Page 106 - JSOM Fall 2020

clinical features, and risk factors for infection were not com- only one case that suggests canines are at risk of developing
pletely known at the start of the outbreak. Although many clinical disease. In that case, however, it remains unknown
great strides have been made in identifying key factors regard- if another disease or condition led to the dog’s clinical signs.
ing viral transmission, many urgent questions and concerns There are no data or evidence to suggest an infected canine
still remain. One of the most important is whether the widely plays any role in the spread of the virus to other animals or
disseminated COVID-19 virus is transmissible to other animal to people.
species, which can then serve as reservoirs of infection and
vectors of disease. Fewer than 25 cases have been reported Another important, yet unanswered question is what role, if
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worldwide of domestic animals (i.e., dogs and cats), large cats, any, do dogs play as a potential fomite (i.e., and object capable
and minks becoming infected with SARS-CoV-2. The over- of harboring an infectious pathogen) for spreading the virus
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whelming similarities between all of the cases were that symp- to people? This is not a simple question to answer, rather, this
toms were often mild, if present, and most had exposure from one question opens up a series of questions, such as:
a confirmed positive caretaker. In China, Sit et al. reported
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that of the 15 dogs their group quarantined after COVID-19 1. What is the probability that a dog’s hair coat can become
developed in their owners, only two tested positive for SARS- contaminated with the virus if an infected person touches,
CoV-2. In the United States, as of this writing, one dog has hugs, sneezes, or coughs on or near the dog?
been confirmed positive for SARS-CoV-2. These are the only
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three dogs officially confirmed by a recognized diagnostic lab- and/or
oratory to test positive for SARS-CoV-2. A few noteworthy 2. Can a dog “pick up” the virus on its hair coat or paws
points regarding the first two dogs are: simply by walking around and working in an area densely
populated with COVID-19–positive people (e.g., New
• the viral genetic sequences from both dogs were identi- York City)?
cal to the virus detected in the respective human cases,
and so provide support for human-to-K9 transmission; If so, then:
• although both dogs developed immunological response • How readily is that virus able to transfer to the next
(antibodies), neither developed clinical signs consistent uninfected person who touches the dog?
with COVID19 during the time of viral shedding; and • Does the amount of virus transferred onto the dog (if
• other pets in household in close contact lacked symp- that is even possible) even equate to a high enough viral
toms and tested negative for SARS-CoV-2. load to be of any risk to a person?
• How long does the virus survive on the dog’s hair coat?
To date, there remains a significant lack of information re- • If a fomite exposure risk is possible, how long can
garding specific details of the US confirmed case. Despite the subsequent dog-to-human interactions remain a risk,
confirmed dog being infected with SARS-CoV-2 and displaying knowing that, over time, the viral load on the hair coat
symptoms of a respiratory disease, another dog in the same will progressively decline?
home never displayed symptoms, although it tested positive for
antibodies, indicating an exposure. It still remains unknown SARS-CoV-2 is primarily transmitted person to person, via
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whether the clinical disease is caused by SARS-CoV-2 or an- contact with an infected person’s respiratory droplets (e.g.,
other disease of condition. Experimentally, Shi et al. investi- saliva, mucus droplets in a cough or sneeze) and/or by being
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gated the replication and transmission of SARS-CoV-2 in dogs in immediate proximity to an infected person (e.g., within 6
by housing virus-inoculated dogs with uninoculated dogs. They feet). Although transmission via fomites (i.e., touching a con-
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found that neither of the two uninoculated dogs developed an taminated surface or object and then touching your mouth,
immunological response. Based on their findings, the investi- nose, and/or eyes) is considered a possible secondary exposure
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gators concluded that dogs have a low susceptibility to SARS- for people, this route is not thought to be the main route by
CoV-2, which was the same conclusion suggested by Larkin. 10 which the virus spreads. van Doremalen et al. concluded that
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aerosol and fomite transmission of SARS-CoV-2 are plausible
What Seems to Make Dogs Less Susceptible because the virus can remain viable and potentially infectious
to the Virus Compared With Humans, Cats, in aerosols for hours and on surfaces up to days (depending
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Ferrets, and Minks? on the inoculum shed). Guo et al. conducted a study that
tested for SARS-CoV-2 on various surfaces and in air sam-
Current data and molecular modeling indicate that effective ples collected from an intensive care unit (ICU) and a general
binding of the virus to the host receptor, angiotensin-convert- COVID-19 ward at a hospital in Wuhan, China. The results
ing enzyme-2 (ACE2) protein, is the first prerequisite for infec- of the study revealed a high rate of positivity for floor swab
tion of cells required for viral replication and amplification in samples, positive test results on the soles of half of ICU med-
a permissive host. Zhai et al. recently demonstrated that dogs ical staff shoes, and a high rate of positivity for the surface
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express very little ACE2 protein in their respiratory tract (na- of the objects that were frequently touched by medical staff
sal turbinates); thus, these findings provide a valid explanation or patients (computer mice > trash cans > sickbed handrails
for the dogs low susceptibility for SARS-CoV-2, lack of sus- > doorknobs). A couple of implied conclusions from their
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ceptibility to clinical disease, and support for the notion that study include: (1) a potentially high exposure risk exists for
dogs play little to no role in transmission of SARS-CoV-2. 8 medical staff and other close contacts working in locations
that house a dense population of patients with COVID-19,
and (2) recovery of virus from the environment does not nec-
Bottom Line Up Front
essarily reflect the potential to pick up the virus from the en-
Although it appears K9s may become infected with SARS- vironment simply through casual contact (i.e., virus detected
CoV-2 and produce antibodies to the virus, to date, there is does not equate to infection risk).

104 | JSOM Volume 20, Edition 3 / Fall 2020