H-14 Berliner against Simulium damnosum sensu lato Theobald (Diptera: Simuliidae) larvae were investigated. A standard formulation was assayed 130 times over 15 months using a mini-gutter system at a field station beside the River Pra in Ghana. The lethal concentration (LC) values, river temperature, conductivity, turbidity and pH were analysed using univariate and multivariate statistics to identify which of these parameters influenced its performance. River temperature, conductivity and turbidity (in that order) were identified as having direct effects on the potency of VectoBac. Water temperature and conductivity were negatively correlated, whereas turbidity and pH were positively correlated with LC values. Analyses of river water samples revealed that despite observed differences in total solids, sodium and potassium cations and chloride concentrations, all the parameters measured did not differ significantly between wet and dry seasons. A simple method for rearing S. damnosum s.l. in the laboratory was then adopted to study the effect of conductivity on potency of VectoBac under controlled conditions. Increasing the conductivity of the water medium up to 3,000 microS enhanced potency by about 42%, whereas increasing that of the insecticide alone raised it by 37%. The results obtained suggest that for effective use of VectoBac for blackfly control in West Africa, river temperature, conductivity and turbidity should be taken into consideration, perhaps by only selecting rivers with optimal conditions for treatment. The laboratory-based system developed for assaying the product overcomes the vagaries associated with field conditions and also the demand for huge logistic requirements of the mini-gutter system, which has to be sited near rivers.

A pictorial guide to the chromosomal identification of members of the Simulium damnosum Theobald complex in west Africa with particular reference to the Onchocerciasis Control Programme Area.

Simulium damnosum Theobald is made up of a complex of sibling species. Nine species are described in the area covered by the World Health Organisation's Onchocerciasis Control Programme in West Africa (OCP). These are, S. squamosum, S. yahense, S. canctipauli, S. soubrense, S. leonense, S. konkourense, S. damnosum s.s., S. sirbanum and S. dieguerense. All of them are vectors of human onchocerciasis, albeit to different capacities. Reliable species determination presently depends on larval cytotaxonomic criteria. The diagnostic chromosomal inversions and other micromorphological characters used in the identification of the species found in the OCP area are presented with figures for their recognition, some distributional information is also given.

Low temperature storage and pupal survival in the Simulium damnosum complex.

Pupae of the Simulium damnosum complex were exposed for different time periods to temperatures of 0, 4, 8 and 12 degrees C before returning to ambient temperature (24-28 degrees C). As the period of exposure to the low temperatures increased, pupal survival decreased. A one day exposure even to 0 degrees C had little effect on survival, whereas for a 4 day exposure, the optimum survival occurred at 8 degrees C with a total of 46% emergence. Young pupae (pale cuticle) had greatest emergence after exposure to 12 degrees C, the old ones (dark sclerotised cuticle) after exposure to 8 degrees C. Exposure to the different cold temperatures did not significantly affect the longevity of the emerging adults. Low temperature storage of pupae is thus a viable method for long distance transportation of living specimens of blackflies.

The distribution and chromosome polymorphism of Simulium dieguerense (Diptera: Simuliidae).

Simulium dieguerense has been identified from Senegal, Mali and Guinea, in the Western Zone of the World Health Organization/Onchocerciasis Control Programme thus considerably extending its known distribution and indicating the need to reassess its possible importance as a vector of human onchocerciasis. A distribution map based on these identifications has been drawn. Examination of the larval polytene chromosomes revealed the presence of a hitherto unreported sex chromosome system. About 90% of males and 17% of females were found to be heterozygous for an altered segment of the centromere region on chromosome I.