Study demonstrates a reduction in IBR in herds

editorial image

Infectious Bovine Rhinotracheitis (IBR) is a highly contagious infectious disease, caused by a Herpesvirus - Bovine Herpes Virus 1 (BoHV1).

Just like cold sores or human Herpesvirus infections, the virus will live in symptomless carrier animals and emerge at times of stress.

The first serious outbreak of IBR was reported in the UK in the late 1970’s and is now endemic with more than 75% of herds affected in the UK and Ireland.

Risk factors for IBR are large herd size, open herd policy and poor biosecurity. The virus commonly enters the herd via latently infected carrier animals.

Infection occurs when a naïve animal is exposed to the IBR virus, and is commonly associated with clinical signs of acute IBR disease which range from mild to severe. Once an animal has been infected, it will become a latent carrier for life. Latent carriers are a potential source of infection and can shed virus at times of stress resulting in disease in in-contact animals.

Clinical signs of IBR are upper respiratory disease (the virus will target the eyes, nose and throat) and reproductive disease with symptoms of infertility and abortion. IBR can act alone or be part of a mixed infection along with other pneumonia viruses and bacteria. Clinical symptoms will be more severe if BVD is present in the herd at the same time.

IBR is not commonly seen in young calves below three months of age, probably due to the good protection afforded by colostral antibodies.

Adult dairy cows will suffer variable symptoms ranging from subclinical disease to milk drop, mild conjunctivitis, fever, infertility/ abortion and even severe respiratory disease/death.

The majority of dairy herds in the UK are endemically infected, with adult cows being latent carriers of infection. And in most dairy herds, calves are removed from dairy cows very shortly after birth and reared separately. Therefore they may remain “clean” or “naïve” throughout the rearing and first breeding season until they mix with the lactating cows after 1st calving. This is a very stressful time for dairy heifers, which makes them susceptible to disease if the virus is endemic in the herd. Therefore in many dairy herds the common disease pattern is that heifers become infected when they enter the milking herd.

A good starting point to control IBR in the dairy herd would be to establish the disease status. This can be done through bulk milk antibody testing, targeted blood or milk sampling. Live and inactivated vaccines are available. The use of marker vaccines will allow control and eradication or monitoring of the level of infected animals within the herd. IBR Marker vaccination has several advantages. It will allow protection of naïve (at risk) animals in a herd where there is still risk of infection and it can be used in eradication/accreditation programmes that require animals to be blood tested clear, but still want to be protected from disease. The use of IBR Marker vaccines makes it possible to differentiate animals infected by wild type virus from vaccinated animals.

Live IBR vaccination (Rispoval ®IBR Marker Live) should be used to protect naive and high risk animals against disease, and inactivated IBR vaccines (Rispoval®IBR Marker Inactivated) can be used in already infected animals within endemically infected herds to help reduce the risk of latent carriers shedding.

Animals at three months of age or older at first vaccination should be given one intramuscular vaccination. To reduce abortions associated with BoHV-1female cattle require a primary course of two intramuscular doses of vaccine three to five weeks apart. Animals initially vaccinated with Rispoval® IBR Marker Live may be given a single dose booster within six months after the first vaccination to provide six months of protection or Rispoval IBR Marker Inactivated to provide a duration of protective immunity of 12 months. Thereafter, single booster vaccinations should be administered every six months (if using Rispoval® IBR Marker Live) or every 12 months (if using Rispoval® IBR Marker Inactivated).

An ongoing study in a closed 220 cow dairy herd in Scotland using Live IBR Marker vaccine in heifers and Inactivated IBR Marker vaccine in cows has generated some interesting field data, demonstrating how use of this combination vaccination programme can protect naïve animals from wild type IBR infection in the face of a high herd prevalence. At the start of the study in 2012, 99% of the milking herd were infected with wild type IBR. On this farm, the young stock are housed and grazed separately from adult cows until late pregnancy. For the last two years they have been tracking the IBR status of the youngstock as they join the adult dairy herd.

The aim is to keep the youngstock protected from IBR virus using the vaccine, and eventually replace all of the latently infected older cows with protected heifers. So far the vast majority of heifers that were IBR seronegative prior to entry into the milking herd have stayed seronegative to the wild-type IBR virus as shown by subsequent individual milk testing. Alongside the normal herd culling policy this has reduced the percentage of infected animals in the herd from 99% to 65% in just two years. This study is ongoing, but results to date suggest that this combined vaccination approach is proving effective in protection against both clinical disease, and seroconversion in the incoming heifers.