Studies on the Pathogenesis of Rabies in Insectivorous Bats

Abstract

Studies on the pathogenesis of rabies in two species of experimentally infected insectivorous Chiroptera, the Mexican free-tailed bat (Tadarida mexicana), a quasi hibernator, and the little brown bat (Myotis lucifugus), a deep hibernator, provided evidence that brown adipose tissue may serve as an extraneural site for storage and multiplication of rabies virus. Although the Mexican free-tailed bat proved to be relatively insusceptible to experimental rabies infection, virus was demonstrated in the brown fat of 22 per cent of those animals shown to be infected by viral assay in white Swiss mice. Rabies infection in this species was most evident 20 to 40 days after intramuscular inoculation of virus. Rabies virus was found to be widely distributed in the little brown myotis 9 to 26 days following inoculation and virus concentrations in some of the tissues approached the level of the stock mouse brain virus suspension used in inoculating these bats. The shorter incubation period and higher virus titers in the tissues assayed reflect the increased susceptibility of Myotis lucifugus as compared with the Mexican free-tailed bat. Virus was demonstrated in the brown fat of 30 per cent of the experimentally infected Myotis. In the experimentally infected Myotis lucifugus and in the Syrian hamster which is highly susceptible to rabies infection, rabies virus was isolated more frequently from the brown fat than from the salivary gland indicating that in a susceptible host brown adipose tissue may be as frequent a site of viral proliferation as salivary gland. Since rabies virus was found to persist for long periods of time in the brown fat of experimentally infected bats and was occasionally demonstrated in this tissue alone, it is suggested that brown adipose tissue provides a mechanism by which these animals may serve as reservoirs for this agent in nature. The possibility that similar mechanisms may be involved in the maintenance of other viral agents during interepidemic periods is discussed.

Susceptibility of North American big brown bats (Eptesicus fuscus) to infection with European bat lyssavirus type 1

“…As reported previously by Sulkin et al (1959) and Bell & Moore (1960) for RABV, we also detected EBLV-1aSK (EBLV-1aGE was not tested) in the brown fat of bats that succumbed to infection, but the quantity of viral RNA was lower than in the brain, as compared by a semi-quantitative gel-electrophoresis-based analysis. On the basis of our observations, we doubt that brown fat has any significant role in lyssavirus pathogenesis other than being a destination for virus spread through innervation.…”

Bats in Relation to Arthropod-Borne Viruses: An Experimental Approach with Speculations

“…Of particular interest was the demonstration that rabies virus invades and multiplies in the interscapular brown adipose tissue of the experimentally infected bat. 22 The high metabolic activity of brown adipose tissue in the active animal, together with the evidence that this tissue sustains the hibernating animal during periods of winter sleep23 and subsequently functions as a thermogenic effector of arousal,24 supports the hypothesis that brown fat could serve as a site of virus sequestration in the latently infected bat. 22 The isolation of rabies virus from the brown adipose tissue of experimentally infected active22 and cold-exposed25 bats, and from active naturally infected bats,26 supports this postulate.…”

“…22 The high metabolic activity of brown adipose tissue in the active animal, together with the evidence that this tissue sustains the hibernating animal during periods of winter sleep23 and subsequently functions as a thermogenic effector of arousal,24 supports the hypothesis that brown fat could serve as a site of virus sequestration in the latently infected bat. 22 The isolation of rabies virus from the brown adipose tissue of experimentally infected active22 and cold-exposed25 bats, and from active naturally infected bats,26 supports this postulate. More recent experiments with the bat have included studies of the susceptibility of these animals to various strains of arthropod-borne viruses to determine if the bat could serve as a reservoir host for these agents in a manner similar to that suggested for rabies virus.27 The phenomenon of hibernation common to certain bat species and the seasonal migrations of other species would allow for overwintering or reintroduction of a virus into a particular area and suggest that these animals might be particularly effective reservoir hosts of the arboviruses.…”

Rabia Transmitida Por Murciélagos en Brasil

“…Sin embargo, años más tarde Moreno y Baer (1980) realizaron nuevamente estos experimentos y no observaron recuperación espontánea ni excreción viral en la saliva de portadores sanos. El estado de portador asintomático, pudo haber sido confundido con la forma paralitica de la rabia, pero la ausencia de signos en murciélagos experimentalmente o naturalmente infectados continuó siendo documentada en murciélagos no hematófagos (Sulkin et al, 1959) y en D. rotundus (Setien et al, 1998;Rodrigues y Tamayo, 2000;Aguilar-Setien et al, 2005).…”