Microbiologist Doronina explained how bats could cause a new deadly pandemic

The other day, Reuters published data from its research: journalists identified bat habitats in 113 countries on all continents. These areas cover more than 9 million square kilometers, where every fifth person on Earth lives and all the conditions for a new catastrophe are created. For example, in Laos, scientists have already discovered viruses similar to the one that causes COVID-19. High-speed rail, like the line China is building in Southeast Asia, could help spread these infections from once remote areas to the rest of the world.

Since 2018, outbreaks of the deadly Nipah virus (also a “gift” from bats) have already been detected in India three times. Outbreaks of Ebola and Marburg have become a regular occurrence in West Africa as more trees are cut down in searches for gold, iron ore and other minerals. For example, last June, a 26-year-old farmer named Mahama Faati from Ghana died of a mysterious illness after three days of high fever and bleeding from the abdomen, mouth and nose. Laboratory tests confirmed he had Marburg, a deadly virus found in the Egyptian red bat that is also spread by the African fruit bat. Soon after this, Faati’s little son also died. Their deaths came unexpectedly: it was the first known appearance of Marburg in Ghana.

Brazil is also being considered as a likely cradle of a future pandemic: the rapid destruction of tropical forests has led to the fact that 1.5 million square kilometers have become dangerous in terms of human infection with pathogens carried by bats. This is more than in any other country.

Humans are increasingly encroaching on the habitats of wild bats: forests infested with them are being cut down to make way for agriculture, mining, roads, infrastructure and so on. As the number of contacts between humans and bats increases, so do the number of animal-borne disease outbreaks, which have killed millions around the world over the past two decades.

Viruses carried by bats carry high risks of a new pandemic. Chiropterans are the main reservoir of infections (according to some data, they can carry up to 72 thousand different pathogens). They pose no harm to the mice themselves, but can cause serious problems for people who encroach on their habitat. Scientists do not fully understand why this is so, but they note the superpower of bats to collect viruses. Most likely, they spread the infection through saliva, urine, blood and excrement. These pathogens can then reach humans through direct contact or through other animal hosts (pigs, chimpanzees or civet cats). Bats are not only exceptional incubators, but also powerful spreaders: some can fly hundreds of kilometers in search of food, spreading viruses far and wide.

What is the secret of bats, what to expect from them and whether it is possible to prepare for potential pandemics, Victoria Doronina told MK.

— Why are bats most often considered as possible reservoirs of viruses with pandemic potential?

— Bats have a very active immune system; they practically do not suffer from infectious diseases. But at the same time, they are reservoirs of a variety of mainly RNA-containing viruses that can infect many species of mammals. One study documented 61 viruses that could be harmful to other animals out of 137 found in bats. Naturally, the composition of viruses will differ greatly between populations that live in different regions.

The danger comes from all mice, not just blood-sucking ones. Cases have been recorded in which the rabies virus was transmitted not through sick animals, but directly from bats to humans – through inhalation of dust from dried feces in the caves where they live.

To become infected, people or animals do not even need to be in places where bats gather—contact with a single individual is enough. For example, flying foxes from the fruit bat family feed on the juice and pulp of fruits; In Australia, the Hendra virus was found among other pathogens in the saliva, feces and urine of these bats. Flying foxes eat fruit on farms, dropping saliva-covered scraps onto the ground. If horses graze under trees, they can become infected by eating these fruits or grass that have been exposed to dangerous saliva. Hendra can be transmitted from horses to people, although not yet effectively – just as the COVID-related MERS virus was poorly transmitted from camels.

—Where do such mice most often live?

“They are much more common than they seem.” It’s just that since they are nocturnal animals, we rarely see them. Even in Europe there are dozens of species of bats. They live in agricultural buildings, in forests. But especially large colonies can form in caves, and it is such colonies that can be a source of transmission of viruses directly to humans.

Thus, the first known infections with Marburg virus, an Ebola-related hemorrhagic fever pathogen, can be traced to a colony of bats in Kitum Cave in Kenya: in 1980, two people who visited the cave fell ill and died from the virus. By the way, Ebola, with its 90% mortality rate, is also carried by bats, and one of the first epidemics may have begun with a colony of bats that nested on the ceiling of a factory building in Africa.

— What groups of viruses do these animals carry and which ones can they theoretically carry?

— As I already said, RNA viruses, among which there are many different groups. The databases contain more than 12,000 genome sequences of viruses from 30 families (168 in total). Of these, 25 families were found in bats of Asia and Africa.

We all know about coronaviruses. But the Hendra virus and another pathogen that tries to “jump” from animals to people, Nipah, belong to a different group – henipaviruses. An unpleasant feature of RNA-containing viruses is their ability to undergo frequent mutations (with a much higher frequency than DNA-containing viruses), as well as to exchange sections of the genome, which creates another reservoir of variability. The virus closest to COVID-19 in genome sequence was isolated from samples from bats, as many people now know. But probably not everyone is aware that this virus was just one of a large number of others isolated at the same time. And that COVID-19’s ability to mutate is relatively low: it took about a year of its active spread among people before the much more pathogenic “Alpha” variant emerged. Other RNA viruses, such as the influenza virus, mutate much faster.

— Can you give examples of the introduction of zoonotic infections from bats?

– Yes, sure. The rabies virus, SARS, COVID-19, Nipah, Hendra, Marburg, and Ebola passed from bats to humans.

— How likely is it that viruses transmitted by bats will become the culprits of a new pandemic?

— Very likely, especially for henipaviruses. If we look at the history of coronaviruses, before 2019 there were several “failed pandemics” involving them – it’s like missing a target at a shooting target. So far, for henipaviruses, there is also an “inaccurate hit”—mass infection of animals with rare cases of infection of humans. But there are many variants of the virus, they are constantly mutating and recombining, creating new variants. One of them will sooner or later do what COVID-19 did – begin to spread very efficiently between people. There is a vaccine for Hendra for horses, but not for people, and it is unknown whether the success of quickly creating a vaccine like for Covid can be replicated.

And yet henipaviruses are widely known today. But it is possible that the cause of the next pandemic will be a representative of a completely different group of viruses – bats have many of them.

— Is it possible to avoid dangerous scenarios involving them?

“I would like to believe that the WHO and other international organizations, as well as the governments of developed countries, have drawn conclusions from the COVID-19 pandemic and will develop and adopt international programs to prevent epidemics.

“So wouldn’t it be easier to kill all the bats and remove this reservoir of viruses?”

— Simple solutions rarely work in biology. For example, when sparrows that pecked grain were killed during the Cultural Revolution in China, this led to the proliferation of rodents that competed with them for it. This proliferation led to the destruction of much more of the crop than the sparrows would have eaten, plus an increase in disease in humans. Likewise, bats kill a significant number of insects, such as mosquitoes, which also carry viruses pathogenic to humans. Tropical bats that eat fruit and drink nectar are pollinators. So killing bats can lead to even worse consequences.

— What other animals could pose a similar danger?

– Almost any warm-blooded animal, starting with the “kings of infectiousness” – rodents. Even such an exotic animal as the pangolin could be an intermediate host for COVID-19. Wild ducks and domestic pigs were a possible cause of the Spanish flu, an influenza virus that killed tens of millions of people a century ago. Cattle, in principle, have been a source of various infections since domestication, and in the quantities in which we raise them now, this is also an excellent reservoir – yes, they are vaccinated, but against already known diseases, and not completely new ones.

COVID has been a dead-end route for spreading among cats and dogs, but one can imagine a situation where the infection goes in the opposite direction – and they become a source of infection for people. In North America, a prion is now spreading among deer – it is not a virus, but it has similar transmission mechanisms. Fortunately, for the “human” prion, which began to be transmitted from cows and which was therefore called “mad cow disease”, humans were a dead end – the pathogen did not spread as an infection. But it can be assumed that if the highly infectious deer prion can “jump” to humans, the human variant will also be infectious and can be transmitted, like in deer, through saliva.