The bovine respiratory disease (BRD) complex is a multietiological and multifactorial disease associated with a wide range of viral and bacterial pathogens. This study evaluated the contribution of specific infectious disease agents in the development of BRD in cattle from Brazil and determined if a virus within the malignant catarrhal fever virus (MCFV) group and Mycoplasma bovis, acting individually or in conjunction, can be associated with the development of BRD. Formalin-fixed paraffin-embedded pulmonary sections were used in immunohistochemical assays to determine the intralesional presence of six antigens associated with BRD: bovine alphaherpesvirus 1 (BoHV-1), bovine parainfluenza virus 3 (BPIV-3), bovine viral diarrhea virus (BVDV), bovine respiratory syncytial virus (BRSV), MCFV, and M. bovis. Pneumonia was diagnosed in 82.7% (120/145) of all cattle evaluated. Interstitial pneumonia (60%, 72/120) and suppurative bronchopneumonia (25.8%, 31/120) were the most frequent patterns of pneumonia identified. Intralesional antigens of MCFV (53.3%, 64/120) were the most frequently associated with BRD, followed by M. bovis (47.5%, 57/120), BVDV (42.5%, 51/120), BoHV-1 (28.3%, 34/120), BRSV (24.2%, 29/120), and BPIV-3 (8.3%, 10/120). Additionally, antigens of BVDV, MCFV, and M. bovis were the most frequently identified agents associated with singular and concomitant infections. The MCFV identified during this study is more likely to be ovine gammaherpesvirus 2 (OvHV-2), since OvHV-2 is the only MCFV identified within the geographical region of this study. Interstitial pneumonia with proliferative vascular lesions may be a useful histologic feature to differentiate MCFV-induced pneumonia from other viral pneumonias of cattle. These results demonstrate that MCFV and M. bovis, in single or mixed infections, can produce pneumonia in cattle and should therefore be considered as primary agents in the development of BRD.

Bovine gammaherpesvirus 6 (BoGHV6), previously known as bovine lymphotropic virus, is a member of the Macavirus genus, subfamily Gammaherpesvirinae. Other members of the genus Macavirus include viruses that produce malignant catarrhal fever (MCF) in mammalian hosts, collectively referred to as the MCF virus (MCFV) complex, and the porcine lymphotropic herpesvirus (PLHV). However, the current role of BoGHV6 in the development of diseases and/or disease syndromes remains uncertain and controversial. This paper investigated the participation of BoGHV6 in the development of pulmonary disease in a cow with interstitial pneumonia by histopathology and molecular testing. Tissue antigens of common viral agents of respiratory diseases and Mycoplasma bovis were not identified by immunohistochemistry. Additionally, molecular assays designed to amplify common bacterial and viral pathogens of pulmonary disease did not amplify the nucleic acids of these agents. However, a pan-PCR assay amplified the DNA of the herpesvirus polymerase gene, while the specific BoGHV6 nested-PCR assay amplified the partial fragment of the BoGHV6 polymerase gene derived from the pulmonary tissue with interstitial pneumonia. Phylogenetic analysis revealed that the BoGHV6 strain herein identified had 99.8% nucleotide (nt) sequence identity with reference strains of BoGHV6, but only 72.2–73.5% and 67.9–68.6% nt identity with reference strains of MCFV and PLHV, respectively. Consequently, these results suggest that BoGHV6 was associated with the pulmonary disease observed in this cow.

This study investigated the occurrence of selected pathogens of bovine respiratory disease in fetal pulmonary tissue of cattle and associated these with patterns of disease. Fetal pulmonary (n = 37) tissues were evaluated by histopathology; immunohistochemical assays identified intralesional antigens of bovine alphaherpesvirus 1 (BoAHV1), bovine viral diarrhea virus (BVDV), bovine parainfluenza virus 3 (BPIV-3), bovine respiratory syncytial virus (BRSV), and Mycoplasma bovis. Molecular assays were performed to amplify reproductive disease pathogens and bovine gammaherpesvirus 6 (BoGHV6) from 12 lungs. The 2 patterns of pulmonary diseases were interstitial pneumonia (12/37) and suppurative bronchopneumonia (1/37). The frequency of the intralesional antigens identified was BRSV (16.2%; 6/37), BVDV (13.5%; 5/37), BoAHV1 (8.1%; 3/37), M. bovis (5.4%; 2/37), and BPIV-3 (2.7%; 1/37). Interstitial pneumonia was associated with BRSV (n = 3), BoAHV1 (n = 3), and BVDV (n = 2); suppurative bronchopneumonia contained a Gram-positive bacterium and BVDV and BRSV. Reproductive pathogens detected included Leptospira spp., (n = 3), BVDV, Neospora caninum, and Brucella abortus (n = 2). BoGHV6 DNA was identified in the lungs of two fetuses with interstitial pneumonia. These findings suggest that these fetuses were infected transplacentally by several pathogens. The role of some of these pathogens herein identified must be further elucidated in the possible participation of fetal disease.