Since the SARS-CoV-2 coronavirus began to spread worldwide, scientists have feared that it could pass from humans to wild animals. If this is the case, it can hide in different species, mutate, and resurface in humans after the pandemic. The virus can develop as it circulates among animals. This threatens the effectiveness of vaccines or makes the virus more dangerous and contagious to humans.
Coronaviridae is a family of viruses that can cause various diseases, from mild colds to deadly respiratory infections. Coronaviruses are transmitted between different animal species and humans, causing changes in cells or tissues. So there are new diseases of animals and humans.
When different virus strains simultaneously infect a single animal, new viral strains appear to infect a person. This process is called recombination. Recombination is characteristic of the human immunodeficiency virus, classical swine fever, and coronaviruses. The SARS-CoV-2 coronavirus is highly contagious to humans. When co-infected with different coronaviruses, new viruses may appear with both the infectivity of SARS-CoV-2 and the additional pathogenicity of other viruses of the Coronaviridae family.
As the virus multiplies in the body, it can mutate, leaving clues in its genome about its past journeys. Genome sequence analysis and epidemiological studies show that the SARS-CoV-2 coronavirus that causes the COVID-19 disease originated in bats and passed to humans through an intermediate carrier, probably the pangolin.
From which animals it may come?
Scientists at the University of Liverpool in the UK investigated the links between 411 known coronaviruses and 876 mammalian species and found that the number of mammalian species with more than one coronavirus is much more significant than is currently known. These mammals are potential sources of new strains of coronavirus.
The Malay palm marten (Paradoxurus hermaphroditus) is native to south and southeast Asia and is used by humans to produce Copi-Luwak coffee-a potential carrier of 32 different coronaviruses, in addition to SARS – CoV-2. Analysis of genetic evolution has shown that SARS-CoV-2 is closely related to coronaviruses derived from P.hermaphroditus and has also highlighted the palm marten’s role as a reservoir for SARS-CoV.
Horseshoe bats: Rhinolophus ferrumequinum is a known recombination carrier of SARS-CoV, Rhinolophus affinis is a recombination carrier of SARS-CoV-2. R. ferrumequinum can be a carrier of 68 different coronaviruses, including SARS-CoV-2 and R.affinis – of 45 coronaviruses.
Pangolin (Manis javanica) – the suspected intermediate carrier of SARS-CoV-2-may be the carrier of 14 different coronaviruses.
Scientists have named a wide range of species that are not yet associated with SARS-CoV-2 recombination but are predicted to be carriers of SARS-CoV-2 and other coronaviruses. Among them: the Asian yellow bat (Scotophilus kuhlii), typical in East Asia, the common hedgehog (Erinaceus europaeus), the European rabbit (Oryctolagus cuniculus) and the domestic cat (Felis catus). Previously, it was confirmed that the hedgehog and rabbit are carriers of other beta-coronaviruses that do not affect human health. However, these coronaviruses’ potential interaction with SARS-CoV-2 and the close association of the hedgehog, rabbit, and cat with humans shows that the risk of new coronaviruses among these species is underestimated.
Given their relationship to humans, other priority species for observation are the chimpanzee (Pan troglodytes) and the African green monkey (Chlorocebus aethiops). These species play an essential role in the emergence of dengue and HIV viruses.
Not only wild animals have attracted the attention of scientists. Studies have shown that SARS-CoV-2 can infect many domestic and captive animals, from cats and dogs to cougars, gorillas and snow leopards in zoos and farmed mink. Outbreaks on mink farms have shown that infected animals can transmit the virus to humans.
Coronavirus in minks
An unusual spike in mink deaths at two farms in the Netherlands alerted scientists to the first coronavirus outbreaks in April 2020. By the end of 2020, SARS-CoV-2 had reached 70 Dutch farms and farms in about a dozen other countries, including Denmark, Greece, Canada, and the United States.
Susceptible minks are kept together and regularly come into contact with infected farmers. For example, about 97% of the minks tested on one Danish farm had antibodies to SARS-CoV-2. Using genome analysis and tracking interactions between infected humans and animals, Dutch scientists have confirmed that two farm workers contracted COVID-19 from mink. It was the first evidence that animals can transmit the coronavirus to humans. To date, it is estimated that at least 60 people have contracted the virus from mink.
On October 1, 2020, researchers from the US Department of Agriculture caught a wild mink in Utah, which was found to have the SARS-CoV-2 coronavirus. Previously, no cases of infection of free-roaming animals were known. Mink sometimes run away from farms and take root in the wild. More than a dozen minks caught in the wild but likely escaped from farms with active outbreaks have tested positive for viral RNA or antibodies to SARS-CoV-2 in the US and the Netherlands.
Some countries have taken extensive measures to prevent the spread of the virus among minks. Denmark – the world’s largest producer of mink skins. The Netherlands have wiped out an entire mink population of nearly 20 million. Other countries are considering vaccinating minks.
While these cases are worrisome, viral outbreaks in domestic and farm animals can be contained through quarantine, vaccination, and culling. However, if the virus spreads among wild animals, it will be much more difficult to control.
Coronavirus in pigs
At the beginning of the pandemic, pigs were at the top of the watch list. The domestic pig (Sus scrofa) is a recombination carrier of SARS-CoV-2 and 121 other coronaviruses. Pigs live in considerable numbers close to humans – about 300 million pigs are raised in China, where the pandemic began.
In 2018, researchers described a new bat coronavirus that killed about 25,000 pigs in southern China. Moreover, in February 2020, researchers studying SARS-CoV-2 showed that it could enter pig cells through the protein ACE2 – the same receptor that the coronavirus uses to infect humans. Nevertheless, when the researchers started artificially infecting pigs and piglets with SARS-CoV-2, they found that the pigs were mainly resistant to infection with the virus.
Coronavirus in cats and dogs
As new reports of pets that have contracted COVID-19 from their sick owners have emerged, researchers have taken an increased interest in cats, which are often free to move between homes and mix in the wild.
Scientists at the University of Colorado (USA) assessed the susceptibility to coronavirus of domestic cats and dogs. Although none of the species developed a clinical disease in this study, the cats isolated the virus for 5 days and infected healthy cats through direct contact, while the dogs did not secrete the virus. Cats that were re-infected with SARS-CoV-2 developed an effective immune response and did not re-infect.
There is currently no evidence that cats or dogs play a significant role in human infection. However, the human-to-animal transmission is possible if infected owners expose their pets to the virus during an acute infection. In some of these cases, including domestic cats at the Bronx Zoo and domestic cats in New York and Europe, the animals showed signs of respiratory illness or conjunctivitis. Pathological changes in cats suggest that in healthy animals, the symptoms of COVID-19 will be minimal. Resistance to re-infection offers hope that a vaccination strategy can protect cats and, more broadly, humans.
The role of cats in the transmission of coronavirus remains an open question, but the relatively short duration of virus release and resistance to re-infection suggest that the risk of this is shallow, especially when cats are kept indoors and thus have limited contact with humans or other susceptible animals.
Infected cats secrete the virus for no more than 5 days after contact, which indicates that cats will quickly get rid of the infection when they come into contact with infected people. For comparison, the incubation period in humans is about 5 days, and the period of virus isolation is more than 3 weeks. If people with symptoms observe quarantine and stay at home with their pets, there is minimal risk of another person’s potentially infected cat becoming infected. Infected domestic cats should not be allowed to roam freely in the open air to prevent the potential risk of spreading the infection to other outdoor cats or wild animals.
Outbreaks of coronavirus in animals in different countries
The World Organization for Animal Health (OIE) monitors SARS-CoV-2 outbreaks in animals reported by individual countries. An outbreak – is one or more cases of viral RNA detected in an animal. By February 15, 2021, governments had reported 458 outbreaks.
| Region | Cats | Dogs | Minks | Ferrets | Lions | Tigres | Cougars | Snow Leopards | Gorillas |
| Africa | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 0 |
| America | 40 | 32 | 19 | 0 | 1 | 2 | 0 | 1 | 1 |
| Asia | 9 | 13 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| Europe | 16 | 2 | 317 | 1 | 2 | 1 | 0 | 0 | 0 |
| Total | 65 | 47 | 336 | 1 | 3 | 3 | 1 | 1 | 1 |
Observing domestic, farm and wild animals and knowing where SARS-CoV-2 may be lurking will help reduce the likelihood of new coronaviruses in humans and develop mitigation measures in advance.
Sources
- Predicting mammalian hosts in which novel coronaviruses can be generated
- The search for animals harbouring coronavirus — and why it matters
- Experimental infection of domestic dogs and cats with SARS-CoV-2: Pathogenesis, transmission, and response to reexposure in cats
