Clinicopathological features of 11 suspected outbreaks of bovine adenovirus infection and development of a real-time quantitative PCR to detect bovine adenovirus type 10

CASE HISTORY: A retrospective study was conducted to investigate 11 outbreaks of presumptive fatal adenovirus infection diagnosed through two New Zealand diagnostic laboratories during 2014 and 2015. Outbreaks occurred in 6–12-month-old Friesian or Friesian cross cattle during autumn, winter and spring. Individual outbreaks were short in duration, with mortality rates ranging from 3/250 to 20/600 (1.2 to 3.3%).

CLINICAL AND PATHOLOGICAL FINDINGS: Clinical signs included severe diarrhoea, depression, recumbency, and death. Post-mortem examination revealed congestion and oedema of the alimentary tract and fluid to haemorrhagic intestinal contents. Histopathological lesions were characterised by congestion and haemorrhage of the alimentary tract mucosa, oedema of the submucosa, and mild interstitial inflammation in the kidneys. Large basophilic intranuclear inclusion bodies were identified in vascular endothelial cells of the alimentary tract in 11/11 cases and of the kidney in 8/9 cases.

MOLECULAR TESTING: A real-time quantitative PCR (qPCR) assay was designed to detect bovine adenovirus type 10 (BAdV-10) using hexon gene sequences available in GenBank. DNA extracted from a field case and confirmed by sequencing was used as a positive control. The qPCR had a reaction efficiency of 101% (R²=0.99) and the limit of detection was <10 DNA copies/reaction. The qPCR detected BAdV-10 in formalin-fixed paraffin-embedded (FFPE) tissue from 10/11 cases. DNA sequencing of PCR products from nine of these cases showed them to be identical to BAdV-10 sequences in GenBank. For the PCR-negative case, the PCR product had a hexon sequence 99% similar to bovine adenovirus Wic isolate Ma20-1, a close relative of BadV-10.

DIAGNOSIS: Bovine adenovirus type 10 was identified in FFPE tissues from cattle with histopathological evidence of adenovirus infection.

CLINICAL RELEVANCE: Bovine adenoviruses, and especially BAdV-10, should be considered in the differential diagnosis for acute enteric disease and death in young cattle. The qPCR detected BAdV-10 from FFPE tissue of cattle with suspected adenoviral infection diagnosed by histopathology. However results should be interpreted in light of clinical and pathological findings due to the possibility of adenovirus shedding by healthy cattle and the presence of pathogenic adenoviruses other than BAdV-10.