Interspecies transmission of coronaviruses and immunization: An Indian perspective

INTRODUCTION

Modern transport converts the world into a global village, allowing the rapid spread of infectious diseases. The current COVID-19 pandemic has spread to over 210 countries around the globe, including India.^[1]

The SARS-CoV-2, like any other respiratory virus, is transmitted from an infected person to a susceptible host, through droplets, and surface contact.^[2] There are currently seven characterized coronavirus strains (229E, NL63, OC43, HKU1, SARS, MERS, and SARS-CoV-2) known to be infective to humans.^[3] Out of these, four strains cause milder forms of infection, while three others, including SARS-CoV-2, cause severe illnesses.^[3]

The confirmed SARS-CoV-2 cases and associated mortality has been on the rise globally. COVID-19 has been declared a public health emergency and has put all health organizations on high alert. The need for a reliable vaccine or antiviral drug cannot be understated. From our current understanding of the disease, it is clear that the seriousness of the illness across geographical regions is different. Surprisingly, it is the developed nations that are more severely affected than the under-developed and developing countries. It is our understanding that a more in-depth analysis of this contrast may help build newer and more reliable therapies.

THE INDIAN SCENARIO

India’s coronavirus fatality rate (FR) has been remarkably low compared to most other countries. Reported global COVID-19-associated FR is pegged at 7–7.5%. In contrast, with an FR of 2.87%, India is one of the lowest in the world.^[4] Despite being a developing country with a significantly large rural/ suburban population that lacks essential healthcare resources and facilities, India’s remarkably low FR indicates a likely intervention of other factors and “unconventional” biological mechanisms in shaping the nature of this pandemic.

Researchers speculate that the relatively low numbers of elderly individuals in the population, high ambient temperature and humidity, mandatory administration of the BCG vaccination to the public, and possible resistance to malaria may have contributed to the low FR.^[1,5] Even in the past, India has displayed relatively low mortality rates to infectious diseases such as tuberculosis and malaria, and it is critical to acknowledge a plausible link to epigenetic immune factors and understand their role in infectious disease prevention and prognosis.^[5]

CORONAVIRUSES: A STRUCTURAL AND FUNCTIONAL PERSPECTIVE

SARS-CoV-2 infects epithelial cells of the respiratory tract through receptor-mediated endocytosis facilitated by Spike-protein-mediated recognition of and attachment to the ACE-2 receptor on the cell membrane. A recent study reported remarkably high levels of sequence similarity of ACE2 between domestic animals and humans.^[6] Another study revealed that the Bovine and Canine Respiratory Coronaviruses displayed high-sequence homology to the SARS-CoV-2 Spike protein.^[2,7] These findings suggested that the viral particles are likely to interact with a wide array of host cells, facilitating potential inter-species transmission.

FUTURE DIRECTIONS

The above discussion sheds light on the potential of canine and BCoV strains as candidates for human-SARS-CoV-2 vaccines. We hypothesize that these coronavirus strains, on isolation from Indian stray dogs and cattle, when adequately attenuated, can be trialed as potential vaccine candidates. The limiting factor in our proposed hypothesis is the assumption that sufficient SARS-CoV-2 viral titers are transmitted from patient to patient.^[15] Studies on animal coronaviruses have revealed that successful transmission through direct contact depended on the presence of high viral titers in respiratory and salivary aerosols.^[8] Thus, further investigations assessing the rates and modes of interspecies transmission of CCoV and BCoV to humans are required to better suit our current hypotheses.

CONCLUSION

Human–wildlife interactions affect individuals’ livelihoods, attitudes, and tolerance. Animals continue to play a crucial role in governing the emergence, etiology, and evolution of human pandemics. Given their pivotal role as viral reservoirs, it is vital to thoroughly evaluate their potential in conferring preventive immunity in humans and considers their prospects as therapeutic agents and vaccine candidates.