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

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 data sets).) The data set 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 < or =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.

Individual behavioural characteristics in pigs--influences of group composition but no differences in cortisol responses.

To determine the effect of group composition on backtest (Bt) responses and to determine the predictive value of the Bt for the physiological stress response to weaning and mixing, 814 pigs were backtested at 3, 10 and 17 days of age. Twenty-nine percent of all pigs were cross-fostered at 3 days according to Bt responses and groups were formed of animals with high responses (HR) only, low responses (LR) only or mixed groups of animals with high, intermediate and low responses (MISC). Original litters (OR, no cross-fostering) were used as controls. Cortisol responses were measured in saliva after weaning at 4 weeks of age and after moving and mixing at 9 weeks of age. In HR groups, mean Bt responses decreased after cross-fostering while in LR groups, mean Bt scores increased. In both groups, Bt responses of individual animals before and after cross-fostering were not correlated. In MISC and OR groups, all Bt scores were correlated. Weaning and mixing caused a significant rise in cortisol in all animals while moving or weighing did not. No relations were found between Bt scores and cortisol levels. We conclude that Bt behaviour can change according to the social environment between 3 and 10 days. This could be intentional, to form a varied group, or it might be caused by a change in the hypothalamic-pituitary-adrenal (HPA) function due to social stress. At an older age, this ability is lost and common farm practises such as regrouping, weaning and mixing of piglets at ages >10 days might have a negative effect on the piglets.

A longitudinal study of Salmonella enterica infections in high-and low-seroprevalence finishing swine herds in The Netherlands.

The purpose of this investigation was to study the incidence and course of Salmonella infections in finishing pig herds in order to asses the stability of a given Salmonella herd status. Five low- and 7 high-seroprevalence herds were followed for seven sampling rounds. Each round, blood and faecal samples were tested in an indirect ELISA and by bacteriological culturing, respectively. In high-seroprevalence herds a positive Salmonella status was an indication of a long-term problem and the status was relatively stable over time. The herds experiencing clinical salmonellosis were not necessarily the herds with the highest seroprevalence. It is possible to deliver sero-negative finishers to the slaughterhouse, even though these pigs were seropositive as growers. In three out of five low-prevalence herds, major infection incidents occurred, indicating that changes in the Salmonella status should be anticipated. Low-prevalence herds can remain negative over a longer period of time as a result feeding a complete liquid feed containing fermented by-products.

Administration of acidified drinking water to finishing pigs in order to prevent Salmonella infections.

The aim of the study was to test whether acidified drinking water, with two millilitres of an acid mixture per litre, was able to reduce the number of Salmonella infections in finishing pig herds. In each compartment, half of the pens were supplied with acidified water and the other pens served as negative control. In three herds the required dose was not applied to the pigs as a result of various practical problems. In another herd, all pigs remained seronegative throughout the study. Analysis of the remaining three herds showed a large and significant treatment effect in one herd (P<0.001). As a result of the small number of observations and the overall lower seroprevalence in the control groups, the other two herds only showed a statistical trend to a treatment effect (0.10

A note on the influence of starting position, time of testing and test order on the backtest in pigs.

The backtest determines the coping behaviour of a piglet in a standardised stress situation, which might be a measure for the coping style of that animal. Backtest results are related to other parameters such as immune responses and production. In this study, the backtest was standardised and it was studied if time of testing or the order in which animals were tested influenced backtest results. One hundred and eight-four piglets from 18 sows were tested at 3, 10 and 17 days of age. Before testing, the sow was disturbed to ensure that all piglets were awake. This standardisation of the starting position before testing did not improve the correlations between backtest results in the successive tests. No relations were found between backtest results and time of testing or test order.

Salmonella seroprevalence at the population and herd level in pigs in The Netherlands.

The aim of this study was to provide baseline data on the population and herd Salmonella seroprevalence in sows and finishers. For the population estimates in 1996 and 1999 and the herd prevalences for sows and gilts, blood samples from swine vesicular disease (SVD) and pseudorabies monitoring programmes were used and tested in an indirect Salmonella enzyme-linked immunosorbent assay (ELISA). The herd prevalence for finishers was determined using blood samples collected at two slaughterhouses. The population prevalence for finishers in 1996 and 1999 was 23.7 and 24.5%, respectively, and for sows 40.5 and 60.4%, respectively. The prevalence in free range (FR) finishers was significantly higher (44.6%) than in intensively housed finishers in 1999, identifying a hazard group for possible extra pork and pork product contamination. Of 406 finishing herds, 9% were completely seronegative for Salmonella (cut-off OD%>10). Of these 406 finishing herds, 69.7% had Salmonella-status I (low prevalence), 21.7% status II (moderate prevalence) and 8.6% status III (high prevalence) (cut-off OD%>40). In 46 multiplying sow herds, 20 breeding sow herds and 20 matching replacement gilt herds, the average herd prevalences were 54, 44.4 and 19.3%, respectively. Two gilt herds were completely seronegative. The prevalence in the gilt herds was never higher than in the matching breeding sow herds. Agreement on methodology and calibration of ELISA tests would make these results comparable between countries and is a prerequisite for a co-ordinated and integrated program to reduce Salmonella in pork in the European Union.

Herd level husbandry factors associated with the serological Salmonella prevalence in finishing pig herds in The Netherlands.

A national program to reduce Salmonella in pork and pork products should include monitoring and intervention at farm level. To develop an adequate intervention strategy at farm level, risk factors for Salmonella infections in finishing pigs have to be determined. In this study, blood samples were collected randomly at two slaughterhouses from slaughter pigs. Samples were tested by the Dutch Salmonella ELISA, based on the O-antigens 1, 4, 5, 6, 7 and 12, using a cut-off of OD%=10. This ELISA has been calibrated against the Danish ELISA to give comparable results. Workers from herds from which at least forty blood samples had been collected, were asked to participate in a questionnaire. In total, 353 questionnaires were obtained and analysed. Significant risk factors associated with the proportion of seropositive samples were identified by multiple linear logistic regression. The feeding of a complete liquid feed containing fermented by-products and the omission of disinfection after pressure washing a compartment as part of an all-in/all-out procedure, were both associated with a lower Salmonella seroprevalence. A small to moderate herd size (<800 finishing pigs), a previous diagnosis of clinical Salmonella infection in the herd, the use of tylosin as an antimicrobial growth promoter in finishing feed, or herds which had more than 16% of the livers of their pigs condemned at the slaughterhouse as a result of white spots were associated with a higher Salmonella seroprevalence. Hypothetical intervention strategies based on these risk factors can be studied for their effect on the Salmonella seroprevalence and practical applicability in field studies.

A concept for a decision support system based on practical experiences from a national disease emergency. The Dutch experience.

In 1997-1998, the Netherlands experienced a large epidemic of classical swine fever (CSF). The magnitude of this epidemic stressed the role information systems could play in supporting the management during an eradication campaign. The enforcement of an eradication strategy can become very complicated, especially with large epidemics, due to time pressure and many different procedures that have to be executed at the same time. The application of comprehensive information systems may result in more control over the process and in a relief of the operational management. After a brief description of the Dutch epidemic the authors provide an overview and the general application of four different types of information systems, classified as decision support systems. The application of these information systems in animal disease control is illustrated by providing concepts for a system architecture for transaction processing, management and executive information support and decision support. The application of a data warehouse as part of this systems architecture is explained. The eradication of CSF from the Netherlands was complicated by several factors. It is important to notice that information systems cannot prevent these factors. However, information systems can support disease control authorities in controlling these factors.

[Investigation of the mite fauna content of dust samples collected from pig and poultry farms. Report of the first finding in Western Europe of the house-dust mite Dermatophagoides evansi in dust from poultry houses]. / Een oriënterend onderzoek naar de mijtenfauna in stofmonsters uit varkens- en pluimveestalen in Nederland. Eerste vondst van de huisstofmijt Dermatophagoides evansi in pluimvee-stalstof in West-Europa.

Mites can be important sources of airborne allergens, especially on farms. Two dust samples from pig farms and three dust samples from poultry farms were investigated for mites. House-dust mites were present in the poultry-dust samples, but not in the pig-dust samples. Furthermore, storage mites and predatory mites also were found in the poultry-dust samples. Specifically, the house-dust mite Dermatophagoides evansi was found in the dust samples from two poultry farms. Subsequently, a dust sample was collected from five other poultry farms. Again, D. evansi was present in dust from these farms. This is the first time that D. evansi is reported in dust from poultry farms in Western Europe outside Norway. If D. evansi cross-reacts with other Dermatophagoides spp., then poultry farmers and their families, but also other professionals working in the poultry industry, such as veterinarians, may be exposed to house-dust mites with potential clinical consequences, both domestic and occupational.

[Individual behavioral characteristics of pigs and their impact on production]. / Individuele gedragskarakteristieken van varkens en de relatie met productieresultaten.

Two studies were carried out with pigs to determine the relationship between back test results and production parameters and between back test results and other factors. In the first study, 823 piglets were tested with the back test at 10 and 17 days of age. Production parameters such as average daily weight gain and lean meat percentage were determined. In the second study, the back test was performed on 566 piglets at 3, 10, and 17 days of age. The number of escape attempts in the back test (back test score) of the mother was known for 364 piglets. Parameters concerning the health of the sow and piglets were recorded, as well as the sow's reaction to piglet removal for testing. The relationships between production parameters and back test scores of the animals were calculated, as well as the influence of birth weight, sex (all males were castrated), parents, and health parameters on back test scores. Back test scores were fairly consistent over successive tests for each piglet. Males had higher back test scores than females, and piglets from sows with low back test scores also had low scores. Finally, a higher back test score was correlated with a higher lean meat percentage and a better carcass grading at slaughter; no relation with daily weight gain was found. It is concluded that there are individual differences in the way pigs cope with a stressful situation, as measured with the back test, and that this coping behaviour is consistent. A positive correlation exists between back test scores at a young age and lean meat percentage at slaughter. The response to stress, and hence back test scores, is assumed to be inheritable.

Longitudinal changes in bronchial responsiveness associated with swine confinement dust exposure.

STUDY OBJECTIVES: Acute exposure to the air in swine confinement units causes bronchial hyperresponsiveness and inflammation of the airways. This study was performed to assess the longitudinal development of bronchial responsiveness in pig farmers and to establish exposure-response relationships. METHODS: A cohort of 171 pig farmers was followed over a 3-year period. Bronchial responsiveness was assessed by a histamine provocation test. Long-term average exposure to inhalable dust and endotoxin was determined by personal monitoring in summer and winter, using data on farm characteristics and activities. Time-weighted average (TWA) personal exposure to ammonia was measured. Data on farm characteristics were gathered in the same period. RESULTS: Mean increase in responsiveness was 2.52 doubling concentrations of histamine for a 10% decrease in FEV(1) and 1.36 doubling concentrations for a 20% decrease in FEV(1). Long-term average exposure to dust was 2.63 mg/m(3) and to endotoxin was 105 ng/m(3). TWA exposure to ammonia was 1.60 mg/m(3). After adjusting for age and smoking behavior, long-term average exposure to inhalable dust was associated with increases in bronchial responsiveness expressed as steps for provocative concentration causing 10% fall in FEV(1). TWA exposure to ammonia, use of wood shavings as bedding, and automated dry feeding were associated with increases in responsiveness expressed as steps for provocative concentration causing a 20% fall in FEV(1). CONCLUSIONS: Exposure to dust and ammonia in pig farms contributes to chronic inflammation of the airways and should be reduced.

The effectiveness of routine serological surveillance: case study of the 1997 epidemic of classical swine fever in The Netherlands.

The authors describe the value of routine serological surveillance in detecting the introduction of classical swine fever virus into a disease-free population. The first investigation concerned the question of whether the epidemic of classical swine fever (CSF), which occurred from 1997 to 1998 in the Netherlands, could have been detected using the existing monitoring system for notifiable diseases. The investigation used data from the CSF epidemic of 1997/1998 and from the existing monitoring system. Secondly, the probability of detecting a case of CSF using routine serological surveillance was modelled both for multiplier herds and for finishing herds, and then for different herd size categories. The first investigation concluded that the probability of detecting the epidemic at the current level of routine serological surveillance is very low. The second investigation concluded that even employing a sampling scheme of sixty blood samples per month, the probability of detecting an outbreak of CSF within forty days of the introduction of the virus, is less than 40%.

Salmonella infections in finishing pigs in The Netherlands: bacteriological herd prevalence, serogroup and antibiotic resistance of isolates and risk factors for infection.

Salmonellae are wide spread in man and animals world wide and are of increasing significance as causative agents of foodborne diseases in man. The European Union, national authorities and the pig industry are therefore more and more interested in the Salmonella status of the pig population. The aim of this study was to estimate the bacteriological prevalence of Salmonella in finishing pig herds, the serogroup and the resistance to antibiotics of the isolated Salmonellae and a preliminary risk analysis of factors associated with infection. For this, 317 finishing pig herds were randomly selected from a database containing 1500 herds in the southern part of the Netherlands. In each herd 24 samples of fresh faeces were collected from two compartments with pigs close to market weight. Per compartment 12 samples of faeces were pooled into one pooled sample. Pooled samples were cultured in duplicate. Salmonella spp. were recovered from 71 out of 306 herds (23%) in which two compartments could be sampled. A total of 108 isolated Salmonella's were serotyped: 71 serogroup B, 3 serogroup C1, 6 serogroup C2, 22 serogroup D1, and 6 isolates neither serogroup B, C or D1. Of a total of 115 Salmonella isolates tested, none were resistant to colistin, enrofloxacin, flumequin or gentamicin. Automated liquid feeding of by-products, and membership of an Integrated Quality Control (IQC) production group were associated with a decreased risk of infection, while use of trough feeding was associated with an increased risk of infection. It is necessary to test these presumed risk factors in intervention studies to evaluate their potency to reduce the Salmonella prevalence in finishing pigs and thereby reduce the risk of Salmonellosis in people consuming pork.

Low prevalence of antibodies against the zoonotic agents Brucella abortus, Leptospira spp., Streptococcus suis serotype II, hantavirus, and lymphocytic choriomeningitis virus among veterinarians and pig farmers in the southern part of The Netherlands.

Serum samples from 102 veterinarians and 191 pig farmers from the southern part of the Netherlands were investigated for antibodies against Brucella abortus, Leptospira spp, Streptococcus suis serotype II, Hantavirus (HV), and lymphocytic choriomeningitis virus (LCMV). All samples were collected in 1993 and stored until this study was performed. The prevalence of antibodies against B.abortus in veterinarians (4.5%) was significantly higher (P = 0.01) than in pig farmers (0%). None of the veterinarians (0%) and only one pig farmer (0.5%) had antibodies against Leptospira spp. Furthermore, significantly (P = 0.015) more veterinarians (6%) than pig farmers (1%) had antibody titres against muramidase-released protein (MRP),a protein of pathogenic S. suis serotype II strains. None of the veterinarians and a total of 3 (1.6%) pig farmers had antibody titres against HV. The prevalence of antibodies against LCMV tended to be higher in pig farmers (2.6%) than in veterinarians (0%) (P = 0.10). It can be concluded that the prevalence of antibodies against the investigated zoonotic agents in veterinarians and pig farmers is low.

Health-based selection for asthma, but not for chronic bronchitis, in pig farmers: an evidence-based hypothesis.

In cross-sectional surveys among pig farmers an elevated prevalence of chronic bronchitis is usually reported, but not of asthma, despite many factors promoting the manifestation of asthma. To investigate this apparent contradiction a postal questionnaire survey was performed among 239 pig farmers and 311 rural controls. Pig farmers reported an elevated prevalence of symptoms of chronic bronchitis (20.2 versus 7.7%, p<0.001), but not of asthma (5.9 versus 5.5% for chest tightness). Among pig farmers the use of disinfectants (prevalence odds ratio (POR) 9.4, 95% confidence interval (CI) 1.6-57.2 for quaternary ammonium compounds) and aspects of the disinfecting procedure were associated with the prevalence of asthma symptoms. Compared with controls, pig farmers reported fewer allergies to common allergens (4.6 versus 14.6%, p<0.001 for pollen) and fewer symptoms of atopy in childhood (9.9 versus 17.2, p<0.05 for one or more of four symptoms). Atopy in childhood was strongly associated with the prevalence of asthma symptoms (POR 4.1, 95% CI 2.2-7.7), but not with chronic bronchitis. Health-based selection of nonasthmatics for pig farming, which tends to mask a work-related hazard for asthma, is offered as an explanation for these results.

A descriptive study of visits by animal health specialists in pig farming: type, frequency, and herd-health management factors.

This research was carried out to analyse the visits specialists of the Dutch Animal Health Service made to growing and fattening pig farms. The type and frequency of the visits and identified herd-health management factors that did not meet accepted standards were investigated. In total 373 visit reports were studied. The majority of the visits (n = 306 of 373) were made to investigate the cause of health, welfare, and performance problems ('problem-solving visits'). Respiratory disorders were the main reason for requesting a specialist to assess farm conditions and management (n = 156). In the other 67 of 373 visit reports the specialists screened for herd-health management factors that did not meet standards for the prevention of disease ('screening visits'). For both types of visits, the main factors detected were abrupt changes in feeding regimens (e.g. changes in feed type, feed composition or feed supplier) (37%), inadequate measures to prevent introduction of pathogens by people and trucks (83%), and incorrect adjustment of the ventilation system (58-60%). The specialists focusing on housing-climate management, identified the majority of factors in an equal number irrespective of whether the visit was a problem-solving visit or a screening visit. This implies that even on farms that appear not to have health or performance problems, factors that relate to disease are present and may cause problems sooner or later. Although veterinary practitioners and other farm advisors assist farmers in their management to optimize herd health, the findings of the research suggest that advisors could provide additional support in situations where environmental and managerial factors play a role in pig health and performance. The knowledge of advisors about integrated herd-health management can be broadened by means of textbooks, courses, or computer programs.

Endotoxin exposure as a major determinant of lung function decline in pig farmers.

Exposure-response relationships for endotoxin as measured in dust and longitudinal decline in lung function were studied. A cohort of 171 pig farmers was followed over a 3-yr period. Long-term average exposure to dust and endotoxin was determined by personal monitoring in summer and winter, using data on farm characteristics and activities. Mean decline in FEV1 was 73 ml/yr and in FVC 55 ml/ yr. Long-term average exposure to dust was 2.63 mg/m3 (geometric SD [GSD] 1.30), and to endotoxin, 105 ng/m3 (GSD 1.5). Annual decline in FEV1 was significantly associated with endotoxin exposure. An increase in exposure with a factor 2 was associated with an extra decline of FEV1 of 19 ml/yr.

The effects of mixing on behavior and circadian parameters of salivary cortisol in pigs.

The present study describes an experiment that was carried out to study the effects of mixing pigs once at 25 kg, preceded by transportation for 1.5 h, on the behavior and the circadian rhythmicity of salivary cortisol. The frequency of agonistic interactions was higher for mixed pigs. This was not only the case immediately after mixing, when pigs started to fight to establish a new social rank (p < 0.05), but also 5 to 6 weeks later; still more headknocks and bites towards other pigs were seen at that time among mixed pigs (p < 0.01). However, neither the basal cortisol concentration, assessed as the MESOR of the circadian rhythm of salivary cortisol, nor the amplitude of that rhythm was different between the groups.

Effect of natural infection with minor pathogens on susceptibility to natural infection with major pathogens in the bovine mammary gland.

OBJECTIVE: To evaluate the effect of natural udder infection with minor pathogens on subsequent natural infection with major pathogens. SAMPLE POPULATION: 7 dairy herds with low bulk milk somatic cell count. PROCEDURE: During a 20-month prospective study, milk samples were collected from diary cows at regular intervals and from quarters with clinical signs of mastitis. Incidence of intramammary infection was calculated in uninfected quarters and in quarters infected with minor pathogens. A within-cow, matched case-control analysis was used to evaluate the effect of minor pathogens on subsequent infection with major pathogens. RESULTS: Quarters infected with minor pathogens had higher somatic cell count than did uninfected quarters. In quarters infected with Corynebacterium bovis, the rate of infection with major pathogens was lower, whereas in quarters infected with coagulase-negative Micrococcaceae, the rate of infection with major pathogens was higher than that in uninfected quarters. From the within-cow comparison, it appeared that, in quarters infected with minor pathogens, infection with major pathogens was significantly lower than that in comparable control quarters not infected with minor pathogens. CONCLUSIONS: Minor pathogens have a protective effect against infection with major pathogens. The protective effect of C bovis against subsequent infection with major pathogens appears to be greater than the effect of coagulase-negative Micrococcaceae.

Bronchial hyperresponsiveness and exposure in pig farmers.

OBJECTIVE: To study the effect of exposure on bronchial responsiveness in pig farmers. METHOD: A group of 196 pig farmers were tested for lung function and bronchial responsiveness to histamine in the summer of 1992. To achieve sufficient contrast in respiratory morbidity and exposure, 96 of the farmers were selected because they had chronic respiratory symptoms and the remaining 100 because they were free from any respiratory symptoms. Personal exposure to dust, endotoxins and ammonia was measured during 1 working day in the summer of 1991 and 1 day in the winter of 1992. Data on farm characteristics were gathered in the same period. RESULTS: After adjusting for age and smoking behaviour, mild bronchial responsiveness, defined as PC10 < or = 16 mg/ml, was associated with the use of quaternary ammonium compounds as disinfectant [prevalence odds ratio (POR) 6.7, 95% confidence interval (CI) 1.4-32.8], use of wood-shavings as bedding (POR 13.3, CI 1.3-136.7), use of automated dry feeding (POR 2.8, CI 1.0-7.8), use of pellets as feeding material (POR 4.8, CI 1.1-21.1) and location of air exhaust via pit or roof in the confinement units (POR 2.7, CI 1.2-6.3). The association with the use of disinfectants other than quaternary ammonium compounds was not significant (POR 2.4, CI 0.7-8.4). No associations between bronchial responsiveness and measured exposure to dust, endotoxins or ammonia were discernible. CONCLUSION: Protective measures, designed to prevent airway disease in confinement farming, should be based on information about the operational and other characteristics of farms that are related to high exposure and health effects. Specifically, the use of quaternary ammonium compounds as disinfectant, the use of wood-shavings as bedding and the use of automated dry feeding should be discouraged.