Studying what drives spillovers is important

Conservationists argue that incorrect interpretation of scientific facts may impede important conservation efforts needed to preserve bats and their fragile ecosystems.

Manuel Ruedi who has been studying bats from Europe and Southeast Asia, said the demonisation of the animal group may undo the important efforts in outreach on the significance of bats in ecosystems.

“It took several decades in Europe to change the idea and inform people that bats are really beneficial for humans in many ways (feeding on pests for instance). The more information people have the better they understand that spillover is different from just having a bat in the house. The widespread misinformation does harm to all the efforts we made in informing people,” pointed out Ruedi.

Bats can carry viruses that are deadly to other mammals without themselves showing serious symptoms and they have a suite of antiviral defenses that keep the amount of virus in check, scientists have said.

Scientists at ICMR’s National Institute of Virology who detected the presence of pathogenic bat coronaviruses in two species of Indian bats in a screening study published in April, 2020, to understand the coronavirus circulation in them also underscored that these reported coronaviruses are “far different” from SARS-CoV-2.

“Coronaviruses are reported from several vertebrate species and they are normally very host-specific. Similarly, several bat coronaviruses have been reported from various parts of the world,” said study author Pragya Yadav, of NIV’s Maximum Containment Laboratory.

“The bat coronaviruses we reported are far different from SARS CoV-2 [COVID-19] and there is no association of COVID-19 from bats in India in the present context,” Yadav told Mongabay-India.

The study authors, however, underscored the need for enhanced screening for novel viruses in Indian bats, calling for ‘One Health’ approach with collaborative activities by the animal health and human health sectors in these surveillance activities shall be of use to public health.

This would help in the development of diagnostic assays for novel viruses with outbreak potential and be useful in disease interventions. Proactive surveillance remains crucial for identifying the emerging novel viruses with epidemic potential and measures for risk mitigation, they write in the study.

The research emphasis on bats makes a lot of practical sense because bats are hosts of numerous medically significant viruses (Ebola virus, rabies virus, Nipah virus, Hendra virus, among others) notes Barbara Han, disease ecologist at the Cary Institute of Ecosystem Studies.

“These pathogens cause zoonoses with high case fatality rates in humans, and some of these zoonoses do not have countermeasures (e.g., Nipah virus). So, understanding what drives the spillover of bat-borne viruses is, therefore, an easily justifiable research area. However, there does appear to be disproportionate villainisation of bats compared to other animal groups,” Han told Mongabay-India.

There is clear evidence linking bat-borne viruses to numerous human diseases, but Han thinks making generalisations about the risk of bat-borne coronaviruses in humans is “premature.” Many species carry coronaviruses, which naturally circulate in many vertebrates (even in aquatic mammals), she says.

But in general, the number of viruses in any animal group (bats, rodents, carnivores, primates, etc) scales with the number of species in a group. This means that groups with more species will also have more viruses.

“The number of viruses in bats and rodents (that have over 2200 species) is expected to be proportionally greater than viruses found in, for example, primates or carnivores, which each have less than 300 species and are therefore likely to have fewer viruses. The number of zoonotic viruses seems also to follow this same pattern,” said Han.

Han said the high number of coronaviruses observed from bats is not that surprising.

“Bats have a high species diversity; in addition to this, they have been sampled more intensively for viruses than perhaps any other group.”

A recent study published in PNAS suggests the number of zoonotic viruses linked to each animal order appeared to be a consequence of species richness: more diverse animal orders hosted more viruses in general and by extension, more zoonotic viruses.
These findings suggest previous scientific thinking—that certain animal reservoirs, such as bats, pose a heightened risk of spreading viruses to humans—may not be accurate. This means that ongoing efforts to identify potential future threats to human health by screening animals for undiscovered viruses will need to focus on a much wider range species than is currently the case.

“We fear most what we understand least”

Veteran bat conservationist Merlin Tuttle observed there are more than 1400 species of bats spread throughout the world and so we would expect them to have a wide variety of viruses but it is yet to be documented that bats are any more dangerous than other animals.

Writing in the Journal of Bat Research and Conservation, Tuttle says that “historically, the world’s greatest zoonotic pandemics have not come from bats. Currently, H7N9 bird influenza, and drug-resistant microbes, pose significant threats but are gaining far less research or media attention. It is time to focus more on known threats, and less on speculation about possibilities not yet verified.”

“In fact, they (bats) have one of our planet’s best records for not spreading diseases. We still don’t even know if bats actually have more viruses than other animals. They have been far better searched. New viruses can be discovered wherever we look, even on our own bodies. Huge numbers have yet to be identified,” Tuttle told Mongabay-India.

The vast majority of viruses are either innocuous or beneficial. However, when a new virus is found in a bat, it’s automatically speculated to be potentially dangerous, he rued.

According to a World Health Organisation situation report, another coronavirus, SARS-CoV-1, the cause of the Severe Acute Respiratory Syndrome (SARS) outbreak in 2003, was also closely related to other coronaviruses isolated from bats. These close genetic relations of SARS-CoV-1, SARSCoV-2 and other coronaviruses, suggest that they all have their ecological origin in bat populations.”

“The big problem is that since it was concluded that SARS came from bats, which hasn’t yet been actually proven, there has been a huge focus on bats, and whenever there is concern about a new virus, it is mostly looked for in bats; this has turned into a viral witch hunt,” Tuttle said, adding that we are looking almost exclusively in bats for many of these things (potential pathogens) and of course, we are going to find more viruses in the animals we most often search.

Tuttle also elaborated on the sampling bias. Bats are by far the easiest mammals to sample quickly.

“When COVID first broke out some of the early speculations were that it even came from cobras. Can you imagine being told that you have to sample 30 cobras? 30 bats would be so much easier and safer. Virologists get quick publications easily from bats and bats have few defenders and it is easy to scare people with bats because we fear most what we understand least. The marriage between bats and viruses seems to provide the perfect storm for scaring people,” he said.

Even Ebola, which has been widely attributed to bats and intensely searched for in them, has not been confirmed from bats. “Bats still get the primary blame, even for MERS, despite clear documentation that human cases originate in camels who are ideal reservoirs. In case after case, so-called virus hunters have prematurely speculated bat origins, then attempted to prove rather than test this hypothesis. Such biases delay much-needed progress,” said Tuttle.

Manuel Ruedi said having a catalog of viruses in bats is fine but you need to research how it passed into humans in the spillover.

“We did find an Ebola-like virus in one species of bat (fruit bat in Africa). It’s the closest we have found so far, but not identical to the one infecting humans. We do have a scenario but that is not the bat itself (as a source). It’s a whole series of events that led to a spillover of infection,” Ruedi said.

Coexisting with bats

The experts also underscored the long history of co-association of bats and humans.

“We have a long history of co-association, in caves, thatched huts, and log cabins. Millions of humans in Africa, Asia, and the Pacific and Indian Ocean Islands still eat bats. Thousands of inhabitants of the Old-World tropics spend countless hours in bat caves collecting guano for fertilizer. Thousands of sport cavers explore caves worldwide. Millions of Africans share their cities with huge bat colonies, all without detected disease outbreaks,” elaborated Tuttle.

Referring to the bat harvests and consumption of the animals in remote northeastern regions in India, Ruedi who also works on the group in northeast India said: “If you consider rabies, it is a major issue over the years. 20,000 of an estimated global annual 55,000 rabies deaths occur in India because they are bitten by stray dogs. This is much more an issue than a spillover that didn’t occur in thousands of years in India.”

Ruedi co-authored an inventory with ZSI’s Uttam Saikia “The Bat Fauna of Meghalaya, Northeast India: Diversity and Conservation” that discusses the diversity of bats in Meghalaya (65 species) and the conservation challenges, including indiscriminate mining.

They also communicated to the community the “role of bats in their environment, and how important they are to help control pest insects and also that they should not only be viewed as potential proteins to eat but also creatures of God worth protecting.” Their communication efforts encouraged the community in the village of Pynurkba in East Jaintia hills to dedicate a small patch of their forest to save the rare Wroughton’s free-tailed bats.

“It took us almost one year to convince the village elders to declare the area as a community reserve. It is a 2.4 hectares patch and surrounds the cave. The area is now notified as a community conservation reserve,” H. Lato, divisional forest officer of Jaintia Hills added.

 

Banner image: Bats emerge out of their roosting cave at dusk. Photo by Yashpal Rathore.