We have seen the advent of zoonotic coronavirus (CoV) outbreaks 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 the current SARS-CoV-2 (COVID-19 pandemic) continuously wreaking agony all across the globe. This malevolent virion particle (SARS-COV-2) has just upstretched as a new peril to humankind, which has now distressed millions and killed thousands of people globally.
Though SARS-CoV-2 is less morbific than previous outbreaks like SARS-CoV and MERS-CoV, it is very contagious and spreads in a jiffy, letting the transmission channels infect a substantial number of persons. These nefarious virus particles infect humans because of their eclectic host range, persistence in animal hosts, environmental contamination, transmission potential, and affinity for human cell receptors, which is aided by bigger mutation rates. The origin of SARS-CoV was reported from China's Guangdong Province and was transmitted to the public by civet cats that got an infection from bats. MERS caused by MERS-CoV was detected in Saudi Arabia, spreading from bats to people via dromedary camels. The latest COVID-19 caused by SARS-CoV-2 started in Wuhan, China, and it is believed to be transferred from bats to individuals via an unidentified intermediate animal host, with snakes or pangolins being of primary attention. Also, genomic and phylogenetic studies have shown a close relationship between SARS-CoV-2 and CoVs (coronaviruses) isolated from the bat population. Studies also claim that coronaviruses have the capacity to pass from one animal species to another and are recognized for their ability to leap across species.
Human expansion into jungles and commercialization of wild creatures are the two major aspects that allow and enhance adequate conditions for illnesses to pass the species barrier in the case of wild animal to human transmission. Additionally, as there is a greater demand for wild animal meat, wild animals are being commodified for meat, particularly in tropical and subtropical zones. These actions have created an animal-human interface, which can aid in the transmission of zoonotic CoVs across species barriers.
Talking of its host range, CoVs require two types of animal hosts for transmission: the reservoir host harbouring the initial CoVs and considered to be the source of infection, and the intermediate host, which transmits CoVs from animals to individuals. Bats are frame-up as the reservoir of these viruses and they transmit the virus to humans through intermediate animal hosts without becoming infected because they are frequently exposed to such infections thus generating a less complex immune response against CoVs compared to that of humans. Chinese horseshoe bat, Pearson's horseshoe bat, and big-eared horseshoe bats are known to be a source of coronaviruses. In addition to bats; cattle, equines, camels, pigs, dogs, cats, poultry, rodents, ferrets, mink, turtles, snakes, frogs, marmots, hedgehogs, Malayan pangolin, and some wild animals act as the possible reservoir for these viruses.
The intermediate host for Covid-19 has yet to be identified; however, a number of animal species are being measured as possible intermediate hosts for Covid-19, although without solid confirmation. Pangolins and snakes are alleged to be the intermediate hosts as the initial cases of COVID-19 had links to the Wuhan wet animal market where these creatures were being traded; however, investigative studies are required to reach an irrefutable hypothesis. Based on the genomic and evolutionary analysis of its genome, Pangolin-CoV was found to be tantamount to the SARS-CoV-2 and BatCoV RaTG13. Covid-19 has been found in felines, canines 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. Covid-19 was also discovered in a Malayan tiger at New York City's Bronx Zoo that got infected by a zookeeper who was asymptomatic for COVID-19, and the tiger exhibited respiratory symptoms and tested positive for the same.
SARS-CoV-2 infection was also recorded in minks with rapid transmission and large-scale mortality in the mink farms which was later transmitted to humans. The virus is supposed to have spread by fomites, infectious droplets, or fecal matter dust laden with infectious virus.
Prevention and control
Based on the above-mentioned facts, dodging contact with wild creatures is one of the most vital and ostensible stratagems for thwarting and controlling CoV zoonotic transmission. Going for vaccines jabs (such as inactivated, mRNA, protein subunit, non-replicating viral vector, or virus-like particle-based vaccines) have recently emerged and may be beneficial in prevention and management. However, until the prophylactics are successful, current preventive and control approaches like social distancing, sanitization, wearing of personal protective equipment, respiratory etiquettes, and frequent testing, as well as isolation/quarantine of sick, are need of the hour. As the most significant emerging human CoVs have originated from bats, consumption and selling of bats in live animal markets should be verboten in order to avoid the zoonotic transfer of any novel CoVs from bats to humans. The CoVs carried by bats must be explored and scrutinized using a routine and innovative ecological surveillance system. Bats should not be allowed in close proximity to agricultural livestock. Deforestation and human infringement on forests should be reduced or eradicated, as this may result in bats migrating into neighbouring human households.
The wild animal and exotic pet trade in Chinese traditional medicine must be entirely barred. Pet proprietors globally should implement preventive steps instead of waiting for more convincing proof of animal-to-human transfer, and felines should be maintained under disease monitoring. Since Covid-19 emerges at the animal-human interface, one health strategy must be prioritized to combat the threat posed by this notorious virus not adhering to the laws of the species barrier.
The one health concept accentuates the interdependence of human, environmental, and animal health and hence envisages methods to manage and reduce disease outbreaks. To reduce the threat of zoonotic diseases, therefore it is critical to implement ‘One Health’ procedures 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 Haq Wani, Assistant Professor, Dept. of Medicine, Khalsa College of Veterinary and Animal Sciences, Amritsar (GADVASU -Punjab, India)