Transmission of classical swine fever virus within herds during the 1997-1998 epidemic in The Netherlands     

Stegeman A  Elbers AR  Bouma A  de Smit H  de Jong MC 《Preventive veterinary medicine》1999,42(3-4):201-218

In this paper, we describe the transmission of Classical Swine Fever virus (CSF virus) within herds during the 1997–1998 epidemic in the Netherlands. In seven herds where the infection started among individually housed breeding stock, all breeding pigs had been tested for antibodies to CSF virus shortly before depopulation. Based upon these data, the transmission of CSF virus between pigs was described as exponential growth in time with a parameter r, that was estimated at 0.108 (95% confidence interval (95% CI) 0.060–0.156). The accompanying per-generation transmission (expressed as the basic reproduction ratio, R₀) was estimated at 2.9. Based upon this characterisation, a calculation method was derived with which serological findings at depopulation can be used to calculate the period in which the virus was with a certain probability introduced into that breeding stock. This model was used to estimate the period when the virus had been introduced into 34 herds where the infection started in the breeding section. Of these herds, only a single contact with a herd previously infected had been traced. However, in contrast with the seven previously mentioned herds, only a sample of the breeding pigs had been tested before depopulation (as was the common procedure during the epidemic). The observed number of days between the single contact with an infected herd and the day of sampling of these 34 herds fitted well in the model. Thus, we concluded that the model and transmission parameter was in agreement with the transmission between breeding pigs in these herds.

Because of the limited sample size and because it was usually unknown in which specific pen the infection started, we were unable to estimate transmission parameters for weaned piglets and finishing pigs from the data collected during the epidemic. However, from the results of controlled experiments in which R₀ was estimated as 81 between weaned piglets and 14 between heavy finishing pigs (Laevens et al., 1998a. Vet. Quart. 20, 41–45; Laevens et al., 1999. Ph.D. Thesis), we constructed a simple model to describe the transmission of CSF virus in compartments (rooms) housing finishing pigs and weaned piglets. From the number of pens per compartment, the number of pigs per pen, the numbers of pigs tested for antibodies to CSF virus and the distribution of the seropositive pigs in the compartment, this model gives again a period in which the virus most probably entered the herd. Using the findings in 41 herds where the infection started in the section of the finishers or weaned piglets of the age of 8 weeks or older, and of which only a single contact with a herd previously infected was known, there was no reason to reject the model. Thus, we concluded that the transmission between weaned piglets and finishing pigs during the epidemic was not significantly different from the transmission observed in the experiments.  相似文献   

Quantification of the transmission of classical swine fever virus between herds during the 1997-1998 epidemic in The Netherlands     

Stegeman A  Elbers AR  Smak J  de Jong MC 《Preventive veterinary medicine》1999,42(3-4):219-234

In this study, we describe a method to quantify the transmission of Classical Swine Fever Virus (CSFV) between herds from data collected during the 1997–1998 epidemic in the Netherlands. From the contacts between infected herds and the serological findings shortly before depopulation, we estimated the week of virus introduction and the length of the period over which the herd emitted virus for each CSFV-infected herd. From these data, we estimated the infection-rate parameter β (the average number of herds infected by one infectious herd during one week) and the herd reproduction ratio, R_h (the average total number of secondary outbreaks caused by one infectious herd, i.e. in its entire infectious period), using a SIR-model for different sets of CSF control measures. When R_h > 1, an epidemic continues to grow. On the other hand, when R_h < 1 an epidemic will fade out.

During the phase before the first outbreak was diagnosed and no specific measures had been implemented, β was estimated at 1.09 and R_h at 6.8. In the subsequent phase infected herds were depopulated, movement restrictions were implemented, infected herds were traced forward and backward and the herds in the protection and surveillance zones were clinically inspected by the veterinary authorities (regional screening). This set of measures significantly reduced β to 0.38. However, R_h was 1.3 and thus still >1. Consequently, the number of outbreaks continued to grow. After a number of additional measures were implemented, the value of R_h was reduced to 0.5 and the epidemic came to an end. These measures included pre-emptive slaughter of herds that had been in contact with infected herds or were located near an infected herd, increased hygienic procedures, replacement of transports of pigs for welfare reasons by killing of young piglets and a breeding ban, and regional screening for CSF-infected herds by local veterinary practitioners.  相似文献   

Classical swine fever in The Netherlands 1997-1998: a description of organisation and measures to eradicate the disease     

Pluimers FH  de Leeuw PW  Smak JA  Elbers AR  Stegeman JA 《Preventive veterinary medicine》1999,42(3-4):139-155

The central and regional organisation of the campaign to eradicate the CSF epidemic in the Netherlands in 1997/1998 is described. The main instruments used in the campaign were based on stamping-out and movement restrictions specified by the European Union. Additional instruments were used for the first time, namely, pre-emptive culling of contact and neighbouring farms, compartmentalisation of transport, monthly serological screening in established surveillance areas and supervised repopulation of all farms in the former surveillance zone. Two other measures, the killing of very young piglets and a breeding ban were introduced to reduce production in established surveillance zones. Several factors complicated the eradication campaign, for instance, the late detection of the first infection; artificial insemination as a source of infection; the organisation of pig farming in the Netherlands, with its highly concentrated production and dependence on the transport of stock from one unit to another; insufficient rendering capacity; decreasing sensitivity of clinical inspection; and extremely high costs.  相似文献   

Herd management practices associated with paratuberculosis seroprevalence in Dutch dairy herds     

Muskens J  Elbers AR  van Weering HJ  Noordhuizen JP 《Journal of veterinary medicine. B, Infectious diseases and veterinary public health》2003,50(8):372-377

We describe the paratuberculosis management practices applied in dairy herds in the Netherlands. The findings from paratuberculosis seronegative and seropositive herds were compared to discover possible risk factors. In total, 370 randomly selected herds with > or =20 dairy cows were surveyed. A questionnaire was used to collect data on current and previous paratuberculosis management practices. All cattle aged > or =3 years were serologically tested for paratuberculosis using an enzyme-linked immunosorbent assay. Herds with >33 tested cattle, of which only one was seropositive, were excluded to reduce the risk of including false-positive herds in the analysis. A comparison of the management data of the seronegative herds (n = 166) and the seropositive herds (n = 143) showed that in both groups important management measures for the prevention of paratuberculosis, such as calving in a cleaned calving area, removing the calf immediately after birth, and feeding paratuberculosis non-suspect roughage to calves, were used only rarely. However, such measures should be regarded as the critical first step to control the disease and/or reduce its prevalence. Using univariable analysis, four factors were statistically different between seronegative and seropositive herds: herd size, cows with clinical signs of paratuberculosis, prompt selling of clinically diseased cattle and feeding milk replacer. Using a multivariable logistic regression model, only herd size was a significantly different factor. These results indicate that most of the paratuberculosis preventive management measures were executed on these Dutch dairy farms only to a limited extent.  相似文献   

Neighbourhood infections of classical swine fever during the 1997-1998 epidemic in The Netherlands     

Crauwels AP  Nielen M  Elbers AR  Stegeman JA  Tielen MJ 《Preventive veterinary medicine》2003,61(4):263-277

Data of the 1997–1998 epidemic of classical swine fever (CSF) in The Netherlands were analysed in survival analysis to identify risk factors that were associated with the rate of neighbourhood infections. The study population consisted of herds within 1000 m of exclusively one previously infected herd. Dates of virus introduction into herds were drawn randomly from estimated probability distributions per herd of possible weeks of virus introduction. (To confirm the insensitivity of the results for this random data-selection procedure, the procedure was repeated 9 times (resulting in 10 different datasets).) The dataset had 906 non-infected and 59 infected neighbour herds, which were distributed over 215 different neighbourhoods. Neighbour herds that never became infected were right-censored at the last date of the infectious period of the infected source herd. Neighbour herds that became empty within the infectious period or within the following 21 days due to preventive depopulation or due to the implemented buying-out programme were right-censored 21 days before the moment of becoming empty. This was done as a correction for the time a herd could be infected without being noticed as such.

The median time to identified infection of neighbour herds was 2 weeks, whereas the median time to right censoring of non-infected neighbour herds was 3 weeks. The risk factors, radial distance ≤500 m, cattle present on source herd and increasing herd size of the neighbour herd were associated multivariably with the hazard for neighbour herds to become infected. We did not find an association between time down wind and infection risk for neighbour herds. Radial dispersion of CSFV seemed more important in neighbourhood infections than dispersion along the road on which the infected source herd is situated. The results of this study support the strategy of preventive depopulation in the neighbourhood of an infected herd. Recommendations are presented to adapt the applied control strategy for neighbourhood infections.  相似文献   

Comparison of the efficacy of two different iron supplements for anemia prevention in piglets     

Vermeer JE  Kuijpers AH  Elbers AR 《Tijdschrift voor diergeneeskunde》2002,127(4):110-114

In a randomized, confirmatory study performed between July and October 2000 the efficacy of two iron products in preventing iron deficiency anaemia was compared. A total of 102 newborn piglets from ten litters were treated intramuscularly with 200 mg iron as iron dextran per ml, or 200 mg iron as gleptoferron per ml. For true comparison, piglets within a litter of a sow were subdivided into pairs on the basis of birth weight (one pair of the two heaviest piglets, et cetera). Within a pair, treatment with the iron supplements was randomly allocated. One group of piglets was injected at an age of 1 day (experiment 1) and the other group of piglets was injected at an age of 3 days (experiment 2). The piglets were weighed and blood samples were taken at an age of 18 days (experiment 1) or at an age of 19 days (experiment 2). Average daily weight gain and haemoglobin concentrations of both treatment groups were compared. Both products were very effective in preventing anaemia. No significant differences could be found between the two formulations. It can be concluded that iron-dextran and gleptoferron can be used with similar effect for anaemia prevention in piglets.  相似文献   

Transmission of classical swine fever virus by artificial insemination during the 1997-1998 epidemic in The Netherlands: a descriptive epidemiological study   总被引：3，自引：0，他引：3  

Hennecken M  Stegeman JA  Elbers AR  van Nes A  Smak JA  Verheijden JH 《The Veterinary quarterly》2000,22(4):228-233

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.  相似文献   

Experimental quantification of the transmission of Sarcoptes scabiei var. suis among finishing pigs     

Stegeman JA  Rambags PG  van der Heijden HM  Elbers AR  Hunneman WA 《Veterinary parasitology》2000,93(1):57-67

In this study, the rate of S. scabiei var. suis transmission among finishing pigs was quantified in a contact transmission experiment. Forty piglets originating from a mange free farrow-to-finish herd were randomly allocated to three groups and one S. scabiei var. suis infested finishing pig was subsequently added to each of these groups. After 35 days, the three seeder pigs were removed from the groups and the remaining 40 pigs were re-allocated to five pens. Ear scrapings, to be examined for mites, were collected from each pig on days 1, 14, 28, 42, 56, and 84 of the experiment. Blood samples, to be tested for antibodies against S. scabiei, were collected from each pig on days 0, 14, 28, 42, 56, 70, 84 and 112 after the introduction of the seeder pigs.From the results of the ear scrapings and the blood samples the number of susceptible (not infested) and infested pigs was derived at the time of each sample collection and the number of new infestations in the intervals between the sample collections. From these data the infestation rate parameter beta (average number of new infestations per infested pig per day) was estimated by use of a Generalised Linear Model (GLM) and accordingly, beta was estimated at 0.056 (95% CI: 0.037-0.085) infestations per infested pig per day.Next, by use of beta, the transmission of S. scabiei was simulated in a population of 100 finishing pigs for 100 days after the introduction of a single infested pig. For this purpose, 500 simulations were done. The 90% confidence interval of the number of infested pigs at day 100 ranged from 12 to 88 (median: 63). It was concluded that transmission of S. scabiei among finishing pigs is slow. Due to the presumed lower contact rate between sows as compared to finishing pigs, it is anticipated that transmission of S. scabiei among sows will even be slower than among finishers These findings are of particular interest for the development of surveillance programmes for S. scabiei free herds.  相似文献   

Validation of ELISAs for the detection of antibodies to Sarcoptes scabiei in pigs     

van der Heijden HM  Rambags PG  Elbers AR  van Maanen C  Hunneman WA 《Veterinary parasitology》2000,89(1-2):95-107

An Enzyme-linked ImmunoSorbent Assay (ELISA) was developed for the detection of antibodies to Sarcoptes scabiei. This 'Animal Health Service'-ELISA (AHS-ELISA) was compared with a commercial test (Checkit(R) Sarcoptest) using experimental and field sera. The experimental study was a contact infestation experiment. Eighty piglets were randomly divided between the experimental and control group. After introduction of three Sarcoptes scabiei var. suis infested pigs in the experimental group, both groups were monitored by determining scratching indices, taking ear scrapings and blood samples in Weeks 0, 2, 4, 6, 8, 12 and 16. Four pigs in the control group were immunised with either Dermatophagoides pteronyssinus (Dp) antigens (n=2), or Acarus siro (As) antigens (n=2). In the control group all (non-immunised) pigs were negative in all tests. In the experimental group only slightly elevated scratching indices were observed, with a maximum in Week 8. After 2 weeks for the first time an ear scraping was positive (2.5%). In Week 8 the highest number of positive ear scrapings were found (25.0%). Positive results in the Sarcoptest were first obtained in Week 12 (10.5% positive), while eventually 29.0% of the finishing pigs were positive after 16 weeks. The AHS-ELISA first detected a serological response after 6 weeks (5. 0% positives), increasing until after 16 weeks a large proportion (74.2%) of the finishing pigs were seropositive, making the AHS-ELISA the most sensitive test. In the AHS-ELISA one As-immunised pig remained seronegative, but the other hyper-immunised pigs crossreacted. In the Sarcoptest, only Dp-immunised pigs had elevated Optical Densities (OD's) albeit below the cut-off level. Although hyper-immunisation is not a representation of field conditions, it cannot be excluded that the AHS-ELISA is not 100% specific.Field samples were taken from 20 sows in 30 herds, classified as mange-free, suspect, or infested. On a herd level there was high agreement among the ELISAs. Both serological tests were suitable to distinguish mange-free herds from infested herds. In one infested herd the decline of maternal antibody in piglets was studied by sampling 40 piglets from 20 different litters. The lowest average OD using the AHS-ELISA was found at 5 weeks of age, followed by a significant increase at 7 weeks. The average OD with the Sarcoptest was at a minimum level at 3 weeks, but no increase was found later. For screening of herds, interference of maternal antibodies is avoided by sampling at an age of 7 weeks or older.  相似文献   

Goat paratuberculosis in Chile: first isolation and confirmation of Mycobacterium avium subspecies paratuberculosis infection in a dairy goat.     

Juan Kruze  Miguel Salgado  Enrique Paredes  Armin Mella  Michael T Collins 《Journal of veterinary diagnostic investigation》2006,18(5):476-479

In October 2004, 41 goats > 2 years old from a Saanen dairy goat herd located in Purranque County, 10th Region, Chile, were sampled and tested for paratuberculosis. While collecting samples it was observed that several goats were thin and emaciated. One goat was sufficiently debilitated to warrant humane euthanasia. This animal was brought to the Veterinary School at the Universidad Austral de Chile for necropsy. The goat selected for necropsy was a 12-year-old doe. The animal showed classical clinical signs of caprine paratuberculosis: emaciation despite willingness to eat, dry and rough hair coat, and no evidence of diarrhea. Gross pathology and histopathology of the necropsied goat were consistent with paucibacillary paratuberculosis. Bacteriology, serology, and PCR confirmed the diagnosis. This is the first published report of goat paratuberculosis in Chile confirming a case of caprine paucibacillary paratuberculosis.  相似文献