Bovine viral diarrhoea virus seroprevalence and vaccination usage in dairy and beef herds in the Republic of Ireland

Background

Bovine viral diarrhoea (BVD) is an infectious disease of cattle with a worldwide distribution. Herd-level prevalence varies among European Union (EU) member states, and prevalence information facilitates decision-making and monitoring of progress in control and eradication programmes. The primary objective of the present study was to address significant knowledge gaps regarding herd BVD seroprevalence (based on pooled sera) and control on Irish farms, including vaccine usage.

Methods

Preliminary validation of an indirect BVD antibody ELISA test (Svanova, Biotech AB, Uppsala, Sweden) using pooled sera was a novel and important aspect of the present study. Serum pools were constructed from serum samples of known seropositivity and pools were analysed using the same test in laboratory replicates. The output from this indirect ELISA was expressed as a percentage positivity (PP) value. Results were used to guide selection of a proposed cut-off (PCO) PP. This indirect ELISA was applied to randomly constructed within-herd serum pools, in a cross-sectional study of a stratified random sample of 1,171 Irish dairy and beef cow herds in 2009, for which vaccination status was determined by telephone survey. The herd-level prevalence of BVD in Ireland (percentage positive herds) was estimated in non-vaccinating herds, where herds were classified positive when herd pool result exceeded PCO PP. Vaccinated herds were excluded because of the potential impact of vaccination on herd classification status. Comparison of herd-level classification was conducted in a subset of 111 non-vaccinating dairy herds using the same ELISA on bulk milk tank (BMT) samples. Associations between possible risk factors (herd size (quartiles)) and herd-level prevalence were determined using chi-squared analysis.

Results

Receiver Operating Characteristics Analysis of replicate results in the preliminary validation study yielded an optimal cut-off PP (Proposed Cut-off percentage positivity - PCO PP) of 7.58%. This PCO PP gave a relative sensitivity (Se) and specificity (Sp) of 98.57% and 100% respectively, relative to the use of the ELISA on individual sera, and was chosen as the optimal cut-off since it resulted in maximization of the prevalence independent Youden’s Index.The herd-level BVD prevalence in non-vaccinating herds was 98.7% (95% CI - 98.3-99.5%) in the cross-sectional study with no significant difference between dairy and beef herds (98.3% vs 98.8%, respectively, p = 0.595).An agreement of 95.4% was found on Kappa analysis of herd serological classification when bulk milk and serum pool results were compared in non-vaccinating herds. 19.2 percent of farmers used BVDV vaccine; 81% of vaccinated herds were dairy. A significant association was found between seroprevalence (quartiles) and herd size (quartiles) (p < 0.01), though no association was found between herd size (quartiles) and herd-level classification based on PCO (p = 0.548).

Conclusions

The results from this study indicate that the true herd-level seroprevalence to Bovine Virus Diarrhoea (BVD) virus in Ireland is approaching 100%. The results of the present study will assist with national policy development, particularly with respect to the national BVD eradication programme which commenced recently.     

In vitro comparison of feline bone marrow-derived and adipose tissue-derived mesenchymal stem cells

Mesenchymal stem cells (MSC) are increasingly being proposed as a therapeutic option for a variety of different diseases in human and veterinary medicine. At present, MSC are most often collected from bone marrow (BM) or adipose tissue (AT) and enriched and expanded in vitro before being transferred into recipients. However, little is known regarding the culture characteristics of feline BM-derived (BM-MSC) versus AT-derived MSC (AT-MSC). We compared BM-MSC and AT-MSC from healthy cats with respect to in vitro growth and cell surface phenotype. Mesenchymal stem cells isolated from AT proliferated significantly faster than BM-MSC. Phenotypic differences between BM-MSC and AT-MSC were not present in the surface markers assessed. We conclude that BM-MSC and AT-MSC are similar phenotypically but that cultures of AT-MSC are easier to generate because of their higher intrinsic proliferative rate. Thus, AT-MSC may be the preferred MSC for clinical applications where rapid and efficient generation of MSC is important.     

The avoidance of ammonia by sheep

The avoidance of ammonia by sheep was tested using operant conditioning techniques, training 12 sheep to operate a lever to open a door that would allow them to traverse a chamber with or without ammonia and obtain a food reward. One half of the sheep had been previously exposed to ammonia at 45 ppm in a simulated ship voyage, and the other half were kept in identical conditions but without ammonia. The maximum number of lever presses, or breakpoint, achieved when the chamber contained 45-ppm ammonia was compared with the number when the chamber contained no ammonia. There was a significantly lower mean breakpoint when the sheep traversed the chamber filled with ammonia (mean: 4.2 presses), compared with the chamber filled with fresh air (mean: 6.6 presses), demonstrating that sheep exhibited a moderate aversion to 45-ppm ammonia. Although the scale of the reduction in mean breakpoint was considerable, the aversion was only clearly demonstrated in 75% of the sheep, and there was no evidence that prior exposure influenced this aversion. It is therefore concluded that sheep show a moderate aversion to 45-ppm ammonia, with no evidence of sensitivity being affected by previous exposures.     

Protecting islands from pest invasion: optimal allocation of biosecurity resources between quarantine and surveillance

Removing pests from islands, and then keeping them pest free, is a common management goal. Given that goal we face a decision: how much effort should we invest in quarantine to reduce the risk of a pest arriving vs. surveillance, looking for the pest on the island with the view of eradicating it before it gets out of control. We use models of an island under threat of invasion by a pest (animal, plant or disease) and a cost minimisation approach to optimally allocate management resources between quarantine and surveillance. In the optimal allocations joint investment in both quarantine and surveillance is uncommon. Investment in quarantine is optimal if quarantine is more effective than surveillance or if large costs associated with pest impact and eradication are incurred at low pest density. Investment in quarantine is also favoured as our ability to eradicate a pest declines. Surveillance is optimal if it is considerably more cost-effective than quarantine and we can generate significant savings through early detection of the pest population. We illustrate how theses models are useful ways to examine these trade-offs by applying the model to the prevention of black rat (Rattus rattus) invasion on Barrow Island, Western Australia. Our model predicts an optimal strategy different to the management strategy currently being used on the island. We suggest that this is due to a risk-averse tendency in managers and the difficulty of estimating costs that combine management, environmental and social factors.     

Molecular characterization, ecology, and epidemiology of a novel Tymovirus in Asclepias viridis from Oklahoma

Native virus-plant interactions require more understanding and their study will provide a basis from which to identify potential sources of emerging destructive viruses in crops. A novel tymovirus sequence was detected in Asclepias viridis (green milkweed), a perennial growing in a natural setting in the Tallgrass Prairie Preserve (TGPP) of Oklahoma. It was abundant within and frequent among A. viridis plants and, to varying extents, within other dicotyledonous and one grass (Panicum virgatum) species obtained from the TGPP. Extracts from A. viridis containing the sequence were infectious to a limited number of species. The virus genome was cloned and determined to be closely related to Kennedya yellow mosaic virus. The persistence of the virus within the Oklahoma A. viridis population was monitored for five successive years. Virus was present in a high percentage of plants within representative areas of the TGPP in all years and was spreading to additional plants. Virus was present in regions adjacent to the TGPP but not in plants sampled from central and south-central Oklahoma. Virus was present in the underground caudex of the plant during the winter, suggesting overwintering in this tissue. The RNA sequence encoding the virus coat protein varied considerably between individual plants (≈3%), likely due to drift rather than selection. An infectious clone was constructed and the virus was named Asclepias asymptomatic virus (AsAV) due to the absence of obvious symptoms on A. viridis.     

Quality of life and stress factors for veterinary medical students

Psychological distress has been shown to affect the academic success, health, emotional well-being, and dropout rates of medical students. Although it can be assumed that stress has similar effects on veterinary students, there is a paucity of research pertaining to the psychological stressors and coping strategies of this group. This article focuses on selected non-academic areas (as identified through a survey of currently enrolled students) that can create significant stressors for veterinary students. Also assessed and discussed here are poor coping strategies (e.g., substance abuse) and gender differences in perceived stressors and coping strategies that emerged from the survey. Results suggest the need for veterinary programs to integrate academic and professional skills instruction with personal life balance training and access to psychological services.     

QUANTIFICATION OF LEFT VENTRICULAR MASS USING CARDIAC MAGNETIC RESONANCE IMAGING COMPARED WITH ECHOCARDIOGRAPHY IN DOMESTIC CATS

The hypotheses were that cardiac magnetic resonance imaging (cMRI) would accurately determine LV mass in domestic cats and would do so more accurately than echocardiography (ECHO). ECHO was performed on seven sedated cats. LV mass was calculated using the truncated ellipse formula from a right parasternal long-axis view. T1 weighted gradient echo cMRI was acquired from anesthetized cats during multiple phases of the cardiac cycle. Short-axis images were obtained by acquiring 3 mm thick contiguous slices perpendicular to the cardiac long axis. LV mass was determined using Simpson's rule. Endocardial and epicardial borders were traced on each slice at end-systole, end-diastole, and mid-cycle and the difference in areas was myocardial area. Myocardial area was multiplied by slice thickness to calculate myocardial volume. Total (summated) myocardial volume was multiplied by myocardial density (1.05) to obtain LV mass at three measured phases of the cardiac cycle. Cats were euthanized and the LV was dissected and weighed to determine true mass. CMRI at end-systole most accurately quantified LV mass and was more accurate than echocardiography (P = 0.0078). Actual LV mass ranged from 6.5 to 10.5 g (mean = 8.5 g, SD = 1.6 g) compared with MRI LV mass at end-systole, which ranged from 6.7 to 11.1 g (mean = 8.7 g, SD = 1.7 g) and echocardiographic LV mass at enddiastole, which ranged from 5.2 to 9.1 g (mean= 7.1 g, SD = 1.8 g). Inter- and intraobserver variability for cMRI was 2%. CMRI obtained at end-systole accurately and reliably quantifies LV mass in domestic cats. It is more accurate than the echocardiographic method used in this study.