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Query: UMLS:C0042961 (volvulus)
 4,305 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

During a routine entomological survey conducted within the framework of the Program to Control Onchocerciasis in West Africa, a female simulium forest fly was found to be contaminated by 13 Onchocerca volvulus larvae and 7 Onchocerca ochengi larvae. The two Onchocerca species were identified using specific DNA probes. We speculate that cross infection could be related either to behavioral factors, e.g. interruption of blood meals on two different hosts, or developmental factors, e.g. asynchronous development of parasites of the same species or specific differences in the duration of parasite cycles. Further study will be needed to determine the incidence and scope of cross infection in areas where accurate assessment of the impact of vector control on transmission of onchocerciasis in man is required.
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PMID:[A case of cross infection by Onchocerca volvulus and Onchocerca ochengi in Simulium damnosum S.L]. 1008 5

The parasitic nematode, Onchocerca volvulus is a major cause of blindness and dermal pathology in tropical regions. A vaccine directed to infective larvae would provide a valuable control tool alongside the current methods of chemotherapy and vector control. Previously we have described the identification of a chitinase cDNA that is expressed in a stage specific manner by O. volvulus infective third stage (L3) larvae. To evaluate its host protective potential, the complete open reading frame was cloned into the eukaryotic expression plasmid pJW4303 and used to vaccinate mice by DNA immunisation with the Accell GeneGun. The survival of challenge infective larvae was monitored using implanted micropore chambers. In the first trial, mice immunised 3 times over 4 months with 1 microg O. volvulus chitinase DNA responded with modest antibody responses dominated by IgG2a and exhibited a 36% (p=0.189, NS) reduction in parasite survival compared with challenge controls. In the second trial, an increased dose of DNA (5 microg) and more frequent immunisations (5 times over 6 months) stimulated an IgG1 dominant response and a 53% reduction in parasite survival (p=0.042). Antibodies from the vaccinated mice reacted with the cuticle of post-infective L3 larvae, implying that this may be the site of immune attack following secretion of chitinase.
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PMID:DNA immunisation with Onchocerca volvulus chitinase induces partial protection against challenge infection with L3 larvae in mice. 1054 24

The gene encoding the cytoplasmic copper/zinc superoxide dismutase (AVSOD1) from the filarial parasite Acanthocheilonema viteae was isolated from a genomic DNA library using a degenerate oligonucleotide probe. Additionally, cDNAs of the AVSOD1 and the secreted extracellular SOD (AVSOD2) were both cloned by RT-PCR, and the AVSOD2 was expressed at high levels in E. coli. The amino acid sequence of the AVSOD1 is 89.5 and 87.5% identical to that of the corresponding enzymes of Brugia pahangi and Onchocerca volvulus, respectively. In contrast, the AVSOD2 shows a lower degree of identity to the other filarial SODs and is extensively glycosylated. RT-PCR studies demonstrate the expression of both SOD subtypes in all developmental stages of A. viteae and indicate up-regulation of the AVSOD2 expression after transmission from the vector to the definitive host. This suggests an enhanced requirement for SOD activity in post-infective larval stages and adults of A. viteae. ELISAs performed with purified recombinant AVSOD2 show that the AVSOD2 is not a major target for the immune system in naturally infected jirds.
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PMID:Up-regulation of extracellular copper/zinc superoxide dismutase mRNA after transmission of the filarial parasite Acanthocheilonema viteae in the vertebrate host Meriones unguiculatus. 1057 30

Detection of Onchocerca volvulus larvae in vector populations is of prime importance in the assessment of the effectiveness of onchocerciasis control programmes. Traditionally, detection of larvae is attained by the dissection of flies, but this time-consuming method cannot easily discriminate between species of Onchocerca. The genome of all Onchocerca species has a unique 150 bp repeat, which can be amplified by PCR, and O. volvulus-specific DNA probes can detect these products by Southern blot (SB). This study optimizes a PCR/SB assay, and compares it with fly dissection to estimate the prevalence (p) and intensity of infection (m) in the local vector population of a Mexican community that has become hypoendemic as a result of 7 years of treatment with ivermectin and nodulectomy. The PCR detected 1 infected fly in a pool of 99 uninfected flies, but the optimal pool size was 50 flies. At the community level, 1 out of 10,550 flies was positive (p = 0.0095%, 95% confidence intervals CI = 0.00024-0.05280%; m = 0.00027 larvae/parous fly, CI = -0.00026-0.00081) by PCR, and 4 out of 10,772 flies (p = 0.0371%, CI = 0.01012-0.09505%; m = 0.00107 larvae/parous fly, 95% CI = 0.00002-0.00212) by dissection (observed m = 0.0005). Both methods produce statistically similar estimates of the prevalence and intensity, indicating that pool screening is a viable alternative for entomological surveillance in areas where the intensity of transmission is becoming extremely low as a result of control interventions.
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PMID:Detection of Onchocerca volvulus infection in Simulium ochraceum sensu lato: comparison of a PCR assay and fly dissection in a Mexican hypoendemic community. 1063 23

The mosquito-borne filarial worm, Dirofilaria immitis, causes heartworm disease in dogs. Detection of this parasite in its mosquito intermediate host currently involves dissection and microscopic examination for larval stages. Although this method is used commonly as a screening tool for epidemiological surveys, it lacks both sensitivity and specificity. In this study, a more efficient PCR- and probe-based diagnostic assay was developed. The target selected for this assay is a segment of the 16 S rRNA gene. The assay specifically detects as little as 10 pg of D. immitis genomic DNA, equivalent to DNA derived from one third stage larva (L(3)), but does not detect 100 ng (10 000-fold excess) of the purified DNA from several other filarial nematodes, including Dirofilaria striata, Dirofilaria tenuis, Dipetalonema reconditum, Wuchereria bancroftii, Brugia pahangi, B. malayi, Onchocerca volvulus or Loa loa. This assay also detects one L(3)of D. immitis, the minimal biological unit of infection, in a pool of 200 mosquito heads. This assay can serve as a highly specific and sensitive tool for efficiently screening the large numbers of mosquitoes to determine, with statistical validity the seasonal transmission pattern of D. immitis in a locality prior to designing a rational preventive medication program for that parasite.
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PMID:Development of a PCR- and probe-based test for the sensitive and specific detection of the dog heartworm, Dirofilaria immitis, in its mosquito intermediate host. 1065 47

The filarial nematodes Wuchereria bancrofti, Brugia malayi and Onchocerca volvulus represent major public health problems in the Tropics. Effective diagnosis of infection with these parasites is required both for administration of drugs to infected individuals and for monitoring of control programs. However parasitological diagnosis is associated with a number of problems including frequently inadequate sensitivity, long pre-patency of infection and inconvenience for patients. For these reasons there has been considerable effort expended in developing other forms of diagnosis, in particular immunoassays for measuring antibody and circulating parasite antigen as well as molecular-biology-based assays for detecting parasite DNA. This article reviews the progress and achievements obtained to date. The latter include the development of ELISAs employing recombinant antigen for detection of antibody to O. volvulus which have both high sensitivity and specificity, the commercial availability of immunoassays to measure circulating antigen in W. bancrofti infection and the generation of specific DNA-based detection systems for all three parasites.
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PMID:Molecular and immunodiagnosis of human filarial nematode infections. 1066 Sep 32

Chaperonin 60 (cpn60) belongs to the group of ubiquitous molecular chaperones that comprise the heat shock proteins, nucleoplasmins and chaperonins. Antibodies to recombinant CPN60 from humans was used to screen a cDNA library of Onchocerca volvulus and antigen-positive clones were selected. Sequencing of the DNA inserts confirmed their identity as cpn60 transcripts. These are distinct from a cpn60 sequence recorded previously from O. volvulus (GenBank accession number Y09416) that appears to be of endobacterial origin, rather than derived from the parasite itself. The full-length sequence of the cDNA (designated Ov-cpn60) codes for a protein of 64.3kDa (598 amino acid residues) and shares significant identity with homologous gene products from Caenorhabditis elegans (72%), humans (69%), yeast (53%) and Escherichia coli (50%). The endobacterial and parasite sequences are 41% conserved. Ov-CPN60 migrates with an apparent molecular mass of 65kDa on SDS-PAGE and is present in all life-cycle stages, as determined by immunoblotting with rabbit antibodies raised against the recombinant protein. Immunogold electron microscopy identified the protein within mitochondria, as expected, but also in extra-mitochondrial sites, including inclusion bodies of the glandular oesophagus (in infective larvae), the uterine wall, cytosol of developing spermatids, and the hypodermis and cuticle. Endobacteria were also labelled, indicating cross-reactivity between CPN60 from the parasite and its intracellular symbiont. In human infections, serum antibodies to Ov-CPN60 were present in only 11% of cases from Ecuador, but in 81-89% of subjects in three separate foci from West Africa. There was no relationship between antibody levels and age, sex, or infection intensity, and no consistent association between the serological response and immune status. An evaluation of antibody specificities in individual sera revealed a mixture of parasite-specific and host crossreactive anti-CPN60 antibodies, the ratio of which varied amongst geographic areas. It is concluded that antibody responses to Ov-CPN60 are unlikely to contribute either to host protection or pathology in onchocerciasis.
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PMID:Characterization of the heat-shock protein 60 chaperonin from Onchocerca volvulus. 1077 93

The objective of this study was to evaluate whether the distinct immune responses invoked by epidermal and intramuscular DNA immunization could be harnessed to improve upon the levels of protection to Onchocerca volvulus infective larvae achieved previously by recombinant protein immunization. Intramuscular (IM) and epidermal (GeneGun) routes of DNA immunization generally drive T helper1 and Th2 dominant responses, respectively. This dichotomy was used in an attempt to further define the nature of host-protective immunity in a mouse model of onchocerciasis. Mice were immunized with DNA plasmids expressing the O. volvulus antigens, Ov-TMY-1 (tropomyosin) and OvB20 (a nematode specific gene product). While, IM and GeneGun immunization of mice with Ov-tmy-1 induced expected Th1/Th2-associated IgG isotype profiles, mice responded to OvB20 immunization with a Th2 dominant response, irrespective of the delivery route. Despite inducing potent serological responses, neither DNA construct promoted statistically significant levels of protection to L3 challenge infection. We conclude that DNA immunization has good potential for induction of humoral responses against nematode infections and that serological responses alone do not predict vaccination efficacy under the conditions used here to measure host resistance to parasite challenge.
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PMID:DNA immunization with Onchocerca volvulus genes, Ov-tmy-1 and OvB20: serological and parasitological outcomes following intramuscular or GeneGun delivery in a mouse model of onchocerciasis. 1079 64

Samples of human serum, skin and urine, collected in Cameroon, were used to assess the value of some newer methods for the diagnosis of onchocerciasis. Parasite DNA was detected in skin snips and urine by PCR, and parasite antigen was detected in serum and urine by immunoblotting. Serum concentrations of IgG4 antibodies reacting with recombinant Onchocerca volvulus antigens (OC3.6 and OC9.3) were also measured, using an ELISA. The PCR-based tests of skin snips and the serological tests for antigen and antibody tests showed higher sensitivities (90%-100%) than the urine PCR (14%) or the urine antigen test (68%). Although antibody detection is much easier to perform than tests based on PCR or antigen detection, the latter have an advantage in that they are only positive in people with current infections. Thus, antibody testing may be more useful for screening populations for infection or exposure to O. volvulus, whereas PCR and antigen testing are potentially more useful for diagnosis of infections in individuals and for monitoring the success of therapy.
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PMID:A comparison of newer tests for the diagnosis of onchocerciasis. 1088 70

The northernmost focus for Onchocerca volvulus Leuckhart (Nematoda: Onchocercidae), the causative agent of human onchocerciasis, is found along the Nile near the town of Abu Hamed in Sudan. The vector for O. volvulus at this focus is a single monomorphic population of Simulium (Edwardsellum) damnosum Theobald. This black fly population is limited to a small area between the fourth and fifth cataracts of the Nile River that is isolated geographically from all other populations of S. damnosum sensu lato. Phylogenies produced from cytological analyses and sequence data derived from the NADH dehydrogenase subunit 4 and 16S rRNA genes indicate that Abu Hamed black flies are similar to, but distinct from, the savanna-dwelling sibling species of S. damnosum s.l., Simulium (Edwardsellum) damnosum sensu strictu Theobald, and S. (Edwardsellum) sirbanum Vajime & Dunbar. The DNA sequence and the cytological data support the hypothesis that the black fly population present in Abu Hamed may represent a new sibling species of S. damnosum s.l. We propose that this population be informally designated as the hamedense form of the Simulium damnosum complex.
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PMID:Cytotaxonomic and molecular analysis of Simulium (Edwardsellum) damnosum sensu lato (Diptera: Simuliidae) from Abu Hamed, Sudan. 1091 95


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