BOVINE RESPIRATORY DISEASE

Bovine Respiratory Disease Complex: IBR

Bovine Herpes Virus / Infectious Bovine Rinotracheitis

Etiology/History
BHV-1 was first discovered in the early 1950’s in feeder cattle in the Western United States.  BHV-1 or as it’s commonly called IBR (Infectious Bovine Rhinotracheitis) has three main subtypes; BHV-1.1 (IBR), BHV1.2 and BHV-1.3 (which was just re-classified as BHV-5).  BHV-1.1 has many different symptoms, in feedlot cattle respiratory problems tend to predominate, while in breeding animals genital lesions and abortions tend to be most frequent.  Affected animals can also show signs of eye infections or conjunctivitis, brain infections, generalized disease in newborn calves, and a susceptibility to secondary bacterial infections.      
     
Distribution/Prevalence and Transmission
The disease is found across most of North American and in a multitude of places around the world.  It is difficult to understand the extend at which BHV is found because of its unique ability to undergo a latency phase inside the host and only replicate at times when the animal is stressed.  As well some animals may never show clinical signs; therefore, a herd may only have sporadic problems resulting in a lack of herd screening.  The disease is transmitted from one infected individual to another.  In feedlot cattle the disease is primarily transmitted through the virus being aerosolized or through direct exchange of nasal discharge.  In breeding cattle the disease can be transmitted while mating or in a similar fashion as feedlot cattle.  It has been shown that even in the absence of visible lesions, in breeding cattle, the infection can still be passed on.  In addition, the use of AI (artificial insemination) can still allow transmission to proceed if semen from a subclinically infected bull was used.  Embryo transplant has shown success in preventing the spread of virus from an infected donor cow to the surrogate mother if the embryo is properly washed with trypsin.       

Clinical Findings & Lesions
The incubation period for the disease ranges from just a couple days to about a week.  After the initial incubation period a variety of symptoms and results can manifest.  The virus may become latent in the individual causing little to no symptoms, until the animal is stressed or the animal becomes susceptible for some other reason.  When the disease presents it can come in the form of a high fever, coughing, respiratory distress, nasal discharge, conjunctivitis, or abortion (tending to occur in the last trimester). All these symptoms are most likely to present after about a three month post infection.  BHV-1 also has been shown to associate with shipping fever, a disease caused by M. hemolytica.  It is thought that BHV-1 causes the animal to be susceptible to secondary bacterial infection, one of which is M. hemolytica.  Together they cause the common respiratory signs associated shipping fever.  The genital form of the disease can result in signs that range from excess urination to vaginal swelling, as well as discharge, a raised tailhead, or erosive ulcers in the mucosal surface.

As one would think most of the lesions as a result of BHV-1 are in the upper respiratory tract and trachea.  Hemorrhages may be found in the membranes of the nasal cavity, larynx and/or trachea.  The sinuses can be filled with a serous light mucous that may or may not have a bloody tinge.  The tracheitis may extend into the pulmonary system (bronchi and bronchioles).  This results in the epithelium being sloughed off making it easier for any secondary bacterial infection.  It’s also common for white foci to be found on the liver, kidneys, spleen and lymph nodes. In the result of an abortion fetuses may display lesions in a variable number of tissues especially noticeable in the liver.

Diagnosis
Diagnosis is best made by viral isolation. Testing antibody serum levels can also be done if the animal has been infected for a lengthy period of time, as the virus needs time to evoke a large enough antibody titer against the disease.  It is also possible to test following abortions as the infection has had sufficient time to raise a high enough titer level by this point.  BHV-1 abortions can be diagnoses in the fetus by virus isolation, PCR or immunoflorescent antibody staining of fetal tissues.  Diagnosis is strengthened based on herd history, vaccination protocol and symptoms.        

Treatment and Prevention (Vaccination)

As with most viral infections there are no treatments, antibiotics are only administered to prevent secondary bacterial infections but do nothing to alter the viral infection.  The disease is best controlled through the use of vaccinations.  A modified live vaccine either intramuscular or intra nasal is used.  The IM vaccine is most often used in feedlot cattle or non-pregnant breeding cattle, while the intranasal vaccine is used to provide intense shot-lived immunity in pregnant cows.  Pregnant cattle should never be given a IM modified live vaccine as its been known to produce similar effects as the actual virus.  It is recommended that breeding heifers should be done at 6-8 months of age with a secondary booster later.  Feedlot animals should be vaccinated at least two weeks before entry into a feedlot.  New innovations are working at developing vaccines that will allow for separate identification of antibodies from natural versus vaccinated exposure.

 

Produced by Chase Wendorff, Tim Ritson-Bennett, Adam Schierman, Troy Gowan, Justin Rosing for WCVM class project