Re-emergence of viral diseases
Emerging outbreaks, zoonotic diseases and the current upwards trend, have necessitated for the people from scientific and non-scientific background to understand the factors associated with the emergence/re-emergence of viruses. The host-pathogen-environment interacts, a key to the evolution of pathogens (microorganisms capable of causing disease). The past three decades have seen a jump in emerging infectious diseases in humans and among these, 60 per cent of the infectious diseases known to people are of zoonotic origin, of which two-thirds originating in wildlife. The emergence of infectious diseases is primarily caused by the relocation of pathogens. The factors that boost such relocation and helps a virus to find its host are driven by the socio-environmental changes. Unlike DNA viruses which are evolving from millions of years, RNA viruses have possibly evolved more recently, only thousands of years.
David Quammen, author of Spillover: Animal Infections and the Next Pandemic, science writer in the New York Times, recently wrote "We cut the trees; we kill the animals or cage them and send them to markets. We disrupt ecosystems, and we shake viruses loose from their natural hosts. When that happens, they need a new host. Often, we are it.”
Some key factors that drive the evolutionary tree of viruses 1. Upheavals, caused by migration, war or mass gatherings (mostly virus transmission rates are higher in dense than in sparse populations)
2. Modernisation (farming practices, habitat destruction, pushing wildlife and livestock into overlapping environments.)
3. Climate change
4. Interactions between pathogens-hosts-other species, (wildlife, livestock and humans)
Among all, Agricultural drivers are significant and include a major chunk of the changes implemented in modernization and intensification of farming systems. Asia-Pacific region has been the global hot-spot for such emergence of RNA viruses, for example, recent outbreaks of SARS-CoV-2, Zika virus, and outbreaks in other regions such as H1N1, hCoV, Hendra virus, MERS-CoV. But what makes these regions as the hotspot and vulnerable for such outbreaks, are the illegal trades of wild animals.
Wet market:
Following the magnitude of the recent outbreak, Chinese authorities have shut down the Wuhan market that sells live animals. On the other hand, Lagos wet market is like a viral bomb waiting to explode. Moreover, the mammalian hosts for the hepatitis E virus (HEV) including deer, boar, mongoose, rabbit, rat, goat, camel, bat, ferret, moose, etc. are growing wide. However, we have limited knowledge about the virus species that harbour in these wild animals. But the current data suggest that bats carry a pool of diverse CoVs and vary according to the region and the composition of such a viral pool is changing over time.
Mass gathering:
India is one of the hubs of festivals and religious congregations that pulls large numbers of people, such as Kumbh Mela, one of the biggest human mass gatherings on earth, held in every 12 years, Maha Pushkaram festival, an annual pilgrimage to Sabarimala temple and Velankanni- the biggest Catholic pilgrimage centre. This kind of mass gatherings hosts around 40-50 million people. Such gatherings create situations for a transmission to be more likely and present the challenges to maintain good sanitation practices. Additionally, every year massive numbers of Muslim followers return from the Hajj and Umrah pilgrimage, increasing the likelihood of acquiring infections with MERS-CoV and during the event and may provide platforms for subsequent introduction in India. Human metapneumovirus (hMPV), identified first 2001, Netherlands, influenza A strain (H7N9) of “bird flu” in 2013, China and the re-emergence of Ebola virus, 2015/2016. It is almost impossible to predict where and when the next outbreak will come from. Perhaps, what is sure is that the next pandemic can certainly be above the horizon in any minutes.