Respiratory disorders

Chapter 5 Respiratory disorders




Introduction


Although respiratory diseases have a variety of causes, infectious agents predominate, e.g., infectious bovine rhinotracheitis (IBR) is caused by a herpesvirus that can affect several body systems.


A second group of important respiratory infections is caused by Pasteurella spp., usually following exposure of young cattle to stress (hence the alternative name for pasteurellosis, “shipping fever”). Both Mannheimia haemolytica serovar 1 and P. multocida are normal inhabitants of the upper respiratory tract and in particular the tonsillar crypts. In order to permit colonization of the lungs, stress or a primary viral infection such as bovine virus diarrhea/mucosal disease (BVD/MD), respiratory syncytial virus (RSV), or parainfluenza type 3 (PI-3), must compromise the defense mechanisms of the body.


A third respiratory infection, termed endemic or enzootic calf pneumonia, affects groups of young calves and is of major economic importance. Both viruses (e.g., PI-3, BVD, IBR, RSV, adeno- and rhinoviruses) and mycoplasmas may be primary agents, but the etiology of many outbreaks remains uncertain, since bacterial colonization by Pasteurella spp. tends rapidly to supervene. Consequently, the primary virus infection may have been cleared by the time of autopsy. The role of Chlamydia is unclear.


Histophilus somni is of major importance as a cause of suppurative pneumonia (9.29), but, having effects on several organ systems, it is presented as infectious thromboembolic meningoencephalitis in Chapter 9.


Respiratory diseases in young cattle are of great economic importance, since their immunity to many etiological agents is poor and vaccination regimes therefore have severe limitations. Antibiotic therapy can be very costly, and recovering cattle often show poor weight gain. Contagious bovine pleuropneumonia (CBPP) is a problem in many developing countries, such as parts of Africa, India, and China, where eradication through a slaughter policy and vaccination programs presents major organizational problems.


Chapter 5 is divided into infectious (viral, bacterial, and other agents) and noninfectious (allergic, iatrogenic, circulatory, and physiological) etiology. Where appropriate, cross-reference is made to other sections for lesions affecting other systems, e.g., both calf diphtheria and laryngeal abscessation (2.42–2.46) are shown in the neonatal chapter, even though they sometimes occur in older animals.



Infectious disorders



Infectious bovine rhinotracheitis (IBR) (“rednose”)




Clinical features


the common respiratory form of IBR has major clinical signs involving the nostrils (hence the alternative name of “rednose”) and the eyes. Feedlot cattle are at particular risk. Within a group of young cattle, several individuals may be affected simultaneously with epiphora and depression. Severely affected animals, such as the crossbred neonate in 5.1, are dull, somnolent, anorexic with a tucked-up belly, and have a mucopurulent nasal discharge, nasal mucosal congestion and lymphadenopathy, and sometimes a harsh cough. The palpebral conjunctivae may be intensely injected or congested in the acute stage (5.2). Characteristic, small, raised, red plaques are visible near the lateral canthus. Secondary infection may lead to a purulent oculonasal discharge (5.3) as well as a typical purulent IBR conjunctivitis, without blepharospasm.





Autopsy examination of this animal (5.4) reveals a severe necrotizing and hemorrhagic laryngotracheitis. Another severe case is shown in 5.5. In severe cases the nasal septum (5.6) sloughs its necrotic mucosa. Epistaxis may follow the rupture of mucosal vessels.





Balanoposthitis can occur with bovine herpesvirus 1 infection (p. 182). In 5.7, the separated vulval lips reveal the multiple, discrete pustules of infectious pustular vulvovaginitis (IPVV). The similarity of the male and female lesions is obvious (compare 10.29).






Pasteurellosis (“shipping fever”, “transit fever”)





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Jul 8, 2016 | Posted by in SUGERY, ORTHOPEDICS & ANESTHESIA | Comments Off on Respiratory disorders
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