Eradication of Bovine Viral Diarrhoea (BVD) in Cattle in Switzerland: Lessons Taught by the Complex Biology of the Virus

Abstract

Bovine viral diarrhoea virus (BVDV) and related ruminant pestiviruses occur worldwide and cause considerable economic losses in livestock and severely impair animal welfare. Switzerland started a national mandatory control programme in 2008 aiming to eradicate BVD from the Swiss cattle population. The peculiar biology of pestiviruses with the birth of persistently infected (PI) animals upon in utero infection in addition to transient infection of naïve animals requires vertical and horizontal transmission to be taken into account. Initially, every animal was tested for PI within the first year, followed by testing for the presence of virus in all newborn calves for the next four years. Prevalence of calves being born PI thus diminished substantially from around 1.4% to <0.02%, which enabled broad testing for the virus to be abandoned and switching to economically more favourable serological surveillance with vaccination being prohibited. By the end of 2020, more than 99.5% of all cattle farms in Switzerland were free of BVDV but eliminating the last remaining PI animals turned out to be a tougher nut to crack. In this review, we describe the Swiss BVD eradication scheme and the hurdles that were encountered and still remain during the implementation of the programme. The main challenge is to rapidly identify the source of infection in case of a positive result during antibody surveillance, and to efficiently protect the cattle population from re-infection, particularly in light of the endemic presence of the related pestivirus border disease virus (BDV) in sheep. As a consequence of these measures, complete eradication will (hopefully) soon be achieved, and the final step will then be the continuous documentation of freedom of disease.

Benefit of Bovine Viral Diarrhoea (BVD) Eradication in Cattle on Pestivirus Seroprevalence in Sheep

“…The economic impact of infection with BVDV on cattle farming has led to eradication programs in many countries ( 15 , 32 – 36 ). Although it has been known for many years that BVDV may also infect sheep and that BDV, mostly found in sheep, may infect cattle, the possible implications for the pestivirus status in these two species are little studied ( 8 , 22 , 37 , 38 ).…”

“…By contrast, interspecies transmission of BDV seems to be rare ( 8 ). Due to the genetic and antigenic relatedness of pestiviruses, most routine diagnostic tools used for detection of BVDV cross-react with BDV strains, which impedes routine differentiation of these ruminant pestiviruses ( 8 , 15 ).…”

“…The finding of cattle that are PI with BDV is of concern mainly in countries that have ongoing BVD eradication programs, as it exacerbates contact tracing and identification of the source of infection. In 2008, Switzerland started a mandatory national BVD eradication program in cattle ( 15 ). During the first year, all cattle were tested for antigen or viral RNA and animals identified as PI were eliminated.…”

“…During the first year, all cattle were tested for antigen or viral RNA and animals identified as PI were eliminated. In the following years, all newborn calves were similarly screened and in 2013, surveillance was switched to testing for pestivirus-specific antibodies, either in the blood of young calves (“spot test”), in milk of first-lactating cows, or in bulk milk ( 15 – 19 ). Prior to the start of the eradication program, around 1.3% of all newborn calves and 0.7% of all cattle were PI, and ~60% of the cattle population was seropositive ( 17 , 20 ).…”

“…Over the course of the eradication program, the epidemiological situation changed markedly. Whilst PI animals were detected in some 12% of herds before the start of the program ( 20 ), currently ~99.5% of all cattle herds are certified free of BVDV ( 15 ). Since the start of the eradication, vaccination was prohibited in Switzerland as this would interfere with serology as a tool to monitor the progress of the program.…”