SARS-CoV-2, a novel coronavirus with high nucleotide identity to SARS-CoV and SARS-related
coronaviruses detected in horseshoe bats, has spread across the world and impacted
global healthcare systems and economy
1,2
. A suitable small animal model is needed to support vaccine and therapy development.
We report the pathogenesis and transmissibility of the SARS-CoV-2 in golden Syrian
hamsters. Immunohistochemistry demonstrated viral antigens in nasal mucosa, bronchial
epithelial cells, and in areas of lung consolidation on days 2 and 5 post-inoculation
(dpi), followed by rapid viral clearance and pneumocyte hyperplasia on 7 dpi. Viral
antigen was also found in the duodenum epithelial cells with viral RNA detected in
feces. Notably, SARS-CoV-2 transmitted efficiently from inoculated hamsters to naïve
hamsters by direct contact and via aerosols. Transmission via fomites in soiled cages
was less efficient. Although viral RNA was continuously detected in the nasal washes
of inoculated hamsters for 14 days, the communicable period was short and correlated
with the detection of infectious virus but not viral RNA. Inoculated and naturally-infected
hamsters showed apparent weight loss, and all animals recovered with the detection
of neutralizing antibodies. Our results suggest that SARS-CoV-2 infection in golden
Syrian hamsters resemble features found in humans with mild infections.
SARS-CoV-2 was first detected from a cluster of pneumonia patients in Wuhan, Hubei
Province, China in December 2019. Although 55% of the initial cases were linked to
one seafood wholesale market where wild animals were also sold
3
, multiple viral (sustained human-to-human transmissibility by symptomatic and pre-symptomatic
patients
4
) and ecological factors (extensive domestic and international travel during Chinese
Lunar New Year) have contributed to the rapid global spread of the virus. The clinical
spectrum of patients with the novel coronavirus disease (COVID-19) is wide, 19% of
72,314 symptomatic patients in China progressed to severe and critical illness
5
with an estimated 1.4% symptomatic case fatality risk
6
. There is no approved vaccine or treatment against SARS-CoV-2, and the available
interventions including country lock-down and social distancing have severely disrupted
the global supply chain and economy.
A suitable animal model is essential for understanding the pathogenesis of this disease
and for evaluating vaccine and therapeutic candidates. Previous animal studies on
SARS-CoV suggested the importance of the interaction between the viral spike protein
and the host angiotensin converting enzyme 2 (ACE2) receptors
7–10
as well as age and innate immune status of the animals
11–14
in pathogenesis. As with SARS-CoV, the spike protein of SARS-CoV-2 also utilizes ACE2
receptors that are distributed predominantly in the epithelial cells of the lungs
and small intestine to gain entry into epithelial cells for viral replication
1,15
. SARS-CoV-2 showed good binding for human ACE2 but limited binding to murine ACE21,
which has limited the use of inbred mice for research. Macaques and transgenic ICR
mice expressing human ACE2 receptor were shown to be susceptible for SARS-CoV-2 infection
16–18
; however, there is limited availability of these animal models. Cynomolgus macaques
and rhesus macaques challenged with SARS-CoV-2 showed pneumonia with limited
17
and moderate
18
clinical signs, respectively. The challenged transgenic mice showed pneumonia moderate
weight loss, and no apparent histological changes in non-respiratory tissues
16
. Previously generated transgenic mice expressing human ACE2 receptor have been reported
to support SARS-CoV replication in the airway epithelial cells but were associated
with neurological-related mortality due to high ACE2 expression in the brain
7–10
.
Golden Syrian hamster is a widely used experimental animal model and was reported
to support replication of SARS-CoV
19,20
but not MERS-CoV
21
, which utilizes the dipeptidyl peptidase-4 (DPP4) protein as the main receptor for
viral entry. Previous study of SARS-CoV (Urbani strain) in 5-weeks-old golden Syrian
hamsters showed robust viral replication with peak viral titers detected in the lungs
on 2 dpi, followed by rapid viral clearance by 7 dpi, but without weight loss or evidence
of disease in the inoculated animals
20
. A follow up study reported testing different strains of SARS-CoV in golden Syrian
hamsters and found differences in virulence between SARS-CoV strains; lethality was
reported in hamsters challenged with the Frk-1 strain, which differed from the non-lethal
Urbani strain by the L1148F mutation in the S2 domain
19
. Hamsters are permissive for infection by other respiratory viruses including human
metapneumovirus
22
, human parainfluenza virus 3
23
and influenza A virus and may support influenza transmission by contact or airborne
routes
24,25
. Alignment of the ACE2 protein of human, macaque, mice, and hamster suggest that
the spike protein of SARS-CoV-2 may interact more efficiently with hamster ACE2 than
murine ACE2 (Extended Data Fig. 1). Here, we evaluated the pathogenesis and contact
transmissibility of SARS-CoV-2 in 4–5 weeks old male golden Syrian hamsters.
Hamsters were infected intranasally with 8 × 104 TCID50 of the BetaCoV/Hong Kong/VM20001061/2020
virus (GISAID# EPI_ISL_412028) isolated in Vero E6 cells from the nasopharynx aspirate
and throat swab of a confirmed COVID-19 patient in Hong Kong. On 2, 5, 7 dpi, nasal
turbinate, brain, lungs, heart, duodenum, liver, spleen and kidney were collected
to monitor viral replication and histopathological changes. Peak viral load in the
lungs was detected on 2 dpi and decreased on 5 dpi; no infectious virus was detected
on 7 dpi despite of the continued detection of high copies of viral RNA (Fig. 1a).
Infectious viral load was significantly different between 2 and 7 dpi (P= 0.019, Dunn’s
multiple comparisons test) but not the RNA copy number (P= 0.076). No infectious virus
was detected in the kidney although low copies of viral RNA were detected on 2 and
5 dpi (Fig. 1b).
Histopathological examination detected an increase in inflammatory cells and consolidation
in 5–10% of the lungs on 2 dpi (Fig. 1c, 1d) and 15–35% of the lungs on 5 dpi (Fig.
1e, 1f). Mononuclear cell infiltrate was observed in areas where viral antigen was
detected on 2 and 5 dpi. Immunohistochemistry for SARS-CoV-2 N protein demonstrated
viral antigen in the bronchial epithelial cells on 2 dpi (Fig. 1d) with progression
to pneumocytes on 5 dpi (Fig. 1f). On 7 dpi, there was an increased consolidation
in 30–60% of the lungs (Fig. 1g); however, no viral antigen was detected (Fig. 1h)
and type 2 pneumocyte hyperplasia was prominent (Extended Data Fig. 2a). CD3 positive
T lymphocytes were detected in the peri-bronchial region on 5 dpi, which may facilitate
the rapid clearance of the infected cells (Extended Data Fig. 2b). There was moderate
inflammatory cell infiltration in the nasal turbinate (Fig. 1i), and viral antigen
was detected in the nasal epithelial cells (Fig. 1j) and in olfactory sensory neurons
at the nasal mucosa (Fig. 1j). Infection in the olfactory neurons was further confirmed
in cells expressing both SARS-CoV-N protein and neuron-specific beta-III tubulin (Extended
Data Fig. 2c). Compared to mock infection (Extended data Fig. 2d and 2e), infection
lead to a reduction in the number of olfactory neurons at the nasal mucosal on 2 dpi
(Extended Data Fig. 2f), prominent nasal epithelial attenuation on 7 dpi (Extended
Data Figure 2g), followed by tissue repairing on 14 dpi (Extended data Figure 2h).
Though no inflammation was present (Fig. 1k), viral antigen was detected from the
epithelial cells of duodenum on 2 dpi (Fig. 1l). This resembles the detection of SARS-CoV
virus replication in the epithelial cells of terminal ileum and colon of SARS-CoV
patients without observing apparent architectural disruption and inflammatory infiltrate
26
. No apparent histopathological change was observed from brain, heart, liver, and
kidney on 5 dpi (Extended Data Fig. 2i, 2j, 2k, 2l).
To assess the transmission potential of the SARS-CoV-2 in hamsters, three donor hamsters
were inoculated intra-nasally with 8 × 104 TCID50 of the virus. At 24h post-inoculation,
each donor was transferred to a new cage and co-housed with one naïve hamster. Weight
changes and clinical signs were monitored daily and nasal washes were collected every
other day from donors and contacts for 14 days. In donors, the peak infectious viral
load in nasal washes was detected early post-inoculation followed by a rapid decline,
although viral RNA was continuously detected for 14 days (Fig. 2a). Hamsters inoculated
with the SARS-CoV-2 showed the maximal mean weight loss (mean ± SD, −11.97 ± 4.51%,
N=6) on 6 dpi (Fig. 2b). Transmission from donors to co-housed contacts was efficient,
and SARS-CoV-2 was detected from the co-housed hamsters on day 1 post-contact (dpc),
with the peak viral load in nasal washes detected on 3 dpc (Fig. 2c). The total viral
load shed in the nasal washes was approximated by calculating the area under the curve
(AUC) for each animal. The contact hamsters shed comparable amount of virus in the
nasal washes compared to the donor hamsters (P= 0.1, two-tailed Mann-Whitney test).
Contact hamsters showed the maximal mean weight loss (mean ± SD, −10.68 ± 3.42%, N=3)
on 6 dpc; all animals returned to the original weight after 11 dpc (Fig. 2d). Neutralizing
antibody were detected using plaque reduction neutralization (PRNT) assay from donors
on 14 dpi (titers at 1:640 for all) and from contacts on 13 dpc (titers at 1:160,
1:320, and 1:160). As viral RNA was continuously detected from the donor’s nasal washes
for 14 days while infectious virus titers decreased rapidly, we repeated the experiment
and co-housed naïve contacts with donors on 6 dpi. Low quantity of viral RNA was detected
in the nasal washes in one contact on 3 and 7 dpc without detection of infectious
virus in the nasal washes (Fig. 2e), and none of the contact hamsters showed weight
loss (Fig. 2f). PRNT assay detected no neutralizing antibody (< 1:10) from the contact
animals on 12 dpc. The results suggest that the SARS-CoV-2 inoculated donors have
a short communicable period of less than 6 days. Onward transmissibility from donors
to co-housed contacts was correlated with the detection of infectious virus but not
viral RNA in the donor nasal washes.
Transmission from donor to co-housed contact may be mediated by multiple transmission
routes. To investigate the transmissibility of SARS-CoV-2 among hamsters via aerosols,
donors and naïve aerosol contacts were placed in two adjacent wire cages for 8 hours
on 1 dpi (Extended Data Fig. 3). The experiment was performed in three pairs of donor:
aerosol contact at 1:1 ratio. The animals were single-housed after exposure and were
monitored daily for 14 days. Donor hamsters shed infectious virus in the nasal washes
for 6 days, while viral RNA can be continuously detected for 14 days (Fig. 3a). Viral
RNA was detected in the donors’ fecal samples on 2, 4, 6 dpi without detection of
infectious virus (Fig. 3b). Donors showed comparable weight loss (Fig. 3c) as observed
previously (Fig. 2b). Transmission via aerosols was efficient as infectious virus
was detected in the nasal washes from all exposed contacts on 1 dpc, with peak viral
loads detected on 3 dpc (Fig. 3d). Viral RNA was continuously detected from the fecal
samples of the infected aerosol contacts for 14 days, although no infectious virus
was isolated (Fig. 3e). The aerosol contact animals showed the maximal weight loss
(mean ± SD, −7.72 ± 5,42 %, N=3) on 7 dpc (Fig. 3f). The aerosol contact hamsters
shed comparable amount of virus in the nasal washes (approximated by AUC) compared
to the donor hamsters (P= 0.4, two-tailed Mann-Whitney test). PRNT assay detected
neutralizing antibody from the donors on 16 dpi (titers at 1:320, 1:640, 1:640) and
the contacts on 15 dpc (titers at 1:640 for all). To evaluate transmission potential
of SARS-CoV-2 via fomites, three naïve fomite contacts were each introduced to a soiled
cage housed by one donor from 0 to 2 dpi. The fomite contact hamsters were single-housed
in the soiled cages for 48 hours and were each transferred to a new cage on 2 dpc
(equivalent to 4 dpi of the donors). Viral RNA was detected from different surfaces
sampled from the soiled cages used for housing the fomite contacts, with low titer
of infectious virus detected from the bedding (2 dpi), cage side surface (4dpi), and
water bottle nozzle (4 dpi) (Extended Data table 1). One out of three fomite contacts
shed infectious virus in the nasal washes starting from 1 dpc with the peak viral
load detected on 3 dpc (Fig. 3g). Viral RNA but not infectious virus was detected
from the fecal samples (Fig. 3h). The maximal weight loss was 8.79 % on 7 dpc (Fig.
3i). PRNT assay detected neutralizing antibody from the sera of one out of three fomite
contacts on 16 dpc (titers at 1:320). Taken together, these results suggest that transmission
of SARS-CoV-2 among hamsters were mainly mediated via aerosols than via fomites.
Our results indicate that the golden Syrian hamster is a suitable experimental animal
model for SARS-CoV-2, as there is apparent weight loss in the inoculated and naturally-infected
hamsters and evidence of efficient viral replication in the nasal mucosa and lower
respiratory epithelial cells. The ability of SARS-CoV-2 to infect olfactory sensory
neurons at the nasal mucosa may explain the anosmia reported in COVID-19 patients.
Hamsters support efficient transmission of SARS-CoV-2 from inoculated donors to naïve
hamsters by direct contact or via aerosols. We also show that transmission from the
donors to naïve hamsters may occur within a short period early post-inoculation. Our
findings are consistent with a recent report
27
while the current study was under peer review. Hamsters are easy to handle and there
are reagents to support immunological studies for vaccine development
28–30
. The results also highlighted similarity and differences between the SARS-CoV and
SARS-CoV-2 in the hamster model. Both viruses replicated efficiently in the respiratory
epithelial cells with peak viral load detected early post-inoculation, followed by
infiltration of mononuclear inflammatory cells in the lungs and rapid clearance of
infectious virus by 7 dpi. Understanding the host defense mechanism leading to the
rapid viral clearance in the respiratory tissues of the hamsters may aid the development
of effective counter measures for SARS-CoV-2. The efficient transmission of SARS-CoV-2
to naïve hamsters by aerosols also provide opportunities to understand the transmission
dynamics for this novel coronavirus.
METHODS
Virus.
BetaCoV/Hong Kong/VM20001061/2020 virus was isolated from a confirmed COVID-19 patient
in Hong Kong in Vero E6 cells at the BSL-3 core facility, LKS Faculty of Medicine,
The University of Hong Kong. Vero E6 cells were purchased from ATCC (CRL-1586) without
further authentication, and the cells were routinely tested negative for Mycoplasma
sp. by real-time PCR. Stock virus (107.25
TCID50/mL) was prepared after three serial passages in Vero E6 cells in Dulbecco’s
Modified Eagle Medium (DMEM) supplemented with 4.5 g/L D-glucose, 100 mg/L sodium
pyruvate, 2% FBS, 100,000 U/L Penicillin-Streptomycin, and 25mM HEPES.
Animal experiments.
Male golden Syrian hamsters at 4–5 weeks old were obtained from Laboratory Animal
Services Centre, Chinese University of Hong Kong. The hamsters were originally imported
from Harlan (Envigo), UK in 1998. All experiments were performed at the BSL-3 core
facility, LKS Faculty of Medicine, The University of Hong Kong. The animals were randomized
from different litters into experimental groups, and the animals were acclimatized
at the BSL3 facility for 4–6 days prior to the experiments. The study protocol have
been reviewed and approved by the Committee on the Use of Live Animals in Teaching
and Research, The University of Hong Kong (CULATR # 5323–20). Experiments were performed
in compliance with all relevant ethical regulations. For challenge studies, hamsters
were anesthetized by ketamine(150mg/kg) and xylazine (10mg/kg) via intra-peritoneal
injection and were intra-nasally inoculated with 8 × 104 TCID50 of SARS-CoV-2 in 80
μL DMEM. On days 2, 5, 7, three hamsters were euthanized by intra-peritoneal injection
of pentobarbital at 200mg/kg. No blinding was done and a sample size of three animals
was selected to assess the level of variation between animals. Lungs (left) and one
kidney were collected for viral load determination and were homogenized in 1mL PBS.
Brain, nasal turbinate, lungs (right, liver, heart, spleen, duodenum, and kidney were
fixed in 4% paraformaldehyde for histopathological examination. To collect fecal samples,
hamsters were transferred to a new cage one day in advance and fresh fecal samples
(10 pieces) were collected for quantitative real-time RT-PCR and TCID50 assay. To
evaluate SARS-CoV-2 transmissibility by direct contact, donor hamsters were anesthetized
and inoculated with 8 × 104 TCID50 of SARS-CoV-2. On 1 dpi or on 6 dpi, one inoculated
donor was transferred to co-house with one naïve hamster in a clean cage and co-housing
of the animals continued for at least 13 days. Experiments were repeated with three
pairs of donors: direct contact at 1:1 ratio
31,32
. Body weight and clinical signs of the animals were monitored daily. To evaluate
SARS-CoV-2 transmissibility via aerosols, one naïve hamster was exposed to one inoculated
donor hamster in two adjacent stainless steel wired cages on 1 dpi for 8 hours (Extended
Data Fig. 3). DietGel®76A (ClearH2O®) was provided to the hamsters during the 8-hour
exposure. Exposure was done by holding the animals inside individually ventilated
cages (IsoCage N, Techniplast) with 70 air changes per hour. Experiments were repeated
with three pairs of donors: aerosol contact at 1:1 ratio. After exposure, the animals
were single-housed in separate cages and were continued monitored for 14 days. To
evaluate transmission potential of SARS-CoV-2 virus via fomites, three naïve fomite
contact hamsters were each introduced to a soiled donor cage on 2 dpi. The fomite
contact hamsters were single-housed for 48 hours inside the soiled cages and then
were each transferred to a new cage on 4 dpi of the donor. All animals were continued
monitored for 14 days. For nasal wash collection, hamsters were anesthetized by ketamine
(100mg/kg) and xylazine (10mg/kg) via intra-peritoneal injection and 160 μL of PBS
containing 0.3% BSA was used to collect nasal washes from both nostrils of each animal.
Collected nasal washes were diluted 1:1 by volume and aliquoted for TCID50 assay in
Vero E6 cells and for quantitative real-time RT-PCR. The contact hamster were handled
first followed by surface decontamination using 1% virkon and handling of the donor
hamster.
Environmental sampling.
To monitor the level of fomite contamination of SARS-CoV-2 virus in soiled cages,
surface samples (5 cm × 5 cm, except that the whole water bottle nozzle was swabbed)
were collected using flocked polyester swabs (Puritan). Swabs were stored in 0.5 mL
of viral transport medium (VTM, containing 0.45% bovine serum albumin, vancomycin,
amikacin and nystatin) at −80°C. In addition, ten pieces of corn cob bedding were
collected from the soiled cage and were soaked in 1 ml VTM for 30 minutes before titration
of infectious virus and viral RNA extraction. Infectious viral loads were determined
in Vero E6 cells, and viral RNA copy numbers were determined by quantitative real-time
RT-PCR.
Viral load determination by quantitative real-time RT-PCR.
RNA was extracted from 140 μL samples using QIAamp viral RNA mini kit (Qiagen) and
eluted with 60 μL of water. Two μL RNA was used for real-time qRT-PCR to detect and
quantified N gene of SARS-CoV-2 using TaqMan™ Fast Virus 1-Step Master Mix as described
33
.
Plaque reduction neutralization (PRNT) assay.
The experiments were carried out in duplicate using Vero E6 cells seeded in 24-well
culture plates. Serum samples were heat-inactivated at 56°C for 30 min and were serially
diluted and incubated with 30–40 plaque-forming units of SARS-CoV-2 for 1 h at 37 °C.
The virus–serum mixtures were added to the cells and incubated 1 h at 37 °C in 5%
CO2 incubator. The plates were overlaid with 1% agarose in cell culture medium and
incubated for 3 days. Thereafter the plates were fixed and stained with 1% crystal
violet. Antibody titres were defined as the highest serum dilution that resulted in > 90%
(PRNT90) reduction in the number of plaques.
Histopathology and immunohistochemistry.
Tissue (hearts, livers, spleens, duodenums, brains, right lungs and kidneys) were
fixed in 4% paraformaldehyde and were processed for paraffin embedding. The 4-μm sections
were stained with hematoxylin and eosin for histopathological examinations. For immunohistochemistry,
SARS-CoV-2 N protein was detected using monoclonal antibody (4D11)
34
, CD3 was detected using polyclonal rabbit anti-human CD3 antibodies (DAKO), and the
neuron-specific beta-III tubulin was detected using monoclonal antibody clone TuJ1
(R&D Systems). Images were captured using a Leica DFC 5400 digital camera and were
processed using Leica Application Suite v4.13.
Statistics and reproducibility.
Kruskal-Wallis test and Dunn’s multiple comparisons test were used to compare viral
loads in the lungs and kidney on 2, 5, 7 dpi. Area under the curve was calculated
from the nasal washes of the donor and contact hamsters followed by Mann-Whiteny test.
Data were analyzed in Microsoft Excel for Mac, version 16.35 and GraphPad Prism version
8.4.1. For the detection viral replication in hamsters, 9 hamsters were inoculated
and tissues were collected from animals on 2 (N=3), 5 (N=3), 7 (N=3) dpi; the results
from the three animals were similar (Fig. 1a and 1b). Inoculation of the donor hamsters
was independently performed twice and the inoculated hamsters showed comparable weight
loss and shed comparable amount of virus in the nasal washes (Fig. 2a, 2b, 3a, 3b).
Transmission by direct contact, via aerosols or fomites were performed with three
pairs of donor: contacts at 1:1 ratio.
Extended Data
Extended Data Figure 1.
Sequence alignment of ACE2 proteins (1–420) from human, macaca, hamster, and mouse.
Amino acid residues of human ACE2 that are experientially shown to interact with the
receptor binding domain (RBD) of SARS-CoV-2
35
are denoted by *. Amino acid residues that are important for the interaction between
human ACE2 and RBD of SARS-CoV are highlighted in red boxes
36
.
Extended Data Figure 2.
Haemotoxylin and eosin (H&E) staining and immunohistochemistry on SARS-CoV-2 challenged
hamster tissues.
a, Hyperplasia of the pneumocytes detected on 7 dpi. b, Detection of CD3 positive
cells (using rabbit anti-human CD3 polyclonal antibody) in the lungs on 5 dpi. c,
Detection of SARS-CoV-2 N protein (red staining, using monoclonal antibody 4D11) and
olfactory neurons (brown staining, using monoclonal antibody TuJ1) from the nasal
turbinate on 5 dpi. d, Detection of olfactory neurons (using monoclonal antibody TuJ1)
from the nasal turbinate of a mock infected hamster (N=1). e, Nasal epithelial cells
from the nasal turbinate of a mock infected hamster (N=1) showed negative staining
for TuJ1. f, Detection of olfactory neurons from nasal turbinate on 2 dpi. g, Detection
of olfactory neurons from nasal turbinate on 7 dpi. h. Detection of olfactory neurons
from nasal turbinate on 14 dpi. i, H&E staining of the brain tissue on 5 dpi. j, H&E
staining of the heart on 5 dpi. k, H&E staining of the liver on 5 dpi. l, H&E staining
of the kidney on 5 dpi. Hamsters were intra-nasally inoculated with PBS (mock infection,
N=1) or with 8 × 104 TCID50 of SARS-CoV-2 (N=9) and the tissues were collected on
2 (N=3), 5 (N=3), 7 (N=3) dpi. H&E and immunohistochemistry with tissues from three
animals showed similar results and the representative results were shown.
Extended Data Figure 3.
Experimental layout for the aerosol transmission experiment in hamsters.
To evaluate SARS-CoV-2 transmissibility via aerosols, one naïve hamster was exposed
to one inoculated donor hamster in two adjacent stainless steel wired cages on 1 dpi
for 8 hours. DietGel®76A (ClearH2O®) was provided to the hamsters during the 8-hour
exposure. Exposure was done by holding the animals inside individually ventilated
cages (IsoCage N, Techniplast) with 70 air changes per hour. Experiments were repeated
with three pairs of donors: aerosol contact at 1:1 ratio. After exposure, the animals
were single-housed in separate cages and were continued monitored for 14 days.
Extended Data Table 1.
Detection of SARS-CoV-2 in the soiled cages.To evaluate transmission potential of
SARS-CoV-2 virus via fomites, three naïve fomite contact hamsters were each introduced
to a soiled donor cage on 2 dpi. The fomite contact hamsters were single-housed for
48 hours inside the soiled cages and then were each transferred to a new cage on 4
dpi of the donors. The soiled cages were left empty at room temperature and were sampled
again on 6 dpi of the donor. Surface samples and corn cob bedding were collected from
the soiled cages on different time points to monitor infectious viral load and viral
RNA copy numbers in the samples.
Days post-inoculation
Animal cage info
Sampled area
Material
log10 TCID50/ mL
log10 RNA copies/ mL
Day 2
donor cage A
1.79
6.70
donor cage B
bedding
corn cobs
<
5.18
donor cage C
<
5.79
Day 4
fomite contact cage A
cage side (in directcontact with theanimals)
<
6.89
fomite contact cage B
plastic
<
5.21
fomite contact cage C
1.79
6.33
fomite contact cage A
<
3.76
fomite contact cage B
cage lid
plastic
<
4.33
fomite contact cage C
<
4.10
fomite contact cage A
<
5.26
fomite contact cage B
pre-filter
paper-based
<
5.27
fomite contact cage C
<
5.31
fomite contact cage A
<
3.64
fomite contact cage B
water bottle nozzle
stainless steel
<
4.20
fomite contact cage C
2.21
6.06
fomite contact cage A
<
4.84
fomite contact cage B
bedding
corn cobs
<
5.27
fomite contact cage C
<
6.06
Day 6
fomite contact cage A
cage side (in directcontact with theanimals)
<
5.70
fomite contact cage B
plastic
<
5.61
fomite contact cage C
<
6.51
fomite contact cage A
<
4.75
fomite contact cage B
cage lid
plastic
<
3.46
fomite contact cage C
<
4.24
fomite contact cage A
<
5.48
fomite contact cage B
pre-filter
paper-based
<
5.23
fomite contact cage C
<
5.36
fomite contact cage A
<
5.12
fomite contact cage B
bedding
corn cobs
<
6.24
fomite contact cage C
<
5.58
Supplementary Material
1