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J H Verheijden

Publications and source records attributed to J H Verheijden.

At least 19 recordsLinked to original sources
PubMed2001

Pseudorabies virus is transmitted among vaccinated conventional pigs, but not among vaccinated SPF pigs.

Whereas the reproduction ratio (R) of pseudorabies virus (PRV) in vaccinated specific pathogen free (SPF) pigs without maternally derived antibodies under experimental conditions has repeatedly been shown to be significantly below 1, R in vaccinated conventional pigs in the field with maternally derived antibodies was significantly above 1. To exclude the difference in husbandry conditions as a cause for this discrepancy, we quantified and compared the transmission of PRV in both groups under identical experimental conditions. Whereas none of the SPF sentinel pigs became infected (R=0, significantly<1), all conventional sentinel pigs did become infected (R=2.5, significantly>1). Moreover, only one SPF pigs shed virus in saliva, the mean cumulative titre being almost a 100-fold less than in conventional pigs (17 pigs, P=0.003). In addition, the mean proliferation of peripheral blood lymphocytes in response to PRV antigens was significantly higher in SPF pigs than in conventional pigs at all points studied (P<0.0001). Moreover, the virus-neutralising antibody titre after vaccination was significantly higher in SPF pigs than in conventional pigs. We conclude that the discrepancy in transmission between vaccinated SPF pigs and vaccinated conventional pigs cannot be attributed to the experimental conditions.

Animal Husbandry↗
PubMed2001

A quantitative assessment of the effectiveness of PRRSV vaccination in pigs under experimental conditions.

This paper presents a quantitative approach to evaluate effectiveness of vaccination under experimental conditions. We used two consecutive experimental designs to investigate whether PRRSV transmission among vaccinated pigs was reduced compared to control pigs and to estimate the reproduction parameter R. Based upon data analysis and power calculations the series of small-scale vaccination-challenge experiments ended with multiple one-to-one experiments. This new experimental design has considerable power to detect the effect of vaccination on transmission if R is close to but still above one in vaccinated pigs. The last experiment showed that transmission was not significantly reduced and the R for vaccinated pigs was estimated to be larger than 4.9. This is remarkable because duration and level of viremia were significantly reduced by vaccination.

Animals↗
PubMed2001

Monitoring of transmission of Salmonella enterica serovars in pigs using bacteriological and serological detection methods.

The standard method to detect Salmonella positive pigs is bacteriological examination of the faeces, but in recent years the use of Salmonella-ELISA's have become available to screen pigs for serological evidence of infection. This study was conducted to monitor the transmission of five different Salmonella enterica serovars (S. Typhimurium, S. Brandenburg, S. Panama, S. Livingstone, and S. Goldcoast) in fattening pigs and to test the feasibility of Salmonella-ELISA, using seeder pigs as a mode of transmission. Serovar dependence in transmission was observed. The Salmonella-ELISA proved to be useful to detect S. Typhimurium and S. Brandenburg in herds but was of limited value to demonstrate S. Livingstone, S. Goldcoast, and S. Panama.

Animals↗
PubMed2001

Pharmacokinetics of sulfadimethoxine and sulfamethoxazole in combination with trimethoprim after oral single- and multiple-dose administration to healthy pigs.

The pharmacokinetics were studied of sulfadimethoxine (SDM) or sulfamethoxazole (SMX) in combination with trimethoprim (TMP) administered as a single oral dose (25 mg + 5 mg per kg body weight) to two groups of 6 healthy pigs. The elimination half-lives of SMX and TMP were quite similar (2-3 h); SDM had a relatively long half-life of 13 h. Both sulfonamides (S) were exclusively metabolized to N4-acetyl derivatives but to different extents. The main metabolic pathway for TMP was O-demethylation and subsequent conjugation. In addition, the plasma concentrations of these drugs and their main metabolites after medication with different in-feed concentrations were determined. The drug (S:TMP) concentrations in the feed were 250:50, 500:100, and 1000:200 mg per kg. Steady-state concentrations were achieved within 48 h of feed medication, twice daily (SDM+TMP) or three times a day (SMX+TMP). Protein binding of SDM and its metabolite was high (>93%), whereas SMX, TMP and their metabolites showed moderate binding (48-75%). Feed medication with 500 ppm sulfonamide combined with 100 ppm TMP provided minimum steady-state plasma concentrations (C(ss,min)) higher than the concentration required for inhibition of the growth of 90% of Actinobacillus pleuropneumoniae strains (n = 20).

Administration, Oral↗
PubMed2001

Intestinal absorption of octreotide using trimethyl chitosan chloride: studies in pigs.

PURPOSE: To investigate the enhancing effect of trimethyl chitosan chloride (TMC) on the enteral absorption of octreotide and to delineate the required doses of both TMC and peptide in vivo in juvenile pigs. METHODS: Six female pigs (body weight, 25 kg) were operated to induce a stoma at the beginning of their jejunum and to insert an in-dwelling fistula for intrajejunal (IJ) administration of the formulations. A silicone cannula was inserted at the jugular vein for blood sampling. One week after surgery the pigs received IJ octreotide solution administrations with or without TMC at pH 7.4 or chitosan HCl at pH 5.5. For determining bioavailability (F) values, the pigs also received an octreotide solution intravenously (IV). Blood samples were taken from the cannulated jugular vein and subsequently analyzed by radioimmunoassay. RESULTS: Intrajejunal administration of 10 mg octreotide without any polymer (control solution) resulted in F values of 1.7 +/- 1.1% (mean +/- SE). Chitosan HCl 1.5% (w/v) at pH 5.5 led to a 3-fold increase in F compared to the control (non-polymer containing) formulations. Co-administration of octreotide with 5 and 10% (w/v) TMC at pH 7.4 resulted in 7.7- and 14.5-fold increase of octreotide absorption, respectively (F of 13.9 +/- 1.3% and 24.8 +/- 1.8%). IJ administration of 5 mg octreotide solutions resulted in low F values of 0.5 +/- 0.6%, whereas co-administration with 5% (w/v) TMC increased the intestinal octreotide bioavailability to 8.2 +/- 1.5%. CONCLUSIONS: Cationic polymers of the chitosan type are able to enhance the intestinal absorption of the peptide drug octreotide in pigs. In this respect, TMC at neutral pH values of 7.4 appears to be more potent than chitosan HCl at a weak acidic pH of 5.5.

Animals↗
PubMed2001

Effect of fermented feed on the microbial population of the gastrointestinal tracts of pigs.

An in vivo experiment was performed with pigs to study the inhibitory effect of fermented feed on the bacterial population of the gastrointestinal tract. Results demonstrated a significant positive correlation between pH and lactobacilli in the stomach contents of pigs in dry feed as well as in the stomach contents of pigs fed fermented feed. Furthermore, a significant positive correlation between the pH and the numbers of bacteria in the family Enterobacteriaceae in the contents of the stomach of pigs fed dry feed was found. In the stomach contents of pigs fed fermented feed, a significant negative correlation was found between the concentration of the undissociated form of lactic acid and the numbers of Enterobacteriaceae. The numbers of Enterobacteriaceae in the contents of the stomach, ileum, cecum, colon, and rectum of pigs fed fermented feed were significantly lower compared with the contents of the stomach, ileum, caecum, colon, and rectum of pigs fed dry feed. The numbers of total lactobacilli were significantly higher in the stomach contents of pigs fed fermented feed and in the ileum contents of one pig group fed fermented feed compared with the contents of pigs fed dry feed. However, the influence of lactobacilli on numbers of Enterobacteriaceae could not be demonstrated. It was concluded that fermented feed influences the bacterial ecology of the gastrointestinal tract and reduces the levels of Enterobacteriaceae in the different parts of the gastrointestinal tract.

Animal Feed↗
PubMed2001

An analysis of a presumed major outbreak of pseudorabies virus in a vaccinated sow herd.

We describe a major outbreak of pseudorabies virus (PRV) in a sow herd in which the sows were vaccinated simultaneously three times a year with a vaccine containing Bartha strain. Also in the associated rearing herd in which the gilts were vaccinated twice an outbreak of PRV occurred. The outbreak was analysed with mathematical models, statistical methods and Monte-Carlo simulation. Under the assumption that the outbreak started with one introduction of virus the reproduction ratio R(ind)--as a measure of transmission of PRV between individuals--in the sow herd was estimated with a Generalized Linear Model to be 1.6. Also under the assumption of one introduction of virus R(ind) in the rearing herd was estimated with a martingale estimator to be 1.7. Both estimates were significantly larger than 1. Mathematical analysis showed that heterogeneity in the sow herd, because of the presence of not-optimally immunized replacement sows could not be the only cause of the observed outbreak in the sow herd. With Monte-Carlo simulations, the duration of an outbreak after a single introduction of virus and R(ind) = 1.6 did not mimic the data and thus the hypothesis of a single introduction with R(ind) = 1.6 could also be rejected and R(ind) is thus, not necessarily above 1. Moreover, with statistical analysis, endemicity in the combination of herds as a cause for the observed outbreak could be rejected. Endemicity in the rearing herd alone could not be excluded. Therefore, multiple introductions from outside and most probably from the rearing herd were possibly the cause of the observed outbreak(s). The implications for eradication of pseudorabies virus were discussed.

Animals↗
PubMed2000

[The leukocyte count is a valuable parameter for detecting classical swine fever].

In this paper we describe a study of the use of the white blood cell count (wbcc) as a parameter for detecting outbreaks of Classical Swine Fever (CSF). Meta-analysis of the results of challenge experiments revealed that oronasal infection of SPF-pigs with the virulent CSF virus (CSFV) strains Brescia or NL9201 resulted in a significant decrease in the average white blood cell count during the first week after inoculation of the virus. Challenge of conventional finishing pigs and sows with the moderately virulent strain Paderborn also resulted in a significant decrease in the average wbcc. However, this decrease was not observed after inoculation of SPF pigs with the mildly virulent CSFV strains Henken, Zoelen, or Bergen. The usefulness of clinical inspection in combination with wbcc to detect CSF outbreaks in the field was examined using the results of 214 EDTA blood specimens collected from 22 infected herds and 7250 EDTA blood specimens collected from 1450 non-infected herds. Half of the infected herds had been infected with the moderately virulent CSFV strain Venhorst (closely related to strain Paderborn) during the 1997-98 epidemic in the Netherlands. The other half had been infected with the moderately virulent CSFV strain Loraine. Using these data as a starting point, 1000 samples of one to ten specimens were generated by Monte Carlo simulation. These simulated samples and the samples of the non-infected herds were analysed by use of Receiver Operating Characteristic curves. On the basis of that analysis, the optimal number of animals whose wbcc needed to be determined to detect a CSF outbreak was five. With this number of animals, in conjunction with the threshold of 8000 white blood cells per mm3 (meaning that a herd is designated as CSF suspect if one or more of the five specimens has a white blood cell count of 8000 leukocytes/mm3 or less), the test procedure had a herd sensitivity (HSE) of 94.5% and a herd specificity (HSP) of 97.2%). The HSE is defined as the percentage of samples of infected herds with a positive result of the test procedure; HSP is defined as the percentage of uninfected herds with a negative result of the test procedure. We conclude that the wbcc can help the veterinary practitioner to detect outbreaks of CSF caused by (moderately) virulent CSFV strains. However, for the detection of outbreaks caused by mildly virulent CSFV strains, the contribution of the wbcc is doubtful. Development of additional tools that can improve the clinical diagnosis of the veterinary practitioner remains desirable.

Animals↗
PubMed2000

Introduction, persistence and fade-out of porcine reproductive and respiratory syndrome virus in a Dutch breeding herd: a mathematical analysis.

The objective of this study was to investigate the dynamics of PRRSV infection and to quantify transmission within a breeding herd, and its impact on herd performance. For this purpose a longitudinal study was performed in a closed breeding herd of 115 sows. Statistical methods and Monte Carlo simulations based on stochastic SIR models were used to analyse the observational data. Moreover, a case-control study was performed to determine whether seroconversion of sows during gestation was associated with aberrant litters. The transmission parameter R was estimated to be 3.0 (95% confidence interval 1.5-6.0) for the model version based on the most plausible assumptions that the infectious period lasts 56 days and no lifelong immunity exists after infection. Based on simulations using a breeding herd of equal size the average time-to-extinction was estimated to be 6 years; using a herd of twice the size, it was 80 years. Furthermore, in contrast to the epidemic phase of the disease, the endemic phase was not detrimental to herd performance.

Animals↗
PubMed2000

Prevention of pleuropneumonia in pigs by in-feed medication with sulphadimethoxine and sulphamethoxazole in combination with trimethoprim.

The prophylactic effect of in-feed medication of conventional pigs with sulphadimethoxine (SDM), sulphamethoxazole (SMX), and trimethoprim (TMP) was tested by using an Actinobacillus pleuropneumoniae infection model. In each of five experiments, six pigs were given medicated feed twice daily and three pigs received antibiotic-free feed and served as positive (unmedicated, infected) controls. The following drugs or drug combinations were tested (in mg per kg feed): 500 SDM + 100 TMP, 500 SMX + 100 TMP, 125 SMX + 25 TMP, 125 SMX (alone) and 25 TMP (alone). After six days of feed medication, all animals were endobronchially inoculated with A. pleuropneumoniae in a dose of 1-3.10(4) colony-forming units (CFU). The response to the challenge in all control pigs was characterized by fever, lethargy, anorexia, reduced water consumption, and laboured breathing. At autopsy all controls manifested a fibrinous haemorrhagic pleuropneumonia. In-feed medication with 500 SDM + 100 TMP, 500 SMX + 100 TMP as well as 125 SMX + 25 TMP resulted in an effective protection against the challenge in all treated animals. After consumption of feed medicated with 125 mg per kg SMX or 25 mg per kg TMP, pleuropneumonia was evident in all challenged pigs. The results of this study indicate an in vivo potentiation of SMX and TMP in pigs against this respiratory tract pathogen.

Actinobacillus Infections↗
PubMed2000

Transmission of classical swine fever virus by artificial insemination during the 1997-1998 epidemic in The Netherlands: a descriptive epidemiological study.

In the course of the 1997-1998 CSF epidemic in the Netherlands, two semen collection centres (SCC) became infected. As an eradication strategy for an acute crisis situation, it was concluded that all semen of the boars at the SCCs collected and distributed in the risk period of 28 January to 7 March 1997 was potentially contaminated (suspect semen). As a consequence, a total of 1,680 pig herds, mainly located in the southern part of the Netherlands, were officially declared CSF suspect. The purpose of this study was to investigate whether infection of farms through contaminated semen played a significant role in the CSF epidemic. A total of 123 CSFV infected herds were identified, that had received suspect semen from one or both of the infected SCCs. In 87 out of these 123 infected herds, infection by way of artificial insemination (AI) could be excluded either according to the insemination information or the infection pattern observed. In only 21 herds, infection by way of AI was regarded as possible according to the insemination information and infection pattern. Owing to missing information, no conclusion could be drawn about the possibility of infection of 15 farms by way of AI. Thus, we conclude that at most 36 farms may have been infected through AI during the CSF epidemic in the Netherlands.

Animals↗
PubMed1999

Effects of enrofloxacin on porcine phagocytic function.

The interaction between enrofloxacin and porcine phagocytes was studied with clinically relevant concentrations of enrofloxacin. Enrofloxacin accumulated in phagocytes, with cellular concentration/extracellular concentration ratios of 9 for polymorphonuclear leukocytes (PMNs) and 5 for alveolar macrophages (AMs). Cells with accumulated enrofloxacin brought into enrofloxacin-free medium released approximately 80% (AMs) to 90% (PMNs) of their enrofloxacin within the first 10 min, after which no further release was seen. Enrofloxacin affected neither the viability of PMNs and AMs nor the chemotaxis of PMNs at concentrations ranging from 0 to 10 microg/ml. Enrofloxacin (0.5 microg/ml) did not alter the capability of PMNs and AMs to phagocytize fluorescent microparticles or Actinobacillus pleuropneumoniae, Pasteurella multocida, and Staphylococcus aureus. Significant differences in intracellular killing were seen with enrofloxacin at 5x the MIC compared with that for controls not treated with enrofloxacin. PMNs killed all S. aureus isolates in 3 h with or without enrofloxacin. Intracellular S. aureus isolates in AMs were less susceptible than extracellular S. aureus isolates to the bactericidal effect of enrofloxacin. P. multocida was not phagocytosed by PMNs. AMs did not kill P. multocida, and similar intra- and extracellular reductions of P. multocida isolates by enrofloxacin were found. Intraphagocytic killing of A. pleuropneumoniae was significantly enhanced by enrofloxacin at 5x the MIC in both PMNs and AMs. AMs are very susceptible to the A. pleuropneumoniae cytotoxin. This suggests that in serologically naive pigs the enhancing effect of enrofloxacin on the bactericidal action of PMNs may have clinical relevance.

Actinobacillus pleuropneumoniae↗
PubMed1998

Implications derived from a mathematical model for eradication of pseudorabies virus.

Simple mathematical models based on experimental and observational data were applied to evaluate the feasibility of eradicating pseudorabies virus (PRV) regionally by vaccination and to determine which factors can jeopardise eradication. As much as possible, the models were uncomplicated and our conclusions were based on mathematical analysis. For complicated situations, Monte-Carlo simulation was used to support the conclusions. For eradication, it is sufficient that the reproduction ratio R (the number of units infected by one infectious unit) is < 1. However, R can be determined at different scales: at one end the region with the herds as units and at the other end compartments with the pigs as units. Results from modelling within herds showed that contacts between groups within a herd is important whenever R between individuals (R(ind)) is > 1 in one or more groups. This is the case within finishing herds. In addition, if the R(ind) is more than 1 within a herd, the size of the herd determines whether PRV can persist in the herd and determines the duration of persistence. Moreover, when reactivation of PRV in well-vaccinated sows is taken into account, R(ind) in sow herds is still less than 1. In sow herds with group-housing systems, it is possible that in those groups R(ind) is > 1. Results from modelling between herds showed that whether or not Rherd is < 1 in a particular region is determined by two factors: (1) the transmission of infection between nucleus herds and rearing herds through transfer of animals and (2) contacts among finishing herds and among rearing herds. The transmission between herds can be reduced by reduction of the contact rate between herds. reduction of the herd size, and reduction of the transmission within herds.

Animals↗
PubMed1998

New GnRH-like peptide construct to optimize efficient immunocastration of male pigs by immunoneutralization of GnRH.

Castration of male pigs is routinely performed in order to prevent the occurrence of boar taint in pig carcasses. However, boar taint can also be eliminated by immunological castration using a synthetic peptide vaccine against GnRH. For pig farming, to make immunocastration a feasible alternative method to surgical castration, the composition of the vaccine has to be not only reliable and effective but also cost-efficient and safe. Previously the authors have developed an effective immunocastration vaccine by replacing the monomer GnRH by a much more immunogenic tandem peptide. However, this tandem-GnRH vaccine preparation needs Complete Freund's adjuvant and to be applied at a relatively high dose. Therefore, alternative antigens were designed to cope with this problem and tested with different adjuvants and dosages. An effective new antigen was designed based on a GnRH-tandem peptide, which was dimerized and modified in one amino acid position of the decapeptide to allow conjugation of this tandem-dimer to ovalbumin. In mild adjuvants and in low dosage, this antigen was very effective in reducing testis weight, serum LH and androstenone level in backfat. Thus, an improved immunocastration vaccine has been designed that is relatively cost-efficient and highly efficacious in two vaccinations at low dose.

Adjuvants, Immunologic↗
PubMed1997

No massive spread of pseudorabies virus in vaccinated sow herds.

In this study, we quantified transmission of PRV in 99 sow herds in which the sows were vaccinated three times a year with strain 783 O/W and found that the reproduction ratio R was 0.66, which is significantly below one. This implies that massive spread of PRV cannot occur in such herds.

Animals↗
PubMed1997

Seroprevalence of porcine reproductive and respiratory syndrome virus in Dutch weaning pigs.

To determine whether under Dutch field conditions PRRSV infection occurs in weaning pigs before the finishing period, a cross-sectional study was performed on 32 breeding farms to estimate the seroprevalence of antibodies directed against PRRSV in 4- to 5-week-old and 8- to 9-week-old pigs. Farms were visited twice within 5 months, and during each sampling an average of 20 sera were randomly collected from a unit of 4- to 5-week-old and a unit of 8- to 9-week-old pigs. The sera (n = 2568) were tested in the IDEXX-ELISA for the presence of antibodies directed against PRRSV. The seroprevalence of PRRSV in 4- to 5-week-old pigs and 8- to 9-week-old pigs varied between both samplings for each farm. The seroprevalence in the younger pigs was significantly higher than in the older pigs for both samplings (p < 0.05), suggesting the presence of maternal antibodies. In addition, a longitudinal study was performed to evaluate the IDEXX-ELISA in detecting maternal antibodies directed against PRRSV and to determine the rate of decline of these antibodies in field sera. From serological results of eight litters, an average decay function was computed to quantify the maternal immunity to PRRSV. A seroprevalence in 8- to 9-weeks-old pigs of > or = 0.20 was calculated to indicate an active immune response to PRRSV. In the cross-sectional study in the pigs twenty-three percent of the units with 8- to 9-week-old pigs were considered to have an active serological response against PRRSV. We conclude that most Dutch pigs are seronegative for PRRSV at the start of the finishing period, since the results of this study showed that 77% of the units with 8- to 9-week-old pigs had a seroprevalence < 0.20.

Aging↗