Since the 2019 novel coronavirus (SARS-CoV-2) pandemic, in addition to paying attention to cases of human infection, the scientific community has gradually discovered that many animals may also be infected with the virus. The phenomenon of animals and humans sharing viruses is called " zoonotic spillover ", and the new coronavirus is a typical example. Knowing which animals can be infected with the new coronavirus is not only crucial to public health, but also helps to more fully understand the virus's transmission mechanism and its potential hosts in nature.

This article will conduct an in-depth analysis of the infection of the new coronavirus on different animal species and explore the related risks and impacts.

1. The origin and cross-species transmission of the new coronavirus

1. Origin of the novel coronavirus

The new coronavirus is a coronavirus that belongs to the same family of viruses as the SARS (Severe Acute Respiratory Syndrome) virus that broke out in 2002 and the MERS (Middle East Respiratory Syndrome) virus that broke out in 2012. Coronaviruses are widely present in nature, especially in wild animals such as bats. Studies have shown that the new coronavirus is likely to have originated from bats and then passed to humans through some intermediate host (such as pangolins or other wild animals).

2. Mechanisms of cross-species transmission

The cross-species transmission of the new coronavirus is related to the spike protein on the surface of the virus . The spike protein binds to the receptor on the surface of the host cell, thereby entering the cell and starting to replicate. For the new coronavirus, the main receptor is angiotensin-converting enzyme 2 (ACE2). The ACE2 receptor structure of many animals is similar to that of humans, which allows the virus to spread across species and infect different animal species.

2. Which animals can be infected with the new coronavirus?

As the COVID-19 pandemic continues, more and more studies are revealing the wide range of animals that the virus infects. The following are some of the animal categories that have been confirmed to be infected with the new coronavirus:

1. Cats

1.1 Domestic cat

Domestic cats (Felis catus) were one of the first animals confirmed to be infected with the new coronavirus. In the early days of the pandemic, several domestic cats from homes or pet hospitals were tested positive for the new coronavirus. Studies have shown that domestic cats can be infected with the virus through droplet transmission, and even cats can infect each other under some experimental conditions.

When a domestic cat is infected, it usually presents with mild respiratory symptoms, such as coughing and sneezing, but in most cases it does not develop into a serious illness. Nevertheless, domestic cats may act as an intermediate host for the virus and spread the virus in the home, so humans need to maintain certain hygiene habits when in contact with pets, especially if there is an infected person at home.

1.2 Tigers and Lions

At the beginning of the COVID-19 pandemic, several tigers and lions at the Bronx Zoo in New York City were tested positive for the coronavirus. The animals showed symptoms similar to respiratory illness, such as coughing and shortness of breath. Scientists believe that the big cats contracted the virus through contact with infected people or airborne transmission.

The ACE2 receptors of cats are very similar to those of humans, which explains why lions, tigers and domestic cats can be infected with the new coronavirus. Although the symptoms of these animals are relatively mild, their infection has raised concerns about the health of animals in places such as wildlife parks and animal sanctuaries.

2. Canines

2.1 Dog

Although dogs can be infected with the new coronavirus, they do not seem to be as susceptible to infection as cats. In some families, domestic pet dogs have been tested positive for the new coronavirus, but they usually have no obvious symptoms or very mild symptoms. Studies have found that the structure of dogs' ACE2 receptors is different from that of humans, which may make them less sensitive to the virus.

Nevertheless, dogs may still serve as transient hosts for the virus, so pet owners should take appropriate measures during the outbreak, such as limiting their dogs' contact with the outside world and maintaining good hygiene habits.

3. Mink and mink

3.1 Outbreaks on mink farms

Minks (Mustela lutreola) were one of the animals that were first infected during the COVID-19 pandemic. Mink farms in several countries have experienced COVID-19 outbreaks, with tens of thousands of minks infected. Some minks showed severe respiratory symptoms, and even suffered large numbers of deaths.

It is particularly noteworthy that minks can not only be infected with the new coronavirus, but can also transmit the virus back to humans. In countries such as Denmark and the Netherlands, virus transmission between minks and humans has been recorded. This phenomenon has aroused widespread concern, and many countries have taken measures, including large-scale culling of farmed minks, to prevent further spread of the virus.

3.2 Infection risk in mustelids

Close relatives of minks, such as the domesticated ferret (Mustela putorius furo), have also been shown to be very susceptible to the new coronavirus. Ferrets are used to study the spread of the new coronavirus and vaccine development under laboratory conditions because they have many similarities with the structure of the human respiratory system.

4. Rodents

4.1 Hamster

Hamsters (Mesocricetus auratus) are very sensitive animals to COVID-19 infection. In the laboratory, hamsters are widely used in COVID-19 research because they can show mild to moderate infection symptoms similar to humans, such as weight loss and lung lesions. Through the hamster model, scientists can better study the transmission mechanism of the virus, the effectiveness of vaccines, and potential treatments.

4.2 Other rodents

In addition to hamsters, other rodents, such as rats and mice, can also be infected under certain experimental conditions. However, their symptoms are usually mild, and in the natural environment, there are relatively few cases of rodents being infected with the new coronavirus.

5. Primates

5.1 Macaques and other experimental primates

In the study of the new coronavirus, macaques (Macaca mulatta) and other primates have been widely used for virus transmission and vaccine testing. Because primates are highly similar to humans in genetic and physiological structure, they have become important experimental models.

After being infected with the new coronavirus, macaques show symptoms similar to those of humans, including fever, lung inflammation, etc. Through these experimental models, scientists can better understand how the virus affects the human body and test the effectiveness of new vaccines and drugs.

6. Deer

6.1 White-tailed Deer

In 2021, American researchers discovered COVID-19 infection in white-tailed deer (Odocoileus virginianus) in the wild. Investigations showed that these wild deer may have been infected with the virus through contact with humans or infected animals. The discovery of white-tailed deer infected with COVID-19 has sparked discussions about the potential role of wild animals in the virus transmission chain.

White-tailed deer do not usually show severe symptoms after infection, but they may act as a "reservoir" to retain the virus in the wild, increasing the risk of the virus spreading again to humans or other animals. This discovery prompted researchers to further study the role of wildlife in the COVID-19 pandemic and how to control this potential transmission route.

7. Bats: Potential Original Host

Although bats have not been identified as hosts that directly infect humans, they are believed to be the original source of the new coronavirus. Bats carry a variety of coronaviruses, and their immune systems are able to coexist with these viruses, making them an important virus reservoir in nature.

Studies have found that coronaviruses, which are close relatives of the new coronavirus, have existed in some bat species for thousands of years, but bats themselves do not show serious symptoms of the disease. Although there is currently no evidence that bats directly transmitted the new coronavirus to humans, they may have indirectly caused the cross-species transmission of the virus through some intermediate host (such as pangolins).

3. Risks and impacts of animal infection with COVID-19

1. Potential threats to human health from animal infections

Although most cases of animals being infected with the coronavirus are relatively rare, these cross-species transmissions still attract great attention from scientists. In particular, the phenomenon of viruses being transmitted from animals back to humans has been found in animals such as minks, which shows that cross-species transmission is not just one-way. Viruses may mutate in animals to form new strains, which have the potential to reinfect humans and even render existing vaccines and treatments ineffective.

2. Wildlife protection and epidemic prevention

As more and more wild animals are found to be infected with the new coronavirus, the contact between human activities and wild animals has become an important public health issue. During the epidemic, how to protect wild animals while reducing the risk of virus transmission has become an important topic in the field of biological conservation and public health.

3. The importance of animal experimental models in COVID-19 research

During the outbreak, experimental animals played a key role in the study of the new coronavirus. Animal models such as hamsters and macaques not only help us better understand the transmission mechanism of the virus, but also accelerate the development of vaccines and drugs. However, animal experiments are also accompanied by ethical controversies, and scientists are actively looking for more humane and effective alternatives.

IV. Conclusion

The cross-species transmission of the novel coronavirus shows that animals are not only potential hosts of the virus, but may also become vectors of virus transmission. In the process of epidemic prevention and control, the interaction between humans and animals needs to be more cautious, especially in the management of domestic pets, wildlife protection, and farms.

Understanding which animals can be infected with the new coronavirus can help us better prevent the spread of the virus and reduce the risk of cross-species transmission. Research in this field is still ongoing. As scientists explore the new coronavirus in depth, more animals may be found to be at risk of infection in the future, which will further affect the global epidemic prevention and control strategy.

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