PubMed Health⌕ Search

Biomedical subjects

C P Muller

Publications and source records attributed to C P Muller.

At least 19 recordsLinked to original sources
PubMed2006

Avian flu: multiple introductions of H5N1 in Nigeria.

As the avian influenza virus H5N1 swept from Asia across Russia to Europe, Nigeria was the first country in Africa to report the emergence of this highly pathogenic virus. Here we analyse H5N1 sequences in poultry from two different farms in Lagos state and find that three H5N1 lineages were independently introduced through routes that coincide with the flight paths of migratory birds, although independent trade imports cannot be excluded.

Agriculture↗
PubMed2006

Seroprevalence of avian influenza virus, infectious bronchitis virus, reovirus, avian pneumovirus, infectious laryngotracheitis virus, and avian leukosis virus in Nigerian poultry.

Eight poultry farms in Nigeria, including chickens from nine breeder, 14 broiler, 28 pullet, 11 layer, and three cockerel flocks, were tested for antibody seroprevalence to the following poultry viruses of potential economic importance: infectious bronchitis virus (IBV), avian reovirus, avian pneumovirus (APV), infectious laryngotracheitis virus (ILTV), avian influenza virus (AIV), and avian leukosis virus (ALV). Serum samples were collected between 1999 and 2004 and were tested for antibodies using commercial enzyme-linked immunosorbent assay (ELISA) kits. Seroprevalence was very high for IBV (84%); intermediate for reovirus (41%), APV (40%), and ILTV (20%); and very low for ALV (<5%) antibodies. By commercial ELISA, the seroprevalence of antibodies against AIV was, in some flocks, up to 63%. However, more specific assays did not confirm AIV antibodies, indicating that all flocks tested were free of avian influenza antibodies. Birds seemed to be first infected by IBV (at about 7 wk of age), then by reovirus at 12 wk, before they became infected by APV (week 25) and ILTV (week 30). This is the first report of serological evidence of the above viruses in West Africa. Further studies are necessary to assess economic losses due to these avian viruses and the costs and benefits of countermeasures.

Aging↗
PubMed2005

Molecular epidemiology of chicken anemia virus in Nigeria.

Between February 2002 and May 2004, chicken anemia virus (CAV) was detected by PCR in organ samples from 14 flocks of poultry farms in Lagos, Ogun and Oyo States in Southwestern Nigeria. The farms reported low (<5%) to high mortalities (up to 100%) with various lesions at necropsy. The complete VP1 gene of 30 of these positive strains was sequenced. Strains that diverged by up to 4.4% on a nucleotide level differed only by up to 2.5% at the amino acid level (7 aa) as a result of clustered silent mutations. No amino acid substitutions specific for Nigerian strains were observed. Some birds had a CAV mixed infection. Genetic clustering of the VP1 gene did not correlate with differences in flock mortality but the co-infection of CAV with IBDV may be particularly lethal. This first molecular epidemiological study of CAV in Africa shows that the Nigerian strains cluster with viruses from very diverse geographic origins and were almost as diverse (4.4%) as all other strains combined (5.8%).

Animals↗
PubMed2004

Passive immunity to measles in the breastmilk and cord blood of some nigerian subjects.

Maternal and cord blood collected from 33 Nigerian mother-child pairs were tested for measles-sepcific IgG. All 33 had protective measles antibodies at the time of delivery with a positive correlation of r = 0.87. Determination of the rate of waning of these antibodies revealed that 58 per cent of these children had lost the protective maternal antibody by the age of 4 months and only 3 per cent of the children had enough antibody to protect them between the ages of 6-9 months. Fifty-five colostrum samples from the same mothers and 347 breastmilk samples collected at various periods of breastfeeding also showed that anti-measles IgA had dropped below the protective cut-off within the first 2 weeks of birth. It is evident that the Nigerian child is born with solid anti-measles antibody but the rate of waning has left a large number unprotected before the first dose of the vaccine. There is an urgent need to review the measles vaccination programme in Nigeria to protect these susceptible infants.

Antibodies, Viral↗
PubMed2004

High sequence diversity in infectious bursal disease virus serotype 1 in poultry and turkey suggests West-African origin of very virulent strains.

Fifty-eight outbreaks of Infectious bursal disease virus (IBDV) were observed in vaccinated chicken flocks in four Southwestern states of Nigeria between 1995 and 2000. Bursa samples from 40 flocks were found virus-positive in VP2-specific nested RT-PCR. Sequences of the hypervariable region of VP2 were compared to reference strains of the different IBDV variants including also 1988 isolates from Nigeria. Sequence analysis revealed that all 40 Nigerian isolates belonged to the very virulent (vv) variant. The maximum sequence diversity of 5.7% was higher than in all other vvIBDV sequences listed in Genbank (3.6%). Two clusters within Nigerian isolates are unique to this region. Serotype 1 IBDV was also detected in four symptomatic turkey flocks. The turkey isolates were found within 2 of the 3 VV-clusters of chicken isolates. Full length sequence of a turkey isolate (NIE009t) confirmed its close relation to vvIBDV strain D6948NET for both segment A (1.4% sequence diversity) and segment B (2.1%). Thus, turkeys should be considered susceptible to vvIBDV infection. The unusually high sequence diversity of vvIBDV may be an indication of a West-African origin of this virus, from where it spread to other continents.

Amino Acid Sequence↗
PubMed2003

Immunodominant domains of the Measles virus hemagglutinin protein eliciting a neutralizing human B cell response.

The most important neutralizing and protective antibodies against Measles virus (MeV) are directed against the hemagglutinin protein (MeV-H). To define the MeV binding domains recognized by human antibodies a set of 10 non-redundant MeV-H-specific monoclonal antibodies (mabs) was used to block their binding in a competition ELISA. Sera from both naturally infected and vaccinated individuals showed similar competition patterns. Two distinct domains were identified as the main target of human antibodies. One domain corresponded to the region of the previously described hemagglutinin noose epitope (HNE, aa 380-400) [35], which is recognized by hemagglutination-inhibiting, neutralizing and protective mabs. The second region is defined by a mab with strong neutralizing but weak hemagglutination-inhibiting activity. Mabs with a strong neutralizing capacity with respect to wild-type viruses seemed to displace more human antibodies than those with a weaker neutralizing activity. Human antibodies seem to react more weakly with the hemagglutinin regions that bind the CD46 and the fusion protein and more strongly with the putative CD150 binding site and the top loops of beta-sheet 2 and 3 of the hemagglutinin.

Adolescent↗
PubMed2003

Neutralizing immunogenicity of transgenic carrot (Daucus carota L.)-derived measles virus hemagglutinin.

Although edible vaccines seem to be feasible, antigens of human pathogens have mostly been expressed in plants that are not attractive for human consumption (such as potatoes) unless they are cooked. Boiling may reduce the immunogenicity of many antigens. More recently, the technology to transform fruit and vegetable plants have become perfected. We transformed carrot plants with Agrobacterium tumefaciens to generate plants (which can be eaten raw) transgenic for an immunodominant antigen of the measles virus, a major pathogen in man. The hemagglutinin (H) glycoprotein is the principle target of neutralizing and protective antibodies against measles. Copy numbers of the H transgene were verified by Southern blot and specific transcription was confirmed by RT-PCR. The H protein was detected by western blot in the membrane fraction of transformed carrot plants. The recombinant protein seemed to have a 8% lower molecular weight than the viral protein. Although this suggests a different glycosylation pattern, proper folding of the transgenic protein was confirmed by conformational-dependent monoclonal antibodies. Immunization of mice with leaf or root extracts induced high titres of IgG1 and IgG2a antibodies that cross-reacted strongly with the measles virus and neutralized the virus in vitro. These results demonstrate that transgenic carrot plants can be used as an efficient expression system to produce highly immunogenic viral antigens. Our study may pave the way towards an edible vaccine against measles which could be complementary to the current live-attenuated vaccine.

Animals↗
PubMed2001

New strategies for closing the gap of measles susceptibility in infants: towards vaccines compatible with current vaccination schedules.

Peptides representing epitopes of the measles virus glycoproteins have been designed to induce neutralizing and protective antibodies. Those that escape recognition by passively acquired anti-whole virus antibodies could potentially be used as components of a 'pre-vaccine' that could be given during early childhood irrespective of persisting maternal antibodies. Unlike vaccines based on recombinant proteins, epitope-based vaccines can be designed to be compatible with a subsequent boost with the standard life attenuated vaccine. Although synthetic peptides may induce only short-term immunity they have the potential to close in young infants the gap of vulnerability until the standard live attenuated vaccine can be given at 9 or 15 months of age.

Amino Acid Sequence↗
PubMed2001

Monitoring of measles elimination using molecular epidemiology.

The different measles virus genotypes are confined to more or less distinct geographic regions. Molecular characterization of virus isolates has been successfully used to determine epidemiological links between cases and the geographic origin of imported viruses. In Europe, indigenous measles has been eliminated in some countries, but in others the disease is still endemic. Intra-outbreak variability can be used to differentiate between sporadic endemic cases and a 'pseudo-outbreak' of unrelated imported cases. The interruption of virus circulation by mass vaccination campaigns could be demonstrated by comparing the variability of pre-campaign viruses with post-campaign isolates. Simplified tools are being developed that could bring genotyping within reach of laboratories that do not have the possibility of sequencing.

Environmental Monitoring↗
PubMed2001

Measles elimination: old and new challenges?

Life attenuated measles vaccines have dramatically reduced measles morbidity and mortality world-wide. Despite high vaccination coverage, measles outbreaks continue to occur both in developed and developing countries. While secondary vaccine failure may be responsible for disease in some seroconverted individuals, evidence suggests that many more vaccinees who are protected against disease may not be fully protected against virus infection. In low-income developing countries protection by maternal antibodies seems to erode faster than previously estimated especially in infants who were born to vaccinated mothers. Problems of infectivity and susceptibility of vaccinees will be compounded in case wild-type viruses become less sensitive to vaccine induced immunity. These observations suggest that elimination may be more easily achieved as long as large proportions of populations are protected by wild-type virus-induced immunity.

Adult↗
PubMed2001

Genetic analysis of Asian measles virus strains--new endemic genotype in Nepal.

In many parts of Asia measles virus (MV) continues to be endemic. However, little is known about the genetic characteristics of viruses circulating on this continent. This study reports the molecular epidemiological analysis based on the entire nucleocapsid (N) and hemagglutinin (H) genes of the first isolates from Nepal and Taiwan, as well as of recent MV strains from India, Indonesia, and China. Four isolates collected in various regions in Nepal during 1999 belonged to a new genotype, tentatively called D8. Another Nepalese isolate and one from India belonged to genotype D4. The diversity of the Nepalese strains indicated that measles continues to be endemic in this country. The isolate from Taiwan grouped with D3 viruses and one Chinese strain isolated in The Netherlands was assigned to the previously described clade H, known to be endemic in Mainland China. Molecular characterization emerges as an important tool for monitoring virus endemicity and vaccination efforts.

China↗
PubMed2001

Antigenic and immunogenic phage displayed mimotopes as substitute antigens: applications and limitations.

The most exciting potential of phage displayed peptide libraries is to obtain small peptide molecules that mimic an antigen, at least with respect to a particular epitope. In addition to their interest as research tools, such mimotopes could in principle be useful as diagnostic tools or for eliciting antibodies to a predefined epitope. However, the reduction of the phage insert sequence to a short peptide that can compete with the antigenic and in particular with the immunogenic properties of the natural antigen faces considerable difficulties. This review assesses critically the antigenicity of phage displayed peptides as free peptides and in different molecular environments. The difficulties to use mimotopes to induce antibodies that bind to the natural antigen (crossreactive immunogenicity) and the considerable discrepancy between antigenicity and immunogenicity of phage-derived peptides are discussed. Peptides selected with antibodies from phage displayed random peptide libraries have raised considerable expectations as low molecular weight substitutes of the natural antigen. This review will focus on the results of phage displayed random peptide libraries screened with antibodies specific for proteins, carbohydrates and nucleic acids and critically examine how the above expectations have been met.

Antigens↗
PubMed2001

Phylogenetic analysis of new hepatitis B virus isolates from Nigeria supports endemicity of genotype E in West Africa.

Isolates of hepatitis B viruses were collected from 20 acute and chronic hepatitis patients in a highly endemic region of Nigeria. Sequencing classified the isolates to the ayw4, as they all contained the amino acid variations characteristic for that serotype. In the pre-S2 region of five isolates, three to seven amino acids were deleted, suggesting that immune escape mutations previously associated only with chronic HBV infection may be observed also in acute disease. Phylogenetic analysis of the complete pre-S2/S (large S) genes (831 nt) demonstrated that all the viruses belonged to the same genotype E. So far, no isolates of genotype E have been found in any other region of the world, including the Americas. This may suggest a relatively recent introduction of this genotype into humans and would explain the relatively low genetic diversity of viruses belonging to this genotype. One genotype E virus had been found previously in a chimpanzee, and viruses belonging to the CHIMP genotype are related to other genotype E viruses. These findings are compatible with a transmission of genotype E viruses from chimpanzees to humans.

Amino Acid Sequence↗
PubMed2000

Differential antigenicity of recombinant polyepitope-antigens based on loop- and helix-forming B and T cell epitopes.

To investigate a strategy for the design of chimeric antigens based on B cell epitopes (BCEs) we have genetically recombined multiple copies of loop- (L) and helix-forming (H) sequential and protective BCEs of the measles virus hemagglutinin protein (MVH) in a number of high-molecular-weight polyepitope constructs (24.5-45.5 kDa). The BCE cassettes were combined semi-randomly together with a promiscuous T cell epitope (TCE; tt830-844) to yield 13 different permutational constructs. When expressed in mammalian cells, all constructs were detectable by Western blot as distinct bands of predicted molecular weight. Flow cytometry with conformation-specific antibodies revealed the Cys-loop in two [(L(4)T(4))(2) and (L(2)T(2))(4)] and the helix conformation in one [(H(2)T(2))(4)] of the different permutational constructs. The larger constructs, containing 16 epitope cassettes, seemed more likely to express the BCEs in their native conformation than the 8-mers. In the T cell proliferation assay, constructs with a higher copy number of TCEs, such as (L(2)T(2))(4), were more antigenic, as long as tandem repeats were separated by spacers. Since the conformation of even sequential BCEs and the processing of TCEs are both sensitive to their molecular environment it is difficult to predict the antigenic properties of polyepitopes. However, with the permutational approach we have developed several polyepitope constructs [(L(4)T(4))(2), (L(2)T(2))(4), (H(2)T(2))(4)] based on complex sequential BCEs that are antigenic for both T and B cells. Several constructs induced sera that reacted with reporter peptides, demonstrating that the sequential nature of the viral epitopes was conserved in the polyepitopes. Although several sera contained antibodies directed against amino acids critical for neutralization, only one construct induced antibodies that cross-reacted with the virus. Our results show the difficulty of designing chimeric antigens based on B cell epitopes mimicking their antigenic and immunologic properties even when these are sequential in nature.

Amino Acid Sequence↗
PubMed2000

Resistance of recent measles virus wild-type isolates to antibody-mediated neutralization by vaccinees with antibody.

The neutralization capacity of sera from Luxembourgian adolescent vaccinees and from Nigerian women with measles-induced immunity to a number of measles virus strains was compared. Although both cohorts were matched for their hemagglutination inhibition and standard neutralization titers, 12 of the 22 late convalescent sera, and only 6 of 24 vaccinees neutralized all viruses. Similarly, only 2 of 20 viruses were not neutralized by at least 75% of late convalescent sera, in comparison to 10 of 20 viruses that resisted neutralization by at least 75% of the vaccinees. The more resistant viruses were not limited to a certain clade. One Nigerian virus was resistant to neutralization by 30% of the late convalescent women and by 75% of vaccinees. These results suggest that qualitative differences in neutralizing antibodies may reduce further protection of infants by passively acquired immunity against wild-type viruses when vaccinated girls become mothers.

Adolescent↗
PubMed2000

Genetic variability of measles viruses circulating in the Benelux.

In Europe measles incidence remains high and in some parts the disease is likely to be still endemic due to insufficient vaccination. Luxembourg experienced an outbreak with at least 110 cases in 1996, and cases continued to be reported throughout 1997. We used molecular epidemiology to investigate this apparent endemicity. On the basis of their N gene sequences, the isolates were assigned to the typical European C2 and D6 genotypes. Sequence diversity within the outbreak was 0.2%. The nucleotide distance between the C2-viruses of the outbreak and the other C2 isolates was at least three or four times higher, suggesting an independent origin of the latter viruses. Similarly, the four D6 viruses found in Luxembourg were thought to be of at least two or three origins. Thus, we propose here to use intra-outbreak sequence diversity to differentiate between sporadic endemic cases and a "pseudo-outbreak" of multiple unrelated imported cases.

Belgium↗