Epsilon Open Archive

Abstract

This thesis deals with aspects of the epidemiology of bovine viral diarrhoea virus (BVDV) of relevance to control, with particular focus on the situation in Peruvian smallholder dairy farms. In addition, the importance of Neospora caninum and bovine herpesvirus type 1 (BHV-1) is addressed, as these are important differential diagnoses to BVDV. The prevalence of BVDV and BHV-1 was studied in smallholder dairy farms in a rural area. Using bulk tank milk testing for detection of antibodies it was shown that the prevalence of active BVDV infection was low, and that a large proportion of the herds were free from BHV-1. A study of the BVDV situation in the major dairy region in the country demonstrated a very high level of exposure to BVDV. Individual testing of young stock indicated, however, that many herds might be cleared from BVDV without intervention, and that a long-term reduction in prevalence can be achieved as long as adequate attention is given to systematic measures aimed at preventing re-introduction of infection. An endemic abortion problem in a dairy herd with concurrent infections with Neospora caninum and BVDV was investigated. Using a prospective seroepidemiological approach it was possible to estimate the magnitude of associations between the infections and risk of abortion, and to demonstrate that Neospora caninum infection significantly affected the risk within the herd. Evidence of active BVDV infection, on the other hand, was not associated with abortions. The phylogenetic analysis of BVDV strains isolated from animals detected as persistently infected, demonstrated that all belonged to genotype 1, subtype 1b. The genetic similarity with previously described strains reflected the role of livestock trade for the diversity of BVDV. Imported livestock is the probable source of BVDV strains circulating in the country, and this was supported by the phylogenetic analysis. Finally, it was demonstrated that a molecular epidemiological approach might be used to trace routes of transmission, and to identify and prevent risky behaviour.