Biomedical subjects

B A Boatin

Publications and source records attributed to B A Boatin.

At least 19 recordsLinked to original sources

PubMed2004

Association between microfilarial load and excess mortality in onchocerciasis: an epidemiological study.

BACKGROUND: Infection with the parasitic filarial nematode Onchocerca volvulus can lead to severe visual impairment and ultimately blindness. Excess mortality has been noted among people with onchocerciasis, but it is not clear whether this effect is entirely due to blindness, or mediated by some more direct effects of the infection. METHODS: We assessed the relations between infection with O volvulus, visual acuity, and host mortality with data obtained by the Onchocerciasis Control Programme in West Africa from 2315 villages in 11 countries. FINDINGS: 297,756 people were eligible for follow-up, and accumulated 2,579449 person-years of follow-up from 1971 through 2001. 24,517 people died during this period; 1283 (5.2%) of these deaths were due to onchocerciasis. Mortality of the human host was significantly and positively associated with increasing microfilarial burden (p<0.00001), but not with blindness after adjustment for microfilarial load and other variables. Overall, after adjustment for microfilarial load and other variables, female individuals had a risk of death about 7.5% lower than males (p<0.00001). Rates of mortality peaked in the mid 1980s but generally decreased thereafter. INTERPRETATION: We have shown a direct relation between O volvulus microfilarial load and host mortality in a comprehensive dataset and in both sexes.

Adolescent↗

PubMed2004

An investigation of persistent microfilaridermias despite multiple treatments with ivermectin, in two onchocerciasis-endemic foci in Ghana.

If ivermectin-based programmes for the control of human onchocerciasis are to be successful, the drug must remain effective for as long as necessary. In an open, case-control study, an attempt was made to determine if the persistent, significant, Onchocerca volvulus microfilaridermias seen in some individuals who had received at least nine treatments with ivermectin were the result of the development of drug resistance in the parasite. Twenty-one of these 'sub-optimal' responders (cases) were matched, by age, weight, number of treatments, locality and skin microfilarial counts, with seven amicrofilaridermic responders and 14 ivermectin-naive subjects. The number of treatments taken, any potential drug interactions and significant underlying disease were determined from detailed clinical and laboratory studies. Each subject was treated with ivermectin during the study, so that plasma concentrations of the drug could be determined for 72 h from the time of dosage. The microfilarial and adult-worm responses to this treatment were assessed from skin microfilarial counts (obtained before the treatment and at days 8, 90 and 365 post-treatment), day-90 embryogrammes, and the results of fly-feeding experiments. Parasite-sensitivity criteria for various time-points were derived from earlier data on skin microfilaridermias and the effects of ivermectin on the adult worms. The results indicate that the significant microfilaridermias that persist despite multiple treatments with ivermectin are mainly attributable to the non-response of the adult female worms and not to inadequate drug exposure or other factors. The possibility that some adult female worms have developed resistance to ivermectin cannot be excluded. These results justify the routine monitoring of treatment efficacy in any ivermectin-based programme of disease control.

Adolescent↗

PubMed2004

Thirty-month follow-up of sub-optimal responders to multiple treatments with ivermectin, in two onchocerciasis-endemic foci in Ghana.

The pathogenesis of the sub-optimal response of Onchocerca volvulus to ivermectin was investigated in a 30-month follow-up of 28 individuals who, in a previous study, had been found to show a sub-optimal (N = 15) or adequate response (N = 13) to multiple treatments with the drug. Verbal informed consent was obtained before each subject was given a general clinical and ocular examination. Skin snips were taken from both iliac crests and both calves. Seventeen nodule carriers were hospitalized for nodulectomy. Adult worms were harvested, embryogrammes were constructed and all developmental stages were counted; degenerate, stretched microfilariae were noted separately. All the subjects were in good general health and all except one had received at least one additional treatment with ivermectin since the earlier study. A large proportion of the adult female worms in 10 out of the 11 sub-optimal responders who were nodule carriers were in full embryonic production but most of the stretched microfilariae they carried were degenerate. This picture is similar to that found in adult worms exposed to the first dose of ivermectin. In one subject who had no viable worms in his nodules, the existence of occult but actively reproductive worms was inferred from the high level of microfilaridermia observed less than 12 months after treatment. These observations confirm the existence of populations of adult female O. volvulus that respond poorly to repeated doses of ivermectin. The use of suramin in the treatment of the sub-optimal responders is discussed.

Adult↗

PubMed2003

Y chromosome STR haplotypes and the genetic structure of U.S. populations of African, European, and Hispanic ancestry.

To investigate geographic structure within U.S. ethnic populations, we analyzed 1705 haplotypes on the basis of 9 short tandem repeat (STR) loci on the Y-chromosome from 9-11 groups each of African-Americans, European-Americans, and Hispanics. There were no significant differences in the distribution of Y-STR haplotypes among African-American groups, whereas European-American and Hispanic groups did exhibit significant geographic heterogeneity. However, the significant heterogeneity resulted from one sample; removal of that sample in each case eliminated the significant heterogeneity. Multidimensional scaling analysis of R(ST) values indicated that African-American groups formed a distinct cluster, whereas there was some intermingling of European-American and Hispanic groups. MtDNA data exist for many of these same groups; estimates of the European-American genetic contribution to the African-American gene pool were 27.5%-33.6% for the Y-STR haplotypes and 9%-15.4% for the mtDNA types. The lack of significant geographic heterogeneity among Y-STR and mtDNA haplotypes in U.S ethnic groups means that forensic DNA databases do not need to be constructed for separate geographic regions of the U.S. Moreover, absence of significant geographic heterogeneity for these two loci means that regional variation in disease susceptibility within ethnic groups is more likely to reflect cultural/environmental factors, rather than any underlying genetic heterogeneity.

Africa↗

PubMed2002

Can ivermectin mass treatments eliminate onchocerciasis in Africa?

OBJECTIVE: To elucidate the conditions in which mass treatment with ivermectin reduces the transmission of Onchocerca volvulus sufficiently to eliminate infection from an African community. METHODS: ONCHOSIM, a microsimulation model for onchocerciasis transmission, was used to explore the implications of different treatment intervals, coverage levels and precontrol endemicities for the likelihood of elimination. FINDINGS: Simulations suggested that control strategies based exclusively on ivermectin mass treatments could eliminate onchocerciasis. The duration of treatment required to eliminate infection depended heavily on the treatment programme and precontrol endemicity. In areas with medium to high levels of infection, annual mass treatments with 65% coverage for at least 25 years were necessary. Model predictions suggested that durations exceeding 35 years would be required if there were much heterogeneity in exposure to vector bites and, consequently, wide individual variation in microfilaria counts. If the treatment interval were reduced from 12 to 6 months the time for completion of the programme could be more than halved and elimination could be accomplished in areas of hyperendemicity, provided that the effects of each treatment would be the same as with annual treatments. However, it was doubtful whether high coverage levels could be sustained long enough to achieve worldwide eradication. CONCLUSION: Elimination of onchocerciasis from most endemic foci in Africa appears to be possible. However, the requirements in terms of duration, coverage, and frequency of treatment may be prohibitive in highly endemic areas.

Africa↗

PubMed2002

Detection of Onchocerca volvulus infection in low prevalence areas: a comparison of three diagnostic methods.

The standard assay for onchocerciasis diagnosis is microscopical detection of microfilariae in skin snips. Skin snipping is painful, requires appropriate sterilization of equipment, and may fail to diagnose light infections. Two alternatives are a polymerase chain reaction (PCR) test which detects parasite DNA in pieces or scrapings of skin and a test based on allergic reactions to topical application of diethylcarbamazine (DEC). We compared these 2 diagnostics with standard skin snip microscopy in 313 individuals from 2 villages in Guinea, with low prevalence after over 10 years of control by the Onchocerciasis Control Programme. Lower and upper bounds on sensitivities and specificities of these 3 tests were estimated. In addition, these parameters were estimated using 5 different statistical models. Where prevalence was low, PCR and the DEC patch test appeared to be more sensitive than skin snipping which has low sensitivity. As the DEC test is non-invasive, simple and cheap, it may provide a good alternative to skin snipping alone for surveillance in low prevalence areas.

Adolescent↗

PubMed2001

Macrofilaricides and onchocerciasis control, mathematical modelling of the prospects for elimination.

BACKGROUND: In most endemic parts of the world, onchocerciasis (river blindness) control relies, or will soon rely, exclusively on mass treatment with the microfilaricide ivermectin. Worldwide eradication of the parasite by means of this drug is unlikely. Macrofilaricidal drugs are currently being developed for human use. METHODS: We used ONCHOSIM, a microsimulation mathematical model of the dynamics of onchocerciasis transmission, to explore the potentials of a hypothetical macrofilaricidal drug for the elimination of onchocerciasis under different epidemiological conditions, as characterized by previous intervention strategies, vectorial capacity and levels of coverage. RESULTS: With a high vector biting rate and poor coverage, a very effective macrofilaricide would appear to have a substantially higher potential for achieving elimination of the parasite than does ivermectin. CONCLUSIONS: Macrofilaricides have a substantially higher potential for achieving onchocerciasis elimination than ivermectin, but high coverage levels are still key. When these drugs become available, onchocerciasis elimination strategies should be reconsidered. In view of the impact of control efforts preceding the introduction of macrofilaricides on the success of elimination, it is important to sustain current control efforts.

Animals↗

PubMed2001

Eliminating onchocerciasis after 14 years of vector control: a proved strategy.

From 1976 through 1989, weekly aerial spraying operations against blackflies were carried out along the rivers of a wide savanna area of West Africa (approximately 700,000 km(2)) where onchocerciasis was hyperendemic. The level of endemicity began to decrease significantly after 4 years of vector control and became very low in 1989. This situation has been maintained without any vector control activity or chemotherapy, and no incidence of any new cases has been detected. An ophthalmological study carried out in 2000 has confirmed these good results, showing only cicatricial ocular lesions in the examined population. These results led to the conclusion that 14 years of vector control may achieve long-term elimination of onchocerciasis, even in the absence of chemotherapy, provided that the treated areas are not subjected to any contamination by exogenous parasites carried in infected humans or flies.

Adult↗

PubMed2000

Chemokine RANTES promoter polymorphism affects risk of both HIV infection and disease progression in the Multicenter AIDS Cohort Study.

OBJECTIVE: To examine whether polymorphism in the RANTES gene is associated with HIV disease outcome. DESIGN: RANTES, a ligand of the major HIV co-receptor, CCR5, is known to block HIV-CCR5 interactions. Recently, two single nucleotide polymorphisms in the RANTES gene promoter region, designated -403G/A and -28C/G, have been described. Both polymorphisms can affect in-vitro promoter activity, and the RANTES -403A, -28G haplotype has been associated with a slower CD4 cell count decline rate in a Japanese cohort. METHODS: We compared RANTES compound genotype frequencies between HIV-positive and exposed-uninfected participants of the Multicenter AIDS Cohort Study (MACS) and rates of progression to AIDS for MACS seroconverters. RESULTS: We found that the two most common RANTES promoter compound genotypes, G1 (-403G/G, -28C/C) found in 67% of Caucasians, and G4 (-403G/A, -28C/C) found in 23% of Caucasians, were associated with altered risk of HIV transmission and progression, particularly in individuals who lacked the protective CCR5 mutation, CCR5delta32. In this study, individuals with a G4 compound genotype were more likely to acquire HIV than individuals with a G1 compound genotype (OR 1.72, P = 0.016) and the risk increased when individuals possessing CCR5delta32 were omitted from consideration (OR 2.13, P = 0.005). Among seroconverters lacking CCR5delta32, those who had the G4 compound genotype progressed significantly slower to AIDS-1993 than those with the G1 compound genotype (median time to AIDS 7.6 versus 5.4 years; RH 0.65; P = 0.007). CONCLUSIONS: These data implicate the RANTES-403A allele as a risk factor for HIV transmission and as a protective factor for HIV progression.

Acquired Immunodeficiency Syndrome↗

PubMed1999

Emergence of FY*A(null) in a Plasmodium vivax-endemic region of Papua New Guinea.

In Papua New Guinea (PNG), numerous blood group polymorphisms and hemoglobinopathies characterize the human population. Human genetic polymorphisms of this nature are common in malarious regions, and all four human malaria parasites are holoendemic below 1500 meters in PNG. At this elevation, a prominent condition characterizing Melanesians is alpha(+)-thalassemia. Interestingly, recent epidemiological surveys have demonstrated that alpha(+)-thalassemia is associated with increased susceptibility to uncomplicated malaria among young children. It is further proposed that alpha(+)-thalassemia may facilitate so-called "benign" Plasmodium vivax infection to act later in life as a "natural vaccine" against severe Plasmodium falciparum malaria. Here, in a P. vivax-endemic region of PNG where the resident Abelam-speaking population is characterized by a frequency of alpha(+)-thalassemia >/=0.98, we have discovered the mutation responsible for erythrocyte Duffy antigen-negativity (Fy[a-b-]) on the FY*A allele. In this study population there were 23 heterozygous and no homozygous individuals bearing this new allele (allele frequency, 23/1062 = 0.022). Flow cytometric analysis illustrated a 2-fold difference in erythroid-specific Fy-antigen expression between heterozygous (FY*A/FY*A(null)) and homozygous (FY*A/FY*A) individuals, suggesting a gene-dosage effect. In further comparisons, we observed a higher prevalence of P. vivax infection in FY*A/FY*A (83/508 = 0.163) compared with FY*A/FY*A(null) (2/23 = 0.087) individuals (odds ratio = 2.05, 95% confidence interval = 0.47-8.91). Emergence of FY*A(null) in this population suggests that P. vivax is involved in selection of this erythroid polymorphism. This mutation would ultimately compromise alpha(+)-thalassemia/P. vivax-mediated protection against severe P. falciparum malaria.

Animals↗

PubMed1999

Eotaxin expression in Onchocerca volvulus-induced dermatitis after topical application of diethylcarbamazine.

In persons with onchocerciasis, topical application of the anthelminthic diethylcarbamazine (DEC) induces clinical and histologic responses similar to acute papular onchodermatitis, including recruitment of eosinophils to the skin. To determine whether the eosinophil chemokine eotaxin is likely to be associated with eosinophil recruitment in onchodermatitis, DEC was applied to a 5-cm2 area on the skin of infected persons, and biopsies were taken from lesions 24 h later. Histologic analysis showed elevated dermal and epidermal eosinophils compared with tissue from an adjacent (untreated) site. Reverse transcription-polymerase chain reaction showed that eotaxin gene expression in DEC-treated skin was elevated 2- to 17-fold compared with control tissue. Eotaxin immunoreactivity was noted in mononuclear cells and eosinophils in the perivascular region of the dermis and in lymphatic and vascular endothelial cells. Together, these observations are consistent with a role for eotaxin in recruitment of eosinophils to the dermis in early stage onchocercal skin disease.

Administration, Topical↗

PubMed1999

Pool screen polymerase chain reaction for estimating the prevalence of Onchocerca volvulus infection in Simulium damnosum sensu lato: results of a field trial in an area subject to successful vector control.

Detection of infective parasites in the vector population can be an early indicator of recrudescence in areas freed of new cases of onchocerciasis. However, dissection of vector black flies is inefficient in areas subject to effective control. Recently, a polymerase chain reaction (PCR)-based assay has been used to detect a single Onchocerca volvulus-infected black fly in pools containing large numbers of uninfected flies. This method had not been validated on wild-caught black flies in an area subject to effective vector control. Here, we report a method of restricting the pool screen PCR assay to infectious parasites and the results of a field test in an area subject to long-term vector control. The prevalence of infection determined by dissection did not differ from that determined by pool screen PCR. The results suggest that the PCR assay may be a useful tool for epidemiologic surveillance for 0. volvulus infection.

Animals↗

PubMed1998

Detection of Onchocerca volvulus infection by O-150 polymerase chain reaction analysis of skin scratches.

The standard assay for onchocerciasis diagnosis is microscopic detection of parasites in skin snips. Skin snipping is painful and may potentially transmit bloodborne infections. Thus, an alternative method for the diagnosis of onchocerciasis that does not require skin snipping is needed. A polymerase chain reaction (PCR)-based assay was shown to detect the presence of parasite DNA in superficial skin scrapings. Detection of parasite DNA in both skin snips and skin scratches was found to be more sensitive for detecting low-density infections than was microscopic examination of skin snips. The skin scratch PCR assay is minimally invasive and painless and does not present the risk of transmitting bloodborne infections. These properties make the skin scratch an attractive alternative to the skin snip for detecting O. volvulus infection.

Adolescent↗

PubMed1998

Three new DP alleles identified in sub-Saharan Africa: DPB17401, DPA102013, and DPA1*0302.

HLA-DP genotyping of over 400 individuals from sub-Saharan Africa identified three new DP alleles: DPB1*7401, DPA1*02013, and DPA1*0302. DNA sequencing confirmed that DPB1*7401, found in one individual, is a novel combination of previously described sequence motifs in the six variable regions of DPB1. DPA1*02013, found in one individual, is identical to DPA1*02012 except for two silent substitutions, a T to C transition in codon 37, and an A to G transition in codon 38. DPA1*0302, identified in seven individuals, is identical to DPA1*0301 except for a C to T transition at the second position of codon 66. The identification of these novel alleles brings the total number of reported DPB1 alleles to 77 and DPA1 alleles to 11.

Africa South of the Sahara↗

PubMed1998

Delivery systems and cost recovery in Mectizan treatment for onchocerciasis.

The efficiency of on-going delivery systems and cost recovery in Mectizan (ivermectin, MSD) treatment for onchocerciasis are reviewed. The search is on for an effective system of Mectizan delivery, involving drug procurement, delivery from port to districts and distribution to eligible persons, which can be sustained by the endemic countries for many years. The mechanisms for procuring and clearing the drug at the ports, and the drug's integration into the existing delivery systems of each national health service, need to be improved. Although large-scale treatments by mobile teams or community-based methods evidently achieve high and satisfactory rates of coverage, they also incur high recurrent costs which have to be covered by external partners and are not sustainable by national health services. Cost-sharing is considered an important factor in a sustainable delivery system and community-directed treatment, in which the community shares the cost and ownership of local distribution and is empowered to design and implement it, is likely to be more cost-effective and sustainable.

Africa↗

PubMed1998

Diagnostics in onchocerciasis: future challenges.

The classical method of determining the prevalence and intensity of onchocercal infection is by the demonstration and counting of microfilariae in biopsies obtained by skin snipping. Although very specific, this technique is inadequate for detecting early, light or prepatent infections, and is also becoming increasingly unacceptable to the populations investigated. The prolonged clearing effect that Mectizan (ivermectin, MSD) treatment has on skin microfilariae also renders the skin-snip method of diagnosis less appropriate in areas with Mectizan treatment. Given all these factors, the greater challenge in the area of diagnostics for onchocerciasis is to develop a less invasive, adequately sensitive, and equally specific diagnostic test, either to replace or to be an adjunct to the present skin-snip method. This challenge is being addressed, with at least three new diagnostic tests for onchocerciasis under development: an immunological assay, based on a three-antigen cocktail; a PCR-based assay, which may also be used for 'pool screening' of blackflies; and the diethylcarbamazine (DEC) patch test. Of all these tests, the DEC patch test seems to fit best the criteria of an ideal test. The PCR assay would be better than the patch test if the cost of using it could be reduced substantially.

Animals↗

PubMed1998

The impact of Mectizan on the transmission of onchocerciasis.

For many years there was no suitable drug available for the control of onchocerciasis. The advent of Mectizan (ivermectin, MSD; an effective microfilaricide), its registration in October 1987 for the treatment of human onchocerciasis, and its suitability for large-scale application were major break-throughs in the control of human onchocerciasis via chemotherapy. Several studies, both fly-feeding experiments and community trials, have established that Mectizan treatment causes a significant reduction in the transmission of infection. Although long-term treatment in some isolated foci (such as occur in the New World and in some hypo- and meso-endemic areas elsewhere) appears to interrupt transmission, more prolonged treatment is required to prove if transmission can be stopped. Advantage could be taken of the significant impact of Mectizan on transmission by giving treatment while or just before transmission by blackflies is most intense.

Africa, Western↗

PubMed1997

The diverse expression of immunity in humans at distinct states of Onchocerca volvulus infection.

This study examined the development and persistence of immunity in humans presenting defined states of Onchocerca volvulus infection, i.e. in exposed endemic control individuals without microfilaridermia and clinical disease, in patients with patent or post-patent onchocerciasis, and in patients concurrently infected with Mansonella perstans. Onchocerca volvulus antigen (OvAg)-specific cellular reactivity was significantly diminished in microfilariae (mf)-positive patients, while the highest reactivity was measured in exposed but mf-negative endemic controls, those being free of any clinical signs of onchocercal disease. In patients who became post-patent, responses to OvAg were significantly augmented, but did not approach entirely the magnitude observed in endemic controls. In onchocerciasis patients with concurrent mansonelliasis, cellular unresponsiveness to OvAg persisted, even when mf of O. volvulus were eliminated permanently by repeated ivermectin therapy. Cells from mf-positive onchocerciasis patients produced significantly less interferon-gamma (IFN-gamma) (P < 0.01) and interleukin-5 (IL-5) (P < 0.05) in response to OvAg than those taken from endemic controls or post-patent individuals in whom IFN-gamma and IL-5 production was similarly high. In contrast, both OvAg-driven as well as spontaneous IL-10 secretion was higher in mf-positive patients than in endemic controls or post-patent cases. In all individuals examined, serological recognition of OvAg by immunoglobulins was dominated by IgG4; in mf-positive patients OvAg of 205,000-12,000 molecular weight (MW) were strongly bound. In post-patent individuals, and similarly in endemic controls. OvAg recognition by IgG4 varied from intense (with numerous antigens being recognized) to weak or absent antigen binding. Significantly elevated OvAg-specific IgG isotypes were measured in mf-positive onchocerciasis patients in comparison with endemic controls or post-patent individuals (with the exception of IgG3). IgG1, IgG2 and IgE were higher, but IgG4 was lower in endemic controls compared with post-patent onchocerciasis patients. The ratios of IgG4/IgG1 differed (P < 0.001) between endemic controls and mf-positive or post-patent onchocerciasis patients, with IgG4/IgG1 ratios of R < 3.0 being characteristic for endemic controls and post-patent O. volvulus infection. In conclusion, this cross-sectional immunoepidemiological investigation showed that distinct states of O. volvulus infection correlate with a particular cellular and humoral immune response. The mf-free condition appeared to be associated with a vigorous parasite-specific cellular reactivity and a particular cytokine production profile, while concurrent M. perstans infection depressed OvAg-specific cellular responsiveness. Antibody responses, in all likelihood, reflected the intensity and state of infection, and not the degree of acquired immunity protective against parasite aggregation.

Adolescent↗