Infectious bovine rhinotracheitis is of major importance to cattle populations throughout the world.
IBR infections are responsible for a number of different disease syndromes including respiratory disease, eye infections and abortion.
The virus that causes IBR is found only in cattle but it is from the herpes virus family, which is the same virus family as the viruses that cause chicken pox and shingles in people. These diseases all share the ability to have latent infections. The virus can remain in the tissues of the body without causing clinical signs and be reactivated after stress.
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Cattle can become latent carriers of the virus and although they appear normal, if they are introduced into a population of animals that are unvaccinated, they may spread this highly contagious disease throughout the herd.
IBR virus infections can cause inflammation and damage to the upper respiratory tract of cattle and impair normal defence mechanisms of the upper respiratory tract and trachea.
As a result, these viral infections often become complicated by severe bacterial pneumonias.
The use of antibiotics might help treat the secondary bacterial infection, but has no impact on the original IBR infection because it is viral.
IBR outbreaks in feedlot cattle are difficult to treat and can cause severe mortality in affected pens.
Another clinical syndrome caused by IBR virus is also devastating and difficult to treat. IBR virus in pregnant cows can cause a late-term abortion, usually after seven months gestation.
The virus infects the cow’s respiratory tract initially and then circulates in the blood stream, passing through the placenta into the fetus. The fetal infection eventually kills and expels the fetus, which may occur weeks or up to three months after the cow was originally infected. Abortion rates of five to 60 percent have been reported in IBR outbreaks.
It is especially disheartening because it is an abortion outbreak that was easily preventable.
IBR still remains one of the most commonly diagnosed causes of abortion in cattle in North America.
Fortunately, we can prevent IBR through the use of biosecurity (avoiding introductions to the herd) and through vaccination programs.
Vaccines provide immunity to the dam and protect the fetus. A recent paper in the latest edition of the journal Preventive Veterinary Medicine summarized all of the past scientific studies on IBR virus to evaluate how well the vaccines worked to prevent abortion.
This particular type of meta-analysis study is commonly used in human and veterinary medicine to determine how well a particular treatment or vaccine works by summarizing all the clinical trials that have been carried out and combining the results.
The researchers from the University of Auburn used a large database of 1,724 articles about IBR virus in cattle, but after removing studies that did not address the vaccine question or studies that were poorly designed, they were left with 15 studies on IBR vaccines that evaluated the effect of the vaccine on preventing abortion.
These 15 studies used a combined total of more than 7,500 animals. It would be difficult to find funding to do one clinical trial of this size, so the 15 smaller studies are combined in this meta-analysis to come up with a more definitive answer.
The authors of the study concluded that there was a significant decrease in abortion risk in vaccinated cattle with 60 percent fewer abortions in vaccinated cattle than in unvaccinated cattle.
Some of these studies were challenge studies, in which cattle were infected by researchers with the IBR virus and some of the trials were field trials, where the researchers would rely on natural exposure to IBR virus. In both cases, the vaccines showed a significant reduction in abortion risk. Both modified live vaccines and killed vaccines were shown to decrease the abortion risk.
IBR vaccines are an important component of our herd health programs in cow-calf herds, dairy cows and feedlot cattle. IBR virus is an extremely common virus in cattle populations and if a latent carrier is introduced into an unprotected herd, it can have devastating consequences.
Although the study results do not show that the vaccines provide 100 percent protection to the fetus, our anecdotal evidence suggests that we rarely see outbreaks of IBR infections in well-vaccinated herds.
It should be noted that modified live IBR vaccines can cause abortion when administered to pregnant cows and are often given pre-breeding.
However, several modified live vaccines can be given to pregnant cows if the cow had been previously vaccinated with the same vaccine in the previous year.
Producers should consult a veterinarian to establish what vaccination program would work best in their circumstances and make sure that label instructions are followed, especially when considering using modified live IBR vaccines in pregnant cows.
