COVID: human transmission from minks

 The Danish government is planning to kill about 15 million minks in >1000 mink farms because of their transmission of a mutated SARS-CoV-2 virus to humans (see covid mink to human transmission biorxiv2020in dropbox, or doi.org/10.1101/2020.09.01.277152.).This story was reported in the NY Times: https://www.nytimes.com/2020/11/04/health/covid-mink-mutation.html , though the relevant medical article is in pre-print and pre-peer reviewed form. [though the formal article was just printed in Science (see covid mink to human transmission science2020 in dropbox, or DOI: 10.1126/science.abe5901 ). to my perusal, does not seem that the final publication was significantly different from the pre-print text, though is shorter.]

 

Details: 

-- initial detection of SARS-CoV-2 in mink was on April 23 in 2 mink farms, associated with respiratory signs and increased mink mortality (though minks can also have asymptomatic infections) 

-- on May 7, two other mink farms in the same region had infected minks

-- by the end of May the Dutch Minister of agriculture decided that all minks in infected farms had to be culled (a euphemism for a very high short-term mortality...)

-- the current report has data until June 26, when a total of 16 mink farms were found to have minks positive for SARS-CoV-2 

-- backward and forward tracing of possible high-risk human contacts to the farms was done 

 

Results: 

-- 97 potential human contacts were tested: 

    -- 43 out of 88 (49%) of upper respiratory tract samples were positive by PCR 

    -- 38 out of 75 (51%) of serum samples tested positive for SARS-CoV-2 antibodies 

    -- overall total of 66 out of 97 (67%) had evidence of SARS-CoV-2 infection 

-- the overall SARS-CoV-2 positivity rate for employees and family members in the 16 targeted farms range from 0% to 100% for PCR (mean of 49%), and 0-100% by serology (mean of 51%) 

-- overall positivity rates for employees and family members with PCR and/or serology had a mean positivity of 68% [sounds like a superspreading event...]

 

Zoonotic transmission: 

-- April 28: 4 out of 5 employees in the 1^st farm reported they had respiratory symptoms before the outbreak was detected in minks, but none had been tested for SARS-CoV-2

-- one employee on the 2^nd farm was diagnosed on March 31, when hospitalized with Covid-19 

-- the virus sequence from animals in the 2^nd farm was distinct from on the 1^st farm, indicating a separate introduction of the virus

-- May 7: on the 3^rd farm, minks were found to have SARS-CoV-2 (with the same strain is in the 1^st farm), workers were tested on May 19 and were negative by PCR. but on May 26 they developed Covid-related symptoms [the time sequence suggesting transmission from animals to humans was highly likely]

-- on the 7^th farm, there was a similar sequence of likely mink to human transmission 

-- comparing the phylogenetic sequences from those people who were infected on the mink farms as compared to those of people living in close proximity, the genetics were significantly different. However, the phylogenetics from the mink farm employees/close contacts were near identical to the sequences in the minks at the same farms 

-- in terms of the clustering of phylogenetic SARS-CoV-2 profiles, there were clearly some relationships between farms that had the same owner and having the same viral phylogenetic sequences in the minks , but most of these clusterings could not be explained by looking at farm owners, shared personnel, feed suppliers, etc. 

 

 Commentary: 

-- this virus is highly likely introduced to minks from humans, then circulated widely in mink farms 

-- this study then provides quite clear documentation of the first animal to human SARS-CoV-2 transmission 

-- there was high genetic diversity from some of the mink farms, perhaps suggesting that there were many generations of infected animals prior to the increase in animal mortality. Alternatively, this high sequence diversity in minks found in farms that tested negative one week beforehand suggests that the virus might replicate more efficiently in mink, may be more susceptible to viable mutations, or may make the virus more virulent. 

    --Of course, the high density of animals in these farms would lead to quite high viral dose exposures, and this might accelerate the spread of the virus

-- overall the number of SARS-CoV-2 infected individuals in the Netherlands was decreasing at that time this mink-related outbreak occurred 

-- there have been more than 15 million minks in Denmark scheduled for their untimely death. 

 

-- it is clear that SARS-CoV-2 can infect nonhuman primates, dogs, cats, ferrets, hamsters, rabbits, and bats. 

    -- There is good experimental data that cats can infect other cats, not so clear with dogs: see http://gmodestmedblogs.blogspot.com/2020/04/covid-dogs-are-clearly-better-than-cats.html . There is experimental evidence that tree shrews, hamsters, and ferrets could also potentially transmit the virus 

 

So, what does this all mean? 

-- animals could be significant vectors for continuing Covid infections, both in themselves and in humans 

-- there is the potential that mutations occurring in animals that then bounce back to humans could potentially undercut the effectiveness of a vaccine or from prior immunity from a prior Covid-19 infection, or even create a more virulent virus (none of this has been found so far, but....)

    --and, this is somewhat more likely given the apparent accelerated rate of mutations in the mink

the presence of SARS-CoV-2 in animals can serve as a continuing reservoir of virus for reinfecting the human population

-- having the huge number of ongoing human infections that we have now is likely to increase this human to animal and back to human transmission cycle 

    -- which all really reinforces the importance of decreasing ongoing infections in humans to the extent possible, including reinforcing social distancing, mask use, etc. as well as contact tracing and isolation of Covid positive people. These are effective interventions when applied systematically, and need to be adopted internationally  (and, in the US, consistently across state lines)

        -- for example, a second covid-19 wave in Beijing occurred after 56 days of zero infections: initially 2 cases, aggressive contact tracing leading to 335 confirmed positives (10% asymptomatic/28% presymptomatic), isolation of infected people, and complete elimination of the virus within 3-4 weeks (see http://gmodestmedblogs.blogspot.com/2020/09/covid-second-wave-in-china-aggressively.html ). 

    -- so, covid-19 infections can be controlled with a strong, enforced, systematic approach, one far different from what is happening in the US as we now have 130K infections/day, >10 million cases so far, 238K deaths and a current all-time high in hospitalizations.... And, El Paso is bringing in more new mobile morgues (per today's NY Times)

-- i really don't mean to be too inflammatory, but i have not seen sufficient data assessing specifically the domestic cat to human transmission. are we going to get to the point where pet cats need to be "culled" in order to control the virus?? or pet ferrets??  we certainly know that bats can transmit the virus. and now minks. so, it is certainly conceivable that cats could do it as well.

    -- hopefully, a new vaccine will work well and really help propel us out of this current devastating pandemic. and, assuming the advanced mRNA vaccine headlines are accurate and appropriate, the 90% efficacy touted suggests it works really well (even if there are culprit cats).  hopefully we will be able to see the study/data soon to assess the vaccine study..... 

geoff

 

If you would like to be on the regular email list for upcoming blogs, please contact me at gmodest@uphams.org

to get access to all of the blogs:

1. go to http://gmodestmedblogs.blogspot.com/ to see them in reverse chronological order

2. click on 3 parallel lines top left, if you want to see blogs by category, then click on "labels" and choose a category​

3. or you can just click on the magnifying glass on top right, then  type in a name in the search box and get all the blogs with that name in them

 

please feel free to circulate this to others. also, if you send me their emails, i can add them to the list