Alasdair Marshall BVSc MRCVS, Molecare Veterinary Services
IBR is a highly infectious and contagious bovine herpes 1 virus that can infect cattle of all ages. Cattle are usually infected by inhalation allowing the virus to spread quickly through a group. It is also spread via semen.
Once recovered from the initial infection, cattle develop a latent (hidden) infection where the virus remains in certain nerve cells. This means they will carry the virus often showing minimal or no symptoms. These latently infected animals can shed the virus during periods of stress, typically during periods of other disease, transport or around calving. This is known as recrudescence and allows the virus to keep spreading within a herd. When a latently infected animal begins to shed, it may show few symptoms but are a major source of the virus for naïve younger cattle who often show more severe disease.
Clinical symptoms range from mild to severe, depending on whether the animal is latently infected, the age of the animal, vaccination status, strain of the virus and level of other stressors present. Primarily, disease is seen affecting the respiratory and reproduction systems. Rare cases of encephalitis and enteritis are also seen. Mild signs include nasal discharge, conjunctivitis, reduced feed intake, early embryo loss, vulvovaginitis in cows and balanoposthitis in males. More severe symptoms tend to be seen in naive animals and will also include high temperatures (over 40 degrees), loss of appetite, abortions, severe ocular and nasal discharges, ulceration in the oral cavity, larynx and trachea or severe secondary pneumonia, possibly leading to death. IBR has an affinity for corpus luteal tissue on the ovaries therefore will often have effects on the fertility of the herd.
IBR is endemic in the UK and it is thought that around 40% of cattle have come into contact with the virus. Finical losses due to IBR can build up due to permanent lung scarring leading to reduced growth rates and milk yield alongside fertility problems and costs if calving patterns slip.
IBR is diagnosed using clinical signs alongside rising titre serology tests. PCR and fluorescent antibody tests can also be carried out on secretions, further testing can also be carried during post mortem examinations. There are many other diseases with similar symptoms including bluetongue, FMD, bovine corona virus, bovine respiratory complex (PI3, BVD, RSV), bacterial pneumonia, mucosal disease, malignant catarrhal fever and lungworm among other diseases.
IBR is often found alongside other respiratory viruses including PI3, RSV and BVD. Together these viruses cause damage to the respiratory defence mechanisms of cattle allowing bacteria to enter the lungs, then leading to pneumonia and resulting in production losses. The animal has to fight the virus off themselves as antibiotics have no effect on these viruses and will not kill IBR.
There is no specific treatment for IBR. Treatment is based on supportive therapy as these animals are often not eating due to severe ulceration of their larynx. These would include anti-inflammatories, pain relief and fluid therapy. Antibiotics may be needed if bacterial pneumonia is present. Isolation and vaccination of other stock can be carried out to help reduce spread. Managing stress is important to minimise and manage outbreaks.
Control of IBR is vital to minimise financial impacts of either pneumonia outbreaks or poor fertility.
Vaccination plays a vital role in management and prevention of IBR. There are many different vaccines available, many of which contain other viruses/pathogens to reduce severity of problems. Many of these are ‘marker’ vaccines. This means it is possible to identify wild virus in a vaccinated herd. Different vaccines can be given to different aged cattle by different routes. Work with your vet to identify the best vaccine for your farm which is practical, covers the risk periods and is cost effective for your system.
Identify the IBR status of your farm – is the disease present possibly causing underlying losses or is your farm IBR free?
Speaking to your vet to draw up a viral control plan for your farm will help reduce the impact of IBR or reduce the potential of IBR introduction where the effects are often more severe.
Buying in latently infected cattle or nose to nose contact over fences are common routes of IBR spread. High levels of biosecurity and targeted testing/monitoring are vital if farms are to maintain free status.
There are many CHeCS accreditation schemes which farms can achieve to increase value of sale stock. Freedom from IBR is often required when sending animals to stud or during international trade.
For more information on Molecare Veterinary Services, please phone 01392 872934.