Zoonotic perspectives of Covid-19

We have seen the emergence of zoonotic coronavirus infections in the 21st century, such as those caused by severe acute respiratory syndrome CoV (SARS-CoV) from China in 2003, Middle East respiratory syndrome CoV (MERS-CoV) from Saudi Arabia in 2012, and SARS-CoV-2 (COVID-19 pandemic) that is continuously inflicting pain and melancholy all across the globe. This malicious corona virus (SARS-COV-2) has just surfaced as a new threat to humanity, creating the Covid 19 pandemic, which has currently troubled millions and killed thousands of people in over 220 nations and territories globally. Although SARS-CoV-2 is less pathogenic than previous outbreaks like SARS-CoV and MERS-CoV, it is very contagious and spreads fast because its reproduction number (Ro-value) is about 2.6, allowing the transmission channels to infect a significant number of individuals. These viruses can infect humans because of their wide host range, persistence in animal hosts, environmental contamination, transmission potential, and affinity for human receptors, which is helped by greater mutation rates. SARS caused by SARS-CoV was originally detected in China’s Guangdong Province and was transmitted to people by civet cats from bats. MERS caused by MERS-CoV was initially detected in Saudi Arabia, and it was spread from bats to people via dromedary camels. The latest COVID-19 caused by SARS-CoV-2 started in Wuhan, China, and it is thought to have been transferred from bats to people via an unidentified intermediate animal host, with snakes or pangolins being of primary interest. Also, early epidemiological research has shown a possible connection to animal-human transmission and it has been reported that SARS-CoV-2 and CoVs isolated from bats are also related, according to genomic and phylogenetic studies.

Corona viruses may be passed from one animal species to another and are well-known for their ability to leap across species.

CoVs require two types of animal hosts for transmission: the reservoir host, which harbours the initial CoVs and is considered to be the source of infection, and the intermediate host, which transmits CoVs from animals to people. Bats are considered as reservoir of these viruses and they transmit the virus to humans through intermediate animal hosts without becoming infected because of their frequent exposure to such infections, their less complex immune response against CoVs compared to that of humans, and the development of natural immunity. Chinese horseshoe bat, Pearson’s horseshoe bat, and big-eared horseshoe are among the bats known to be a source of CoVs. Besides bats, cattle, horses, camels, swine, dogs, cats, chicken, birds, rabbits, rodents, ferrets, mink, turtles, snakes, frogs, marmots, hedgehogs, Malayan pangolin, and some wild animals act as the potential reservoir for these viruses. The intermediate host for SARS-CoV-2 has yet to be identified; nevertheless, a number of animal species are being considered as possible intermediate hosts for SARS-CoV-2, although without solid proof. Though the intermediate host for SARS-CoV-2 is unknown, pangolins and snakes are suspected as the intermediate hosts because the initial cases of COVID-19 had links to the Wuhan wet animal market where these animals were being sold; however, exploratory studies are required to reach a conclusive hypothesis. Based on the genomic and evolutionary analysis of its genome, Pangolin-CoV was found to be identical to the SARS-CoV-2 and BatCoV RaTG13. SARS-CoV-2 has been found in cats, dogs, tigers, and lions, as well as experimental animal models such as African green monkeys, cynomolgus monkeys, rhesus macaques, new world monkeys, transgenic mouse models, Chinese hamsters, Syrian hamsters, ferrets, and others. SARS-CoV-2 was also discovered in a Malayan tiger at New York City’s Bronx Zoo. The virus is thought to have been spread by a zookeeper who was asymptomatic for COVID-19, and the tiger exhibited respiratory symptoms and tested positive for SARS-CoV-2. SARS-CoV-2 infection was also recorded in minks with rapid transmission and large-scale mortality in the mink farms. The virus is thought to have spread by fomites, infectious droplets, or faecal matter dust laden with infectious virus. The fast spread of SARS-CoV-2 in mink farms contributed to the development of a mink-associated variation, which was later transmitted to humans. The inhalable dust collected from the farm premises tested positive for SARS-CoV-2 RNA, indicating the presence of an infectious virus that might enable indirect transmission from mink to human/or other animals.

Human expansion into forests and commercialization of wild animals are the two major factors that allow and enhance adequate conditions for illnesses to pass the species barrier in the case of wild animal to human transmission. Furthermore, as there is a greater demand for wildlife meat, wild animals are being commodified for meat, particularly in tropical and subtropical areas. These activities have created an animal-human interface, which can aid in the transmission of zoonotic CoVs across species barriers.

Prevention and control

Avoiding contact with wild animals is one of the most essential and apparent strategies for preventing and controlling CoV zoonotic transmission. Vaccines (such as inactivated vaccinations, mRNA, protein subunit, non-replicating viral vector, or virus-like particle-based vaccines) have recently emerged and may be useful in prevention and management. However, until the prophylactics are successful, current preventative and control methods like as social distancing, sanitization, wearing of personal protective equipment, respiratory etiquettes, and frequent testing, as well as isolation/quarantine of sick, are required. As the most important emerging human CoVs have originated from bats, eating bats and selling them in live animal markets should be prohibited in order to avoid the zoonotic transfer of any novel CoVs from bats to humans. The CoVs carried by bats must be investigated and monitored using a routine and advanced ecological surveillance system. Bats should not be permitted in close proximity to agricultural livestock. Deforestation and human encroachment on forests should be reduced or eliminated, as this may result in bats migrating into neighbouring human houses. The trade of wild animals as exotic pets or utilizing them in Chinese traditional medicine must be entirely prohibited. Pet owners all around the globe should adopt preventative steps instead of waiting for more conclusive proof of animal-to-human transfer, and felids should be maintained under disease monitoring. Because SARS-CoV-2 emerges at the animal-human interface, one health strategy must be prioritized to combat the threat posed by a new virus that does not adhere to the laws of the species barrier. The One Health idea emphasizes the interdependence of human, environmental, and animal health and hence envisions methods to manage and reduce disease outbreaks. To reduce the threat of zoonotic diseases, it is critical to implement One Health measures such as bio-surveillance of live animal markets, biosecurity of animal farms, public awareness, contact investigation, patient isolation and care, community disease control, and collaboration among different agencies. Therefore, appropriate mitigation strategies inclusive of one health are warranted to be strictly implemented to tackle COVID-19 in a comprehensive manner.

Dr. Abrar Ul Haq1*, Dr. Sarnarinder Singh Randhawa1, Dr. Nazir Ahmed Sudhan1 and Dr. Shagufta Azmi2

1Department of Veterinary Medicine, 2 Department of Veterinary Pathology
Khalsa College of Veterinary and Animal Sciences, Amritsar-143001, Punjab
(Guru Angad Dev Veterinary & Animal Sciences University, Ludhiana, Punjab)