Evaluation of the effects of long-term storage of bovine ear notch samples on the ability of 2 diagnostic assays to identify calves persistently infected with bovine viral diarrhoea virus
Journal of the South African Veterinary Association
Vetdiagnostix, Veterinary Pathology Services, PO Box 13624, Cascades, 3202, South Africa; Department of Veterinary Tropical Diseases, University of Pretoria, Private Bag X04, Onderstepoort, 0110, South Africa; Veterinary House Hospital, 339 Prince Alfred Street, Pietermaritzburg, 3201, South Africa
Research aimed at optimising diagnostic laboratory procedures is central to the development of effective bovine viral diarrhoea virus (BVDV) control programmes. BVDV is a single-stranded RNA virus that crosses the placenta to infect foetuses, resulting in reproductive losses due to foetal death or persistently infected calves that die early in life. Persistently infected animals are widely accepted to be the primary reservoir of BVDV and the largest source of infection. This poses important challenges to overall animal/herd health and can cause major losses to the cattle industry. Long-term storage of bovine ear notch samples from calves persistently infected with BVDV may adversely affect the ability of diagnostic assays to detect the virus efficiently. In order to test this hypothesis, ear notch samples from 7 animals were divided into 2 groups. One set was subjected to prompt formalin fixation and the other set stored either as fresh samples without preservatives at -2 °C, or soaked overnight in phosphate buffered saline followed by freezing of the supernatant fluid at -2 °C. Frozen ear notches and ear notch supernatant yielded positive results with an antigen-capture, enzyme linked immunosorbent assay (AC-ELISA) for the duration of the study (6 months) and optical density (OD) values remained significantly within range. There was no significant difference between storing fresh ear notch samples or PBS at -2 °C. However, positive immunohistochemistry (IHC) staining on formalin fixed ear notches started to fade between Day 17 and Day 29 when stored at room temperature. It was concluded that fresh ear notches could safely be stored at -2 °C for a period of 6 months prior to testing for BVD viral antigens.
formaldehyde; virus antigen; article; bovine viral diarrhea; calf (bovine); ear; enzyme linked immunosorbent assay; female; immunohistochemistry; long term care; nonhuman; optical density; organ preservation; persistent infection; room temperature; Animals; Antigens, Viral; Bovine Virus Diarrhea-Mucosal Disease; Cattle; Diarrhea Viruses, Bovine Viral; Ear; Enzyme-Linked Immunosorbent Assay; Freezing; Immunohistochemistry; Specimen Handling; Tissue Preservation; Animalia; Bos; Bovinae; Bovine viral diarrhea virus 1; RNA viruses