Dynamics of virus infections involved in the bovine respiratory disease complex in Swedish dairy herds

Abstract

The dynamics of bovine respiratory syncytial virus (BRSV), bovine parainfluenza virus 3 (PIV-3), bovine corona virus (BCoV) and bovine viral diarrhoea virus (BVDV) infections were studied in 118 dairy herds in south western Sweden. By using serology on paired samples from three approximately 7 vs. approximately 15-month-old calves per herd, the propagation of infections was investigated over about a 1-year period. The results implied that at least 74% of calves had experienced one or more of the monitored infections at the age of approximately 7 months (Sample 1, Spring); 30%, 48%, 34% and 8% were seropositive to BRSV, PIV-3, BCoV and BVDV, respectively. Seroconversions to BRSV, PIV-3, BCoV and BVDV occurred in 26%, 38%, 50% and 3% of seronegative animals and 63% had antibodies against two or more infections at approximately 15 months (Sample 2). In total, 90-97% of animals that were seropositive in Sample 1 remained positive in Sample 2. A significant association was found between BVDV and BCoV (P = 0.01). Moreover, a significantly higher proportion of herds in which no calves had a recorded history of respiratory disease (n = 15) were classified as negative to all four infections monitored when compared to herds in which disease was observed (P = 0.0002). This study showed a high infection burden in young animals and effective spread of BRSV, PIV-3 and BCoV in one area of Sweden. BVDV infections were restricted to a few herds, reflecting the effect of a voluntary control program against BVDV in Sweden.

Fig. 1

Distribution of ELISA results on serum analyses from 354 animals in 118 Swedish dairy herds (Sample 1). Values are given as corrected optical density (COD) values at 450 nm.

Fig. 2

Number of herds (% within parentheses) classified as infected with different combinations of BRSV, PIV-3 and BCoV in 118 Swedish BVDV positive or negative dairy herds. Herds shown in squares are classified as negative for BRSV, PIV-3 and BCoV. For definition of infection, see text.

Fig. 3

Distribution of ELISA results for antibodies to: (a) BRSV; (b) BCoV; (c) BVDV in bulk tank milk from 115 Swedish dairy herds. Values are given as corrected optical density (COD) values at 450 nm.

Fig. 4

Geographical distribution of 118 Swedish dairy herds with regard to serological status for: (a) BRSV, (b) PIV-3, (c) BCoV and (d) BVDV. Herds classified as infected with respective virus in Sample 1 are shown as filled circles (for classification of infection, see Section 2). Herds not classified as infected in Sample 1, but in which seroconversions were detected between Samples 1 and 2 are shown as circles with cross (for definition of seroconversion, see text). Herds classified as not infected with respective virus in Samples 1 and 2 are shown as empty circles.