Bovine Viral Diarrhea Virus (BVDV): First Detection of Genotype 2 in Spain

Bovine viral diarrhea virus (BVDV), a pestivirus of the Flaviviridae family, circulates worldwide. A recent study* has detected the presence of the much rarer type 2 virus in Spain. This discovery will have implications for the epidemiology, diagnosis, and control of the infection in the Spanish cattle herd… and beyond.   The two genotypes of the virus (BVDV-1 and BVDV-2) are distinguished by serology and molecular biology. In addition, numerous subtypes have been described (BVDV-1a through 1p and BVDV-2a through 2d). BVDV-2 is associated with a severe clinical form of the disease in adult cattle and with a hemorrhagic syndrome in calves. Although this genotype is more prevalent in North America, it is also present in certain European and Asian countries. Over the past two years, a severe form of BVD associated with genotype 2 has caused high mortality, first in Germany and then in the Netherlands. According to several previous studies, the subtype circulating primarily in the Spanish cattle population is BVDV-1b. No evidence of BVDV-2 had been found until now.  

Concordant Detection of BVDV by ELISA and RT-PCR

A total of 47 blood samples were collected from cattle that tested positive by ELISA, from 18 herds located in the northern half of Spain (35 dairy herds, 12 beef herds). In addition, veterinarians reported certain clinical and epidemiological data: reproductive disorders (8 herds), mucosal disease (3), calf mortality (2), no cases of disease (4), or no information provided (1). The 47 blood samples were genotyped using RT-PCR. BVDV-1 was identified most frequently (46 of 47 isolates), compared to BVDV-2 (2 out of 47). The two animals infected with BVDV-2 were from the Asturias region, an area with a high density of dairy farms. Apparently, both were clinically healthy at the time of sampling. In a single blood sample, both pestivirus genotypes, BVDV-1 and BVDV-2, were detected. Superinfection of a persistently infected immunotolerant (IPI) animal with a different genotype could explain this mixed infection. According to the authors, this is the first detection of BVDV-2 in Spain. This type 2 virus was first reported in the United States in 1994, and subsequently in a few European countries, but at a significantly lower rate than type 1, except in Germany in 1997, where a prevalence of over 10% was reported. More recently, in 2014, Poland recorded the first isolation of BVDV-2 in its cattle herd. Due to the small number of isolates analyzed in the study, it is not possible to accurately determine the prevalence of BVDV-2 in Spain. Further research is needed to establish the spread of this pestivirus in Spanish cattle herds and the resulting clinical consequences. Thus, understanding the diversity of BVDV is the first step toward comprehending the epidemiology of the infection and developing effective diagnostic tests and vaccines.  

Spread Facilitated by Global Trade

Animal movements and the trade in embryos and semen are among the main risk factors for BVD infection in livestock. The virus causes significant economic losses, primarily due to its impact on cattle health and reproduction. Control programs based exclusively on the culling of IPI-positive animals were launched in the Nordic countries in 2006. In other European countries, vaccination is used to control the infection. Currently, there is no BVD control program in Spain, and the vaccines available in the country contain only the BVDV-1 valence. However, the antigenic structure of the two genotypes differs, as do their subtypes. While several studies show a certain degree of cross-immunity, better protection of the fetus is ensured when a strain of the same genotype is used. In a recent study (Polak et al. 2014), a vaccine targeting BVDV-1 did not protect against infection with BVDV-2. Thus, the development of effective vaccines against viruses from all antigenic groups appears to be a priority for implementing BVD control programs based on the vaccination of naive cattle.   * Gorka Aduriz et al.: First detection of bovine viral diarrhea virus type 2 in cattle in Spain, Vet. Rec. 2015.