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Animal infection sets the stage for an independent evolution of SARS-CoV-2 which, after an extended evolutionary period, can jump back to humans causing disease with an unpredictable infectivity and case fatality rate.
In Hong Kong, many young children received lovable hamsters over the winter holidays to keep them company, only to have them taken away to be culled to stop a potential COVID-19 outbreak. A disastrous winter holiday for all involved.
The hamster outbreak is just one of a string of recent reports refocusing the public’s attention on the risks COVID-19 poses to animals. What all are agreed upon is a wide variety of animals can become infected with SARS-CoV-2. Epidemiologically, there are three groups of animals. The first are domesticated household pets, the second are farm and zoo animals, and the third are animals in the wild.
Household Pets: There is much attention regarding the safety of household pets. These animals are in close contact with humans, many times jumping on one’s lap and licking faces. The Centers for Disease Control and Prevention has advised that “there is no
evidence that animals play a significant role in spreading SARS-CoV-2 (the virus that causes COVID-19) to people.” However, transmission from humans to household pets, especially cats, can occur. The reason for the one-way transmission may be based in part that the animal is part of a family unit and often has reduced contact with others. It is the human caregivers who bring the virus into the family unit. In other words, if an infected pet were to come in close contact with an uninfected human, I would not be surprised if transmission occurred.
Hamsters have even less contact with the outside world and are kept in cages, but they are often hugged and held up to the face of children. In Hong Kong, over 2000 hamsters arrived from the Netherlands, 11 were infected with SARS-CoV-2. One may have infected a pet shop worker. Now all are sentenced to death in a country with a zero tolerance for SARS-CoV-2. The clinical course and incubation period for SARS-CoV-2 in hamsters is not known and could be long.
The spread of Omicron in hamsters is to be expected. There are 7 genes responsible for transmission of coronaviruses in rodents and all 7 are found in the Omicron variant. The exact origin of Omicron is unknown, but the presence of genes promoting transmissibility in rodents have many speculating the variant arose independently in an animal host, and a few conspiracy theorists believe that it arose in a lab.
Owners frequently pass COVID-19 to their pets, especially to cats who sleep with them. Of household pets, 67% of cats and 43% of dogs were positive for SARS-CoV-2 antibodies. Only 3% of stray cats and 9% of stray dogs were positive, exemplifying that the animals who reside in family units are most at risk for COVID-19 and they are usually infected by their owners. Twenty-seven percent of 48 infected cats had symptoms, three were severe, 20% of 54 infected dogs had symptoms, all were mild. One of the study’s authors, Dorothee Bienzle, PhD, stated that “there was a surprisingly high chance [pet owners] will pass [SARS-CoV-2] to their pets” and she could not exclude transmission of the virus back to people.
Farm Animals and Zoos: In the Fall of 2020, an outbreak of COVID-19 in minks caused Denmark to cull an estimated 17 million animals to prevent spread. There is “strong evidence that at least two people on those farms were infected by minks,” and at least 214 individuals have tested positive for the mink coronavirus. SARS-CoV-2 has also infected a variety of zoo animals, with the deaths of three snow leopards in the Lincoln, Nebraska zoo. Last summer, zoos started administering an experimental vaccine to large animals including bears, baboons, gorillas, and tigers.
Free-Range Animals: There have also been a number of reports regarding COVID-19 in white tail deer. On January 12, 2021, the first outbreak was reported in Ontario, Canada, with three “hunter-harvested” free-ranging deer having a positive PCR test for SARS-CoV-2. Later in the year, the USDA, in an article published in the Proceedings of the National Academy of Sciences, found that 40% of 385 specimens taken from deer in the states of Michigan, Illinois, Pennsylvania and New York were positive for SARS-CoV-2 antibodies. This was followed by a report from Iowa which found 82.5% of white tail deer had detectable SARS-CoV-2 RNA by PCR testing which was performed between November 23, 2020 and January 20, 2021.
After the review of these extensive reports, it is apparent that SARS-CoV-2 can live in a variety of different animals and can then reinfect humans in at least a few cases. This sets the stage for an independent evolution of SARS-CoV-2 which, after an extended evolutionary period, can jump back to humans causing disease with an unpredictable infectivity and case fatality rate. This is what appears to have happened with the Omicron variant. In other words, we all need to start taking this virus more seriously and uniformly enact effective control measures, since SARS-CoV-2 appears to no longer need humans for its survival.