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M C De Jong

Publications and source records attributed to M C De Jong.

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

Herd immunity after vaccination: how to quantify it and how to use it to halt disease.

In comparison to unvaccinated individuals, vaccinated individuals have fewer clinical symptoms, reduced susceptibility and reduced infectivity. The first two effects of vaccination can mean that each vaccinated individual is protected against clinical symptoms. From experiments and field trials, the extent of individual protection can be determined by a statistical analysis of the resulting data. In addition, there is an effect of the vaccination on the populations in which one or more individuals are vaccinated. This effect on the population is due to the effects of vaccination on susceptibility and infectivity of the vaccinated individuals. The population effect is called herd immunity and is observed as a reduction in chance of becoming infected when being part of a population with some of the individuals vaccinated. Note that the protection by herd immunity applies to vaccinated individuals as well as to unvaccinated individuals. Thus, protection against disease can be achieved not only by vaccinating the individuals that have to be protected but also by vaccinating other individuals in the same population. Such an application of herd immunity is especially important in protecting farm animals. To plan and evaluate vaccination at the population level, the herd immunity needs to be quantified. It will be illustrated that it is possible, not only theoretically but also practically, to quantify herd immunity among farm animals with data from small-scale experiments as well as with data from field trials.

Animal Diseases↗
PubMed2001

Evaluation of diagnostic tests for the detection of classical swine fever in the field without a gold standard.

Knowledge of the sensitivity of diagnostic tests for infectious diseases under field conditions can be used to design a surveillance program that increases the effectiveness of the control policy. In this study, the sensitivity of tests for the detection of classical swine fever (CSF) virus (CSFV) under field conditions was estimated without knowledge of the true disease status of the animals tested. During the CSF epidemic of 1997-1998 in The Netherlands, tonsil samples from pigs of CSF suspect farms were collected for laboratory diagnosis of CSE These specimens were tested in a fluorescence antibody test (FAT1) for the presence of CSFV antigen. When at least 1 specimen in a particular sample series from a farm was positive, this farm was declared CSFV infected. Specimens of that series, either FAT1 negative (98) or FAT1 positive (127), were subsequently tested again (FAT2). After that, a suspension was made of the remaining tissue, and this suspension was evaluated with a virus isolation test. In total, 225 tonsil specimens were examined. A statistical model was formulated, and the sensitivity of the 3 tests and the prevalence of positive specimens in the sample were estimated by the method of maximum likelihood. The sensitivity of the FAT1, the test that was used for confirmation of CSFV infection in a pig herd, was approximately 78% (95% confidence interval [CI] = 62-92%). The effectiveness of the selection process of animals on the farm by the veterinarian was estimated to be 77% (64-87%). The sensitivity of the combination of FAT1 and FAT2 (60%) indicates that at least 5 animals should be selected on a CSF-suspect farm to gain a detection probability for CSFV of 99%.

Animal Husbandry↗
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

Determination of the onset of the herd-immunity induced by the E2 sub-unit vaccine against classical swine fever virus.

For a recently developed E2 subunit vaccine against classical swine fever (CSF), the reduction in transmission, at different moments after vaccination, was assessed by animal experiments and statistical calculations. Two experiments were performed to estimate the reproduction ratio R. Experiment 1 consisted of three groups and experiment 2 of two groups each of 10 pigs. In four of these groups, all pigs were vaccinated intramuscularly with the vaccine. The pigs in the fifth group remained unvaccinated (control group). After treatment, half of each group was intranasally inoculated with the virulent CSFV strain Brescia. In the vaccine groups, the following vaccination-challenge intervals were applied: 14, 14, 10, and 7 days, respectively. The occurrence of (contact-) infection was determined using the E(rns) ELISA. In the 7-days interval group and in the control group, virus transmission to all contact pigs occurred, indicating R1. Neither in the two 2-week interval groups nor in the 10-day interval group did contact-infections occur. Hence, the estimated R is less than one, which indicates that an epidemic would fade out. Therefore, the E2 subunit vaccine may be an efficacious tool in a control program during an outbreak of CSF as from 10 days after vaccination.

Animals↗
PubMed1999

Multiple mechanisms confer drug resistance to mitoxantrone in the human 8226 myeloma cell line.

Selection for in vitro drug resistance can result in a complex phenotype with more than one mechanism of resistance emerging concurrently or sequentially. We examined emerging mechanisms of drug resistance during selection with mitoxantrone in the human myeloma cell line 8226. A novel transport mechanism appeared early in the selection process that was associated with a 10-fold resistance to mitoxantrone in the 8226/MR4 cell line. The reduction in intracellular drug concentration was ATP-dependent and ouabain-insensitive. The 8226/MR4 cell line was 34-fold cross-resistant to the fluorescent aza-anthrapyrazole BBR 3390. The resistance to BBR 3390 coincided with a 50% reduction in intracellular drug concentration. Confocal microscopy using BBR 3390 revealed a 64% decrease in the nuclear:cytoplasmic ratio in the drug-resistant cell line. The reduction in intracellular drug concentration of both mitoxantrone and BBR 3390 was reversed by a novel chemosensitizing agent, fumitremorgin C. In contrast, fumitremorgin C had no effect on resistance to mitoxantrone or BBR 3390 in the P-glycoprotein-positive 8226/DOX6 cell line. Increasing the degree of resistance to mitoxantrone in the 8226 cell line from 10 to 37 times (8226/MR20) did not further reduce the intracellular drug concentration. However, the 8226/MR20 cell line exhibited 88 and 70% reductions in topoisomerase II beta and alpha expression, respectively, compared with the parental drug sensitive cell line. This decrease in topoisomerase expression and activity was not observed in the low-level drug-resistant, 8226/MR4 cell line. These data demonstrate that low-level mitoxantrone resistance is due to the presence of a novel, energy-dependent drug efflux pump similar to P-glycoprotein and multidrug resistance-associated protein. Reversal of resistance by blocking drug efflux with fumitremorgin C should allow for functional analysis of this novel transporter in cancer cell lines or clinical tumor samples. Increased resistance to mitoxantrone may result from reduced intracellular drug accumulation, altered nuclear/cytoplasmic drug distribution, and alterations in topoisomerase II activity.

Adenosine Triphosphate↗
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↗
PubMed1997

The influence of maternal immunity on the transmission of pseudorabies virus and on the effectiveness of vaccination.

The purpose of this study was to investigate whether maternal immunity could prevent transmission of pseudorabies virus (PRV) among pigs, and whether it reduced the effectiveness of a single or double vaccination with regard to the transmission of PRV. In five experiments, the transmission of PRV, expressed as the reproduction ratio R, was compared in groups of pigs with maternal immunity and in groups of pigs without maternal immunity. Transmission of PRV among unvaccinated pigs with maternal immunity (R = 0.2) was significantly lower than among pigs without maternal immunity (R = 6.3). Furthermore, maternal immunity in young pigs prevented transmission of PRV, as R was significantly below one. In once-vaccinated groups, PRV spread extensively among pigs with maternal immunity (R = 23), but did not spread extensively among pigs without maternal immunity (R = 0.6). In twice-vaccinated groups, transmission of PRV among pigs with maternal immunity (R = 0.6) did not differ significantly from the transmission of PRV among pigs without maternal immunity (R = 0.3). Thus, a single vaccination of pigs with PRV strain 783 at 10 weeks of age, when they still possessed maternal immunity, seemed not sufficient to prevent transmission of PRV. Virus transmission could be reduced, however, if maternally immune pigs were vaccinated twice at 10 and 14 weeks of age.

Animals↗
PubMed1997

Comparison of two pseudorabies virus vaccines, that differ in capacity to reduce virus excretion after a challenge infection, in their capacity of reducing transmission of pseudorabies virus.

Pseudorabies virus (PRV) vaccines are often compared for their capacity to reduce virus excretion after a challenge infection. Vaccines, used for the eradication of PRV, however, should reduce transmission of PRV among pigs. The purpose of this study was to investigate whether the amount of virus excreted after a challenge infection is an accurate measure of the capacity of a vaccine to reduce transmission of PRV among pigs. Two experiments were carried out, each using two groups of 10 pigs. The pigs in group one were intramuscularly vaccinated once with the glycoprotein E (gE)-negative vaccine X, the pigs in group two with the gE-negative strain 783. Eight weeks later, 5 pigs in each group were inoculated with wild-type PRV. A gE-ELISA was used to detect PRV infection. The transmission of PRV was estimated from the number of contact infections and expressed as the reproduction ratio R. The inoculated pigs vaccinated with vaccine X shed significantly more virus than the inoculated pigs vaccinated with strain 783. However, despite the difference in virus excretion, the transmission of PRV between the two groups did not differ. We conclude that virus excretion is not an accurate measure for determining vaccine effectiveness. However, R of vaccine X (R = 0.98) was not significantly below one, whereas R of vaccine 783 (R = 0) was significantly below one. Consequently, we cannot exclude the possibility that major outbreaks of PRV occur among pigs vaccinated with vaccine X.

Animals↗
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

Evaluation of tests for detection of antibodies to Aujeszky's disease (pseudorabies) virus glycoprotein E in the target population.

Receiver operating characteristic (ROC) curves assess the quality of tests over the entire range of test signals. We compared the ability of an ELISA to detect antibodies to Aujeszky's disease (pseudorabies) virus gE in colostrum (test A) and in a single droplet of whole blood (test B) with the results obtained in serum (gold standard) in the target population by constructing and analyzing such curves. The area under the ROC curve, which is a quantitative measure of test performance, proved to be significantly (p < 0.01) smaller in test A than in test B or the gold standard. No significant differences in the area under the ROC curve were observed between test B and the gold standard.

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↗
PubMed1997

Immunohistological characterization of the local cellular response directed against pseudorabies virus in pigs.

The aim of this study was to investigate the kinetics of a primary and secondary immune response against pseudorabies virus (PRV). Pigs vaccinated with strain 783 and unvaccinated pigs were challenged with wild-type PRV by either intranasal or subcutaneous infection. Non-challenged pigs were used as controls. On days 1, 3 and 7 after challenge, tissues from the site of infection, and the tonsils of intranasally and the draining lymph nodes of subcutaneously challenged pigs were sampled. Immunohistological staining was used to characterize the various cell populations at the primary site of virus replication and in the lymphoid tissue. Tissue sections were stained for the T-cell markers CD2, CD3 gamma delta, CD4 and CD8, for the B-cell markers IgM, IgA and IgG, for a macrophage marker, and for PRV antigen. After challenge, PRV was detected during a shorter period in vaccinated pigs, and was less disseminated than in unvaccinated pigs. Cellular infiltrates were detected both in the nasal mucosa and the subcutaneous tissue of both unvaccinated and vaccinated pigs. Cell infiltrates, however, appeared earlier in vaccinated than in unvaccinated pigs, indicating a difference in kinetics of the primary and secondary immune response. The appearance of T-cells preceded the appearance of B-cells, but the proportion of the various subsets did not differ between unvaccinated and vaccinated pigs. These findings suggest that the early immune response in vaccinated pigs may contribute to the rapid clearance of virus at the primary site of infection. In addition, T-cells appear to have a more important role in the clearance of PRV than B-cells.

Animals↗
PubMed1997

Pseudorabies virus infections in pigs. Role of viral proteins in virulence, pathogenesis and transmission.

This paper reviews new findings on the biological functions of pseudorabies virus (PRV) proteins. It focuses on the role of PRV proteins in the pathogenicity, immunogenicity and transmission of PRV vaccine strains in pigs. Furthermore, it evaluates potential risks that are connected with the use of PRV vector strains. Special emphasis is placed upon the spread of genetically engineered vaccine strains within pigs or between pigs.

Animals↗
PubMed1996

Bullous pemphigoid and epidermolysis bullosa acquisita. Differentiation by fluorescence overlay antigen mapping.

BACKGROUND AND DESIGN: From previous studies, we concluded that the fluorescence overlay antigen mapping (FOAM) technique could be of value to the differential diagnosis of the acquired subepidermal bullous skin disorders, bullous pemphigoid (BP) and epidermolysis bullosa acquisita (EBA). In these diseases, ultrastructural identification of the site of skin-bound IgG deposits at the epidermal basement membrane zone (EBMZ) may be essential to the correct diagnosis. Since ultrastructural studies are more expensive, time-consuming, and less widely available than immunofluorescence, we addressed the question of whether the FOAM technique can reliably identify the site of IgG deposits at the EBMZ, and distinguish BP from EBA. For this purpose, the technique was applied to perilesional skin from seven patients with BP and six with EBA, using computer-aided imaging of red-stained type VII collagen and green-stained IgG, according to previous findings. RESULTS: Digitized multicolor FOAM images of perilesional skin from patients with BP showed nonoverlap band patterns of green-stained lamina lucida IgG deposits (ultrastructurally proven) and red-stained type VII collagen. By contrast, FOAM images of EBA skin typically showed overlap patterns of green-stained sublamina densa IgG deposits and red-stained type VII collagen. These findings were observed also in skin tissue stored in Michel's transport medium or stored frozen for 15 years. CONCLUSIONS: The computer-aided FOAM technique may have great potential in distinguishing between IgG deposits above (BP) and just below (EBA) the lamina densa of the EBMZ in skin tissue. The technique is not as simple as saline-split skin methodology but offers more flexibility, and it certainly is quicker and less expensive than electron microscopy. Furthermore, the use of digitized fluorescence images offers improved possibilities for evaluating the various "linear" patterns of immune reactant deposition at the EBMZ in subepidermal bullous autoimmune skin diseases.

Adult↗
PubMed1996

No major outbreaks of pseudorabies virus in well-immunized sow herds.

In this study we quantified the transmission of pseudorabies virus (PRV) in well-immunized sow herds in The Netherlands. In three herds, sows were tested for antibodies to gE of PRV every time after they had been transported to another barn (survey A). In 99 other herds, sows were tested simultaneously once or twice yearly (survey B). We observed six introductions in survey A and 53 in survey B. None of these introductions resulted in extensive spread of the virus. The reproduction ratio R, which is defined as the mean number of secondary infections caused by one infectious sow, was significantly less than one. We conclude that PRV can be eliminated from sow herds by vaccination.

Animals↗