Bovine herpes virus type-4 infection among postpartum dairy cows in California: risk factors and phylogenetic analysis

Abstract

The aims of this study were to determine the prevalence and associated risk factors of bovine herpes virus type-4 (BoHV-4) infection and describe the genetic characteristics and predominant genotypes of the virus in Yolo and Tulare counties, California. A cross-sectional study involving multi-stage sampling technique was used. One hundred and forty-eight post-partum cows were enrolled from 11 dairy farms. Uterine/vaginal samples were collected and tested for BoHV-4 and other co-infecting viruses using real-time PCR. Data were analysed using multilevel logistic mixed-effect model. Phylogenetic analysis of 10 BoHV-4 isolates was conducted by targeting three open reading frames (ORF3, ORF8 and ORF 22) of the viral genome. The prevalence of BoHV-4 infection was 22.3% (33/148), while post-partum metritis was 33.8% (48/142). Strong association was found between BoHV-4 infection and lactation number, lactation stage and post-partum metritis. The odds of being positive for BoHV-4 infection were 6.47 times (95% CI 1.17-35.92; P 240 days). Cows with post-partum metritis were 4.51 times (95% CI 1.27-16.02; P < 0.05) more likely to test positive for BoHV-4 infection compared with those without post-partum metritis. Phylogenetic analysis of BoHV-4 based on sequencing of glycoprotein and thymidine kinase (TK) genes revealed genetic variability of the virus with glycoprotein B genotype 1 and TK genotype 2 as being dominant genotypes. The reported high genetic variability of BoHV-4 indicates the possibility of co-infection with multiple genotypes.

Keywords: Bovine herpes virus type 4; California; dairy cows; phylogenetic analysis; prevalence.

Fig. 1.

Genetic relatedness of BoHV-4 isolates (n = 10) obtained from uterine/vaginal discharge samples of California dairy cows with post-partum metritis. Phylogenetic tree was constructed using Neighbour-Joining method from sequencing of ORF-3 gene that encodes for thymidine kinase (TK). Movar and DN599 are European and American prototypes of BoHV-4 strains, respectively.

Fig. 2.

Genetic relatedness of BoHV-4 isolates (n = 10) obtained from uterine/vaginal samples of California dairy cows with post-partum metritis. Phylogenetic tree was constructed using Neighbour-Joining method from sequencing of the ORF-8 gene that encodes for glycoprotein (gB).

Fig. 3.

Genetic relatedness of BoHV-4 isolates (n = 10) obtained from uterine/vaginal discharge samples of California dairy cows with post-partum metritis. Phylogenetic tree was constructed using Neighbour-Joining method from sequencing of ORF-22, a gene that encodes for glycoprotein H.