Why bats are a global concern for pandemics: A look at their role in past and emerging viruses

Time of India

2 days ago

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Bats, the winged mammals, are essential to ecosystem pollination, to give just one example, and control of insects, among others. And in addition to their utility to ecosystems, they are also the bearers of a dark reputation: as reservoirs for an impressive variety of deadly viruses that have caused a number of human pandemics. In the past half-century, there has been a foreboding trend—most leading-impact viruses like SARS, MERS, Ebola, Nipah, COVID-19, and more have their origin in bats directly or indirectly through intermediate hosts.
Bats are not villains but their unmatched viral diversity, asymptomatic shedding, and growing contact with humans position them at the heart of emerging infectious disease threats.
20 new bat viruses discovered in China
Researchers have found 20 new bat viruses previously unknown to science, including two that are closely related to the lethal Nipah and Hendra viruses. Experts say this finding may pose critical global public health consequences. The viruses were found in six bats from fruit orchards in Yunnan province, which is in southwest China. The researchers discovered that the bats had unidentified pathogens in their kidneys, which was of concern for possible zoonotic transmission.
Released in the PLOS Pathogens journal, the research identified that of the 20 new viruses discovered, two are part of the henipavirus family and have similar genes to Nipah and Hendra viruses both recognised to inflict extreme and usually deadly diseases on people.
Why are bats linked to so many viral outbreaks
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Tremendous species diversity and global distribution
Bats represent over 22% of all mammalian species, with over 1,400 known species worldwide as per the research published in Nature. Such diversity allows for a wide range of viruses to thrive and evolve within bats. Because they occupy all continents except Antarctica, their extensive global presence increases the possibility of viruses jumping across species to humans or pets.
Immune tolerance to viruses in a special way
Unlike other mammals, bats have evolved an extremely specialised immune system that enables them to carry viruses without exhibiting disease symptoms. Studies show that bats often demonstrate a dampened inflammatory response, allowing viral replication without the lethal immune response. This creates bats as excellent 'incubators' of viruses to evolve, mutate, and in some cases, become more virulent or transmissible to humans.
High levels of viral diversity and co-infection
According to the research, thousands of novel viruses have been discovered in bats, including members of at least 28 viral families, including:
Coronaviruses (SARS-CoV, MERS-CoV, SARS-CoV-2)
Henipaviruses (Nipah, Hendra)
Filoviruses (Ebola, Marburg)
Lyssaviruses (Rabies and related lyssaviruses)
A single bat can be infected with multiple viruses, increasing the potential for viral recombination; the principal mechanism for the emergence of new pathogens infecting humans.
Bat-origin viruses that changed the world
Bats have been directly or indirectly responsible for many of the deadliest viral outbreaks of the 21st century:
Virus linked to bats
SARS (2002): Had its origins in horseshoe bats; civets were an intermediate host.
MERS (2012): Traceable back to bats via camels.
Ebola Virus: Evidence suggests fruit bats were the natural hosts.
Nipah Virus: Spread by consuming contaminated date palm sap in Bangladesh.
COVID-19 (2019): Close relative of bat-borne SARS-related coronaviruses.
These serial spillovers strongly suggest that bats are not only passive vehicles, but active sources of high-risk viruses with the ability to adapt to infect humans.
Ecological triggers behind bat-borne virus outbreaks
Habitat loss and urban expansion
Urbanisation and habitat loss compel bats to have increased contact with humans, increasing the risk of cross-species transmission. For instance, as forests are cleared, bats may roost in houses, fruit plantations, or agricultural fields causing the increased contact of humans with bat saliva, urine, or feces.
Farming practices and livestock interactions
Modern farming systems, especially high-density livestock ones, are generating "spillover hotspots." Intermediate hosts of bat-borne viruses are animals such as pigs and horses that harbor such viruses such as Nipah and Hendra viruses.
Seasonal patterns and nutritional stress
Bats are seasonally breeding and most often have food shortages due to climatic variations. These are stressors that can weaken their immunity and enhance viral shedding. In fact, seasonal surges of virus shedding in bat populations have been coincident with mass outbreaks of Hendra in Australia and Nipah in South Asia, as reported.
Why studying bat viruses remains a scientific challenge
Even with rising awareness, it remains hard to grasp how viruses interact among bats through several obstacles:
Limited longitudinal data:
Most studies track individual bats infrequently, making it hard to examine viral persistence or reinfection.
Shortage of bat-compatible laboratory models:
Human- or monkey-derived cell lines predominate that are utilized, and they are not supportive for the replication of bat viruses.
Mysteries of bat immunity:
Why bats can tolerate, suppress, or shed viruses is yet to be known.
Until these problems are solved, the ability to anticipate or control the next bat-origin pandemic is in question.
Do bats get sick from these viruses
Perhaps the biggest enigma is the fact that bats rarely show signs of sickness, even when infected with viruses that kill humans. Facts suggest:
Innate immunity:
Bats have interferon pathways in baseline activation, which allows them to quell viruses early on without inflammation.
Reduced pathological immune response:
Bats, unlike humans, do not experience the pathological "cytokine storms" typically leading to acute disease during viral infection.
Heterogeneity of adaptive immunity:
Antibodies in bats are transient or non-neutralizing. Viral clearance in most cases is via cell-mediated immunity, rather than by long-term antibodies.
These immune responses possibly facilitate chronic viral infections and asymptomatic transmission—virus persistence and spillover risk absolutely relying on these.
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