SARS-CoV-2 infection, neuropathogenesis and transmission among deer mice: Implications for reverse zoonosis to New World rodents

Abstract

Coronavirus disease-19 (COVID-19) emerged in November, 2019 in China and rapidly became pandemic. As with other coronaviruses, a preponderance of evidence suggests the virus originated in horseshoe bats (Rhinolophus spp.) and likely underwent a recombination event in an intermediate host prior to entry into human populations. A significant concern is that SARS-CoV-2 could become established in secondary reservoir hosts outside of Asia. To assess this potential, we challenged deer mice (Peromyscus maniculatus) with SARS-CoV-2 and found robust virus replication in the upper respiratory tract, lungs and intestines, with detectable viral RNA for up to 21 days in oral swabs and 14 days in lungs. Virus entry into the brain also occurred, likely via gustatory-olfactory-trigeminal pathway with eventual compromise to the blood brain barrier. Despite this, no conspicuous signs of disease were observed and no deer mice succumbed to infection. Expression of several innate immune response genes were elevated in the lungs, notably IFNα, Cxcl10, Oas2, Tbk1 and Pycard. Elevated CD4 and CD8β expression in the lungs was concomitant with Tbx21, IFNγ and IL-21 expression, suggesting a type I inflammatory immune response. Contact transmission occurred from infected to naive deer mice through two passages, showing sustained natural transmission. In the second deer mouse passage, an insertion of 4 amino acids occurred to fixation in the N-terminal domain of the spike protein that is predicted to form a solvent-accessible loop. Subsequent examination of the source virus from BEI Resources indicated the mutation was present at very low levels, demonstrating potent purifying selection for the insert during in vivo passage. Collectively, this work has determined that deer mice are a suitable animal model for the study of SARS-CoV-2 pathogenesis, and that they have the potential to serve as secondary reservoir hosts that could lead to periodic outbreaks of COVID-19 in North America.

Evidence of central nervous system infection and neuroinvasive routes, as well as neurological involvement, in the lethality of SARS‐CoV‐2 infection

“…As compared to postmortem studies, animal experiments have provided detailed information on the neuroinvasive potential of SARS‐CoV‐2, 59‐61,63‐65 which revealed that the predominant target organs were the lung of infected animals at early time points, and variably, the brain at later time points 62,63 . The presence of the virus in CNS was found within neurons in different brain areas with a wide spectrum of neuropathology, well consistent with the reported clinical symptoms in COVID‐19 patients 65 .…”

“…Consistent with this, at least three autopsy studies have described brainstem abnormalities after SARS‐CoV‐2 infection 43‐45 . Brainstem infection with SARS‐CoV‐2 was also reported in an animal experiment, where viral antigen was present multifocally at the level of lateral sulcus nucleus, optic chiasm, hypothalamus, thalamic parabrachial nucleus, and ventral posteromedial nucleus culminating in the gustatory cortex 65 …”

“…The results obtained from animal experiments are generally consistent with each other in terms of neuronal infection, but there are some discrepancies in whether glial cells are infected, which may be due to the different animal sources or virus strains they used. Animal experiments have demonstrated that SARS‐CoV‐2 does possess a neuroinvasive potential similar to its counterpart, SARS‐CoV 57‐60,64,65 . Importantly, the in vivo findings show that CNS involvement may contribute to the lethality of SARS‐CoV‐2 infection.…”

“…By using deer mice, whose ACE2 receptor shares 17 of the 20 critical residues for SARS‐CoV‐2 binding, Fagre et al 65 demonstrated robust virus replication in respiratory, digestive, and nervous systems after intranasal inoculation. Of interest, the glomerular layer of main olfactory bulb became spongiotic and immunoreactive at Day 3 postinoculation, and SARS‐CoV‐2 antigen was detected in the cytoplasm of mitral and microglial cells.…”

Susceptibility of rabbits to SARS-CoV-2

“…In experimental settings, non-human primates, ferrets, cats, dogs, deer mice and hamsters have been found to be susceptible to SARS-CoV-2 infection [2,3,4,5,6]. Moreover, ferrets, cats, deer mice and hamsters were able to transmit the virus via the air [2,4,5,6,7]. In domestic settings, both dogs and cats have been found to carry the virus, displaying very mild to more severe symptoms, respectively [7].…”