Neurovirulence of H5N1 Infection in Ferrets Is Mediated by Multifocal Replication in Distinct Permissive Neuronal Cell Regions

Abstract

Highly pathogenic avian influenza A (HPAI), subtype H5N1, remains an emergent threat to the human population. While respiratory disease is a hallmark of influenza infection, H5N1 has a high incidence of neurological sequelae in many animal species and sporadically in humans. We elucidate the temporal/spatial infection of H5N1 in the brain of ferrets following a low dose, intranasal infection of two HPAI strains of varying neurovirulence and lethality. A/Vietnam/1203/2004 (VN1203) induced mortality in 100% of infected ferrets while A/Hong Kong/483/1997 (HK483) induced lethality in only 20% of ferrets, with death occurring significantly later following infection. Neurological signs were prominent in VN1203 infection, but not HK483, with seizures observed three days post challenge and torticollis or paresis at later time points. VN1203 and HK483 replication kinetics were similar in primary differentiated ferret nasal turbinate cells, and similar viral titers were measured in the nasal turbinates of infected ferrets. Pulmonary viral titers were not different between strains and pathological findings in the lungs were similar in severity. VN1203 replicated to high titers in the olfactory bulb, cerebral cortex, and brain stem; whereas HK483 was not recovered in these tissues. VN1203 was identified adjacent to and within the olfactory nerve tract, and multifocal infection was observed throughout the frontal cortex and cerebrum. VN1203 was also detected throughout the cerebellum, specifically in Purkinje cells and regions that coordinate voluntary movements. These findings suggest the increased lethality of VN1203 in ferrets is due to increased replication in brain regions important in higher order function and explains the neurological signs observed during H5N1 neurovirulence.

Predicting Disease Severity and Viral Spread of H5N1 Influenza Virus in Ferrets in the Context of Natural Exposure Routes

“…This is not a common feature of ferret influenza infection, as seasonal H3N2 influenza virus does not typically spread to the ferret cerebrum and cerebellum (51), although such spread has been observed with pdmH1N109 virus (51,52). The ability of H5N1 virus to cause diffuse CNS infection (30,38,49) has been attributed in part to spread via different cranial nerves into the CNS (34).…”

“…However, some differences between the two species in response to H5N1 have been noted. Infected humans frequently show progression to ARDS, but neurological disease is rarely manifested (2,13,14,19,21,26,32,33), while detection of virus in the brain and neurological disease are common in ferrets experimentally infected by the total respiratory tract (TRT) route (34,35). H5N1 virus spread outside the respiratory tract in ferrets has enabled this model to be employed as a means to study the anatomical pathways of viral dissemination.…”

Pathogens Penetrating the Central Nervous System: Infection Pathways and the Cellular and Molecular Mechanisms of Invasion

“…The neurovirulence of influenza A virus subtypes may be influenced by the ability of the virus to disseminate from the olfactory bulb into other regions of the brain (367), which in turn may be controlled by the host immune response. In vivo, mouse olfactory sensory neurons infected with influenza A R404BP virus displayed apoptotic neurodegradation and were subsequently phagocytosed by Iba1-expressing microglia/macrophages (368).…”

Viruses in human central nervous system — invasion, transmission, and latency: a literature review

“…Нейровирулентность подтипов вируса гриппа A также обусловлена способностью распространяться из обонятельной луковицы в другие отделы голо-вного мозга [7]. Через обонятельный тракт в ЦНС могут проникать также вирус везикулярного стома-тита (VSV), вирус болезни Борна (BDV), рабдовирус (RABV), вирус парагриппа, прионы [8,9].…”