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Clegg, Tracy A.
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Clegg, Tracy A.
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Clegg, Tracy A.
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- PublicationQuantifying the role of Trojan dams in the between-herd spread of bovine viral diarrhoea virus (BVDv) in Ireland(Elsevier, 2018-04-01)
; ; ; ; ; A compulsory national programme to eradicate bovine viral diarrhoea virus (BVDv) began in Ireland on 1 January, 2013. The objective of the current study was to quantify the role of Trojan dams (animal(s) not persistently infected (PI) with BVDv but carrying PI foetus(es) and introduced to the herd while pregnant with the PI foetus(es)) in the farm-to-farm spread of BVDv in Ireland, and to identify herd-level risk factors for producing or introducing a Trojan dam. The study population included all BVD+ calves born in Ireland between 1 January, 2013 and 31 December, 2015, along with their dams. BVD+ calves included all calves on the national programme database with an initial positive or inconclusive virus test, without a confirmatory re-test (status BVDPOS) and those with an initial positive or inconclusive test and a positive confirmatory test (status BVDPI). The Trojan status of dams was determined after considering their history of movement and of potential BVDV exposure, relative to a defined window of susceptibility (WOS; days 30–120 of gestation). During 2013–15, there were 29,422 BVD+ birth events to dams that were not themselves BVD+, including 2526 (8.6%) most-likely attributable to Trojan dams. The percentage of these birth events attributable to Trojan dams was significantly different (P < 0.001) between years, being 7.1% in 2013, 9.2% in 2014 and 10.6% in 2015. During 2013, in 9.9% of herds with one or more BVD+ birth to non-BVD+ dams, at least one of these births was attributed to a Trojan dam. In 2014 and 2015, the percentages were 11.8% and 13.3%, respectively. In 2013, in 7.8% of herds with one or more BVD+ birth to non-BVD+ dams, all of these births were attributable to Trojan dams. In 2014 and 2015, the percentages were 9.2% and 10.7%, respectively. A logistic GEE regression identified dam parity, herd size and an interaction between herd type and season as significant predictors for the birth of a BVD+ calf to a Trojan dam. Significant predictors for the sale of a Trojan dam from BVD+ herds included those selling more than one pregnant female and those with more than 2 BVD+ animals in the herd. Introduction of pregnant adult females is a potential source of BVD+ births in BVD-free herds and may add to the burden of infection in non-BVD-free herds. Addressing this route of transmission will be critical for herds that are now free of infection and wish to continue to purchase animals without introducing it.362Scopus© Citations 20 - PublicationPotential infection-control benefit of measures to mitigate the risk posed by Trojan dams in the Irish BVD eradication programme(Elsevier, 2018-09-01)
; ; ; ; ; In the epidemiology of Bovine Viral Diarrhoea (BVD), Trojan dams (animals that are not persistently infected (PI) with BVD (BVDv) virus but carrying PI foetuses) are a vehicle through which infection can be transmitted. We investigated the degree to which restricting movement of cattle from BVDv infected herds would prevent Trojan births in other herds (effectiveness) and the extent to which this would reduce other, non-Trojan, movements (proportionality). We focussed on Irish herds with BVD + animal(s) present during 2014 and/or 2015. The effect of restricting movements of female animals over 12 months of age from these herds was compared with data collected on Trojan dams that calved in 2015. Four different potential restriction lengths were considered, varying from the period when a BVD + animal was present in the herd, to extending this to 12 months after removal of the last BVD + animal. In terms of effectiveness, none of the four restriction measures evaluated was effective at preventing the movement of all Trojan dams. Between 18.3% and 37.3% of Trojan births in 2015 would have been prevented under the proposed measures, and all Trojan births would have been prevented in between 14.4% and 32.5% of herds with BVD + births. In terms of proportionality, between 4.4% and 15.4% of all females > 12 months of age that moved between herds during 2015 would have been prevented from moving, and between 3.5% and 10.1% of Irish herds with at least one such movement would have been affected. These results show how measures to control the movement of Trojan dams should be targeted in a way that fits the Irish context and reduces the spread of BVDv, without unduly impacting other trade.362Scopus© Citations 5 - PublicationBovine viral diarrhoea virus seroprevalence and vaccination usage in dairy and beef herds in the Republic of Ireland(Springer (Biomed Central Ltd.), 2012)
; ; ; 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.423Scopus© Citations 28