Hypophysiary involvement and immuno/growth depression in rabies. II.

The participation of growth hormone dysfunction through the hypothalamic-hypophyseal-thymic axis in the bovine species

Abstract

A monoclonal antibody characterized bovine paralytic rabies (BPR) virus isolate, ATC vr-985, was inoculated intrathecally (i.t.) or intralingually (i.l.) into 13 Holstein calves (5 controls) weighing 66±15 kg. Infected calves with the highest dose stopped growing earlier, later with the lowest dose: collapse (loss in body weight) was at a steady negative daily rate. Growth rates, collapse rates and chronology were predictable and reproducible, and the kinetics verified in a rabbit model. The BPR virus was found in large numbers in lower and upper spinal cord, cerebellum and hypothalamus. The best diagnostic specimen was the trigeminus nerve, followed by the cerebellum. Immunoperoxidase-PAP staining made Negri bodies very apparent particularly in the hypothalamus. The marked presence of BPR virus in the cerebellum coincided with obvious motor and equilibrium changes. A chronogram of clinical manifestations in 3 calves injected i.t. is presented. Effects on growth, and the linear regression analysis of the different titrations applied to the wasting syndrome phenomenon, are among the aspects tabulated or shown graphically. There are several microphotographs. It is concluded that experimental BPR was clinically indistinguishable from the field disease. It is postulated that BPR acts upon the hypothalamic/hypophysiary/thymic axis by its tendency to infect the hypothalamus and the (adeno-) hypophysis, impairing the production of somatotropic (growth) hormone.