Abstract:
Research aimed at optimising diagnostic laboratory procedures is central to the development
of effective bovine viral diarrhoea virus (BVDV) control programmes. BVDV is a singlestranded
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.
