246 DISEASES OF THE BRAIN 



in which the disease breaks out at different periods, some- 

 times annually, sometimes with several years between out- 

 breaks. It is most apt to occur following wet seasons. The 

 disease is usually confined to certain farms, but during some 

 years becomes a more widely distributed enzootic. 



Etiology. — ^The cause of the disease has not yet been 

 determined. The Borna coccus (Diplococcus intracellularis 

 equi) has not been proved to be the cause. 



Natural Infection. — Horses are probably infected through 

 contaminated food and water. Some authorities believe 

 that the infection is acquired through the respiratory organs. 

 However, Borna disease is more common in the winter and 

 early spring months than in summer, the dusty period of the 

 year. It is possible that the virus is voided with the urine. 

 The disease is not communicable. It is much more common 

 among farm than city horses. 



Necropsy. — ^Macroscopically the brain appears normal, but 

 under the microscope a marked cellular infiltration is noted 

 in the meninges, brain and spinal cord. Especially typical 

 changes have been noted in the ganglionic cells in the olfac- 

 tory lobes and horns of Ammon which contain peculiar, 

 intensively stained bodies within the cell nucleus ("nuclear 

 inclusions"). 



Symptoms. — ^The symptoms are varied, but in general are: 

 Early fatigue, icterus of the mucous membranes and diges- 

 tive disturbances, sometimes amounting to colic attacks. 

 These are followed by symptoms of cerebral excitement; 

 twitching of the muscles of the face; spasms of the muscles 

 of the neck, sometimes producing torticollis; occasionally 

 trismus, nystagmus, unequal dilatation of the pupils, skin 

 hyperesthesia, exaggerated reflexes, occasionally increased 

 sexual desire and psychic phenomena. In some instances 

 the patients are vicious, aggressive; in others they show 

 epileptiform spasms. Later the patients appear depressed, 

 stupid, even soporous, and may show forced movements. 

 Motor paralysis is recognized by a weak, staggering gait, 

 paralysis of the pharynx and general paralysis. The pulse, 

 respirations and temperatures are usually little affected. 

 In a few cases an eczema of the skin appears. 



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