Knowing how bovine viral diarrhoea virus (BVDV) infection spreads via indirect contacts is required in order to plan
large-
scale eradication
schemes against BVDV. In this study, susceptible calves were exposed to BVDV by an unhygienic vaccination procedure, by ambient air and from contaminated pens. Primary BVDV infection was observed in two calves vaccinated with a vaccine against
Trichophyton spp that had been contaminated by smearing nasal secretion from a persistently infected (PI) calf on
the rubber membrane and penetrating it twice with a hypodermic needle. Four o
ther calves, housed in pairs in two separate housing units near a PI calf for one week—at
distances of 1.5 and 10 m, respectively—became infected without having direct contact with
the PI calf. Fur
thermore, two of
the three calves housed in a pen directly after removal of a PI calf, but without
the pen being cleaned and disinfected, also contracted primary BVDV infection, whereas two calves that entered such a pen four days after removal of ano
ther PI calf, did not.
In herds where most animals are seronegative to BVDV, indirect airborne transmission of BVDV or contact with a contaminated housing interior may be an important factor in spreading of the virus, once a PI animal is present. However, the spreading of BVDV within herds can be stopped by identifying and removing PI animals and also by ensuring that susceptible breeding animals do not become infected during this procedure. In contrast, injectables contaminated with BVDV may prove to be a significant vector for spreading the infection, not only within an infected herd but, most importantly, also between herds. In our opinion, it is questionable whether medicine bottles, once opened and used within an infected herd, should be used in other herds. In any case, prior knowledge of a herd’s BVDV status will help practising veterinarians and technicans to undertake appropriate hygienic measures.