Rarer neurologic diseases of food animals (Proceedings)


Rarer neurologic diseases of food animals (Proceedings)

Nov 01, 2010

Bovine Spongiform Encephalopathy (BSE)

BSE is defined as a slow developing neurodegenerative disease of cattle that begins insidiously with subtle signs progressing to terminal recumbency. This is a cerebral disease thus signs are consistent with abnormal mentation. Slight changes in behavior include increased apprehension and tactile and auditory hyperesthesia. The cattle aren't really "mad" but increased aggression may occur. One of the major differences between this disease and other bovine neurological diseases is that BSE typically progresses much slower, over a period of 6 months (can be shorter or longer) whereas most other neurologic diseases of cattle have acute onsets and clinical signs progress rapidly. Government authorities should be notified if cases are suspected. Diagnosis is confirmed by histological examination of brain tissue showing vacuolation and spongiform degeneration of neurons; currently a definitive diagnosis cannot be performed antemortem because there is no apparent immune response. There is no treatment for this disease. The majority of reported cases are between 2 and 6 years old with greater than 50% of cases being 4-5 years old. Less than 0.02% of cases are younger than 3 years old. The disease agent (a prion) has not been found in milk. There is no conclusive evidence of direct transmission. Three cases of BSE have been detected in the US. The first was a Canadian dairy cow that had been moved to Washington State. The second and third cases were atypical BSE and were found in Texas and Alabama. The ban of feeding ruminant meat and bone meal in the UK resulted in a dramatic drop in the incidence.

Pituitary Abscess

This is a relatively rare neurologic disease often caused by Arcanobacterium pyogenes in ruminants. Clinical signs are acute and progress rapidly over a 7-10 day period. General signs include ataxia, head and neck extension, inappetence, depression, and bradycardia (< 60 bpm). Neurologic signs include a base-wide stance, ataxia, head-pressing, asymmetric cranial nerve deficits with dysphagia, blindness, anisocoria, lack of papillary light reflexes, mydriasis, lack of tongue tone, nystagmus, facial paralysis, ventrolateral strabismus, and head tilt. Like many neurological diseases there is eventually recumbency, coma, and death. Diagnosis is challenging and a definitive diagnosis probably requires advanced radiographic imaging. A CSF analysis may reveal a neutrophilic pleocytosis with an elevated protein, both mild to greatly elevated. The most suggestive signs include bradycardia, blindness and a pyogenic CSF process. Treatment is not usually attempted because of poor prognosis but would include long term antibiotics and supportive care. The epidemiology is interesting. The infectious agent reaches the pituitary via hematogenous spread and may infect the rete mirabile (a complex of vessels surrounding the pituitary). A pyogenic infection of the head (e.g. face abscess) may predispose to pituitary abscesses. The disease is most commonly seen in yearlings and older stock and has been associated with nose rings. The prognosis is poor.