When comparing the present with the past, there are several statements that come up again and again from veterinarians and producers alike. “The cows have never been this healthy”, “The herd has never produced so much milk!”, “I think things are good enough”. While animal and veterinary sciences have made massive, progressive strides in the way we care for and feed cattle over time, there is always room to improve. The benchmarks for excellence are always moving, and anyone who is too complacent will be left behind. Can we accept “good enough” when trying to control Herpesvirus-1 (aka Infectious Bovine Rhinotracheitis/IBR) in our herds? Let’s dive into that question a little further.

This is Bovine Herpes – it’s with your cows for life

Bovine Herpesvirus-1 (BHVB-1) causes a variety of disease presentations in cattle. Notably, a key historic presentation of BHV-1 in cattle was IBR. Clinical IBR is characterized by fever, ocular and nasal discharges, increased respiratory rate and effort, and depression. It is commonly found as one of the many viruses associated with bovine respiratory disease (BRD). BHV-1 can also cause reproductive consequences like abortion, early embryotic death, poor conception rates, and inflammation of the vulva and vagina.

The virus is normally introduced into herds via the purchase of or contact with cattle from positive farms. It transmits primarily via nose-nose contact, although aerosol and venereal transmission are also possible¹.   One unique aspect about herpesviruses is their ability to cause life-long infections, entering a dormant state in the nervous system of cattle².  These lifelong-infected cattle can shed and transmit virus during periods of stress (e.g. weather, calving, transportation, poor nutrition, other diseases etc.). This ensures continued viral presence and circulation in a herd once infected.

The virus is normally introduced into herds via the purchase of or contact with cattle from positive farms. It transmits primarily via nose-nose contact, although aerosol and venereal transmission are also possible¹.   One unique aspect about herpesviruses is their ability to cause life-long infections, entering a dormant state in the nervous system of cattle².  These lifelong-infected cattle can shed and transmit virus during periods of stress (e.g. weather, calving, transportation, poor nutrition, other diseases etc.). This ensures continued viral presence and circulation in a herd once infected.

Vaccinating to control IBR in the herd

Over the past 30 years, herds have made major strides towards controlling IBR. Indeed, current multivalent viral vaccines (e.g. Bovi-Shield, Pyramid, Express) have done an excellent job at reducing the clinical signs and mortality associated with IBR infections in cattle³. In herds well vaccinated with a modified live viral vaccine annually (or once per lactation/gestation), it is uncommon to see severe clinical IBR outbreaks. But with IBR, much of the effect is in its subclinical form, resulting in reproductive failures, increased BRD risk, and lower milk production in infected herds and animals^4,5. So, are our herds truly protected against IBR and can more be done to improve protection?

For true IBR control, 6 is better than 12!

There are different strategies for preventing IBR infections in our herds. In many European countries, given the many and varied impacts that IBR can have on herds, there are active elimination schemes in place to rid the country of this virus. This involves vaccination, test and cull, and strict biosecurity protocols to avoid IBR introduction into a herd. Vaccines used allow for the differentiation between vaccinated and naturally infected animals in the herd.

In North America, on the other hand, the focus has been on clinical disease control and not eradication. In doing so, IBR is still present and circulating in our cattle herds. Our control efforts have made huge strides in limiting IBR-induced abortions and the classical “red nose”, especially in herds well-vaccinated with MLV products, but it’s important to remember that IBR can have an unseen influence on animal health (subclinical infections), and with viral circulation comes the risk of reduced animal health and productivity.

Antibody levels drop after 6 months

One of the most effective means of IBR control is through vaccination. Protection against infection depends on high antibody levels and cell-mediated immunity. One of the problems with current vaccine products is that IBR antibody levels are significantly lower by 6 months following vaccination, whereas antibody levels remain at protective levels for over a year following vaccination⁶ (Figure 1).

Indeed, an excellent piece of research was published by Belgian researchers looking at the effects of increasing vaccine frequency on the transmission risk of IBR in beef and dairy herds⁷. The study followed 72 herds (34 dairy and 38 mixed dairy/beef – 7700 adult animals total) over 2.5 years, with whole-herd blood sampling every 6 months. Herds were randomized to 2 treatment groups: annual vaccination versus hyperimmunization (vaccination of the whole herd every 6 months). Researchers were particularly interested on looking at IBR transmission within the herd and the risk of exposure to IBR. Where there is circulating virus, there is potential disease.

The study had some very interesting findings. Briefly, herds hyperimmunized with a modified-live marker live vaccine saw the seroprevalence of IBR significantly decrease in their herds (Figure 2). Herds started at an IBR seroprevalence of roughly 35% (percent of the herd infected with IBR). By the end of the study, herds hyperimmunized against IBR had a seroprevalence of ~17%, whereas annually vaccinated herds saw an increase in IBR seroprevalence!

Figure 2. Change in seroprevalence of IBR in cattle: 6-month vs annual IBR vaccination⁷.

The risk of acquiring new IBR infections in hyperimmunized herds was also significantly lower than herds vaccinated using an annual protocol (Figure 3). Of note, the risks for seroconversion was always higher for annually vaccinated herds, they were substantially higher during the winter months.

Figure 3. Change in risk ratio for gE seroconversion in dairy herds: 6-month vs annual vaccination protocol⁷. Area shaded in green denotes winter/cold weather months throughout the study.

A world-renowned expert that participated in the study – Dr. Etienne Thirny, professor and head of veterinary virology at the University of Liège (Belgium) – agrees: annual protocols are not enough to control IBR.

The path forward…

When MLV vaccines are given on an annual/once-per-gestation basis, they are having a significant influence on the clinical presentation of IBR. It is also clear that transmission can still occur in herds vaccinated annually. This leaves the door open for continued IBR infections in youngstock, subclinical disease, and higher likelihood of break-through infections. So, what can be done?

Multivalent viral vaccines contain an IBR strain that can cause latent infections, abortions in improperly primed pregnant animals, and may contribute to sub-optimal fertility⁸. Conversely killed vaccines, while much safer, are only activating one arm of the immune system – antibodies. We know that effective IBR control relies on both cell-mediated and antibody immunity.

Luckily, there is a modified live vaccine option for IBR control that are completely safe for use in pregnant animals AND activates BOTH the cellular and humoral immune system of cattle. HIPRABOVIS Marker Live is available in Canada and has been shown to reduce the clinical signs of IBR by 75% and, more importantly, lead to a 100-fold reduction in IBR shedding in vaccinated animals post-infection. This is a very flexible product that can significantly reduce the impact of IBR in all age classes on the farm. Boosting all animals on the farm mid-gestation or lactation (e.g. every 6 months) following their normal multivalent viral MLV vaccination as open animals will lead to significantly lower IBR transmission on the farm and improve health and productivity. It will also greatly protect youngstock on the farm – less shedding means less risk of transmission to the most vulnerable age group on the farm!

It is time to get serious about IBR control on the farm.

References

1. Muylkens, B., Thiry, J., Kirten, P., Schynts, F., Muylkens, B., Thiry, J., Kirten, P., Schynts, F., & Thiry, E. (2007). Bovine herpesvirus 1 infection and infectious bovine rhinotracheitis. Veterinary Research, 38(2), 181–209.
2. Nettleton, P., & Russell, G. (2017). Update on infectious bovine rhinotracheitis. In Practice, 39(6), 255–272. https://doi.org/10.1136/inp.j2226
3. Theurer, M. E. et al., (2015). Systematic review and meta-analysis of the effectiveness of commercially available vaccines against bovine herpesvirus, bovine viral diarrhea virus, bovine respiratory syncytial virus, and parainfluenza type 3 virus for mitigation of bovine respiratory di. J Am Vet Med Assoc, 246(1), 126–142. https://doi.org/10.2460/javma.246.1.126
4. Pritchard, G. C., Banks, M., & Vernon, R. E. (2003). Subclinical breakdown with infectious bovine rhinotracheitis virus infection in dairy herd of high health status. Veterinary Record, 153(4), 113–117. https://doi.org/10.1136/vr.153.4.113
5. Statham, J. M. E., Randall, L. V., & Archer, S. C. (2015). Reduction in daily milk yield associated with subclinical bovine herpesvirus 1 infection. Veterinary Record, 177(13), 339. https://doi.org/10.1136/vr.103105
6. Lee, M., Reed, A., Estill, C., Izume, S., Dong, J., & Jin, L. (2015). Evaluation of BHV-1 antibody titer in a cattle herd against different BHV-1 strains. Veterinary Microbiology, 179(3–4), 228–232. https://doi.org/10.1016/j.vetmic.2015.06.009
7. Ampe, B., Duchateau, L., Speybroeck, N., Berkvens, D., Dupont, A., Kerkhofs, P., Thiry, E., & Dispas, M. (2012). Assessment of the long-term effect of vaccination on transmission of infectious bovine rhinotracheitis virus in cattle herds hyperimmunized with glycoprotein E–deleted marker vaccine. J Am Vet Med Assoc, 73(11), 1787–1793. https://doi.org/10.2460/ajvr.73.11.1787
8. Chase, C. C. L., Fulton, R. W., O’Toole, D., Gillette, B., Daly, R. F., Perry, G., & Clement, T. (2017). Bovine herpesvirus 1 modified live virus vaccines for cattle reproduction: Balancing protection with undesired effects. Veterinary Microbiology, 206(2016), 69–77. https://doi.org/10.1016/j.vetmic.2017.03.016