Discussion
According to this expert elicitation of knowledge, forty-six drivers of
COVID-19 emergence in carnivore domestic pets (cats, dogs and ferrets)
were ranked and aggregated into four homogenous groups. The first group
of drivers categorised in the “very high importance” node, will be
further discussed and it includes in decreasing order: availability and
quality of diagnostic tools, human density close to pets, ability of
preventive/control measures to stop the disease from entering the
country or spreading (except for treatment, vaccination and reservoir(s)
control), current species specificity of the disease causing agent and
current knowledge on the pathogen. The sensitivity analysis indicated a
limited effect of the experts involved in the elicitation, which shows
that there is an acceptable robustness of the elicitation.
Considering as the highest driver of emergence of COVID-19 in pets, the
availability and quality of diagnostic tools of COVID-19 infection in
pets seemed to be critical (driver: D3-4). Currently, diagnostic tests
are only available in specialized laboratories, e.g. polymerase chain
reaction assay (PCR), virus neutralisation assay (VNT), microsphere
immunoassay (MIT), enzyme-linked immunosorbent assay (ELISA) (e.g. Zhang
et al., 2020; Sailleau et al., 2020). Indeed, the capacity to confirm a
suspected case is very limited. Some of these laboratories are also
often prioritise to diagnose human cases of COVID-19, and not animal
cases. The PCR assay allows the specific detection of SARS-Cov-2 RNA and
helps finding the source of infection (e.g. phylogenetic tree). Addition
of serological assays would allow differentiating between environmental
contamination (PCR positive and serological test negative) and
(transient) infection (PCR positive or negative depending of the stage
of infection but serological test positive) in pets. Another aspect is
the usefulness to collect and share the different information on pets at
national and international levels to be able to assess properly the true
status of pets in the transmission of the COVID-19, based on evidence,
and to guide both risk management and risk communication under the One
Health approach. This is particularly important to avoid any inadequate
behaviour of owners like panic abandonment of household pets. Recently,
the OIE published guidelines for pet sampling (based on epidemiological
contexts, e.g. close contact with a suspected or confirmed
SARS-CoV-2-infected patient, or animal exposed to a known high-risk
environment, and clinical presentation, e.g. clinical signs suggestive
of SARS-Cov-2 infection), testing (based on validated tests, suitable
for its intended use, which is essential when testing different species
due to possible variation in sensitivity and specificity), and reporting
of SARS-Cov-2 in animals (OIE, 2020). In addition, according to the
Terrestrial Animal Health Code, the notification of COVID-19 cases in
animals should be reported to the OIE as an emerging disease through the
World Animal Health Information System (WAHIS).
The second most important driver was the human density close to pets
(driver: D4-5). Indeed, humans have a strong effect on the introduction
and spread of COVID-19 in pets. In Europe, at least 80 million
households own at least one pet and the number of cats and dogs accounts
for 103,828,000 and 85,184,000 heads, respectively. Around 25% of
owners have at least one cat and 25%, one pet (FEDIAF, 2019). This
percentage is not homogeneous and large disparities exists depending of
the region for a same country. As an example, this percentage is higher
in the Southern part (around 33% - more rural part) than in the
Northern part (around 25%) of Belgium. No data on households with
ferret are available at national level despite its important
experimental susceptibility regarding the SARA-Cov-2. However, more
studies are needed to assess properly the human density close to pets in
Europe, in particular species by species.
The third most important driver was the ability of preventive/control
measures to stop the disease from entering the country or spreading
(containment of the pandemic), except for treatment, vaccination and
reservoir(s) control (driver: D3-1). Most experts mentioned the current
lack of sanitary certification, incomplete traceability of animals,
ineffective disinfection measures, incomplete restriction of contacts
between pets and wild animals and ineffective biosecurity measures. The
main present interest of this driver is that the more human infection
will be limited, the more risks of pet infections by humans will be
reduced. Moreover reporting of all confirmed COVID-19 infections of pets
should be mandatory. Additionally, several initiatives need to be
emphasised to improve the situation like the OIE guidelines for
sampling, testing and reporting of SARS-Cov-2 in animals (OIE, 2020) and
several pet management recommendations given by national (e.g. Académie
Nationale de Médecine, 2020) or international (e.g. American Veterinary
Medical Association. 2020) expert committees. More evidence-base
information and protocols should be stimulated and shared.
The fourth most important driver was the current species specificity of
the disease-causing agent (driver: D1-2). The number of pet species
susceptible to SARS-Cov-2 is not yet completely elucidated (OIE, 2020)
but according to field studies, animals such as cats, dogs, ferrets,
tigers, minks and small rodents have been identified as susceptible
(e.g. Zhang et al., 2020; Almendros, 2020; Almendros & Gascoigne, 2020;
American Veterinary Medical Association. 2020; van der Poel W., 2020).
In addition, experimental infections indicate a particular
susceptibility of bats, cats and ferrets (Sit et al., 2020; Young-Il et
al., 2020; Beer et al., 2020). The species specificity is related to the
aptitude of the coronavirus to interact with the host receptor (Li,
2012). The receptor recognition mechanism of the SARS-Cov-2 regulates,
in great part, its infectivity, pathogenesis and host range (Shang et
al., 2020). SARS-CoV-2, SARS-CoV and RaTG13 (a bat coronavirus that is
closely related to SARS-CoV-2) recognize the same receptor
angiotensin-converting enzyme 2 (ACE2) in humans (Li et al., 2003; Li et
al., 2005; Shang et al., 2020). However, some specific structural
characteristics of the receptor-binding domain (RBD) of SARS-Cov-2 spike
protein increase its ACE2-binding affinity (Shang et al., 2020).
Differences among the three cited viruses in ACE2 recognition could
contribute to explain their differential potentials for animal-to-human
transmission, which appears more limited for SARS-CoV-2 & SARS-CoV1
than for MERS-CoV, but also for human-to-human transmission (conversely
more reduced for MERS-CoV than for SARS-CoV-2 & SARS-CoV1), and
eventually for human-to-animal transmission, which is supposed to occur
for SARS-CoV2 only. With the exception of few works (Xu et al., 2009;
Bao et al., 2020), more studies are needed to investigate the ACE2
receptor in various animal species. In addition, other unknown important
factors conditioning animal-to-human and/or human-to-animal could
deserve to be characterized (McNamara et al., 2020).
The fifth most important driver was the current knowledge on the
pathogen (driver: D1-1). Scientific knowledge on the SARS-Cov2 is
limited so far because it is still under characterization, even if it
belongs to a well-known and studied family of pathogens. The pathogen
includes multiple variants that are not characterised yet. A recent
study on SARS-CoV-2 sequences (N = 95), from the first 3 months of the
pandemic, reveals a beginning of diversification and phylogenetic
clustering due to base substitutions and deletions in the genomes. This
preliminary result should permit tracing of source infection but such
variability could induce differences in virulence or antigenicity, with
possible consequence in virulence (implication on population immunity)
or antigenicity (implication on the diagnostic) (Kaden, 2020). This
variability could also contribute to a change in species barriers, which
could contribute to variants more adapted to pets and potentially to
retransmission to humans (or to reduced zoonotic potential for these
variants). More global studies are needed with good sharing of
information to ensure progress in tracing of source infection and the
development of accurate vaccines and diagnostic assays.
The methodology that was develop in this paper should be extended to a
wide number of other diseases of pets, starting from cats and dogs, the
two main species in households (FEDIAF, 2019). In addition, this expert
elicitation of knowledge should be refined in the future (some months)
when more evidence data will be available. In this case, addition of an
uncertainty rate should be recommended during elicitation.