Aerosol infection of Balb/c mice with eastern equine encephalitis virus; susceptibility and lethality

Abstract

BackgroundEastern equine encephalitis virus is an alphavirus that naturally cycles between mosquitoes and birds or rodents in Eastern States of the US. Equine infection occurs by being bitten by cross-feeding mosquitoes, with a case fatality rate of up to 75% in humans during epizootic outbreaks. There are no licensed medical countermeasures, and with an anticipated increase in mortality when exposed by the aerosol route based on anecdotal human data and experimental animal data, it is important to understand the pathogenesis of this disease in pursuit of treatment options. This report details the clinical and pathological findings of mice infected with EEEV by the aerosol route, and use as a model for EEEV infection in humans.MethodsMice were exposed by the aerosol route to a dose range of EEEV to establish the median lethal dose. A pathogenesis study followed whereby mice were exposed to a defined dose of virus and sacrificed at time-points thereafter for histopathological analysis and virology.ResultsClinical signs of disease appeared within 2 days post challenge, culminating in severe clinical signs within 24 h, neuro-invasion and dose dependent lethality. EEEV was first detected in the lung 1 day post challenge, and by day 3 peak viral titres were observed in the brain, spleen and blood, corresponding with severe meningoencephalitis, indicative of encephalitic disease. Lethality follows severe neurological signs, and may be linked to a threshold level of virus replication in the brain. Effective medical countermeasures for EEEV may necessitate early inoculation to inhibit infection of the brain in zoonotic incidents, and be able to traverse the blood-brain barrier to sufficiently interrupt replication in the brain in cases of aerosol infection.ConclusionsThere is little human data on the hazard posed by aerosol infection with encephalitic alphaviruses, and use of EEEV as a bioweapon may be by the aerosol route. A well characterized model of aerosol exposure that recapitulates some of the most severe human clinical features is necessary to evaluate the efficacy of putative medical countermeasures, and to increase our understanding about how this route of infection induces such rapid neuro-invasion and resulting disease.

Eastern Equine Encephalitis Virus Rapidly Infects and Disseminates in the Brain and Spinal Cord of Infected Cynomolgus Macaques Following Aerosol Challenge

“…Murine studies displayed similar pattern to guinea pigs and marmosets, however, EEEV was detected lung and heart [12,13]. Our NHP data are in agreement with the guinea pig and marmoset studies.…”

“…The dissemination of EEEV following aerosol infection has not been investigated in previous macaque studies; however, it has been examined in mice, guinea pigs, and marmosets [11][12][13][14]. In these previous studies, virus was localized almost exclusively in the brain and was readily detected in the frontal cortex, corpus striatum, thalamus, hippocampus, mesencephalon, pons, medulla oblongata, and cerebellum [11][12][13][14]. In contrast, EEEV could not be detected in the heart, liver, lung, spleen, and kidney of guinea pigs and marmosets [11,14].…”

“…The pathology is comprised of severe pulmonary edema and congestion, multifocal hemorrhage, splenic atrophy, myocarditis, and necrosis [21,23,26,28,48,52,57]. The lack of similar pathology in visceral organs and tissues in animals infected via an aerosol route demonstrates that the route of infection substantially alters the virus dissemination [11][12][13][14]. Limited studies have examined EEEV pathogenesis in the brain utilizing TEM [16,29,36,67].…”

Eastern equine encephalitis virus rapidly infects and disseminates in the brain and spinal cord of cynomolgus macaques following aerosol challenge

“…Although limited pathology was investigated in previous macaque studies, the dissemination of EEEV following aerosol infection was not investigated; however, it has been examined in mice, guinea pigs, and marmosets [14][15][16][17]. In these previous studies, virus was localized almost exclusively in the brain and was readily detected in the frontal cortex, corpus striatum, thalamus, hippocampus, mesencephalon, pons, medulla oblongata, and cerebellum [14][15][16][17]. In contrast, EEEV could not be detected in the heart, liver, lung, spleen, and kidney of guinea pigs and marmosets [14,17].…”

Limbic Encephalitis Brain Damage Induced by Cocal Virus in Adult Mice Is Reduced by Environmental Enrichment: Neuropathological and Behavioral Studies

“…Microgliosis was observed from the fourth day of infection and occurred in areas in which viral antigens were also present. Intranasal infection of mice with Piry virus (a virus from the same group) induces morphological changes in microglia in the olfactory pathway and in the hippocampal region [ 41 ], and a 2nd infection with virus associated with ME7 prion disease, a chronic neurodegenerative disease, induces an additional significant increase in the number of these cells in association with increased activated microglial morphology [ 66 ], suggesting that viral infection during chronic neurodegeneration exacerbates the inflammatory microglial response.…”