The global virome: The viruses have a global distribution, phylogenetic diversity and host specificity. They are obligate intracellular parasites with single- or double-stranded DNA or RNA genomes, and afflict bacteria, plants, animals and human population. The viral infection begins when surface proteins bind to receptor proteins on the host cell surface, followed by internalisation, replication and lysis. Further, trans-species interactions of viruses with bacteria, small eukaryotes and host are associated with various zoonotic viral diseases and disease progression.
Virome interface and transmission: The cross-species transmission from their natural reservoir, usually mammalian or avian, hosts to infect human-being is a rare probability, but occurs leading to the zoonotic human viral infection. The factors like increased human settlements and encroachments, expanded travel and trade networks, altered wildlife and livestock practices, modernised and mass-farming practices, compromised ecosystems and habitat destruction, and global climate change have impact on the interactions between virome and its hosts and other species and act as drivers of trans-species viral spill-over and human transmission.
Zoonotic viral diseases and epidemics: The zoonotic viruses have caused various deadly pandemics in human history. They can be further characterized as either newly emerging or re-emerging infectious diseases, caused by pathogens that historically have infected the same host species, but continue to appear in new locations or in drug-resistant forms, or reappear after apparent control or elimination. The prevalence of zoonoses underlines importance of the animal–human–ecosystem interface in disease transmission. The present COVID-19 infection has certain distinct features which suppress the host immune response and promote the disease potential.
Treatment for epidemics like covid-19: It appears that certain nutraceuticals may provide relief in clinical symptoms to patients infected with encapsulated RNA viruses such as influenza and coronavirus. These nutraceuticals appear to reduce the inflammation in the lungs and help to boost type 1 interferon response to these viral infections. The human intestinal microbiota acting in tandem with the host’s defence and immune system, is vital for homeostasis and preservation of health. The integrity and balanced activity of the gut microbes is responsible for the protection from disease states including viral infections. Certain probiotics may help in improving the sensitivity and effectivity of immune system against viral infections. Currently, antiviral therapy is available only for a limited number of zoonotic viral infections. Because viruses are intracellular parasites, antiviral drugs are not able to deactivate or destroy the virus but can reduce the viral load by inhibiting replication and facilitating the host’s innate immune mechanisms to neutralize the virus.
Conclusion: Lessons from recent viral epidemics - Considering that certain nutraceuticals have demonstrated antiviral effects in both clinical and animal studies, further studies are required to establish their therapeutic efficacy. The components of nutraceuticals such as luteolin, apigenin, quercetin and chlorogenic acid may be useful for developing a combo-therapy. The use of probiotics to enhance immunity and immune response against viral infections is a novel possibility. The available antiviral therapy is inefficient in deactivating or destroying the infecting viruses, may help in reducing the viral load by inhibiting replication. The novel efficient antiviral agents are being explored.