COVID: dogs are clearly better than cats

Yet another small study was done in China, this one looking at SARS-CoV-2 in different animals (see covid pets science2020 in dropbox, or doi.10.1126/science.abb7015). The issue here is that there may well be important intermediate animal sources for viral transmission to humans.

Details:
--they assessed ferrets, cats, dogs, pigs, chickens, and ducks after introducing 10⁵ plaque-forming units of SARS-CoV-2 into these animals

--for each animal group other than ferrets, they tested both the inoculated animals as well as contact animals in adjacent cages to see if they would be infected by airborne virus

Results:
--ferrets: both viral RNA and infectious virus were detected in their nasal turbinates, soft palate, and tonsils in the 4 ferrets tested

    --viral RNA was detected in nasal washes for up to 8 days post-inoculation, but negative at day 10; rectal swabs had lower viral loads than the nasal swab, and no infectious virus was found in the rectal swabs.

    --one ferret became symptomatic with fever/loss of appetite

--cats: inoculated cats had viral RNA in their nasal turbinates, soft palates, tonsils, tracheas, lungs and small intestines, with infectious virus in all of these sites other than the feces

    --non-inoculated cats in an adjacent cage had viral RNA detected in their nasal turbinates, soft palate, tonsils, trachea, and feces, indicating droplet transmission

    --and SARS-CoV-2 antibodies were detected in all of the virus-inoculated cats as well as an exposed cat

    --both juvenile and sub-adult cats had similar findings

--dogs:  five 3-month old beagles were inoculated intranasally

    --oropharyneal and rectal swabs found viral RNA only in the rectal swab in 2 dogs: one on day 2 post-inoculation, and one on day 6. viral RNA was not detected in any organs/tissues. and none of the samples had demonstrable infectious virus. 2 of the 4 dogs did develop antibodies

    --2 contact dogs (not inoculated) were free of viral RNA by swabs and were seronegative for SARS-CoV-2 

--pigs, chickens, and ducks: no viral RNA detected in any swabs in those inoculated with virus 

--so, their summary: ferrrets and cats are highly susceptible to SARS-CoV-2, dogs have low susceptibility, and pigs/chickens/ducks are not susceptible

Commentary:

-- this actually is a real issue: we do have some understanding that the many coronaviruses (including our current one) were from bats, and even pretty long-standing data shows that bats harbor 30+ strains of coronavirus and that about 10 of them have the same potential pandemic effect as our current SARS-CoV-2 [ie, as was noted with SARS-CoA and again with MERS-CoA: for future pandemics, it was a matter of "when" and not "if"; revealing the blatant inadequacy of our preparedness for this pandemic....]

--but there may well be intermediary nonhuman animal sources of the virus, and these may be important mediators of human transmission. sources postulated over the past few months included ferrets and pangolins.

--this study suggests that ferrets and cats are real potential sources (they did not test the pangolins in this study, though prior reports suggested them as well: https://www.ncbi.nlm.nih.gov/pubmed/32197085 )

--and, most importantly, ferrets and cats (as opposed to pangolins) are pretty common household pets.

--ferrets often get human respiratory viruses and often serve as a humanoid model for these viruses.

--in this case the ferrets had virus localized to the upper respiratory tract for up to 8 days without causing severe disease or death (ie, they had potentially transmissable virus to humans)

--but cats up the ante alot here, given their frequent petdom (i should add that the somewhat less commonly household feline, a Bengal Tiger, was recently found to have symptomatic COVID-19 in the Bronx zoo: eg see https://newsroom.wcs.org/News-Releases/articleType/ArticleView/articleId/14010/A-Tiger-at-Bronx-Zoo-Tests-Positive-for-COVID-19-The-Tiger-and-the-Zoos-Other-Cats-Are-Doing-Well-at-This-Time.aspx )

--as mentioned in prior blogs, there are limitations to the test done: the RT-PCR test can be positive with dead virus; the assays of "infectious" virus are lab assays and may not correlate with human infectivity. But the above small study is very concerning

so, what does this mean?

-- this may be an important study, perhaps especially so in the US where there are lots of pets. and knowing that cats especially (and potentially dogs) might be able to be infected and transmit the SARS-CoV-2 virus may be very important information in terms of ending continued viral transmission.

-- even indoor cats who are exposed to Covid-19 positive people might be able to transmit the virus to uninfected people (who then infect more people, and the beat goes on). And it is probably difficult to get a cat to do social distancing through logical discussion (dogs, on the other hand...)

-- if and when we have sufficient testing kits, it might be a reasonable strategy to test pet animals (esp cats or ferrets) for the virus and enforce isolation if positive

-- in the meantime, it probably makes sense to isolate cats exposed to COVID-positive people for at least the 8-10 days after exposure (though this is a difficult goal to fully implement since we have essentially no data on people who are asymptomatic or mildly symptomatic, when human viral loads may be the highest)

just another potential twist in the unfolding story..... 

geoff​

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