What are the implications of tigers being susceptible to SARS-CoV-2?

A partial answer, to the question of how the virus might spread to animals I found several references

• The HongKong dogs, the New York tiger, the Netherlands mink farm and the French cat have been sequenced and can be seen on nextstrain. Note the low amount of mutations in each case, which is intriguing because we expect for example that different ACE2 genes will induce some adaptation at in the viral spike. Those animals had an infection and detectable RNA in the nose for several days. For the dogs the viral load was low and in one case the sequence was identical to the owner. The minks and tiger had noticeable symptoms. A Wuhan cat partial sequence has been uploaded too, as well as a full-length French cat sequence.

• A lab paper said "SARS-CoV-2 replicates poorly in dogs, pigs, chickens, and ducks, but efficiently in ferrets and cats", in particular dogs can't transmit the disease efficiently. According to them subadult cats are susceptible while adult cats are not, and the disease is upper respiratory tract.

  There is a new preprint on a 4 month cat who developed severe disease, dyspnea, and had to be euthanized.

• A paper found antibodies in several Hubei cats from animal shettlers and vet clinics, some of the positive cats are "stray cats", others are sick cats, and a few were cats owned by covid positive people, in those the antibodies were found to be neutralizing the virus much better than in others.

• Another one found that ferrets are efficiently infected in lab and transmit the disease to each other, even if it is mainly upper respiratory tract (no severe pneumonia).

• Rabbits are susceptible though less than ferrets, and asymptomatic.

• Mice are not succeptible but human-ACE2 transgenic mice are and develop a mild pneumonia. Note that SARS-CoV and OC43 produced instead a deadly encephalitis.

  However, through 6 ($10^{5.8}$PFU) passages into mice lungs the researchers could adapt SARS-CoV-2 through acquisition of a single mutation in the RBD allowing the virus to produce a moderate pneumonia into both young and aged mice.

  The same researchers after 30 more passages obtained a super-deadly mouse adapted strain effective even at $10^2$PFU with 3 mutations in the RBD and 9 others mainly in nsp3-4-6 and N. Of note, two of the RBD mutations are in the South African variant N501Y.V2.

  Something similar had been done with SARS-CoV.

• The Baric lab has compared the RBD from SARS-CoV-2 and previous sarbecoviruses, the human and mouse ACE2 protein, and through computer simulations they could find two amino acids to change in order to switch the virus from humans to mice. With 10 more passages they obtained a deadly strain in aged mice.

• There are several mink farms in Netherlands where the animals got infected, this is possibly the most promising species for inter-species transmission. Edit : as predicted (first reported case) of animal to human transmission is believed to have occurred in such a mink farm. A detailed story including severe pneumonia is described in a paper.

• In lab, SARS-CoV-2 is provoking a severe disease in minks as well as in Roborovski dwarf hamsters.

• The Pangolin outbreak(s) : not SARS-CoV-2 but the newly discovered Pangolin-CoV in the same lineage, it killed 16 of 21 Malayan pangolins in March 2019. The virus was identified only in February 2020. The Pangolin-CoV whose RBD is very similar to SARS-CoV-2 was in this outbreak.

• Cats can transmit the virus to each other. In the nose the peak was $10^{4.5}$ PFU / ml which is a medium viral load.

Similar for hamsters and macaques, the latter are used for vaccine development.

Racoon dogs show high shedding and can transmit the virus through present only minor clinical signs.

This kind of result is not surprising, most human viruses can transmit to some species and not to others, often producing a different and milder disease, which is a problem for vaccines and antibodies development.