Cutaneous pathology in onchocerciasis associated with pronounced systemic T-helper 2-type responses to Onchocerca volvulus.

BACKGROUND: Of 18 million people world-wide who are infested with the tissue nematode Onchocerca volvulus, more than 30% are considered to have skin lesions, the pathomechanisms of which are poorly understood. OBJECTIVES: To relate skin changes associated with onchocerciasis to parasitological findings and systemic cellular immune responses. METHODS: In the course of a genetic study, 691 members of 241 families exposed to hyperendemic O. volvulus transmission and free of other filarial or schistosomal infestations were studied clinically, by counting palpable Onchocerca nodules and skin microfilariae, by measuring peripheral blood cell (PBC) counts and total serum IgE, and by determining PBC in vitro proliferation and cytokine secretion in response to O. volvulus antigen. RESULTS: Of 691 individuals studied, 219 presented with onchocerciasis-associated skin changes. The groups of individuals with and without skin lesions neither differed in prevalences nor in average numbers of microfilariae. Compared with individuals without skin lesions, pronounced systemic T-helper (Th) 2-type responses were found with a trend of increasing intensity in the order of depigmentation, papular dermatitis, atrophy and lichenified dermatitis. Differences between the groups were most pronounced for serum IgE, less so for eosinophilia, and relatively weak for PBC proliferation and interleukin-5 secretion. CONCLUSIONS: Skin lesions in onchocerciasis are associated with a spectrum of increasing generalized Th2-type responses ranging from low reactivities in cases of depigmentation alone to strong reactivities in cases of lichenification.

Pattern of connexin 26 (GJB2) mutations causing sensorineural hearing impairment in Ghana.

Mutations of the connexin 26 gene (GJB2) were studied in 365 apparently unrelated individuals with profound nonsyndromic, sensorineural hearing impairment from Ghana, West Africa. Among 121 mutated chromosomes found, 110 carried the previously described R143W mutation. A total of 6 novel mutations: L79P, V178A, R184Q, A197S, I203K, and L214P, were identified, whereby I203K was based on a dinucleotide exchange and R184Q appeared to be dominant. The GJB2 variants found in Ghana tend to comprise less nonsense and frameshift mutations and more mutations located in the C-terminal half of the molecule than the variants found in other parts of the world.

Endosymbiotic bacteria in worms as targets for a novel chemotherapy in filariasis.

Endosymbiotic bacteria living in plasmodia or worm parasites are required for the homoeostasis of their host and should be excellent targets for chemotherapy of certain parasitic diseases. We show that targeting of Wolbachia spp bacteria in Onchocerca volvulus filariae by doxycycline leads to sterility of adult worms to an extent not seen with drugs used against onchocerciasis, a leading cause of blindness in African countries.

Malariometric update for the rainforest and savanna of Ashanti region, Ghana.

The epidemiological features of human infection with Plasmodium were studied in a community-based survey of 35 villages in the Ashanti region of Ghana. The overall prevalences of malarial parasitaemia in subjects aged > or = 2 years were 50.72% in forest areas and 49.72% in savanna. Plasmodium falciparum was the predominant species everywhere, followed by P. malariae in the savanna and P. ovale in the forest. The highest prevalence of asexual parasitaemia (of any species) occurred in the youngest age-group (2-9 years). The geometric mean intensities of parasitaemia among the parasitaemic (i.e. the parasite density indices) were 557, 640 and 452 parasites/microliter for P. falciparum, P. ovale and P. malariae, respectively. For each Plasmodium species encountered, the mean intensity of parasitaemia decreased with age. Mixed infections were observed in 24% and 30% of the parasitaemic subjects from the forest and savanna, respectively. Those infected with P. falciparum were more likely to carry P. ovale (odds ratio = 2.02) or P. malariae (odds ratio = 2.63) than those who were not infected with P. falciparum. Mean intensities of the parasitaemias in mixed infections were substantially higher than the sums of those in the corresponding single infections. When comparing villages, parasite density indices were found to be correlated with the prevalences of parasitaemia (r = 0.56).

STD services for women at truck stop in Tanzania: evaluation of acceptable approaches.

AIDS continues to be the commonest cause of death in Tanzania among those aged between 15 and 45 years. Both ulcerative and non-ulcerative sexually transmitted diseases have been identified as major co-factors in HIV transmission. Certain groups including long distance truck drivers and their sexual partners have been reported as having a disporportionate effect on the transmission dynamics of STD including HIV, in a population. In 1993 African Medical and Research Foundation decided to add an STD component to their HIV/AIDS prevention programme along the Tanzania-Zambia highway which had been targeting truck drivers and their sexual partners through peer education and condom distribution since 1989. A study to evaluate the acceptability and feasibility of four different approaches of delivering STD services, was conducted over a period of one year. The approaches for delivering STD services were: special STD services offered twice a week at a site and at hours of the women's choice, special outreach services once every three months, or STD services integrated into the nearest Primary Health Clinic. Drugs were provided at three of the four interventions. 1,330 women at seven truckstops, participated in the evaluation study. The women were generally satisfied with all approaches that included the provision of drugs. The most expensive and ineffective way of treating STD was by not providing drugs. These findings confirm the fact that it is feasible to provide STD services to women at high risk in HIV high transmission areas. These women would utilise STD services provided in a manner that suits them if mobilised and encouraged by their peer educators.

PIP: Long-distance truck drivers and their sexual partners have a disproportionate effect on the transmission dynamics of sexually transmitted diseases (STDs), including HIV infections, in Tanzania. In 1993, the African Medical and Research Foundation added an STD component (peer education and condom distribution) to its HIV/AIDS prevention program along the Tanzania-Zambia highway. The present study of 1330 women (mean age, 27.3 years) recruited from 7 highway truckstops assessed the acceptability and feasibility of 4 approaches to the prevention of STDs: special STD services offered twice a week at a site and hours chosen by women, special clinic-based outreach services for women once every 3 months, integration of STD services into the nearest primary health care clinic, and provision of STD drugs. Most study participants were local brew sellers (47.2%), bar/guest house attendants (27%), and petty traders (21.1%). The overall HIV prevalence was 50%. Attendance per woman was higher when services were offered outside a health facility (1.23) or at times other than normal clinic hours (1.43) than when STD services were integrated with primary health care (1.0). The total cost per patient was US$11 when the clinic did not provide STD drugs, $12 for special clinic-based services for women, $11.50 for non-clinic-based services, and $11 for the integrated STD/primary health care approach. Women were equally satisfied with the 3 service delivery strategies, but highly dissatisfied when STD-specific drugs were not provided and their infection was not cured.

Putative serine/threonine protein kinase expressed in complement-resistant forms of Entamoeba histolytica.

Entamoeba histolytica is susceptible to complement attack in its lumen-dwelling state and develops complement resistance during pathogenic tissue invasion. As experimental evidence suggests that this change in phenotype is accompanied by a change in gene expression, we constructed a subtractive cDNA library to identify genes involved. Poly(A) + RNA from complement-sensitive trophozoites was subtracted from single stranded cDNA derived from complement-resistant ones. Transcripts enriched in the library were found to code for a putative polypeptide comprising all sequence elements characteristic for serine/threonine protein kinases. The gene contains an intron of 46 nucleotides and two polyadenylation sites. Northern-blot analyses confirmed that the gene is expressed in both tissue-derived and laboratory-grown forms of complement-resistant E. histolytica.

Improved method for the concentration and purification of faecal cysts of Entamoeba histolytica for use as antigen.

Human stool samples are the most widely used source of E. histolytica cysts for diagnosis and research. Cysts concentrated from faecal samples are contaminated with faecal debris and bacteria and are unsuitable for use as antigens. Other gradient purification and sedimentation procedures result in considerable cyst losses. We present an effective and simple purification procedure using varying densities of Percoll that yields an adequate cyst concentration from a moderate cyst load in a single stool sample.

Complement resistance of pathogenic Entamoeba histolytica mediated by trypsin-sensitive surface component(s).

Pathogenic forms of the protozoan parasite Entamoeba histolytica were reported previously to resist the cytolytic effect of the alternative complement pathway (AP) only temporarily during exposure to complement. In contrast, nonpathogenic forms of E. histolytica had been found to show AP resistance as a stable property. We studied the mechanisms of AP resistance of the two forms. Upon exposure to AP activity, resistant pathogenic or nonpathogenic forms bound significantly less C3 products than complement-sensitive pathogenic amebae, indicating that the two resistant forms both inhibited AP amplification. Various enzymatic treatments and inhibition of membrane mobility by cytochalasin B and glutaraldehyde fixation showed that the mechanisms of AP inhibition differed between pathogenic and nonpathogenic forms; in contrast to nonpathogenic forms, pathogenic amebae required intact membrane mobility and a trypsin-sensitive surface component(s) to inhibit AP activation.

Induction of complement resistance in cloned pathogenic Entamoeba histolytica.

The lytic effect of complement activated through the alternative pathway (AP) was studied on pathogenic and nonpathogenic Entamoeba histolytica recently isolated from stool samples. Recent nonpathogenic isolates were nearly unaffected by exposure to AP whereas recent pathogenic stool isolates were highly susceptible to AP dependent complement-mediated lysis. Complement susceptible pathogenic stool isolates developed complement resistance in vivo during hamster liver passage and in vitro during cultivation in the presence of increasing concentrations of normal human serum (NHS). Since a clone of pathogenic HM-1:IMSS which initially was highly susceptible also acquired complement resistance during cultivation in the presence of NHS, it is concluded that complement resistance was caused by induction rather than by selection alone. Because cultivation in the presence of heat-inactivated NHS did not affect complement susceptibility of the cloned HM-1:IMSS, complement activation itself might induce complement resistance in pathogenic E. histolytica.

Lysis of pathogenic and nonpathogenic Entamoeba histolytica by human complement: methodological analysis.

The effect of nonimmune human serum on Entamoeba histolytica trophozoites was studied: (a) using whole serum in the presence of Ca and Mg ions allowing complement activation via both the alternative and classical pathways or in the presence of MgEGTA permitting alternative pathway activation only; (b) using different E. histolytica isolates; (c) varying serum and trophozoite concentrations and the time of incubation; and (d) using three different methods to quantify lysis, i.e., microscopic inspection, flow cytometry and 111In release. All three methods yielded similar results, with flow cytometry being most sensitive in identifying membrane damage and 111In release being most valid in determining cell death. Microscopic analysis was reliable only when a chamber was used to calculate the number of complement treated cells in relation to the initial cell count. E. histolytica isolates were classified into three groups according to their susceptibility to lysis by complement: (i) pathogenic isolates after long term cultivation in vitro were susceptible; (ii) pathogenic isolates after recent in vivo passage were less susceptible; and (iii) nonpathogenic isolates were nearly unaffected by exposure to the alternative pathway alone. The extent of lysis of the various isolates correlated with the degree of complement consumption in the serum samples, suggesting that unlysed isolates did not activate complement under the conditions employed. In general, lysis of susceptible trophozoites increased with the serum concentration and with the time of incubation. However, when the trophozoite concentration was 10(6)/ml or higher, lysis no longer reflected complement susceptibility because of exhaustion of the complement supply.