In Phoenix Park in Dublin, Ireland, a species of deer draws the attention of thousands of visitors every week. However, these tourists who pet the animal may have given it more than food since it was recognized as the first deer in Europe to have acquired the COVID-19 virus. Experts believe that the infection is likely due to human contact.
Viral Transmission from Human Carriers
Scientists discovered that the blood of the fallow deer (Dama dama) contains antibodies to SARS-CoV02, the virus that causes the COVID-19 infection. Although this event has no apparent risk to humans, veterinary microbiologist Eman Anis from the University of Pennsylvania reminded us not to allow viruses to enter the wildlife.
A similar case happened in North America when the coronavirus was reported to have spread among white-tailed deer (Odocoileus virginianus) since 2021. There are also documented cases of human-to-deer, deer-to-deer, and deer-to-human viral transmissions.
What troubles scientists is that groups of wild animals spread viruses among themselves and allow the microorganisms to persist and mutate. As a result, they can potentially transmit a more dangerous strain of the pathogen into humans or other organisms.
To further investigate this risk, veterinary virologist Nicola Fletcher from the University College Dublin has monitored the presence of the SARS-CoV-2 virus in the deer in Phoenix Park since 2020. Since this is the largest urban park in Europe, it usually accommodates about 10 million visitors annually. Although the park staff always tries to keep them at least 45 meters away from tourists, these animals have developed the habit of begging for food.
In late 2020, none of the herds were positive for the virus, but in February 2022, over half of the blood tests conducted on 21 deer revealed the presence of SARS-CoV-2 antibodies. This suggests that most of the overall herd, now about 600 deer, has been exposed to the coronavirus.
This finding is considered the most powerful evidence so far that the virus could become established in the population of European deer, as confirmed by wildlife disease ecologist Erick Gagne. There is still no proof that deer-to-deer virus transmission is happening in the deer herd in Phoenix Park. It is also impossible to monitor the source of the virus just by studying the antibodies alone.
How Does an Animal Become a Reservoir Host?
In April 2020, a four-year-old Malayan tiger named Nadia from New York's Bronx Zoo became one of the first animals known to have acquired the COVID-19 virus from a human. As of May 2022, there are 36 countries across all continents to report cases of coronavirus infection in nonhuman animal species officially.
Interspecies transmission of the virus can develop new animal reservoirs, which give the pathogens a higher chance to multiply or persist for a more extended period. It gives the pathogen a higher chance to be transmitted back to human hosts. The tendency of viruses to jump between species, known as spillover events, is a complicated process, but it plays a significant role in ending the COVID-19 pandemic.
While jumping across species barriers, the virus also adapts to different hosts, leading to mutations that can alter its transmissibility, behavior, and resistance to vaccines. This gives rise to a new variant of coronavirus that looks a lot different and can spread fast.
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