Post-Mortem of a Heifer on Feed: Answer
The team diagnosed this case as a representative example of Infectious Bovine Rhinotracheitis (IBR), often a contributing factor to Bovine respiratory disease (BRD).
Pathogenesis:
IBR is a viral respiratory disease caused by the highly contagious bovine herpesvirus type 1 (BoHV-1). Once established in upper respiratory epithelial cells, BoHV-1 begins a quick lytic replication cycle causing tracheal, pharyngeal and nasal epithelial cell death. BoHV-1 is characterized by establishing latent, life-long infections.
IBR is not typically fatal by itself; however, it is an important factor in the commonly fatal BRD complex. Often, secondary bacterial pneumonia is initiated by BoHV-1 suppressing the immune system.
Epidemiology:
- Regardless of prevalence, IBR often occurs sporadically, most commonly during winter months; recrudescence of latent infections may occur in conjunction with stressful events.
- Cases are often clustered by pen due to direct transmission occurring through nasal secretions.
- Latent carriers are a reservoir for continued transmission and virus maintenance.
Ante-mortem Clinical Symptoms:
- IBR often causes high fever
- and associated anorexia and depressed demeanor.
- Rhinitis causing the nasal pad and mucosa to become inflamed with consolidated hemorrhagic or white plaques, gives IBR the commonly used epithet “red nose”.
- Serous to mucopurulent nasal discharge commonly occurs.
- Stridor can occur subsequent to trachea mucosal inflammation and necrotic debris accumulation, as well as a short and explosive cough.
- Cases may have keratoconjunctivitis, commonly referred to as “Winter Pink Eye”, which is characterized by serous epiphora progressing to mucopurulent, along with corneal edema. Unlike Moraxella bovis, IBR does not cause corneal ulcers.
Management:
- Management of IBR primarily relies on prevention via vaccination (a primary dose followed by a booster dose, or doses, during the feeding period) to reduce clinical disease and shedding. It is particularly beneficial to utilize vaccines prior to a stressful event such as feedlot arrival whenever possible. Similarly, minimizing stressful stimuli could reduce outbreaks.
- While there are no direct treatments for clinical IBR cases, antimicrobials can be effectively used to prevent and/or treat secondary/concurrent bacterial infections.
Post-Mortem Findings:
- The classic IBR lesion, tracheitis, is characterized by severe inflammation, ulceration, necrosis and adherent fibrinonecrotic exudates (diphtheritic membrane) that can extend into lower airways with concurrent sloughing of epithelium (Figure 1). Note that, different from exudates associated with other types of pneumonia, the exudates associated with IBR are adhered to the mucosal surfaces and require scraping away with a knife to reveal the ulcerated submucosa.
- Corneal opacities at the periphery of the cornea, corneal edema and conjunctivitis can be present.
- Animals that die with IBR lesions often have secondary/concurrent bronchopneumonia (Figure 2).
Post-Mortem Series presented in partnership with Feedlot Health management Services, Okotoks, Alberta. For more information, visit their website at www.feedlothealth.com.
Working with crews at client operations, Feedlot Health conducts post-mortem exams on all feedlot and calf-grower mortalities, using a standard protocol for recording the animal’s history, digital images, and post-mortem findings. The group compiles images and post-mortem findings in a central database, for review by the professional team, as an educational tool and to track disease trends within an operation or across their client base.
