Stefaan Ribbens

Assessing biosecurity practices, movements and densities of poultry sites across Belgium, resulting in different farm risk-groups for infectious disease introduction and spread.

The existing diversity within poultry systems affects the potential risk of infectious disease introduction and spread. Population data on the level of biosecurity and between-farm contacts is scarce, despite its importance for identifying possible routes of disease transmission. A study was carried out in Belgium to investigate and differentiate professional and hobby poultry sites based on their biosecurity levels and farm movements. Questionnaire data from a total of 37 professional poultry farms, 19 hatcheries and 286 hobby poultry sites were analyzed using a combination of a linear scoring system, a Categorical principal component analysis (CATPCA) and a Two-Step cluster analysis (TSCA). In general, the level of biosecurity was lower in hobby poultry flocks, mainly due to the poor confinement against the outdoor environment and the poor infrastructural hygiene. Most Belgian professional poultry farms and hatcheries had an acceptable level of adoption of standard biosecurity practices, however less attention was given to the way transportation vehicles and employers were brought onto farms and professional visitors welcomed. Considerable variation in the movements and in the structure of the networks arising from these movements was found. Movement frequencies were higher at professional farms compared to hobby farms. Results showed that multiple category farming systems had the highest total movement frequencies. Monthly frequencies of professional visits often exceeded those of poultry and egg movements. Professional and hobby poultry sites were also connected, but movements of poultry and eggs were found only to occur from professional to hobby sites. However, hobby poultry keepers were personally purchasing the poultry and eggs on the professional poultry sites. Six groups of poultry sites were differentiated, which are interpreted as very low to very high risk groups, based on the potential of infectious disease introduction and spread.

Control of bovine virus diarrhoea at the herd level: reducing the risk of false negatives in the detection of persistently infected cattle.

The need to detect and eliminate cattle persistently infected (PI) with bovine viral diarrhoea virus (BVDV) is key to the control of BVD and has been shown to be very effective in eradicating BVDV from infected herds. However, because of pitfalls in the detection procedures, some PI animals can be missed and, as a result, are not identified and removal is delayed. The high prevalence of BVDV in cattle populations in some countries (such as Belgium and neighbouring countries) means there is a high risk of reinfection of a herd from which BVDV has been eradicated. Based on both practical experience and a literature study, this review considers those points that are critical to minimising the number of false negatives in the detection of PI cattle.

A cross-sectional study to collect risk factors associated with stillbirths in pig herds

The aim of this study was to identify risk factors for stillborn piglets at herd level in commercial pig herds. A written questionnaire, containing semi-open questions directly or indirectly related to stillborn piglets, was sent to 250 randomly selected pig herds (>150 sows) in northern Belgium. In total 111/250 questionnaires were returned (response rate of 44.4%) and 107 were valid for analysis. The average reported frequency of stillbirth was 7.5% (S.D. 2.8%). The relationship between risk factors and stillbirths was evaluated with a generalized linear effects model with the percentage of stillborn piglets as outcome variable. Type of breed used on the farm was significantly (P<0.01) associated with the percentage of stillborn piglets. A high temperature in the farrowing unit (> or =22 degrees C compared to <22 degrees C) was associated with significantly (P<0.01) more stillbirths, whereas showering sows with warm water before parturition resulted in significantly less stillbirths (5.8%) than no showering (7.7%) (P<0.01) and was not significantly different from showering with cold water (7.0%) (P=0.26). When supervision of farrowing was performed occasionally, significantly more stillbirths (8.1%) were observed in comparison with no attending to farrowing (6.5%) (P<0.01) or frequent supervision of farrowing (6.9%) (P<0.01). Significant interactions were found between breed and showering sows prior parturition or supervision of sows at parturition, and between temperature in the farrowing unit at parturition and showering procedure of the sows. In conclusion, this study has clearly demonstrated that breed is a major factor involved in the frequency of stillbirth. Additionally, some management practices before or at parturition may reduce the number of stillborn piglets.

Classical swine fever outbreak containment using antiviral supplementation: a potential alternative to emergency vaccination and stamping-out.

Classical swine fever (CSF) outbreaks may result in huge economic losses to countries with densely populated pig areas (DPLAs). The EU minimum control measures require depopulation of infected farms, movement restrictions, zoning and surveillance (EU Minimum strategy). Emergency vaccination is authorised for DPLAs although the EU Minimum strategy plus culling in a 1-km ring around infected premises is preferred. Nonetheless, vaccination in a 2-km ring has been found equally effective as 1-km ring culling using stochastic modelling. Alternatives control measures (e.g. antiviral agents, in particular small molecule inhibitors of the CSFV replication) are being explored. Hence, the present study was set up to simulate inter-herd CSFV spread when antiviral molecules are supplemented to pig feed in a 1-km ring around infected farms. The effectiveness of the antiviral strategy for containing CSF outbreaks was compared to six other control scenarios including the EU Minimum strategy, the EU preferred policy for DPLAs and the use of 2-km ring vaccination. The InterSpread Plus model was adapted to the 2006 Belgian pig population and outbreak simulations were performed with a fast spreading CSFV strain entering a DPLA in Belgium. Four out of the seven control strategies resulted in outbreaks that were controlled by the end of the simulation period (i.e. 365 days). The distributions of the number of infected herds and the duration of the predicted outbreaks for these four control strategies were not different. This is the first report investigating CSF outbreak containment using antiviral molecules. Although antiviral supplementation was not found to perform any better than some other conventional strategies, such as pre-emptive culling and emergency vaccination, it might be worthwhile considering it further as additional tool in a response to CSF outbreaks.

Association between herd exposure to BVDV-infection and bulk milk somatic cell count of Flemish dairy farms

The purpose of this study was to investigate the statistical association between herd bovine viral diarrhoea (BVD) status based on bulk milk antibody detection and monthly bulk milk somatic cell count (BMSCC) as a reflection of the udder health. A distinction was made between vaccinating and non-vaccinating herds via a questionnaire concerning BVD-vaccination. No significant difference in BMSCC was found between vaccinating (228,300 cells/ml; SD 180,019) and non-vaccinating (237,070 cells/ml; SD 77,900) herds. Non-vaccinating herds (n=243) were selected, and the relationship between a single BVDV-antibody titre and the BMSCC of each herd over a 12-month observation period evaluated. For this purpose, the non-vaccinating herds were divided into five groups depending on bulk milk BVDV-antibody titres. Overall, no significant relationship between the antibody titre and the BMSCC was found. Still, when comparing the category with the lowest S/P ratio (essentially BVDV-naïve herds; BMSCC=211,390 cells/ml) with the combined four other categories (BMSCC=242,790 cells/ml), a significant difference in BMSSC was observed (P=0.01).

Use of a national identification database to determine the lifetime prognosis in cattle with necrotic laryngitis and the predictive value of venous pCO2

Background Necrotic laryngitis, caused by Fusobacterium necrophorum, frequently requires surgical intervention (laryngostomy) in the chronic stage. Hypothesis/Objectives To determine survival until slaughter of cattle surgically treated for necrotic laryngitis and to identify predictors of mortality. Animals A total of 221 cattle diagnosed with necrotic laryngitis by laryngoscopy and surgically treated Methods Retrospective cohort study. Clinical records were matched with the national cattle identification, registration, and movement database. Information on possible predictors including clinical examination, biochemistry, and surgery was collected. A multivariable Cox proportional hazard model was used to identify predictors of mortality. Results The overall survival rate was 65.2% and 58.6% of the animals with a completed life cycle could be slaughtered. Animals <6 months old experienced significantly higher mortality risk (hazard ratio [HR], 2.0; 95% confidence interval [CI], 1.1‐3.5). The venous partial pressure of carbon dioxide (pCO2; HR, 2.4; 95% CI, 1.4‐4.2) at a 64.5 mm Hg cut‐off was most significantly associated with mortality. Sensitivity and specificity of the final model consisting of age and pCO2 were 49.1 and 86.4%, respectively. Instead of pCO2, total carbon dioxide (TCO2) could also be used, with similar diagnostic accuracy. Conclusions and Clinical Relevance The lifetime prognosis for chronic necrotic laryngitis in cattle with surgical intervention appears fair. Age, venous pCO2 and TCO2 are easily accessible predictors of survival to support owners and veterinarians in their decision process of whether or not to operate and to identify high risk animals that require more intensive follow‐up.