Association of ovine gammaherpesvirus 2 with an outbreak of acute respiratory disease in dairy cattle

Abstract

This study investigated the cause of an outbreak of an acute respiratory disease syndrome followed by episodes of diarrhea in a dairy cattle herd from Southern Brazil. Deep nasal swabs (DNS) from asymptomatic calves, calves with pulmonary discomfort, and diarrheic calves after episodes of respiratory distress were used in molecular assays designed to detect the principal pathogens associated with bovine respiratory disease (BRD). Fecal samples were used for the molecular detection of bovine enteric disease agents. Pulmonary tissues from three calves and a cow that died were evaluated by molecular assays to identify 11 agents associated with the development of BRD. The intestinal and pulmonary fragments of one calf and the cow revealed atrophic enteritis and interstitial pneumonia by histopathology, respectively. Immunohistochemistry (IHC) identified intralesional antigens of a malignant catarrhal fever virus, genus Macavirus, within epithelial cells of the lungs and intestines. Molecular assays amplified ovine gammaherpesvirus 2 (OvGHV2) from most of the DNS, and the pulmonary and intestinal fragments from the animals that died, confirming that the Macavirus identified by IHC was OvGHV2. Concomitant pulmonary infections of OvGHV2 with bovine gammaherpesvirus 6 and bovine coronavirus were identified. Additionally, bovine viral diarrhea virus 1b and Aichivirus B were detected in the fecal samples. These findings demonstrated that OvGHV2, a Macavirus, was the disease agent most frequently (81.2%; 13/16) associated with singular pulmonary infections during this outbreak of BRD, suggesting that this virus may be another potential agent of respiratory disease of cattle.

Figure 1

Histopathological and histochemical findings observed in cattle during an outbreak of respiratory disease induced by OvGHV2. Observe interstitial pneumonia in the calf (a) and cow (b), proliferating vascular lesions in the calf (c) and the cow (d) and marked endothelial degeneration (arrow) in the cow and calf (e,f). Observe the proliferative vascular lesions (g,h), with evidence of partial luminal obliteration (i). Hematoxylin and eosin stain (a–e); the Verhoeff-Van Gieson histochemical method (f–i). Bar; (a,c,d,f,g) 50 µm; (b,e) 100 µm; (h,i) 20 µm.

Figure 2

Immunohistochemical identification of MCFV antigens in the lungs and intestines of cattle infected with OvGHV2. There is positive immunoreactivity to MCFV antigens within the epithelial cells of the bronchus (black arrows) and the peribronchial glands (red arrows) of the calf with interstitial pneumonia (A); closer view of the intracytoplasmic accumulations of antigens of MCFV within epithelial cells of the bronchus (B), peribronchial glands (C), and a pneumocyte (D). Observe positive intracytoplasmic immunoreactivity to MCFV antigens within epithelial cells of intestinal crypts (E), which can be better appreciated at a closer view (F). Immunoperoxidase counterstained with Hematoxylin. Bars (A,E) 100 µm; (B–D,F) 20 µm.