Abstract
Recent spillback events of SARS-CoV-2 from humans to animals has raised concerns about it becoming endemic in wildlife. A sylvatic cycle of SARS-CoV-2 could present multiple opportunities for repeated spillback into human populations and other susceptible wildlife. Based on their taxonomy and natural history, two native North American wildlife species —the striped skunk (Mephitis mephitis) and the raccoon (Procyon lotor) —represent a high likelihood of susceptibility and ecological opportunity of becoming infected with SARS-CoV-2. Eight skunks and raccoons were each intranasally inoculated with one of two doses of the virus (103 PFU and 105 PFU) and housed in pairs. To evaluate direct transmission, a naïve animal was added to each inoculated pair 48 h post-inoculation. Four control animals of each species were handled like the experimental groups. At predetermined intervals, we collected nasal and rectal swabs to quantify virus shed via virus isolation and detect viral RNA via rRT-PCR and blood for serum neutralization. Lastly, animals were euthanized at staggered intervals to describe disease progression through histopathology and immunohistochemistry. No animals developed clinical disease. All intranasally inoculated animals seroconverted, suggesting both species are susceptible to SARS-CoV-2 infection. The highest titers in skunks and raccoons were 1:128 and 1:64, respectively. Low quantities of virus were isolated from 2/8 inoculated skunks for up to day 5 post-inoculation, however no virus was isolated from inoculated raccoons or direct contacts of either species. Neither species had gross lesions, but recovering mild chronic pneumonia consistent with viral insult was recorded histologically in 5/8 inoculated skunks. Unlike another SARS-CoV-2 infection trial in these species, we detected neutralizing antibodies in inoculated raccoons; thus, future wildlife serologic surveillance results must be interpreted with caution. Due to the inability to isolate virus from raccoons, the lack of evidence of direct transmission between both species, and low amount of virus shed by skunks, it seems unlikely for SARS-CoV-2 to become established in raccoon and skunk populations and for virus to spillback into humans. Continued outbreaks in non-domestic species, wild and captive, highlight that additional research on the susceptibility of SARS-CoV-2 in wildlife, especially musteloidea, and of conservation concern, is needed.
Highlights
As severe acute respiratory syndrome coronavirus 2 (SARSCoV-2) continues to circulate on a global scale, the need to identify potential animal reservoirs, especially among wildlife, has become a priority, spurring surveillance and susceptibility trials of numerous species [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15]
Skunks H1-L and H2-R were the only animals in this study to have cycle threshold (Ct) values ≤ 28, a threshold that coincides with historic human data for obtaining culturable virus when evaluating the samples for the SARS-CoV2 N gene via RT-PCR (Supplementary Table 2) [55]
Our findings demonstrate that while striped skunks and raccoons are susceptible to SARS-CoV-2 infection, it is unlikely that either species is likely to be a competent reservoir for SARSCoV-2 in a natural setting
Summary
As severe acute respiratory syndrome coronavirus 2 (SARSCoV-2) continues to circulate on a global scale, the need to identify potential animal reservoirs, especially among wildlife, has become a priority, spurring surveillance and susceptibility trials of numerous species [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15]. Ferrets (Mustela putorius furo), close relatives to North American Musteloidea, are wellestablished animal models for SARS [29,30,31,32] and are highly susceptible to SARS-CoV-2 [8,9,10, 33,34,35,36,37,38] Another close relative, mink (Neovison vison), is highly susceptible to SARS-CoV-2 in experimental inoculations trials, as well as natural infections in commercial farms [5, 39,40,41,42,43]. Asian smallclawed otters (Aonyx cinereus) in a zoological institution were infected with SARS-CoV-2 [44] Like ferrets, both mink and otters experienced varying levels of respiratory disease upon infection with SARS-CoV-2. Both species were first found to be susceptible after transmission from an infected human caretaker, highlighting the anthropozoonotic potential of this virus [45]
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