Viruses need an organism to borrow its protein-making machinery to replicate and spread. In other words, they use the tools of animals or bacteria to survive. Some viruses are specialized to infect a particular type of animal or even a bacterium. The coronavirus has been detected in different species of animals throughout the pandemic, several mammals including gorillas, cats, dogs and deer.
The more it infects, the more likely it is to mutate
All organisms mutate, due to external stimuli or failures in cellular controls. Viruses have a much higher mutation rate than other organisms because they lack some of these cellular checkpoints, which make sure they don’t misfire rounds of replication or protein manufacturing. For this reason, variants appear more frequently in viruses than in humans, who have much stricter bug control. In addition, the probability of mutation is maintained each time the virus replicates and this occurs during the infection process in the host.
The presence of the coronavirus that has caused the pandemic, SARS-CoV-2, had already been detected in deer in various regions of the United States in recent years. In the past few days, researchers have taken samples from five white-tailed deer in Ontario, Canada, and sequenced their entire genomes. The results have been published and are pending expert review, but the evidence suggests that these coronavirus samples contain 76 mutations, of which 23 had not been previously detected in deer. Some of these mutations appear to be an evolutionary response due to host characteristics.
Although the coronaviruses detected in deer have a high number of mutations, the study authors do not consider it to pose a risk to humans , based on what is known so far. However, taking into account that the more times the virus replicates, the greater the probability that new mutations will appear, it should not be ruled out that it may occur.
Variants are also found among deer
Another recent study published and yet to be reviewed has presented data on infection rates in populations of white-tailed deer in late 2021 at various points in Pennsylvania, United States. The samples were obtained in a similar way to the human detection system, with nasal swabs. Of more than 90 deer tested, 19.3% were positive for SARS-CoV-2. Whether these deer exhibited any symptoms is unknown, but samples taken from roadkill deer had a higher positive rate than deer sampled by volunteers or at veterinary clinics.
Of all the samples taken, seven of them were sequenced to determine which variant was causing the infection. The results indicate that the Alpha and Delta variants can be found in deer populations, although some of them presented different mutations from the variants detected in humans. These data suggest that the risk of the coronavirus passing from humans to animals seems to be maintained regardless of the variant.
The Alpha variant in humans has been displaced by the Delta and Omicron variants, which are currently the majority. However, in the deer population, the Alpha variant is still detected with a frequency similar to that of the Delta. There is still not enough evidence to determine if one or the other variant has a preference for a specific animal species, because its mutations present an advantage for infection. It is possible that the Omicron variant could be detected in the future in populations of white-tailed deer, or in other animal species. However, it cannot be said that these animals will present symptoms, because the mechanisms of infection in other mammals are only partially known.
These studies help us understand how the coronavirus can spread in other animal species, and this is of vital importance to analyze the risks of the appearance of new variants. The coronavirus undergoes mutations in each round of replication and if it finds a species in which it can be permanently maintained, it could accumulate different mutations than those found in variants that infect humans. Still, these new variants could remain in that animal species and not jump to humans.
Although there are still many unknowns about the mechanism of infection of the coronavirus and its global effect on this pandemic, this evidence helps to understand how it works and, in this way, to be able to take preventive measures if necessary.
References:
Marques et al. 2022. Evolutionary Trajectories of SARS-CoV-2 Alpha and Delta Variants in White-Tailed Deer in Pennsylvania. medRxiv. doi: 10.1101/2022.02.17.22270679.Pickering et al. 2022. Highly divergent white-tailed deer SARS-CoV-2 with potential deer-to-human transmission. bioRxiv. doi: 10.1101/2022.02.22.481551
