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Biomedical subjects

P De Herdt

Publications and source records attributed to P De Herdt.

At least 19 recordsLinked to original sources
PubMed2005

Evaluation of the enzyme-linked immunosorbent assay for the detection of antibodies against infectious bursal disease virus (IBDV) and the estimation of the optimal age for IBDV vaccination in broilers.

In order to evaluate the usefulness of the enzyme-linked immunosorbent assay (ELISA) in determining the optimal age for infectious bursal disease virus (IBDV) vaccination in broilers under field circumstances, the percentage of birds susceptible to vaccine at vaccination age was estimated in 12 flocks on the basis of ELISA titres in newborn chicks. The effective percentage of susceptible birds at the day of vaccination was checked by comparing virus neutralization (VN) titres measured in sera taken immediately before vaccine administration with the breakthrough titre of the vaccine used. In nine of the 12 flocks, the ELISA had largely overestimated the percentage of susceptible birds. Subsequently, to examine the performance of the ELISA kit, 815 chicken sera were comparatively examined in ELISA and VN tests. Results demonstrated a linear relationship between mean ELISA titres and VN titres. It was concluded that the ELISA could be a useful tool in IBDV vaccination timing, but that interpretation criteria should be adjusted to avoid vaccination at too early an age.

Aging↗
PubMed2004

Colibacillosis in caged layer hens: characteristics of the disease and the aetiological agent.

In Europe, outbreaks of acute mortality in layer flocks due to colisepticaemia have frequently been observed since the mid-1990s. The aims of this study were to describe the disease, to identify the serotypes of the avian pathogenic Escherichia coli (APEC) present in these outbreaks, and to detect the presence of F11 fimbriae and flagella in the isolates. For this purpose, 20 flocks with APEC-associated increased mortality and 20 control flocks matched for age were examined. Weekly mortality rates in the colibacillosis-affected flocks reached 1.71%, versus 0.30% in the control flocks. The maximum cumulative mortality over an entire colibacillosis outbreak reached 9.19%. The disease was often flock and hen house associated, with recurrent outbreaks within one round and in successive rounds in the same house. Disease was usually acute without clinical symptoms. Peritonitis with yolk material deposited in the peritoneal cavity and polyserositis were the main lesions at necropsy. O78 strains were isolated in 15 of the 20 colibacillosis flocks, and in only one of the control flocks. The majority of strains from the control flocks could not be serotyped by the 28 O-antisera used. In general, F11 fimbriae and flagella were present in the majority of the strains. F11 fimbriae were significantly more often found in O78 isolates than in the other serotypes, and are thus more often present in isolates from colibacillosis flocks. Strains positive for F11, and for F11 and flagella, were more frequently present in heart and liver of the colibacillosis-affected flocks.

Animals↗
PubMed2004

Significance of interactions between Escherichia coli and respiratory pathogens in layer hen flocks suffering from colibacillosis-associated mortality.

This study aimed to examine the significance of interactions between Escherichia coli and various respiratory pathogens during outbreaks of colibacillosis-associated mortality in layer hen flocks under field conditions. For this purpose, a case-control study involving 20 control flocks with baseline mortality and 20 flocks with increased mortality due to E. coli septicaemia and polyserositis, was conducted. In each colibacillosis flock, blood samples were taken from 20 hens at the onset of clinical disease and three times thereafter at 2-week intervals. Control flocks of comparable ages were sampled in the same way. Pooled sera, taken at the first and last sampling, were examined for antibody titres against infectious bronchitis virus (IBV) and Newcastle disease virus (NDV), and the individual sera from all four samplings were examined for the presence and/or titres of antibodies against avian pneumovirus (APV), Mycoplasma gallisepticum, Mycoplasma synoviae and Ornithobacterium rhinotracheale. Titre increases were seen for IBV D274 (one control flock) and O. rhinotracheale (one control and one colibacillosis flock). An increase in per cent reactors was seen for APV (one control flock), and for M. synoviae (one control and two colibacillosis flocks). The study failed to detect any consistent interactions between E. coli and the aforementioned pathogens. These results indicate that, at least as observed in this study, outbreaks of increased mortality resulting from colibacillosis are not necessarily associated with IBV, NDV, APV, M. gallisepticum, M. synoviae or O. rhinotracheale infections.

Animals↗
PubMed2004

Risk factors associated with colibacillosis outbreaks in caged layer flocks.

Colibacillosis appears to be of increasing significance in layer flocks, but there have been no studies of the risk factors associated with outbreaks. This study aimed to investigate the possible associations between risk factors of non-infectious nature and outbreaks of mortality due to colibacillosis in flocks of caged layer hens. Information on management, biosecurity measures and housing conditions was collected in 20 flocks suffering from the disease and in 20 clinically healthy control flocks. The data were processed using multiple logistic regression. The statistical analysis demonstrated that an increase in the distance to the nearest poultry farm by 1 km was associated with a six-fold decreased risk of an outbreak of colibacillosis (odds ratio=0.16). Furthermore, a 1 l increase in cage volume per hen was associated with a 33% decrease in the risk of an outbreak (odds ratio=0.75). It was concluded that the distance between poultry farms and the hen density in the cages are important risk factors for outbreaks of colibacillosis in flocks of layer hens.

Animal Husbandry↗
PubMed2003

An outbreak of histomoniasis in free-range layer hens.

Histomonas meleagridis was held primarily responsible for an outbreak of 6% increased mortality and 11% decreased egg production between weeks 57 and 72 in a flock of free-range layer hens, concurrently infected with Brachyspira-like bacteria. This case can be considered an example of ancient diseases re-emerging in alternative housing systems that are promoted because of animal welfare considerations, but that at the same time allow rapid spread of pathogens in birds for which only few curative drugs are registered. Therefore, new housing methods should be introduced gradually to gain experience with them.

Animals↗
PubMed2002

Interactions of Salmonella enterica serovar Muenchen with macrophages of the turtle Trachemys scripta scripta.

Interactions of Salmonella with macrophages have been studied in birds and, most extensively, in mammals. In these homeothermic animals, interactions between Salmonella and macrophages are characterized by the following processes. After macropinocytosis, spacious phagosomes are formed within the macrophage. Partial inhibition of phagosome-lysosome fusion and resistance to the formation of reactive oxygen species and reactive nitrogen intermediates enable the bacterium to survive and even multiply within the host macrophage. Eventually, Salmonella will induce apoptosis of the macrophage. In this study, interactions of peritoneal macrophages of the turtle Trachemys scripta scripta with Salmonella enterica serovar Muenchen were examined in vitro. Turtle macrophages were able to phagocytise Salmonella efficiently at both 30 and 37 degrees C. Exposure of macrophages to Salmonella induced the production of reactive oxygen species, which could be partially suppressed by adding the NADPH oxidase inhibitor diphenylene iodonium. Initially, most of the intracellular bacteria were killed. However, Salmonella proved to be able to persist and multiply inside turtle macrophages at both 30 and 37 degrees C for at least 48 h, despite the production of reactive nitrogen intermediates by inducible NO synthase. Salmonella infection of turtle macrophages killed the phagocytes at both 30 and 37 degrees C. These findings demonstrate that no obvious qualitative differences exist between macrophage-Salmonella interactions from homeothermic animals and from turtles. This indicates that other factors are responsible for the different course of Salmonella infections in homeothermic and poikilothermic hosts.

Animals↗
PubMed2002

Failure of a low virulence Streptococcus gallolyticus serotype 1 strain to immunize pigeons against streptococcosis.

Ten pigeons were inoculated intravenously with the low virulence Streptococcus gallolyticus strain PDH 827, which belongs to serotype 1, supernatant phenotype A(-)T2. The birds did not develop clinical disease but shed S. gallolyticus in their faeces, and antibodies against the bacterium were detected in post-inoculation plasma samples of all birds. Seven weeks later, these pigeons, as well as 14 control pigeons, were challenged intravenously with the highly virulent S. gallolyticus strain STR 357, which also belongs to serotype 1 but to the supernatant phenotype A(+)T1. Post-inoculation morbidity in the immunized group amounted to 90%, demonstrating that no protective immunity had been built up after the first infection. These findings indicate that serotype-specific antigens are not, or at least not solely, involved in induction of protection against S. gallolyticus septicaemia in pigeons.

Animals↗
PubMed2002

The effect of Ornithobacterium rhinotracheale vaccination of broiler breeder chickens on the performance of their progeny.

The effect of Ornithobacterium rhinotracheale vaccination of broiler breeders on antibody titres and performance of breeders and broilers was investigated. O. rhinotracheale antibody titres and performance data were recorded from 16 different broiler breeder flocks and from 79 of their broiler progeny flocks. Eight breeder flocks were vaccinated with an inactivated O. rhinotracheale vaccine while the other eight breeder flocks were left unvaccinated against this bacterium. Following vaccination, mean O. rhinotracheale antibody titres in the breeders rose to a 6.5 log(2) units higher value than in unvaccinated breeders, and remained at a mean titre of 15 log(2) units during the entire production period. This resulted in significantly higher maternal antibody titres against O. rhinotracheale in the broiler progeny of vaccinated breeder flocks compared with the offspring of unvaccinated flocks. Statistical analyses revealed no differences in performance between vaccinated and unvaccinated breeders. There was a significantly lower mean mortality rate and higher mean production index in the broilers derived from vaccinated breeders.

Animals↗
PubMed2001

Sequence analysis of a RAPD band differentiating high and low virulence Staphylococcus aureus strains from rabbits.

RAPD typing revealed the presence of a nucleotide band in typical high virulence rabbit Staphylococcus aureus strains which was absent in low virulence strains and in an atypical high virulence strain. The nucleotide sequence of this band was determined. Primers within this sequence were developed and PCR products of eight typical high virulence, one atypical high virulence and nine low virulence rabbit S. aureus strains were sequenced. All low virulence strains and the atypical high virulence strain revealed a constant difference with the typical high virulence strains for nucleotide 377 of the 1055bp sequence. The eight typical high virulence strains possessed a guanine base on this site, while the other strains tested showed an adenine base. These findings support the hypothesis on the clonal origin of typical high virulence rabbit S. aureus strains. After comparison with databases, two open reading frames (ORF) were identified within the sequence, which appeared to encode two structural ribosomal proteins. The single nucleotide mutation does not affect the amino acid sequence of the protein it encodes for.

Animals↗
PubMed2001

Secreted antigens as virulence-associated markers in Staphylococcus aureus strains from rabbits.

Western blot analysis was performed from the culture supernatant of 59 rabbit Staphylococcus aureus strains, classified as high and low virulence strains according to their epidemiological behaviour in commercial rabbitries, bio-, phage- and RAPD-type. Fourteen extracellular antigen bands (A-N) were recognised using sera of rabbits immunised with washed, viable high virulence S. aureus bacteria. Eleven of these bands were found in high virulence as well as in low virulence strains. The band A, approximately 78 kDa, was not seen in any of the 27 high virulence strains, except for one strain which was also typical in other aspects, was detected in all, but one of the low virulence strains. The M and N bands with molecular masses of approximately 29 and 27 kDa, respectively, were recognised in all high virulence strains except for the atypical strain, but in none of the low virulence strains. This indicates that the latter two antigens may be virulence-associated markers for S. aureus strains from rabbits.

Animal Diseases↗
PubMed2000

Adhesion of Streptococcus gallolyticus strains to extracellular matrix proteins.

Fourteen pigeon Streptococcus gallolyticus strains of differing virulence, were tested for their ability to adhere to immobilised fibronectin, collagen types I, III and IV. Eight, 2 and 13 strains were able to bind fibronectin, collagen types III and IV, respectively. None of the strains adhered to collagen type I. Heat treatment, proteolytic digestion or periodate treatment reduced the binding of S. gallolyticus to fibronectin and collagen type IV, suggesting that surface receptors contain proteins and carbohydrates. Although binding to these extracellular matrix proteins can play a role in the pathogenesis of streptococcosis in pigeons, binding properties could not be related to virulence, indicating that other factors determine differences in virulence among pigeon S. gallolyticus strains. Adhesion to collagen type IV may account in part for the distribution pattern of the lesions observed in naturally and experimentally infected pigeons.

Animals↗
PubMed2000

Identification of virulence associated markers in the cell wall of pigeon Streptococcus gallolyticus strains.

The cell wall protein profiles of 56 isolates of Streptococcus gallolyticus of differing virulence for pigeons were compared by SDS-PAGE. Additionally, Western blot analysis was performed on the cell wall proteins of 14 strains using sera of pigeons, experimentally infected with A(+)T1 or A(-)T2 strains of S. gallolyticus. The profile of silver stained gels exhibited a complex array of 20-50 bands ranging from less than 6.5-210kDa. A band with molecular mass of 114kDa was only observed in isolates that belonged to the highly virulent A(+)T1, A(+)T2, A(+)T3 and A(-)T1 culture supernatant groups. A band with a slightly higher molecular mass (115kDa) as well as a 207kDa band were only detected in isolates that belonged to the moderately A(-)T3 or low A(-)T2 virulent culture supernatant groups. The 114 and 115kDa band were recognised by all homologous and heterologous pigeon sera used whereas the 207kDa band was only recognised by sera of pigeons infected with a A(-)T2 strain. These findings may indicate that the 114, 115 and 207kDa bands are useful as additional virulence associated markers for pigeon S. gallolyticus strains.

Animals↗
PubMed2000

Colonisation of rabbits with Staphylococcus aureus after experimental infection with high and low virulence strains.

Four groups of 12 rabbits each were inoculated in the nose with strains with suspected differences in virulence. In the two groups infected with strains from severe outbreaks, belonging to a rabbit-pathogenic biotype-phage type combination, 6-12 rabbits were found positive at the successive bacteriological samplings over a period of 28 days. In the two other groups, infected with strains obtained from rabbitries without a history of staphylococcosis, the number of Staphylococcus aureus positive animals quickly became negative but increased again after 1 week to 1-5 positive animals until the end of the experiment. Two rabbits in each group inoculated with a high virulence strain developed purulent skin lesions, while in the groups inoculated with low virulence strains, all animals remained clinically healthy. Results indicate that colonisation capacity is an important virulence determinant in rabbit staphylococcosis.

Administration, Intranasal↗
PubMed2000

Differentiation between high and low virulence Staphylococcus aureus strains from rabbits by randomly amplified polymorphic DNA (RAPD) analysis.

Randomly Amplified Polymorphic DNA (RAPD) typing was performed on 53 rabbit Staphylococcus aureus strains. Twenty-three strains isolated in 13 different rabbitries with chronic problems of staphylococcosis, showed the same RAPD banding pattern. Twenty of these strains belonged to the 'mixed CV-C' biotype and to the phage-type 3A/3C/55/71, previously described to be highly virulent in rabbits, and three strains belonged to other biotypes or phage-types. None of the strains isolated from rabbitries without chronic problems of staphylococcosis showed this specific RAPD pattern. RAPD analysis can be used as a rapid and reliable test method to differentiate between the characteristic genotype corresponding to high virulence and other S. aureus strains from rabbits. This is useful for the diagnosis and prevention of the introduction of these highly virulent strains in industrial rabbitries.

Animals↗