Scientists are warning that the same chain of events suspected of starting the Covid pandemic in China could take place in Europe.

Under the 'natural origins' hypothesis, backed by the World Health Organization (WHO), scientists argue that the Covid virus jumped from bats to humans via a third 'intermediary' animal, such as a pig or pangolins, likely after it was exposed to bat droppings.

Now, researchers say similar conditions exist in Italy, and likely many other western countries, after they tracked bat activity at 14 pig farms.

Overall, they found bats were present at every piggery, with each hosting 500 to 8,000 pigs, and would pass through farms an average of 45 times a night. A total of eight different bat species were detected at the pig farms.

Tests for coronaviruses showed 15 percent of bats were infected with at least one strain of the virus. The bat species that visited the farms most often was found to carry at least two different types of coronavirus.

This raises the risk of an outbreak by making it more likely that pigs will come into contact with coronavirus-infected bats or their droppings, potentially catching the virus and then passing it on to humans through handling, farming or contaminated food and water. Once inside humans, the virus could acquire mutations that make it better adapted for human-to-human transmission, causing an outbreak.

Despite the potential outbreak risk, the researchers noted that there were no physical barriers to prevent contact between bats and their droppings and pigs, potentially risking the emergence of a new pandemic.

The scientists, from Italian universities in Rome and Padua, wrote in their paper: 'While urbanization and other [human] pressures are known as a threat for biodiversity, animals can be attracted to and thrive in [human] environments.

'Species included in these environments... are more likely to act as a source of pathogens, due to higher interaction with humans and domestic animals.

'Therefore, understanding the actors and the triggers of these interactions might then be a crucial step in the risk assessment for the emergence of novel diseases.' 

The Covid pandemic killed more than 1.2million people in the US alone, and disrupted hundreds of millions of lives, with schools closed, people sent to work from home, and hospitals turned into 'Covid wards'.

In early 2021, a team from the WHO concluded that the most likely cause of the pandemic was a coronavirus spreading from bats to humans via an intermediary animal, such as a pangolin or a pig.

In the agency's latest report from its top panel in June this year, it again concluded that a 'natural origin' was the most likely cause of the pandemic based on 'available evidence', and again said an undetermined intermediate species was likely involved.

Many experts, including US intelligence agencies like the FBI and CIA, believe, however, that SARS-CoV-2 escaped from the Wuhan Institute of Virology (WIV), where coronaviruses were being studied at the time. 

In the Italian study, published in PLOS One, researchers monitored 14 farms in northeastern Italy involved in the production of dry-cured San Daniele ham.

At each, a microphone was set up to record sounds made by bats and was turned on from dusk to midnight, the times when bats are most active, every night for five days. 

It monitored farms in April and October in 2021 and 2022. These recordings were then analyzed to determine the presence of bat species.

Visual inspections also revealed that three pig farms hosted bat colonies, with scientists collecting feces from these six times for analysis for coronaviruses. At least 20 bats were also caught from each of these colonies and tested for coronaviruses.

Scientists also caught bats at three private properties located near at least one of the pig farms and also tested these for the presence of coronaviruses.

Overall, the team obtained 86 days of sound recordings that contained a total of 4,587 calls from bats.

Of the 353 bats that were tested for coronaviruses, 55 tested positive for the presence of coronaviruses, or 15 percent.

Of the three colonies on farms, each was found to be from the species Kuhl's pipistrelle (Pipistrellus kuhlii). Testing on guano from these colonies revealed the presence of coronaviruses in guano in one of these colonies.

Of the eight species detected on the farms, the three most active were: Kuhl's pipistrelle, passing over farms 200 times per night on average and, in one case, more than a thousand times; the pipistrellus species, passing through farms 48 times per night on average; and Savi's pipistrelle, which passed through farms six times per night on average.

The other species detected were: the Serotine bat (Eptesicus serotinus), the Mouse-eared bat (Myotis sp.), the Lesser noctule bat (Nyctalus leislerii), the Lesser horseshoe bat (Rhinolophus hipposideros) and the Greater horseshoe bat (Rhinolophus ferrumequinum). 

The scientists warned: 'Our study outlines a potential transmission route of bat [coronaviruses] to swine.

'[It also] highlights key risk factors [for an outbreak], including farm structures, biosecurity gaps, bat species involved, viral diversity and seasonal patterns of virus circulation.'