? Update on the epidemiology of bovine viral diarrhea virus (BVDV) in Argentina: revising intervention strategies

PEREZ AGUIRREBURUALDE MARIA SOL; ANDREA PECORA; LEON EMILIO; DUS SANTOS MARIA JOSE

SAPPORO

Congreso; XXX World Buiatrics Congress; 2018

Bovine Viral Diarrhoea Virus (BVDV) is endemic in most regions around the world and has a detrimental effect on herds? performance. In Argentina, its high prevalence has been well established, although reports done almost 20 years ago showed quite heterogeneous distributions of prevalence values, going from 25 to 90% depending on the region. Strikingly, this feature was not studied in greater depth. Furthermore, the phylogenetic analyses described by the earliest reports in the 2000, differ significantly from recent findings. Bovine livestock production in Argentina has undergone, in the latest decades, a remodeling process due to the expansion of land used for crop. This had a serious impact in structure of livestock production in the central area, as well as in the marginal territories. This process could have had a great effect on the dynamic of infectious diseases in the population. Even though vaccines are the main intervention strategy applied to control BVDV infection in the country, no control of vaccine matching is being implemented routinely. Purpose: The aim of this study was to assess the prevalence of BVDV in the main cow-calf productive region, and to compare it with historical reports. The serological profile in the population was assessed and interpreted, having into account the current phylogenetic information about BVDV isolates. Furthermore, a preliminary revision of the common management practices in concern to vaccine use was performed. Logic models framework for comprehensive monitoring and evaluation was applied in order to outline a systematic approach that allows to identify weaknesses and challenges. Methods: A cross-sectional study was performed in the Basin of Salado River. Samples were gathered from 100 herds located in 23 districts (the number of sampled herds was proportional to the animal stock per district), collecting an average of 25 samples per herd, making a total of 2750 samples. The samples were evaluated by virus neutralization (VN) for the presence of antibodies against three BVDV strains of different genotypes (1a, 1b, and 2). Endpoint titers were calculated using the Spearman?Karber method of endpoint determination and then the VN results were compared by using the following formula: R = (3 x A) / (A + B+ C). In this way, it was determined if the serological response from each animal was specific for each BVDV strain. The cut-off value to determine the specificity of the serological response was R > 0.2. In addition, a survey was completed on each farm to collect information that could be associated as herd-level risk factors for the disease. Information in concern to the use of vaccines that include BVDV in their formulation was also captured. Results: The results obtained show an individual prevalence of 64.6% (IC: 61.9% - 67.3%), and a 78% (70.3% - 85%) of positive herds, with a median intra-herd of 64.7%. The independent seropositivity against different genotypes tested was analyzed (1a, 1b, 2: 13.4-76.6-10%). Similar distribution of antibody titers where obtained against genotypes 1a and 2, while much more disperse distribution was detected for 1b. This result highlights the higher internal antigenic variability of the BVDV-1b isolates compared to the other ones. In concern to health management practices, 72% of the farms declared that they had vaccinated against BVDV. Strikingly, 56% of the seronegative herds detected, declare to vaccinate, this could be due to the significant variability of vaccine protocols reported in this study. Conclusions: Preliminary results when analyzing the proportions of serologically positive animals against each strain show different frequency distribution among genotypes, which correlates with the phylogenetic results. Current vaccination practices could be jeopardizing the overall effectiveness. These results reinforce how essential is to have current and robust epidemiological information as a starting point to design rationally control plans for BVDV for any particular region. From this study also arouses new questions about the importance of estimating vaccine matching between a vaccine strain and the local isolates.