Susceptibility of ferrets, cats, dogs, and different domestic animals to SARS-coronavirus-2
Jianzhong Shi, Zhiyuan Wen, Gongxun Zhong, Huanliang Yang, Chong Wang, Renqiang Liu, Xijun He, Lei Shuai, Ziruo Sun, Yubo Zhao, Libin Liang, Pengfei Cui, Jinliang Wang, Xianfeng Zhang, Yuntao Guan, Hualan Chen, Zhigao Bu
Abstract
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes the infectious disease COVID-19,
which was first reported in Wuhan, China in December, 2019. Despite the tremendous efforts to control
the disease, COVID-19 has now spread to over 100 countries and caused a global pandemic. SARS-CoV2 is thought to have originated in bats; however, the intermediate animal sources of the virus are
completely unknown. Here, we investigated the susceptibility of ferrets and animals in close contact
with humans to SARS-CoV-2. We found that SARS-CoV-2 replicates poorly in dogs, pigs, chickens, and
ducks, but efficiently in ferrets and cats. We found that the virus transmits in cats via respiratory
droplets. Our study provides important insights into the animal reservoirs of SARS-CoV-2 and animal
management for COVID-19 control.
In late December 2019, an unusual pneumonia emerged in humans in Wuhan, China, and rapidly
spread internationally, raising global public health concerns. The causative pathogen was identified as
a novel coronavirus (1-16) that was named Severe Acute Respiratory Syndrome Coronavirus 2 (SARSCoV-2) on the basis of a phylogenetic analysis of related coronaviruses by the Coronavirus Study
Group of the International Committee on Virus Taxonomy (17); the disease it causes was
subsequently designated COVID-19 by the World Health Organization (WHO). Despite tremendous
efforts to control the COVID-19 outbreak, the disease is still spreading. As of March 11, 2020, SARSCoV-2 infections have been reported in more than 100 countries, and 118,326 human cases have
been confirmed, with 4,292 fatalities (18). COVID-19 has now been announced as a pandemic by
WHO.
Figure 1. Replication of SARS-CoV-2 viruses in ferrets. Viral RNA in organs or tissues of ferrets
inoculated with (A) F13-E virus or (B) CTan-H virus. Viral titers in organs or tissues of ferrets inoculated
with F13-E (C) and CTan-H (D). Viral RNA in nasal washes of ferrets inoculated with F13-E (E) and CTan-H
(F). Viral titer in nasal washes of ferrets inoculated with F13-E (G) and CTan-H (H). Antibodies against
SARS-CoV-2 tested by an ELISA (I, J) and neutralization assay (K, L) with the sera derived from ferrets
inoculated with F13-E (I, K) and CTan (J, L). Each color bar represents the value from an individual
animal. The black bars in the panels I to L indicate the antibody values of sera collected from each
animal before the virus was inoculated. Asterisks indicate animals that were euthanized on day 13 after
virus inoculation, the other four animals were euthanized on day 20 p.i. The horizontal dashed lines
indicate the lower limit of detection.
Although SARS-CoV-2 shares 96.2% identity at the nucleotide level with the coronavirus RaTG13,
which was detected in horseshoe bats (Rhinolophus spp) in Yunnan province in 2013 (3), it has not
previously been detected in humans or other animals. The emerging situation raises many urgent
questions. Could the widely disseminated viruses transmit to other animal species, which then become
reservoirs of infection? The SARS-CoV-2 infection has a wide clinical spectrum in humans, from mild
infection to death, but how does the virus behave in other animals? As efforts are made for vaccine
and antiviral drug development, which animal(s) can be used most precisely to model the efficacy of
such control measures in humans? To address these questions, we evaluated the susceptibility of
different model laboratory animals, as well as companion and domestic animals to SARS-CoV-2.
All experiments with infectious SARS-CoV-2 were performed in the biosafety level 4 and
animal biosafety level 4 facilities in the Harbin Veterinary Research Institute (HVRI) of the Chinese
Academy of Agricultural Sciences (CAAS), which was approved for such use by the Ministry of
Agriculture and Rural Affairs of China. Details of the biosafety and biosecurity measures taken are
provided in the supplementary materials (19). The protocols for animal study and animal welfare
were reviewed and approved by the Committee on the Ethics of Animal Experiments of the HVRI
of CAAS.
Ferrets are commonly used as an animal model for respiratory viruses that infected humans
(20-26). We therefore tested the susceptibility of SARS-CoV-2 in ferrets. Two viruses [SARS-CoV2/F13/environment/2020/Wuhan, isolated from an environmental sample collected in the
Huanan Seafood Market in Wuhan (F13-E), and SARS-CoV-2/CTan/human/2020/Wuhan (CTan-H),
author/funder.
isolated from a human patient] were used in this study. Pairs of ferrets were inoculated
intranasally with 105 pfu of F13-E or CTan-H, respectively, and euthanized on day 4 postinoculation (p.i.). The nasal turbinate, soft palate, tonsils, trachea, lung, heart, spleen, kidneys,
pancreas, small intestine, brain, and liver from each ferret were collected for viral RNA
quantification by qPCR and virus titration in Vero E6 cells. Viral RNA (Fig. 1A, B) and infectious
virus were detected in the nasal turbinate, soft palate, and tonsils of all four ferrets inoculated
with these two viruses, but was not detected in any other organs tested (Fig. 1C, D). These results
indicate that SARS-CoV-2 can replicate in the upper respiratory tract of ferrets, but its replication in
other organs is undetectable.
To investigate the replication dynamics of these viruses in ferrets, groups of three animals were
inoculated intranasally with 105 pfu of F13-E or CTan-H, and then placed in three separate cages within
an isolator. Nasal washes and rectal swabs were collected on days 2, 4, 6, 8, and 10 p.i. from the ferrets
for viral RNA detection and virus titration. Body temperatures and signs of disease were monitored for
two weeks. As shown in Fig. 1, viral RNA was detected in the nasal washes on days 2, 4, 6, and 8 p.i. in
all six ferrets inoculated with the two viruses (Fig. 1E, F). Viral RNA was also detected in some of the
rectal swabs of the virus-inoculated ferrets although the copy numbers were notably lower than those
in the nasal washes of these ferrets (fig. S1A, B). Infectious virus was detected from the nasal washes of
all ferrets (Fig. 1G, H), but not from the rectal swabs of any ferrets (fig. S1C, D).
One ferret from each virus-inoculated group developed fever and loss of appetite on days 10 and
12 p.i., respectively. To investigate whether these symptoms were caused by virus replication in the
lower respiratory tract, we euthanized the two ferrets on day 13 p.i., and collected their organs for viral
RNA detection. However, viral RNA was not detected in any other tissues or organs of either ferret,
except for a low copy number (105.4 copies/g) in the turbinate of the ferret inoculated with CTan-H (fig
S2). Pathological studies revealed severe lymphoplasmacytic perivasculitis and vasculitis, increased
numbers of type II pneumocytes, macrophages, and neutrophils in the alveolar septa and alveolar
lumen, and mild peribronchitis in the lungs of the two ferrets euthanized on day 13 p.i. (fig.S3).
Antibodies against SARS-CoV-2 were detected in all of the ferrets by an ELISA and a neutralization
assay, although the antibody titers of the two ferrets that were euthanized on day 13 p.i. were notably
lower than those of the ferrets euthanized on day 20 p.i. (Fig. 1I-L).