Epidemiology of age-dependent prevalence of Bovine Herpes Virus Type 1 (BoHV-1) in dairy herds with and without vaccinat
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RESEARCH ARTICLE
Open Access
Epidemiology of age‑dependent prevalence of Bovine Herpes Virus Type 1 (BoHV‑1) in dairy herds with and without vaccination Jonas Brock1,2* , Martin Lange1, Maria Guelbenzu‑Gonzalo2, Natascha Meunier2, Ana Margarida Vaz4, Jamie A. Tratalos3, Peter Dittrich5, Michael Gunn2, Simon J. More3, David Graham2 and Hans‑Hermann Thulke1
Abstract Many studies report age as a risk factor for BoHV-1 infection or seropositivity. However, it is unclear whether this pattern reflects true epidemiological causation or is a consequence of study design and other issues. Here, we seek to understand the age-related dynamics of BoHV-1 seroprevalence in seasonal calving Irish dairy herds and provide decision support for the design and implementation of effective BoHV-1 testing strategies. We analysed seropreva‑ lence data from dairy herds taken during two Irish seroprevalence surveys conducted between 2010 and 2017. Age-dependent seroprevalence profiles were constructed for herds that were seropositive and unvaccinated. Some of these profiles revealed a sudden increase in seroprevalence between adjacent age-cohorts, from absent or low to close to 100% of seropositive animals. By coupling the outcome of our data analysis with simulation output of an individual-based model at the herd scale, we have shown that these sudden increases are related to extensive virus circulation within a herd for a limited time, which may then subsequently remain latent over the following years. BoHV-1 outbreaks in dairy cattle herds affect animals independent of age and lead to almost 100% seroconversion in all age groups, or at least in all animals within a single epidemiological unit. In the absence of circulating infection, there is a year-on-year increase in the age-cohort at which seroprevalence changes from low to high. The findings of this study inform recommendations regarding testing regimes in the context of contingency planning or an eradica‑ tion programme in seasonal calving dairy herds. Keywords: infectious Bovine Rhinotracheitis (IBR), infection dynamics, Ireland, seasonal calving, serosurveillance, dairy Introduction Bovine Herpes Virus Type 1 (BoHV-1) is a highly contagious virus of cattle and is known to be the causative agent of the acute respiratory disease infectious bovine rhinotracheitis (IBR). The virus occurs worldwide and is endemic in a number of food-producing countries [1]. Following infection, cattle are lifelong carriers of the virus with the potential of spontaneously reactivated *Correspondence: [email protected] 1 Helmholtz Centre for Environmental Research GmbH-UFZ, Dept Ecological Modelling, PG Ecological Epidemiology, Leipzig, Germany Full list of author information is available at the end of the article
viral shedding, especially at times of increased stress [2]. Infections with BoHV-1 may be associated with various clinical signs and changes in production parameters, ranging from fever, reduced growth rate and milk yield to an increased risk of abortion and death [3, 4]. When a naïve ani
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