RESUMO
Venezuelan equine encephalitis (VEE) viruses cause natural outbreaks in humans and horses and represent a significant biothreat agent. The effect of tunicamycin on the course of the disease in mice with VEE was investigated, and the combined effects of these agents was characterized. CD-1 mice given 2.5 microg of tunicamycin had >1,000-fold more virus in the brain 48 hours after infection with the virulent VEE strain V3000 and > or =100-fold of the attenuated strain V3034 at all tested times than did untreated mice, indicating enhanced neuroinvasion. Tunicamycin did not alter the viremia profiles of these viruses nor the replication of V3000 in the brain itself. Tunicamycin alone caused ultrastructural blood-brain barrier damage, yet neuroinvasion by V3000 in treated mice appeared to occur via the olfactory system rather than the blood-brain barrier. Tunicamycin-treated, V3000-infected mice also exhibited earlier and more severe weight loss, neurological signs, neuronal infection, neuronal necrosis and apoptosis, and inflammation than untreated, V3000-infected mice. The mean survival time of tunicamycin-treated, V3000-infected mice was 7.3 days versus 9.9 days for untreated, V3000-infected mice. These studies imply that animals that ingest toxins similar to tunicamycin, including the agent of annual ryegrass toxicity in livestock, are conceivably at greater risk from infections by encephalitis viruses and that humans and horses exposed to agents acting similar to tunicamycin may be more susceptible to encephalitis caused by VEE viruses. The exact mechanism of tunicamycin-enhanced neuroinvasion by VEE viruses requires further study.
Assuntos
Antivirais/farmacologia , Vírus da Encefalite Equina Venezuelana/efeitos dos fármacos , Encefalomielite Equina Venezuelana/patologia , Tunicamicina/farmacologia , Animais , Encéfalo/patologia , Encefalomielite Equina Venezuelana/mortalidade , Feminino , Masculino , Camundongos , Fatores de Tempo , Carga ViralRESUMO
To assess the potential for aerosol administration of vaccines for Venezuelan equine encephalitis virus (VEE), we compared the neurovirulence and tissue tropism of the wild-type Trinidad donkey (TrD) strain to those of the attenuated TC83 and V3526 strains of VEE in mice. Six to 8-week-old female C3H/HeN and BALB/c mice were aerosol exposed to one of the three VEE strains. Three mice of each strain were euthanatized at different times and their tissues were processed and stained using hematoxylin and eosin, immunohistochemistry, and in situ hybridization. All three viral strains infected the brains of mice and induced encephalitis. TrD spread caudally from the olfactory bulbs to all regions of the brain, caused widespread necrotizing panencephalitis by day 5, and resulted in 100% mortality (geometric mean = 7 days) in both mouse strains. By comparison, TC83 relatively spared the caudal regions of the brain but still caused 100% mortality in the C3H/HeN mice (geometric mean = 12 days), yet it did not kill any BALB/c mice. V3526 infectivity of the brain was the most limited, mainly affecting the neocortex and diencephalon. This virus was not lethal in either mouse strain. The TrD strain also infected the olfactory neuroepithelium, local lymphoid tissues, teeth, and vomeronasal organs, whereas the affinity of TC83 and V3526 outside the brain was essentially limited to the olfactory neuroepithelium. Attenuated VEE strains administered to mice by aerosol have restricted tissue tropism as compared with wild-type virus; however, even attenuated strains can infect the brain and induce encephalitis.