Investigation on the prevalence of BVDV-2 in dairy cattle herds of northern Italy [Indagine sulla prevalenza di infezione da bovine viral diarrhea virus tipo 2 (BVDV-2) in allevamenti bovini da latte del nord Italia]

The study was aimed at obtaining data regarding the prevalence of Bovine Viral Diarrhea Virus type 2 (BVDV-2) in dairy cattle population of the Po Valley, Northern Italy. The survey was carried out in the period 2009-2011 and involved five diagnostic laboratories located in five provinces of Lombardia and Emilia Romagna regions, namely Brescia, Cremona, Lodi, Mantova e Parma. The area is characterized for a high density of bovine dairy herds, even large herds rearing animals with high genetic value. Despite of the lack of official control-eradication programmes by Authorities, the consciousness about BVD damages is widespread among practitioners and dairy farmers. Therefore, voluntary control-eradication programmes to BVDV are set up on herd level. The programmes, besides the vaccination practice, provided for detection and cull of persistently infected (PI) animals. Bulk milk, blood samples, aborted foetuses and specimens from organs of cattle died for suspected BVD were examined by PCR or real-time PCR to detect BVDV-1 and 2. In addition blood serum samples from BVDV unvaccinated herds were submitted to comparative serology through serum neutralization test (SN) to both the viral types. On the whole 4,464 dairy herds were submitted to diagnostic investigation. Direct diagnostic tests (PCR or real-time PCR) allowed BVDV-2 to be detected in 2.9% of the examined herds. Indirect diagnostic test (comparative SN) showed 4% of the tested herds positive for BVDV-2 infection. Sometimes both the viral types were present together in a single herd. Taken together our data pointed out that BVDV-2, introduced in Italy in 1999 by a contaminated vaccine, at present circulates among the considered cattle population but the prevalence is low. So that BVDV-1 must be considered the most relevant viral type circulating among the domestic dairy cattle population. This evidence is consistent with the epidemiological situation of other European Countries but in contrast with the US picture where BVDV-2 infection is widespread in dairy and beef cattle. The reason of this epidemiological disagreement is not yet elucidated.