VIRAL INFECTION IN BATS 



the so-called "hibernatii^gland", abilobed, organ- like accumulation 

 of brown adipose tissue found in the interscapular region of hiber- 

 nating animals (and in certain non-hibernators as well), plays a role 

 in sustaining the hibernating animal during its period of winter dor- 

 mancy, Histochemical analysis of the interscapular brown fat of the 

 little brown bat ( Myotis 1. lucifugus) indicates that this tissue builds 

 up quantities of lipid during pre-hibernation months and that the 

 various biochemical constituents of this tissue are depleted as hiber- 

 nation progresses (Remillard, 1958), Studies comparingthe nature of 

 brown and white fat of several animal species indicate that brown 

 adipose tissue is histologically distinct and physiologically more 

 active than white fat (Fawcett, 1952), Recognition of the role of brown 

 fat in sustaining the hibernating bat during periods of inactivity, to- 

 gether with reports dealing with the multiplication of Coxsackie virus 

 (Pappenheimer et al,, 1950; Grodums and Dempster, 19 59) and polio- 

 virus (Shwartzman, 1952) in the brown fat of mice and hamsters, 

 suggested that this tissue of bats might provide a site for rabies 

 virus sequestration in the asymptomatic host; a latent focus of in- 

 fection from which virus sustained during the period of hibernation 

 by the same mechanism which nutures the whole animal could be 

 activated to invade and multiply in other tissues, including salivary 

 gland, and thereby be perpetuated in nature by this host. Accordingly, 

 experiments were undertaken to determine whether rabies virus in- 

 troduced peripherally would, in fact, invade and multiply in the brown 

 adipose tissue of insectivorous bats. Data compiled from such a 

 study (Sulkin et al,,1959) are summarized inTable I, Two species of 

 bats, the Mexican free- tailed bat (Tadaridab. mexicana ) , which is a 

 quasi- hibernator, and the little brown bat ( Myotis 1. lucifugus ) , a true 

 hibernator, were used in these experiments.A strain of canine rabies 

 virus isolated from the brain of a fatal human case was used. Each 

 bat received an intramuscular injection into the heavy muscle over 

 the chest of approximately 8000 mouse i.e. LD^q contained in 0.1 ml. 



Although the Mexican free-tailed bat proved to be relatively un- 

 susceptible to experimental rabies infection, virus was demonstrated 

 in the brown fat of 22 per cent of those animals shown to be in- 

 fected by viral assay in white Swiss mice. The infection in this 

 species was most evident 20 to 40 days after intramuscular inocu- 

 lation of virus. On the other hand, rabies virus was found to be 

 widely distributed on thelittlebrownbat9 to 26 days following inoc- 



371 



