Review on transmission of SARSCoV-2 at the human-animal interface
Project for reviewing risks of SARS-CoV-2 infection between animals and humans

Abe M, Chen Y, Chizimu JY, Chuluunbaatar T, Hayashi R, Huynh LT, Komu JG,Lokupathirage S, Luo Y, Mohamed I, Muthusinghe DS, Mwale C, Namba T,Sabrin MS, Shawa M, Takahashi Y, Thammahakin P, Tiyamanee W, Wei Z
Supervisor:
Kobayashi S, Henshaw M, Matsuno K, Nao N

DogDogs can be infected with SARS-CoV-2, andhuman-to-dog transmission has been confirmed.
Dogs can acquire infection in households from SARS-CoV-2-infected humans (Sit et al., 2020). In
addition, the virus can infect culture cells expressing canine ACE2 in the laboratory (Zhang et al.,2021). However, in the natural environment, transmission from human to dogs is quite rare
(Temmam et al., 2020). The suggested reasons for this are that SARS-CoV-2 replicates poorly indogs (Shi et al., 2020) and that the binding affinity of receptor binding domain of SARS-CoV-2 tocanine ACE2 is lower than that of human ACE2 (Zhang et al., 2021). Clinically, The oral and nasal
swabs from dogs tested positive for SARS-CoV-2 without symptoms (Sit et al., 2020), and the viralsequences from dogs were identical to SARS-CoV-2 across the full genome (Temmam et al., 2020).
However, there were no obvious changes in clinical condition (Sit et al., 2020) and no antibodies
against SARS-CoV-2 were detectable in their blood one month after the case was reported(Temmam et al., 2020).

Cat
Cats can get infected with SARS-CoV-2 andwere one of the first animals to be diagnosed
with SARS-CoV-2 infection.
Natural cases of infection in cats have been found in several countries. Both human-to-cat andcat-to-cat infections have been confirmed (Vanessa R B. et al., 2020). The symptoms shown incats were identical to those in humans and the specific antibodies for SARS-CoV-2 weredetected in cats (Corinne S. et al., 2020). However, the replication of the virus in cat-derived
cell lines was not efficient compared with human cell lines (Wang L. et al., 2021). Furthermore,SARS-CoV was detected in cats (Martina et al., 2003) and cats have been used as an animalmodel for SARS-CoV (Van Den Brand et al., 2008).

Zoo animals(Tiger & Lion)
Tigers and lions were infected with SARS-CoV-2and the possibility of transmission from theseanimals to human was suggested.
These animals showed clinical respiratory signs such as an intermittent coughor audible wheezing. Live SARS-CoV-2 and viral RNA were detected in therespiratory tract and feces from these animals. Comparative analysis of theviral genome to human-isolated virus support the possibility of transmission
from an infected human to the animals (McAloose et al., 2020).

HamsterGolden hamsters are susceptible to SARSCoV-2 infection.
The virus replicated in the lung with pneumonia (Imai et al., 2021). SARS-CoV-2 wastransmitted efficiently from inoculated golden hamsters to naive hamsters by directcontact and via aerosols (Sia et al., 2020). Amino acid sequence and in vitro experiments
showed the possibility of the binding of hamster's ACE2 and SARS-CoV-2 (Damas et al.,2020). Thus, the golden hamster is a well-established small animal model for the study ofSARS-CoV-2 infection.

RabbitRabbits are susceptible to SARS-CoV-2.
An experimental study showed that rabbits can be infected with the virus in the upper
respiratory tract and can shed infectious agents into the environment (Mykytyn AZ et al.,2021). In amino acid sequence analysis, there was high similarity between rabbit and human
ACE2 (Damas J et al., 2020). The rabbit ACE2 bound to the virus, which supported
proliferation and entry of the virus (Zhao et al., 2020). In other coronavirus infections,
MERS-CoV was detected in rabbit without significant histopathologic changes and symptoms(Haagmans et al., 2015). We could not find a study about natural infection of SARS-CoV-2.

FerretFerrets are susceptible to SARS-CoV-2infection.
ACE2 expression in ferrets was observed in the upper respiratory tracts but not lowertracts (Lean et al., 2021). Inoculation of SARS-CoV-2 into ferrets induced fever and lossof appetite and the viral RNA and infectious virus were detected from nasal washes(Shi J et al., 2020). Furthermore, the Chinese ferret-badger has been reported to besusceptible to SARS-CoV (Gautam et al., 2020).

CattleNo infectious SARS-CoV-2 was detectedfrom experimentally inoculated cattle.
Phylogenetic and structural analysis of ACE2 and SARS-CoV-2 spike protein demonstrated
that ACE2 protein of cattle is one of the most permissive to SARS-CoV-2 (Qiu et al., 2020).
In addition, direct binding of cattle ACE2 and SARS-CoV-2 spike protein was experimentallyconfirmed (Conceicao et al., 2020). However, experimentally SARS-CoV-2-inoculated cattle
showed very limited viral replication and viral neutralizing antibodies and no cattle-tocattle transmission of SARS-CoV-2 was observed (Lorenz et al., 2020 and Shollie et al.,2021).

HorseHorses possibly have the potential to be
infected with SARS-CoV-2.
Sequence identities of horse ACE2 and susceptibility score that predicts therisk of SARS-CoV-2 infection showed that horses have high potential to get
infected with SARS-CoV-2 (Alexander et al., 2020). In vivo experiment andserosurveillance are required for further evaluation of SARS-CoV-2
susceptibility of horses.

Pig
Pig is likely not a potential source forSARS-CoV and SARS-CoV-2.
Experimentally SARS-CoV-2-inoculated pigs showed no viral replication,seroconversion, or pig-to-pig transmission (Kore Schlottau. et al., 2020). In anotherexperiment, SARS-CoV-2-inoculated pigs also showed no viral replication, but pigs
inoculated with SARS-CoV-2 intramuscularly or intravenously showed
seroconversion (Vergara-Alert J et al., 2020).

Poultry(chickens, turkeys, ducks, quail, geese, etc.)

In experimental settings, no poultry wasconfirmed to be susceptible to SARS-CoV-2.
All the results demonstrated that poultry are unlikely to serve as a role in the maintenance ortransmission of SARS-CoV-2 (Schlottau et al., 2020).

Alpaca
Alpaca possibly have susceptibility to SARS-CoV-2.
A novel coronavirus associated with an acute respiratory disease in alpacas(Alpaca Coronavirus, ACoV) was genetically most similar to the common
human coronavirus (HCoV) 229E with 92.2% nucleotide identity over theentire genome (Crossley B M et al., 2012). Experimentally MERS-CoVinoculated alpaca showed viral replication without clear clinical symptoms(Crameri G et al., 2016). In addition, MERS-CoV receptor DPP4 was shown
as a candidate binding target of the SARS-CoV-2 spike protein (Li Y et al.
2020). These data suggest that alpaca possibly have susceptibility to SARSCoV-2, although in vivo experiments are required for further evaluation.

Mink
SARS-CoV-2 was detected in farmed mink withsymptoms of respiratory disease, and the sourceof mink infection was mink farm workers.
SARS-CoV-2 infection in farmed mink was first reported in Netherland and some of infected minks
showed severe respiratory symptom such as interstitial pneumonia (Nadia Oreshkova et al., 2020).
Whole genome sequence and intensive epidemiological analysis demonstrated that both humanto-mink and mink-to-human transmission of SARS-CoV-2 were occurred within mink farms (OudeMunnink BB et al., 2021). Binding region of ACE2 of mink and human were both highly conserved,
suggesting SARS-CoV-2 infection between mink and human (Oude Munnink BB et al., 2021).

Bat
Bats, especially fruit bats, are one of thehigh-risk species to transmit SARS-CoV-2.
Bats are known to be natural hosts of several coronaviruses including SARS-CoV-2-related
coronaviruses (Wacharapluesadee et al., 2021), such as bat CoV RaTG13, which shares the highest
sequence homology with SARS-CoV-2 among known coronaviruses (Zhou et al., 2020). In an
experimental infection of SARS-CoV-2 to Egyptian fruit bats (Rousettus aegyptiacus), infected bats
did not show clinical signs or mortality, while bat-to-bat transmission was confirmed (Schlottau et all.,2020). MERS-CoV can also infect Jamaican fruit bats (Artibeus jamaicensis) without any clinical signs(Munster et al., 2016). Thus, bats are ones of the highest-risk species to transmit SARS-CoV-2.
Furthermore, coronavirus circulation in bats should be monitored to prepare for a future emergenceof novel coronaviruses.

Pangolin
Pangolin is one of the high-risk
species to transmit SARS-CoV-2.
Pangolin-CoV is the second closest relative to SARS-CoV-2 after the bat CoV RaTG13 (Zhanget al., 2020). Pangolin-CoV possesses ACE2 binding motif of SARS-CoV-2, which is not in bat
CoV RaTG13 (Lam et al., 2020). SARS-CoV-2 S protein-binding sites on pangolin ACE2
molecule are similar to those of human ACE2 (Wei et al., 2021), and pangolin ACE2 strongly
binds to SARS-CoV-2 S protein to efficiently support the virus entry (Zhao et al., 2020). Thus,
pangolin is one of the high-risk species to transmit SARS-CoV-2 and also will be a possible
host in the future emergence of new coronaviruses.

Human-animal relationship in SARS-CoV-2 infection
Natural infection

Origin?
SARS-CoV-2

Experimental infection

No report
Human?

Possibility of infection

The host receptor of SARS-CoV-2:
Angiotensin I converting enzyme 2 (ACE2)
A surface spike (S) protein mediates
viral recognition and entry into host.

The affinity determines the host’s
susceptibility to infection.

ACE2 is functional
receptor for S protein.
Du L, et al. Nat. Rev. Microbiol., 2009

ACE2 is expressed in most vertebrates,
but the amino acid sequences differs with species.
Receptor recognition is an important factor determining host range