Dissertations / Theses on the topic 'Onchocerciasis'

<p>Onchocerciasis, or river blindness, is a parasitic disease that affects more than 20 million people globally. The induction of pathology is directly related to the presence and destruction of the microfilarial stages (mf) of this filarial nematode. The disease presents clinically with a wide spectrum of dermal and ocular manifestations, the basis of the variation is believed to involve the immune system. The clinical presentations of infected hosts relate to the intensity of the reactions against the parasite. Anti-microfilarial drugs are also thought to somehow involve the immune system in their pharmacological action. In this study we have investigated some of the factors that might contribute to the pathogenesis, with the aim of gaining a better understanding of the role of immune response in these host inflammatory reactions to <i>Onchocerca volvulus</i> parasite. In the first study we have highlighted the clinically most severe form of dermal onchocerciasis, known as reactive onchocercal dermatitis (ROD), one that is often ignored and has not been properly identified. This form has special characteristics and important biological information that could greatly assist the general understanding of the disease as a whole. Amongst the three major foci of the disease in the study country, Sudan, the prevalence of ROD was found to be associated with different environmental and epidemiological characteristics; strikingly higher in the hypo-endemic areas. Including ROD cases in the prevalence will upgrade the level of endemicity of a locality, and often bring patients much in need of treatment into mass treatment programs that currently only treat localities with medium to high levels of endemicity. In the following research studies, we tried to address the immunological characteristics of the clinically different onchocerciasis patients. Then we also investigated the role of genetic polymorphism in the gene encoding receptor that links innate and adaptive immunity, namely, FcγRIIa.</p><p>Patients with either of two major forms of the clinical spectrum-mild and severe dermatopathology were studied by assaying the antigen-driven proliferation of peripheral blood mononuclear cells and the ability of patients’ serum antibodies to promote cytoadherence activity to mf <i>in vitro</i>. Immune responses of those with severe skin disease were found to be stronger compared with the mild dermatopathology group. Mectizan® treatment was followed by an increase in immune responsiveness in those with initially poor responses. Thus the degree of dermatopathology is related to the host’s immune response against mf and immunocompetence may be necessary for Mectizan® to clear the infection efficiently.</p><p>The infection has also been associated with increased levels of circulating immune complexes (CIC) containing parasite antigens and a cytokine response that involves both pro-and anti-inflammatory cytokines. Our fourth paper investigated the effect of IC from the <i>O. volvulus</i> infected patients on the production of pro-and anti-inflammatory cytokines. CIC were increased in all patients studied. The precipitate from plasma treated with polyethylene glycol (PEG) were added to peripheral blood mononuclear cell (PBMC) cultures, and the levels of IL-10, tumor necrosis factor TNF-α, IL-1β and their endogenous antagonists soluble TNF-Rp75 and IL-1-receptor antagonist (IL-1ra) were measured. A significant induction of all cytokines measured occurred in the onchocerciasis patients compared to healthy controls. However, the IL-1ra level was suppressed. The suppression of the production of IL-1ra suggests that the IC containing antigens may have a selectively suppressive effect on the production of this anti-inflammatory cytokine; thus implicating its possible role in counteracting inflammatory responses associated with the disease, and suggesting a potential therapeutic significance. </p><p>FcgRIIa receptors are involved in many important biological responses, and considered as important mediators of inflammation. A polymorphism in the gene encoding this receptor, that is either arginine (R) or histidine (H) at position 131, affects the binding to the different IgG subclasses. We therefore hypothesized that this polymorphism might be one of the underlying mechanisms to the varied clinical presentations seen in this disease. FcgRIIa genotyping was carried out by gene specific polymerase chain reaction (PCR) and allele-specific restriction enzyme digestion of DNA from clinically characterized patients. The genotype R/R frequencies were found to be significantly higher among patients with the severe form of the disease (including ROD), and it was particularly associated with one tribe (Masaleet) compared to Fulani. Moreover, the H allele was found to be associated with lower risk of developing the severe form. As no significant difference was seen between onchocerciasis cases and controls, the study also implies that this polymorphism influences protection from developing the severe form rather than being related to protection from the infection. </p>

Onchocerciasis, commonly known as "River blindness" is a disease affecting over 37 million people, worldwide. It is caused by the parasitic nematode Onchocerca volvulus and transmitted by the blackfly vector of the genus Simulium. The drug ivermectin (IVM) is the principal means of controlling the disease. As a result of recent reports on sub-optimal response to ivermectin and genetic selection in O. volvulus, we carried out a 21 month epidemiological study to investigate the response of O. volvulus to repeated rounds of IVM treatments in 2501 subjects from 19 Ghanaian communities that have received between 6 and 18 annual treatments and one IVM naive community. Skin microfilaria (mt) assessments were done before IVM treatment and at days 30, 90, 180 and 364 post-IVM treatment. At day 90 after the second IVM treatment, nodulectomies were carried out on 140 patients and embryogrammes constructed on female worms. We found IVM is still an effective microfilaricide, with efficacy of 98-100%. However, its effect on adult worm fertility has been reduced. Day 90 and 180 post-treatment showed significantly higher (p&lt;0.05) skin mf repopulation of 7.1% to 53.9%, and >100% of pretreatment counts at day 364 post-treatment in four communities compared with the other six communities, which had &lt;80% of pretreatment mf counts on day 364. From these results we classified the 10 communities into good IVM response (four communities), intermediate IVM response (two communities), poor IVM response (three communities), and the previously IVM naive community. Nodule and worm viability and worm densities were significantly higher (p&lt;0.05) in the poor response communities compared with the good response communities, with the intermediate falling between the two. Embryogramme analysis showed significantly higher reproductive activity and output in worms from poor response communities with up to 41% of females having live stretched mf in utero compared with good response communities which had no intra-uterine stretched mf. These results show evidence of lack of sustained response of adult O. volvulus to IVM in the poor response communities, manifested as a rapid return to fertility after IVM treatment. We conclude that IVM resistance is emerging in onchocerciasis and is manifested as a loss of effect of IVM on suppression of parasite reproduction.<br>Beta tubulin isotype 1 gene has been shown to be linked to IVM treatment and selection in O. volvulus and veterinary nematodes. Genetic analysis of the full length genomic DNA sequence of beta-tubulin from worms obtained in the three IVM response categories and IVM naive community showed single nucleotide polymorphisms (SNPs) at 24 sites on the entire 3696 bp. The frequencies of eight SNPs were significantly different (p&lt; 0.05) between the poor response communities and the good response/naive communities. Four SNPs, 183 T/G, 1188 T/C, 1309 CIT and 1545 A/G resulting in a genotype configuration GG/CC/TT/GG (183/1188/1309/1545) was significantly higher in the poor IVM response communities than the other communities. The phenotypic and genotypic analyses are consistent with a conclusion that IVM resistance has been selected. These four SNPs could be used to develop a genetic marker for early detection of IVM resistance. This study has shown for the first time that IVM resistance is emerging in Onchocerca volvulus and that there are genetic changes associated with IVM resistance which could be used for epidemiological monitoring for emerging resistance.

Lymphatic filariasis (LF) and onchocerciasis are highly endemic in Sierra Leone. Using World Health Organization (WHO) guidelines for monitoring national programmes where both infections are co-endemic, this study aimed to determine the impact of preventive chemotherapy on transmission intensity by measuring changes in human infection status using standard epidemiological indicators. Separate longitudinal studies designed to deliver WHO outcomes for programmes targeting the elimination of both diseases were conducted. Onchocerciasis mapping surveys from 1988-2005 revealed that twelve of fourteen health districts were endemic. The baseline average mf prevalence was 53.1%, and mf densities in positive-only or entire populations were 28.87 and 15.33 mf/snip, respectively. Mf prevalence and density increased with age and was higher in males than females. Baseline prevalence and intensity surveys showed that LF was endemic in all 14 districts (Wuchereria bancrofti antigenaemia prevalence > 1%). Mean LF prevalence by ICT cards was 21% (males 28%; females 15%) with higher prevalence in the northeast (Bombali 52%; Koinadugu 46%; Tonkolili 37%; Kono 30%) and lower in the southwest (Bonthe 3%; Pujehun 4%). Mf prevalence was also relatively higher in the northeast (Bombali 6.7%; Koinadugu 5.7%; Port Loko 4.4%; Kono 2.4%). Mf prevalence was higher in males (males 2.9%; females 1.8%) and infection rate was higher in the over 20 years age-group (2.5%) than younger (1.7%). Arithmetic mean mf density was 50.30 mf/ml among mf-positive individuals and 1.19 mf/ml in the population examined. Nationwide mass drug administration (MDA) using ivermectin plus albendazole was applied to eliminate both diseases. In 2010, after five rounds of MDA (2005-2009) with effective treatment coverage for onchocerciasis during 4/5 years, overall onchocerciasis mf prevalence was reduced by 60.26% (from 53.10% to 21.10%), overall mf density among positive-only individuals was reduced by 71.29% (28.87 to 8.29 mf/snip) and overall mf density among the entire population studied was reduced by 88.58% (15.33 to 1.75 mf/snip). Mf prevalence and density were higher in males, lowest in the 1-9 and highest in the 40-49 year age groups. Mf prevalence was reduced by >50% in 10/12 districts, and reduction in skin mf density was ≥50% among positives-only in 11/12 districts. After MDAs with effective treatment coverage in 2008-2010, LF mf prevalence decreased to less than 1% in 11/12 districts. Mf prevalence fell by 88.5% to 0.3%, with decreases of 70-95% in seven and 100% (0 prevalence) in four districts, respectively. Overall arithmetic mean mf density after three MDAs was 17.59 mf/ml among mf positive individuals and 0.05 mf/ml for the entire population examined. After five MDAs, the overall mf prevalence was 0.54% and was higher in males (0.7%) than females (0.36%). Eight of twelve districts with < 1% mf prevalence passed the pre-transmission assessment survey (TAS) and therefore qualified for a TAS to determine whether MDA could be stopped. Four districts failed the pre-TAS: Koinadugu (0.98% i.e. close to 1%), Bombali (2.67%), Kailahun (1.56%) and Kenema (0%). Following WHO recommendations, Kenema and Kailahun districts were paired to form a unit of approximately one million. Kenema, the spot check site, was considered to have failed the pre-TAS even though the mf prevalence was 0% because Kailahun, the sentinel site, failed. A qualitative study examining the impact of the Ebola virus disease (EVD) outbreak on the NTD programme found that despite a one-year absence of interventions, two rounds of MDA had been completed, including one during the ongoing outbreak in May/June 2015. Although it compromised the likelihood of achieving the 2020 targets of LF elimination and Onchocerciasis control, the EVD outbreak has enhanced awareness about the important role of community volunteers in ensuring its success. While it may be the ‘endgame’ for LF, the NTD community and collaborating research institutions must address additional challenges if Onchocerciasis is to be eliminated from Sierra Leone.

Onchocerciasis, caused by Onchocerca volvulus remains a major public health and socio-economic problem across the tropics, despite years of mass drug administration (MDA) with Ivermectin to reduce disease burden. Through modelling, it has been shown that elimination cannot be achieved with MDA alone and additional tools are needed, such as vaccination, which remains the most cost-effective tool for long-term disease control. The feasibility behind vaccination against O. volvulus can be demonstrated in the Litomosoides sigmodontis mouse model, which shows that vaccine induced protection can be achieved with immunisation using irradiated L3, the infective stage of L. sigmodontis and with microfilariae (Mf), the transmission stage of the parasite. There is further evidence of protective immunity in humans, with individuals living in endemic areas that show no signs of infection despite being exposed to the parasite (endemic normal). The protective efficacy of promising vaccine candidates were evaluated using an immunisation time course in the L. sigmodontis model, using either DNA plasmid or peptide vaccines. In immunisation experiments in L. sigmodontis, Mf numbers are used as a measure of protection and marks the end of an immunisation time course. However, when changes in gene expression were measured at the end of an immunisation time course, in attempts to identify gene signatures that could be used as markers of protection (correlates of protection) in the blood, no gene signatures were found to be associated with protection. This suggest that at the end of an immunisation time course, when protection is measured (change in Mf numbers), it is too late in infection to measure changes in immune pathways being triggered. Changes in gene expression were therefore measured in blood samples collected throughout an immunisation time course in the L. sigmodontis model, in order to identify the time point in an immunisation experiment which are the most indicative of protection. Two independent immunisation time courses were used, either using irradiated L3 or Mf as vaccine against L. sigmodontis, as these elicit the greatest protection. This generated a large high dimensional dataset, that was too large and complex for a differential fold-change analysis. Therefore, an analysis pipeline was created using machine learning algorithms, to detect changes in gene expression throughout the time courses to detect markers of protection. The 6 hour time point following immunisation showed the greatest change in gene expression, with the analysis pipeline identifying known pathways associated with vaccine-induced immunity. The pipeline was applied to gene expression data from human samples obtained from individuals living in endemic areas who were either infected with O. volvulus or endemic normal (naturally protected), this was to identify pathways associated with protective immunity in humans. When comparing vaccine induced immunity seen in mice and natural protective immunity in humans there was some overlap in pathways being triggered, suggesting that similar pathways are needed for protection and that if a vaccine can trigger the right pathways in mice, it is likely to be effective in humans. Overall the machine learning analysis of the gene expression data, not only shows that it is feasible to measure change in gene expression in blood during filarial infections, but that during an immunisation time course it is the early time points following immunisation that are the most predictive of vaccine efficacy (protection outcome). One of the vaccine candidates, cysteine protease inhibitor-2 (CPI), is a known immuno-modulator that inhibits MHC-II antigen presentation on antigen presenting cells such as dendritic cells (DC). This candidate has consistently been shown to induce protection if its immuno-modulatory active site was modified. In in vitro studies, it was shown that modification of the active site of CPI rescues antigen presentation in DC. This shows the importance of DC activation before the onset of infection, demonstrating the importance of triggering protective responses early in infection, and provides insight on how one of the vaccine candidates achieves protection.

The work represented in this thesis covers three areas: the pathogenesis and immunobiology of nematode infections, the control and elimination of filarial nematode diseases, and lastly contributions to experimental and diagnostic pathology involving different diseases and medical conditions. A number of fundamental concepts are addressed: the role of eosinophil leucocytes in directly killing certain stages of helminths, acting in conjunction with antibodies and complement; the clinical significance of cell mediated immune responses in human onchocerciasis and its relationship to the clinical variation seen in this disease, including the classification of onchodermatitis in humans. The studies in chemotherapy focus not only understanding the pathological effects of chemotherapy in filariasis, but also on understanding the mechanisms of action of these anthelminthic drugs and the role of the host in their action; the function and action of two major anti-filarial agents, diethylcarbamazine and ivermectin, are now understood from this work. The more recent studies describe work towards developing more effective and safer anti-filarial drugs, with flubendazole being a major focus. A central theme of the research is translating laboratory work into field relevance in the diseases that cause significant morbidity in animals and humans, namely onchocerciasis, lymphatic filariasis, and canine dirofilariasis. The fieldwork presented also includes effects of the mass distribution of drugs used to eliminate the infection. A major success has been achieved with the progress towards elimination of onchocerciasis and filariasis from Ecuador, Sudan and Tanzania. Lastly, this collection of studies covers a range of areas that have been investigated by the author as part of serving as a general pathologist in academic setting contributing to equine medicine, wound healing, toxic disasters and breast cancer.

Background. Quantifying and predicting the effect of control interventions against infectious diseases requires knowledge about prevalence prior to the implementation of such control measures as well as knowledge of key parameters which affect model outcomes. Here is presented the first geostatistical map estimating the prevalence of human onchocerciasis in the former Onchocerciasis Control Programme in West Africa (OCP) before the initiation of vector control operations in 1975. The map is used to quantify the burden of onchocercal skin disease prior to interventions. The results of a socioeconomic survey investigating coverage and compliance to community-directed treatment with ivermectin are then presented. Methods and Findings. The OCP epidemiological database was investigated for spatial autocorrelation. A total of 737 village surveys had parasitological examinations conducted prior to the start of control. Using these 737 pre-control data points plus environmental covariates, a Bayesian model-based geostatistical (B-MBG) approach was used to generate a continuous surface (at a pixel resolution of 25km2) of microfilarial prevalence in West Africa prior to the commencement of the OCP. The mean Pearson’s correlation between observed prevalence and model-estimates of prevalence at hold-out locations was 0.693; mean prediction error was 0.77% and mean absolute prediction error was 12.2%. Within OCP boundaries, 17.8 million people were deemed to be at risk and 7.6 million infected in 1975 which is greater than previous estimates. The mean microfilarial prevalence across all countries was 45% (range: 2–90%). Conclusions and Significance. This is the first map of continuous onchocerciasis prevalence in West Africa, developed using robust geostatistical methods. Important environmental predictors of infection prevalence were identified and used in a model that out-performs those without spatial-random effects or environmental covariates. Our results may be compared with recent epidemiological mapping efforts to find areas of persisting transmission, informing feasibility of elimination with current and novel tools.

Onchocerciasis is a blindness-causing disease caused by a nematode called Onchocerca volvulus that is transmitted by Simulium blackflies. The disease is a major epidemiological problem among rural communities living in close proximity to rivers in some population in Sub-Saharan Africa. Recent studies identified Ghana to be a treat of recrudescence of onchocerciasis in neighboring countries. This thesis applies spatial models, predicts, and assesses population at risk of onchocerciasis in Ghana. It also evaluates the disease endemicity in Burundi in order to test the models applied in Ghana. Onchocerciasis prevalence data spanning a period of 2004 (Ghana) and 1985-1992 (Burundi) were integrated together with biophysical variables in a GIS. Next, modeling of the spatial risk of onchocerciasis was based on the principal component analysis (PCA) regression models. The final predictive spatial models represent the risk of the disease. The spatial models showed potential biogeographic zones and epidemiological patterns of onchocerciasis in relation to village settlements that are at risk. Also, the risk of onchocerciasis increased with the proximity to the rivers. The estimated population at risk in Ghana in 2010 was 5,211,808 people (or 21.36% of the total population) and 235,032 people in Burundi (or 2.8% of the total population). Findings from this study can help in the effective design of preventive control measures of the risk of recrudescence of the disease and safeguard the achievements of the OCP and APOC programs.

Il genoma umano tende ad essere gradualmente modificato dalla selezione naturale a causa dell’interazione con diverse condizioni ambientali che possono essere considerate veri e propri fattori selettivi. Lo scopo della presente ricerca è quello di esplorare la variabilità ai loci HLA DQA1 e HLA DQB1 in due popolazioni coresidenti nella foresta pluviale lungo il fiume Rio Cayapa (nord-ovest Ecuador) ed esposti ai medesimi stress ambientali, tra cui l'infezione da O. volvulus. I loci HLA di classe II (HLA DQA1 e DQB1) di 211 individui appartenenti a due distinte popolazioni (Indios Cayapas ed individui di origine africana) sono stati analizzati attraverso una tipizzazione molecolare ad elevata risoluzione. Il confronto tra casi e controlli in entrambe le popolazioni dimostra il ruolo chiave di alcuni alleli HLA DQA1 sia nella predisposizione che nella protezione rispetto all’infezione da O. volvulus. Un unico allele (HLA DQA1*0401) risulta potenzialmente protettivo contro l’oncocercosi in entrambe le popolazioni. Tre differenti alleli sembrano invece responsabili della diversa manifestazione clinica dell’oncocercosi osservata in queste popolazioni: HLA DQA1*0102 e *0103 negli afroecuadoriani e HLA DQA1*0301 negli Indios Cayapas. Al fine di testare le relazioni tra le popolazioni, un campione di amerindi (Indios Tsachilas o Colorados) ed uno di origine africana (Bamileke del Camerun) sono stati tipizzati per confrontare la distribuzione allelica all’HLA DQ attraverso analisi delle corrispondenze ed albero ML. Questo duplice approccio conferma come il sistema HLA possa essere considerato uno strumento prezioso per esplorare sia le differenze immunogenetiche che la somiglianza genetica tra le popolazioni. Parallelamente alle tipizzazioni molecolari, la correlazione tra HLA DQB1*0301 e l'allele T dello SNP rs1056315 è stata valutata al fine di valutare la predittività di questo SNP per inferire la presenza dell’allele DQB1*0301. Tale associazione risulta non utilizzabile a causa dei modesti valori dei coefficienti di correlazione stimati in entrambe le popolazione: ciò sottolinea la necessità di migliorare i dati di associazione genetica per usare gli SNPs come strumento predittivo della variabilità allelica ai loci HLA.<br>Due to its long exposure to infectious diseases, the human genome tends to be gradually modified through natural selection, especially at level of the Human Leukocyte Antigen (HLA) complex. The aim of this study is to explore HLA DQ variability in two populations (Cayapas Indians and Afro-Ecuadorians) living near one another in the same rain forest along the Cayapa river (northwestern Ecuador) and exposed to the same environmental stress, i.e. infection by O. volvulus. Two HLA class II loci (HLA DQB1 and HLA DQA1) of 211 unrelated individuals have been analyzed. HLA high-resolution molecular typing was performed by three different techniques: Sequence Specific Oligonucleotides hybridization (SSO), Sequence Specific Primer amplification (SSP) and direct Sequencing (Sequence Based Typing, SBT). The comparison between cases and controls in both populations shows the key role of several HLA DQA1 alleles in susceptibility and protection from O. volvulus infection. A potential protective allele against onchocerciasis, HLA DQA1*0401, is highlighted in both populations. Three different alleles seem to account for the different clinical display of onchocerciasis in these populations: HLA DQA1*0102 and *0103 in Afro-Ecuadorians and HLA DQA1*0301 in Cayapas Indians. In order to test the relationships among populations, an Amerindian and an African populations (Colorados Indians and Bamileke from Cameroon) have been typed to compare the HLA allelic pool by correspondence analysis and ML tree. This double approach confirms that the HLA system is a valuable tool to explore both immunogenetic differences and genetic relatedness among populations, improving the informative role of such genetic system. The correlation between HLA DQB1*0301 and the T allele of SNP rs1056315 was evaluated in order to detect the predictiveness of this SNP to infer the presence of DQB1*0301 allele. This is not confirmed in both population: it underline the needing to improve genetic association data to use tag SNP as predictive tool.

Onchocerca volvulus, a filarial nematode, is the causative agent of onchocerciasis.<br>O. volvulus is a human parasite with no animal model host and is endemic in the tropics. O. volvulus material is scarce and must be conserved as part of the Onchocerciasis Control Program. A genomic library was constructed to provide a substantial source of renewable genetic material, in place of original parasite DNA.<br>Currently there is only one glutamate-gated chloride channel that has been sequenced from O. volvulus, but this has not yet been characterized. This GluClx partial cDNA sequence isolated by Cully et al., 1997, may be found in GenBank, accession number U59745. Specific primers were designed to amplify this gene from the genomic library. A fragment of this gene was isolated but the primers were non-specific, amplifying genes in addition to GluClx.<br>A motif is a short recognition sequence within a protein that may allow the modification of the protein. The cysteine loop in the N-terminal of all the ligand-gated ion channels is interesting because it contains the neurotransmitter-gated ion channel signature sequence. (Abstract shortened by UMI.)

Both S.ochraceum and S.metallicum, which are vectors of onchocerciasis, are now known to be species complexes (Hirai et in preparation; Conn, 1988). Larval collections were made in a variety of streams in the three onchocerciasis foci in Mexico and identified by cytotaxonomic criteria. S.ochraceum cytotype A was found in the Soconusco focus, cytotype B in the Oaxaca focus and cytotype C in the Chamula focus. Cytotype C was recorded in Mexico for the first time. S.metallicum cytotypes A, B, H and I were found in all three of the foci. Cytotypes B, H and I were recorded in Mexico for the first time. In addition a new cytotype, named X, was discovered in the Oaxaca focus. Attempts to analyse chromosomes of S.ochraceum adults were unsuccessful. The larval head patterns and body colouration of different cytotypes of S.metallicum were examined and variations were found between them, Cytotypes A, B, H and I could be distinguished in the majority of cases on these morphological differences. Cytotype X however resembled cytotype B. Cuticular hydrocarbon analysis by gas liquid chromatography, a technique to distinguish adult members of species complexes, was attempted on S.ochraceum and S.metallicum specimens. Some separation was achieved amongst S.ochraceum cytotypes A, B and C. The distributions and abundances of the larvae of different members of the S.ochraceum and S.metallicum species complexes and other Simulium species were investigated in relation to selected environmental variables, by multivariate analyses. Different cytotypes of each vector complex were found to be associated with characteristic stream conditions. The distribution of the different cytotypes of S.ochraceum and S.metallicum in relation to onchocerciasis is discussed.

Onchocerciasis, or river blindness, has historically represented one of the significant neglected tropical diseases on the planet in terms of socio-economic impact. The discovery that ivermectin was a safe and effective treatment for onchocerciasis, together with the decision of the manufacturer to donate the drug for the treatment of this disease became the basis for several large international programs to control and eventually eliminate the infection. These programs have managed to virtually eliminate transmission of the parasite causing Onchocerca volvulus from many foci in Africa and the Americas. Verifying that transmission has been halted requires sensitive and specific assays to detect the presence of the parasite. The gold standard to accomplish this has been to employ a PCR assay targeting a specific repeated sequence family encoded in the genome of O. volvulus to screen for the presence of the parasite in pools of vector black flies. While this assay is highly sensitive, obtaining the high specificity required to document an absence of transmission requires an independent confirmatory assay. To meet this need, an independent PCR assay targeting the cytochrome B (cytB) gene of the O. volvulus mitochondrion was developed. This assay could detect O. volvulus mitochondrial DNA purified by magnetic bead capture using the primers for the cytB gene and from the nuclear encoded repeated sequence DNA targeted in the primary assay. These preliminary data suggest that the mitochondrial PCR assay may be employed as a confirmatory assay to detect O. volvulus in pools of vector flies.

Onchocerciasis is a severely debilitating yet neglected tropical disease (NTD) currently affecting approximately 15.5 million people, including 12.2 million people with skin disease and 1.025 million with vision loss. The disease causes social stigma, generates and perpetuates poverty, and leads ultimately to irreversible unilateral or bilateral blindness if untreated. Consequently, onchocerciasis is a major impediment to socioeconomic development in addition to being a major public health concern in some African countries. Many control programs have been launched against the disease with moderate successes achieved in Africa. These limited outcomes are partially due to the unavailability of reliable, non-invasive and easily applicable diagnostic tools for mapping endemic regions, monitoring control program successes, determining treatment endpoints and post-elimination surveillance. The current WHO recommendations for certification of elimination include the use of the Ov16 antibody detection ELISA which is flawed by an intrinsic systematic error as 15-25% of infected populations may not produce antibodies against this antigen due to genetic restrictions. With the recent shift in the global health goal of onchocerciasis from control to elimination, there is a need for the development of novel appropriate tools. These tools include amongst others, drugs, diagnostics, and vaccines. In this work, bioinformatics analyses combined with immunological assays were applied in a bid to develop potential tools for the current elimination programs. With regards to chemotherapy, Ivermectin which has been the sole drug for onchocerciasis treatment for over 30 years kills only the microfilariae (mf) leaving the adult worms intact which continue to produce the mf. Moreover, there is a recent problem of development of parasite resistance to this drug. In addition, moxidectin which was recently approved for treatment is contra-indicated in pregnant women and children under 12 who could continue to serve as reservoirs for infection. There is therefore a need to develop new treatment strategies, preferably for macrofilaricidal drugs. For a total eradication of onchocerciasis, diagnosis and treatment must be complemented with vaccine development. The aim of this work was therefore (i) to characterise an O. volvulus antigen, Ov58GPCR and (ii) to design an epitope-based chimeric antigen, which we designated, Ov-DKR-1, within the framework of the development of onchocerciasis control tools. In order to achieve the first goal, towards diagnosis, synthetic peptides representing linear B-epitopes and the recombinant extracellular domain of a G-protein coupled receptor (GPCR) with diagnostic potential were tested for their immune responses using serum from onchocerciasis-infected individuals and various controls. The results obtained indicate that (i) the O. volvulus antigen, Ov58GPCR is a G-protein coupled receptor (GPCR) conserved in related nematodes, (ii) synthetic peptides predicted to be in the extracellular domain (ECD) of Ov58GPCR are indeed immunogenic epitopes in onchocerciasis-infected individuals, (iii) synthetic peptide cocktails discriminate between actively-infected individuals, treated non-infected individuals and healthy African controls, (iv) polyclonal antibodies against one of the peptides or against the bacterially-expressed ECD reacted specifically with the native antigen in O. volvulus total and surface extracts, (v) Ov58GPCR is transcribed in both larvae and adult parasite stages, (vi) IgG and IgE responses to the recombinant ECD decline with Ivermectin treatment. All these findings suggest that the recombinant extracellular domain and synthetic peptides of Ov58GPCR, as well as the specific immune responses generated, could be harnessed in the context of disease diagnosis and surveillance. To assess the potential role of Ov58GPCR in drug or vaccine target development, preliminary examination on the essentiality of the Ov58GPCR for parasite survival was evaluated through RNA interference. A short-interfering RNA (siRNA) sequence targeting the gene designed and tested by soaking with O. volvulus male worms resulted in a reduction in motility. Results indicated that the gene may be involved primarily in motility. Further investigations are recommended in this light. With regards to the second goal, towards the development of a potential immune-protective tool, many indicators reveal the possibility of the development of protective tools against onchocerciasis. Consequently, an immuno-informatics approach was applied to design a filarial-conserved multi-epitope subunit vaccine candidate consisting of B-and T-cell epitopes of proteins reported to be potential novel vaccine candidates. Conservation of the selected proteins in other nematode parasitic species and predicted epitopes suggests that the generated chimera protein (Ov-DKR-1) could be vital in cross-protection. The 3D structure was predicted, refined and validated bioinformatically. Protein-protein docking of the chimeric vaccine candidate with the TLR4 receptor predicted efficient favourable binding. Immune simulation predicted significantly high levels of IgG1, T-helper, T-cytotoxic cells, INF-γ, and IL-2 responses. Overall, the designed chimeric peptide demonstrated antigenicity superior to the current vaccine candidates.<br>L’onchocercose est une maladie tropicale sévèrement débilitante mais négligée qui touche actuellement environ 15,5 millions de personnes, dont 12,2 millions de souffrant de maladies de la peau et 1,025 millions de souffrant de perte de vision. La maladie provoque une stigmatisation sociale, génère et perpétue la pauvreté et finit par conduire à une cécité unilatérale ou bilatérale irréversible si elle n'est pas traitée. En conséquence, l’onchocercose est un obstacle majeur au développement socioéconomique en plus d’être une préoccupation majeure pour la santé publique. De nombreux programmes de lutte ont été lancés contre la maladie, avec quelques succès en Afrique. Ces résultats sous-optimaux (limités) sont en partie dus à l’absence d’outils fiables, non invasifs et facilement applicables pour la cartographie des régions endémiques, le suivi des succès des programmes de contrôle, la détermination des paramètres de traitement et la surveillance post-élimination. Les recommandations actuelles de l’OMS pour la certification de l’élimination incluent l’utilisation du test ELISA de détection d’anticorps Ov16, entaché d’une erreur systématique intrinsèque puisque 15 à 25% des populations infectées peuvent ne pas produire d’anticorps contre cet antigène en raison de restrictions génétiques. Avec l’évolution récente de l’objectif de santé mondial de l’onchocercose de passé de la lutte à l’élimination, il est donc nécessaire de mettre au point de nouveaux outils appropriés. Ces outils nécessaires incluent, entre autres, des médicaments, des diagnostics et des vaccins. Dans ce travail, des analyses bio-informatiques combinées à des tests immunologiques ont été appliquées dans le but de développer des outils potentiels pour les programmes d'élimination actuels. En ce qui concerne la chimiothérapie, l’ivermectine, qui est le seul médicament utilisé depuis plus de 30 ans pour le traitement de l’onchocercose, ne tue que les microfilaires (mf) laissant intacts les vers adultes qui continuent à produire le mf. A ceci joint, il y a le problème récent du développement de la résistance des parasites à ce médicament. En outre, un traitement récemment approuvé, la moxidectine, est contre-indiquée chez les femmes enceintes et les enfants de moins de 12 ans qui pourraient continuer à servir de réservoirs d’infection. Il est donc absolument nécessaire d’élaborer de nouvelles stratégies de traitement, de préférence pour les médicaments macrofilaricides. Pour une éradication totale de l’onchocercose, le développement du vaccin doit être complété par le diagnostic et le traitement. Le but de ce travail est donc de caractériser un antigène d'O. volvulus, Ov58GPCR et de concevoir un antigène chimérique à base d'épitope, que nous avons appelé Ov-DKR-1, dans le cadre du développement d'outils de contrôle de l'onchocercose.Concernant le premier objectif, des peptides synthétiques représentant des épitopes B linéaires et le domaine extracellulaire (DEC) recombinant d'un récepteur couplé à la protéine G (GPCR) présentant un potentiel diagnostique ont été testés pour déterminer leur réponse immunitaire en utilisant du sérum d'individus infectés par l'onchocercose et divers témoins. Les résultats obtenus indiquent que (i) l'antigène d'O. volvulus, Ov58GPCR est un récepteur couplé à la protéine-G (GPCR) conservé dans les nématodes apparentés (ii) les peptides synthétiques prédits comme localisés dans le domaine extracellulaire de Ov58GPCR sont bien des epitopes immunogéniques chez les individus infectés par l’onchocercose, (iii) les cocktails de peptides synthétiques établissent une distinction entre les individus activement infectés avec l’onchocercose, les individus non-infectés traités et les témoins africains en bonne santé, (iv) les anticorps polyclonaux contre un des peptides ou le domaine extracellulaire exprimé au bactéries réagisent spécifiquement avec l'antigène natif dans les extraits total et de surface d'O. volvulus, (v) Ov58GPCR est transcrit aux stades larvaire et adulte, (vi) les niveaux détectés d’IgG et IgE grâce à le DEC recombinant diminuent au cours du traitement par l'ivermectine. Toutes ces découvertes suggèrent que le domaine extracellulaire recombinant et les peptides synthétiques de Ov58GPCR, ainsi que les réponses immunitaires spécifiques générées, pourraient être exploités dans le contexte du diagnostic et de la surveillance de la maladie. Pour évaluer le rôle potentiel d’Ov58GPCR dans le développement de médicaments ou de vaccins cible, un examen préliminaire de l’indispensabilité du gène Ov58GPCR pour la survie du parasite a été évalué par interférence d’ARN. Une séquence d'ARN interférant court (ARNic) ciblant le gène conçu et testé par trempage avec des vers mâles d'O. volvulus a entraîné une réduction de la motilité. Les résultats ont indiqué que le gène pourrait être impliqué principalement dans la motilité. Des investigations complémentaires sont recommandées dans cette optique.Concernant le deuxième objectif, de nombreux indicateurs révèlent la possibilité de développer des outils de protection contre l’onchocercose. En conséquence, une approche immuno-informatique a été appliquée pour concevoir un candidat-vaccin des sous-unités de multi-épitopes conservées-filarienne consistant des épitopes de cellules B et T de protéines qui seraient de nouveaux candidats vaccins. La conservation des protéines sélectionnées chez d'autres espèces parasitaires de nématodes et d'épitopes prédits suggère que la protéine chimère générée (Ov-DKR-1) pourrait être vitale pour la protection croisée. La structure 3D a été prédite, raffinée et validée bioinformatiquement. La fixation protéine-protéine du candidat vaccin chimère au récepteur TLR4 prédit une liaison favorable efficace. La simulation immunitaire prédit des niveaux significativement élevés d'IgG1, de réponses T-helper, de cellules T-cytotoxiques, de INF-γ et d'IL-2. Globalement, le peptide chimère conçu a démontré une antigénicité supérieure aux candidats vaccins actuels.<br>Option Biologie moléculaire du Doctorat en Sciences<br>info:eu-repo/semantics/nonPublished

Le Programme africain de lutte contre l'onchocercose (APOC) et le Programme mondial d'élimination de la filariose lymphatique (GPELF), basés respectivement sur des traitements de masse par ivermectine et par une combinaison d'ivermectine et d'albendazole, sont des succès indéniables. Cependant, en Afrique centrale, région endémique pour la loase, les opérations de lutte sont fortement entravées du fait de la survenue possible d'effets secondaires graves induits par l'ivermectine chez les individus présentant plus de 30.000 microfilaires de Loa loa par mL de sang. Les résultats remarquables de l'APOC ont conduit récemment le programme à afficher un objectif plus ambitieux que celui défini initialement (l'élimination de la maladie comme problème de santé publique) : celui d'une élimination de la transmission. Les objectifs d'élimination d'APOC et du GPELF rendent nécessaires la réalisation d'une cartographie de la filariose lymphatique et de l'onchocercose hypoendémique en Afrique centrale, et imposent de développer des stratégies de lutte alternatives dans les zones coendémiques avec la loase. Nos travaux apportent des éléments nouveaux concernant l'épidémiologie de la filariose lymphatique en Afrique centrale. La distribution très focale de la maladie et les facteurs de risque particuliers que nous avons identifiés devraient être pris en compte pour déterminer l'échelle utilisée pour la réalisation de la cartographie. Par ailleurs, nous avons observé que le test ICT utilisé pour cartographier la filariose lymphatique pouvait se positiver en cas de forte microfilarémie à Loa loa (réaction croisée), ce qui va constituer un défi important pour les programmes de lutte. Nos travaux ont aussi permis de développer des stratégies alternatives permettant de lancer des programmes de lutte dans des zones de coendémie avec L. loa. Ainsi, nous avons participé au développement d'une technique permettant de dépister (et d'exclure des traitements de masse) les individus à risque d'effets secondaires graves post-ivermectine. D'autre part, nous avons montré que des traitements semestriels par albendazole seul pourraient constituer une alternative, applicable en zone de loase, au traitement standard de la filariose lymphatique. Concernant le diagnostic, nous avons montré l'intérêt qu'il y avait à lire les tests de diagnostic de la filariose lymphatique de manière semi-quantitative. Enfin, concernant la loase, nous avons étudié les relations existant, au niveau individuel, entre la microfilarémie à Loa et les antécédents d'œdème de Calabar et de passage sous-conjonctival du ver adulte<br>The African Program (APOC) and the (GPELF), relying on the mass drug administration of ivermectine or of a combination of ivermectin and albendazole, respectively, are undeniably successful. Nonetheless, in Central Africa where loiasis is endemic, control operations are hampered by the possible occurence of ivermectine-induced severe adverse events in individuals harbouring more than 30 000 microfilaria of Loa loa per mL whole blood. The outstanding results obtained by APOC have recently led the programme to adopt a more ambitious goal than originally defined (elimination of the disease as a public health concern) : eliminating transmission. The elimination objectives of APOC and of the GPELF arise the need for mapping lymphatic filariasis and hypoendemic onchocerciasis areas in Central Africa, and strenghten the need to develop control strategies for loiasis coendemic areas. Our researches bring new insight into the epidemiology of lymphatic filariasis in Central Africa. The highly focal distribution of the disease, and the risk factors that we identified should be accounted for when defining the scale used for mapping processes. Furthermore, we observed that the immunochromatographic card test (ICT) used for mapping lymphatic filariasis might display false positive result in case of high L. loa microfilarial density (cross reaction), which will constitute a challenge for control programmes. Our work also allowed to develop alternative strategies for launching control programmes in areas of coendemy with L. loa. We participated in the developement of a technique to test (and exclude from mass drug administration) the individuals at risk of post-ivermectin severe adverse events. Besides, we showed that a semiannual mass drug administration of albendazole alone was deemed to be a suitable alternative strategy to standard lymphatic filariasis treatment applicable in loiasis endemic areas. As for the diagnosis, we highlighted the interest of semi-quantitative reading of diagnostic tests for lymphatic filariasis. Eventually, we studied the relation between the microfilaremia of L. loa and the histories of Calabar oedema and of sub-conjonctival migration of the adult worm, at the individual level

Thesis (Dr.P.H.)--Boston University PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you.<br>The recently classified neglected tropical diseases (NTD), -- onchocerciasis, lymphatic filariasis, schistosomiasis, and soil-transmitted helminthiasis -- are all coendemic in Nigeria. The World Health Organization recommended strategy for addressing these diseases is preventive chemotherapy through annual mass drug administration (MDA) with ivermectin, albendazole, and praziquantel. Integrated delivery of these medicines has become the de facto strategy advocated for in the literature as a means of reducing costs through shared resources. Little empirical evidence, however, exists to support this. This paper explores these diseases and the concept of integration in the context of the global strategies for their control. A literature review was conducted using PubMed to identify articles published containing any of the disease names and costs. Of the 2,028 articles returned, only 14 published between 1998 and 2011 met the criteria for review. All costs were adjusted for inflation. Overall, the mean cost of MDA by any means was 0.83 cents. No data comparing separate MDA to integrated MDA were found. To examine this, a model was created comparing MDA programs with similar distribution strategies and targeting similar diseases. Data from separate articles presenting stand alone MDA were combined to give a mean cost of 0.42 cents to deliver two medicines in two rounds. This was compared with articles showing integrated MDA, which gave a mean cost of 0.25 cents to deliver two medicines in a single round. This suggests a cost savings of 40 percent. To verify this, data from a NTD program in Nigeria that transitioned to integrated MDA was examined in detail. In 2008, eight districts received a single round of ivermectin with albendazole followed at least 1 week later by a single round of praziquantel to school-aged children. The following year, a single round of all three drugs was co-administered. The number of treated individuals was essentially unchanged during both years (1,301,864 in 2008 and 1,297,509 in 2009). The total programmatic costs for the MDA, not including drug and overhead costs, reduced by 41% from $123,624 to $72,870, similar to savings seen in the literature review. Cost savings were attributed largely to transportation and personnel costs. Integrated delivery of medicines is recommended for mature programs targeting these diseases.

Onchocerca volvulus is a filarial parasite transmitted to humans by female Simulium spp. black flies. Infection with this parasite can cause blindness and severe skin disease among humans in Africa and the Americas. Enzyme-linked Immunosorbent Assay serological testing of OV-16 antigen is a diagnostic tool for determining effective elimination of the parasite. Programs typically rely on OV–16 ELISA to evaluate the progress towards interruption and/or elimination of disease by mass drug distribution of ivermectin and vector larvicidal control efforts. As elimination grows closer, monoclonal antibody positive controls for OV-16 ELISA become important to develop for Onchocerca testing due to the limited availability of pooled sera positive controls. Recent evaluation of laboratory designed OV-16 ELISA coating antigen by the Unnasch Lab (University of South Florida) showed that polymorphisms occurred which may alter the ability of the humanized monoclonal antibody to recognize the cognate antigen. With this development, it was important to evaluate these polymorphisms and isolate them for further testing against the standardized monoclonal antibody and positive sera to determine the effects antigenic polymorphisms could have on diagnostic testing. Upon evaluation, the polymorphisms did influence signaling when testing the monoclonal antibody. However, little effect on the recognition of the antigen was seen when different isoforms were evaluated against sera from O. volvulus infected individuals. Data suggest that the epitope recognized by the synthetically produced monoclonal antibody is not immuno-dominant in infected individuals.

Onchocerca volvulus is a parasitic filarial nematode responsible for human onchocerciasis, a disease commonly known as "River Blindness". Although there are no well documented cases of ivermectin resistance in O. volvulus, reports of suboptimal responses to ivermectin have appeared. The purpose of this thesis was to examine genetic polymorphisms in O. volvulus and to determine whether there was genetic evidence of ivermectin selection on O. volvulus genes. Analysis of 17 genes from O. volvulus was undertaken in two populations of worms, either from ivermectin-naive patients or from patients who had been repeatedly treated with ivermectin annually. In 14 of the genes no differences in genetic polymorphism were found (although polymorphisms were identified). However, chi square analysis (chi2=0.05) indicated significant differences in allele frequencies for a P-glycoprotein, a beta-tubulin and a putative dyf=8 gene. Analysis of the O. volvulusbeta-tubulin alleles identified three amino acid substitutions in the H3 region with ivermectin selection. Microtubules play a key structural role in the formation of neurons, and in ivermectin-resistant Haemonchus contortus, amphidial neurons show distorted microtubule bundles. Polymerization and depolymerization assays of the recombinant O. volvulus beta-tubulin alleles showed interesting differences between the polymerized tubulin using the two different alleles. It is speculated that similar differences could cause the disorganization of the microtubules identified in the amphidial neurons in ivermectin resistant H. contortus. In addition to the coding mutations, a 24 bp deletion in the adjacent intron to the H3 was detected. A PCR diagnostic assay was developed to genotype individual macro- and microfilariae. Further analyses were conducted to investigate the possibility of a direct relationship between ivermectin and beta-tubulin. Data obtained from equilibrium dialysis experiments indicated that BODIPY FL ivermectin bound to purified O. volvulus alpha- and beta-tubulins. More interesting, non-fluorescent ivermectin and taxol competed with the BODIPY FL ivermectin. The work presented in this thesis provides evidence of genetic selection by ivermectin on O. volvulus and suggests a putative binding site for ivermectin on tubulin. These data provide novel information on ivermectin selection in O. volvulus and on the possible involvement of tubulin in ivermectin resistance.

Ivermectin (IVM) is the only safe drug for mass-treatment of onchocerciasis. IVM-resistance has been reported in gastrointestinal nematode parasites of animals. A reduction in response to IVM in Onchocerca volvulus could have significant consequences for the onchocerciasis control programs. Over the last few years, studies have reported genetic selection or reduced responses to IVM in some O. volvulus populations. The risk of a recrudescence of the disease was recently reported with the emergence of resistant adult parasite population in Ghana. It is important to understand the effects of IVM on O. volvulus populations to be able to identify genetic markers to follow IVM selection in the field. In this study, O. volvulus samples were derived from a clinical trial in Cameroon, in which patients were sampled before, and following three years (1994-1997) of IVM treatments. There were four treatment groups: 150mug/kg (1xp.a. or 4xp.a.) and 800mug/kg (1xp.a. or 4xp.a.). DNA from macrofilariae was genotyped for beta-tubulin and P-glycoprotein-like protein (PLP) gene, as well as two control genes and other loci. Reproductive organs of female worms were analyzed by microscopy. A correlation was established between the reproductive status of the female worms and beta-tubulin genotype with the beta-tubulin heterozygous female worms being less fertile than the homozygous female worms. This disadvantage in fertility seemed to disappear after repeated exposure with IVM. We have found evidence that repeated IVM treatment selects for specific alleles of beta-tubulin and PLP. We observed that IVM selection pressure was higher in the female worms than in the male worms. Additionally, loss of polymorphism and selection pressure were higher following thirteen three-monthly doses of IVM compared to annual doses of IVM. Moreover, we found evidence of excess of homozygosity in O. volvulus population, that may be caused by non-random mating and/or subdivision population, which may have implication for the control program. PLP and beta-tubulin genes appear to be promising DNA markers for field use to follow IVM selection. In this perspective, alternative control measures could be considered locally in regions where gene selection is apparent, reducing the likelihood that IVM resistance would develop further and spread.

p. 1-112<br>Submitted by Santiago Fabio (fabio.ssantiago@hotmail.com) on 2013-04-24T21:04:41Z No. of bitstreams: 1 11111111111.pdf: 829006 bytes, checksum: d72adf5912d3d4a5a6ab9659a04a516d (MD5)<br>Approved for entry into archive by Maria Creuza Silva(mariakreuza@yahoo.com.br) on 2013-05-04T17:26:41Z (GMT) No. of bitstreams: 1 11111111111.pdf: 829006 bytes, checksum: d72adf5912d3d4a5a6ab9659a04a516d (MD5)<br>Made available in DSpace on 2013-05-04T17:26:41Z (GMT). No. of bitstreams: 1 11111111111.pdf: 829006 bytes, checksum: d72adf5912d3d4a5a6ab9659a04a516d (MD5) Previous issue date: 2008<br>Introducción: El control de las infecciones causadas por geohelmintos está basado en la administración periódica de drogas antihelmínticas a los grupos de alto riesgo, particularmente a niños en edad escolar que viven en áreas endémicas. Existen datos limitados sobre la efectividad de tratamientos antihelmínticos periódicos a largo plazo en la prevalencia de infecciones por geohelmintos particularmente desde programas operacionales. Objetivo: El presente estudio investigó el impacto de 17 años de tratamiento en masa con un antihelmíntico de amplio espectro, la ivermectina, usada para el control de la oncocercosis, en la parevalencia e intensidad de infección por geohelmintos en niños escolares. Métodos: Un estudio transversal fue conducido en comunidades que han recibido tratamientos anuales o bianuales y comunidades adyacentes que no han recibido dicho tratamiento en dos cantones de la Provincia de Esmeraldas en Ecuador. Una única muestra de heces fue colectada de cada niño y fue examinada usando las técnicas de Kato Katz y por concentración con formol-éter. Datos sobre los factores de riesgo para las infecciones por geohelmintos fueron colectadas por medio de cuestionarios aplicados a los padres. Resultados: Un total de 3563 niños en edad escolar (6-16 años) de 31 comunidades tratadas y 27 comunidades no tratadas fueron investigados. El tratamiento con ivermectina tuvo un efecto significante en la prevalencia (ORadj= 0,06; IC 95%: 0,03-0,14) y en la intensidad de la infección (RPadj=0,28; IC 95%: 0,11-0,70) por Trichuris trichiura pero no se observó dicho efecto en la infección por Ascaris lumbricoides o uncinarias. Conclusión: Tratamientos con ivermectina anuales y bianuales por un periodo de alrededor de 17 años tuvieron un efecto significante en la infección por T. trichiura pero no sobre otras infecciones por geohelmintos. La adición de una segunda droga antihelmíntica, tal como el albendazol, sería necesaria para obtener un efecto a largo plazo en la infección por A. lumbricoides en áreas altamente endémicas.<br>Salvador

Em África e no Sul da Arábia, a oncocercose está essencialmente associada ao complexo Simulium damnosum (Ovazza, 1967). A propagação da doença resulta essencialmente do tipo de actividade humana, e das alterações do ambiente, especìalmente a desflorestação maciça, transformando o habitat florestal em habitat de savana (Hocking, 1953, Dadzie, 1980, Amazigo, 1991, Amazigo, 2002 a, WHO, 1995 b). 2- Morfologia 2.1 - O ovo O ovo, têm uma forma triangular, com os vértices arredondados, medindo de 0,1 a 0,5 mm de comprimento. A casca é lisa, não apresentando qualquer adaptação especial e o revestimento é viscoso. São de cor branca aquando da oviposição, escurecendo com a embriogénese, aparecendo então com cores rosadas, amareladas e acinzentadas. 2.2 - A larva A larva dos simulídeos, apresenta um formato mais ou menos cilíndrico, com duas dilatações, uma no tórax, ligeira e outra mais acentuada na parte terminal do abdómen. Pode atingir o comprimento de um centímetro, e uma coloração muito variada, dependendo do tipo de alimentos ingeridos, e apresentar-se de coloração totalmente escura, a esbranquiçada. O corpo da larva é formado por três partes distintas – a cabeça, o tórax e o abdómen. A cabeça: A cabeça de uma larva de simulídeo, à observação dorsal, apresenta-se pigmentada, podendo com essa pigmentação expressar-se de duas formas, ou com manchas escuras em fundo claro (modelo positivo), ou manchas claras em fundo escuro (modelo negativo), e um par de finas antenas. Á observação ventral destacam-se dois caracteres de grande valor sistemático – a fenda pósgenal e o hipostoma.