Principles of IBR eradication

BoHV-1 establishes latency post-infection therefore all sero-positive animals are considered lifelong carriers and potential shedders of the virus. To eradicate BoHV-1 from a cattle population, sero-positive animals are identified and eliminated. This approach has been used in countries with a low prevalence of BoHV-1 infection. It has been implemented in the Scandinavian countries, Austria and Switzerland.

In some countries the prevalence of BoHV-1 is very high and culling of BoHV-1 positive cattle is not economically feasible. In countries with a high proportion of sero-positive cattle, the only feasible way to eradicate BoHV-1 is to first reduce the incidence of sero-positivity in the national herd. Vaccination with DIVA (differentiating infected from vaccinated individuals) vaccines, also known as marker vaccines, can be a useful tool in this process.

The use of marker vaccines to eradicate IBR

Vaccination of cattle with a BoHV-1 marker vaccine has a dual purpose:

• Reduction of the severity of clinical signs due to BoHV-1 infection
• Reduction of circulating virus when BoHV-1 is introduced into a herd or there is reactivation of a latent infection. This is very important in BoHV-1 eradication programmes as the aim of the program is to reduce gradually the number of gE positive animals in a herd. Once gE negative animals come into contact with field virus their status will change and they will be considered infected with BoHV-1.

The speed of the eradication program depends mainly on the initial herd sero-prevalence, culling rate and new infections/reactivations. Read more about marker vaccines.