Imaging of viral neuroinvasion in the zebrafish reveals that Sindbis and chikungunya viruses favour different entry routes

Abstract

Alphaviruses, such as chikungunya virus (CHIKV) and Sindbis virus (SINV), are vector-borne pathogens that cause acute illnesses in humans and are sometimes associated with neuropathies, especially in infants and elderly patients. Little is known about their mechanism of entry into the central nervous system (CNS), even for SINV, which has been used extensively as a model for viral encephalopathies. We previously established a CHIKV infection model in the optically transparent zebrafish larva; here we describe a new SINV infection model in this host. We imaged in vivo the onset and progression of the infection caused by intravenous SINV inoculation. Similar to that described for CHIKV, infection in the periphery was detected early and was transient, whereas CNS infection started at later time points and was persistent or progressive. We then tested the possible mechanisms of neuroinvasion by CHIKV and SINV. Neither virus relied on macrophage-mediated transport to access the CNS. CHIKV, but not SINV, always infects endothelial cells of the brain vasculature. By contrast, axonal transport was much more efficient with SINV than CHIKV, both from the periphery to the CNS and between neural tissues. Thus, the preferred mechanisms of neuroinvasion by these two related viruses are distinct, providing a powerful imaging-friendly system to compare mechanisms and prevention methods of encephalopathies.

High costs of infection: Alphavirus infection reduces digestive function and bone and feather growth in nestling house sparrows (Passer domesticus)

“…Alphaviruses such as Eastern and Western Equine Encephalitis virus, Chikungunya virus, and Sindbis virus are known to cause neuroinvasive disease in humans [ 57 ], especially in children and the elderly [ 28 , 58 ]. The majority of studies performed on age-dependent alphavirus susceptibility have been experimental alphavirus infections of mice or clinical reports of alphavirus infections in humans [ 31 , 32 ].…”

“…Encephalitis is common in neuroinvasive alphavirus disease, but the mechanism of neuroinvasion has not been well studied in any animal model. Chikungunya virus may directly infect endothelial cells of cerebral blood vessels and gain access to the CNS through blood brain barrier disruption, whereas Sindbis virus appears to infect peripheral neurons and gain access to the CNS through axonal transport [ 57 ]. However, how these infection pathways change with age and allow for higher rates of neuroinvasion in the young and old is unknown.…”

Zebrafish as an alternative animal model in human and animal vaccination research

“…Other microorganisms of importance such as fungi which can cause pathologies in humans, such as Candida albicans [10], Cryptococcus neoformans [8,84] and Mucor circinelloides [90] have also been the subject of study with teleosts. In addition, viruses such as Herpes simplex [13,31]; human norovirus [88]; Vesicular stomatitis [33]; hepatite C [21,22]; Chikungunya [1,9,14,68]; Sindib [69] and Influenza A [30] are some of the human viruses already studied by the zebrafish model in both embryos and larvae.…”

Genetic control of alphavirus pathogenesis

“…Most neurotropic viruses enter the CNS via one of three methods: (1) hematogenous entry via infection of endothelial cells, (2) hematogenous entry through breakdown of the BBB; (3) access to the CNS by routes other than through the BBB, such as through peripheral nerves or the blood-cerebrospinal fluid (CSF) barrier, and (4) through virus-infected leukocytes that naturally cross the BBB (“Trojan horse” model) (Swanson and McGavern 2013 ). WEEV, VEEV, and the SINV model of New World alphavirus infection enter the CNS through hematogenous spread to circumventricular organs that lack a normal BBB or via axonal transport via olfactory sensory or peripheral neurons (Charles et al 1995 ; Phillips et al 2016 ; Passoni et al 2017 ; Thach et al 2001 ). In contrast, EEEV and neuroinvasive CHIKV have been shown to enter the brain primarily through a vascular route (Honnold et al 2015 ; Passoni et al 2017 ; Vogel et al 2005 ).…”

“…WEEV, VEEV, and the SINV model of New World alphavirus infection enter the CNS through hematogenous spread to circumventricular organs that lack a normal BBB or via axonal transport via olfactory sensory or peripheral neurons (Charles et al 1995 ; Phillips et al 2016 ; Passoni et al 2017 ; Thach et al 2001 ). In contrast, EEEV and neuroinvasive CHIKV have been shown to enter the brain primarily through a vascular route (Honnold et al 2015 ; Passoni et al 2017 ; Vogel et al 2005 ). Following intranasal VEEV infection, pro-inflammatory cytokines IFN-β, TNF-α, and IL-6 mediate the breakdown of the BBB in conjunction with monocyte infiltration into the brain, allowing for a second wave of neuroinvasion by the virus, and inhibition of BBB opening by using a MMP-9 inhibitor results in delayed disease onset (Cain et al 2017 ; Schäfer et al 2011 ).…”