© (photo credit: YUVAL BARKAI)Fruit Bat in daytime.
More than two-and-a-half years after COVID-19 was first discovered and blamed on bats in China, researchers at Tel Aviv University (TAU) have declared that the correlation between the pandemic and flying mammals "was not based on sufficient compelling scientific proof and caused unnecessary stress and confusion worldwide.
"Bats have a highly effective immune system that enables them to deal relatively easily with viruses considered lethal for other mammals," they declared.
The study was led by Dr. Maya Weinberg from the lab of Prof. Yossi Yovel, head of TAU's Sagol School of Neuroscience and faculty member of the School of Zoology and the Steinhardt Museum of Natural History. The research team reviewed dozens of leading articles and studies in this field, and their conclusions were published in writing in the prestigious iScience Journal under the title "Revising the paradigm: Are bats really pathogen reservoirs or do they possess an efficient immune system?"
"Bats have a highly effective immune system that enables them to deal relatively easily with viruses considered lethal for other mammals."
The researchers explain that the "infamous reputation" of bats (mammals of the order Chiroptera) is well known among both the scientific community and the public at large and that they are often accused of being "blood-sucking Draculas" and being reservoirs of viruses including COVID-19 - thus posing a threat to public health. In the newly published study, Weinberg sought to disprove this "erroneous theory" and prove that bats play an important role in exterminating insects, replanting deforested areas and pollination of crops.
The researchers claim that there is indeed evidence that the origin of the "ancient potential" COVID-19 was in bats, "but on the other hand, until now, two years after the pandemic first broke out, we still do not know for sure what the exact origin of the COVID-19 variant is."
"In general, bats are mistakenly conceived of as reservoirs of many contagious diseases, only due to their being positive serologically positive; in other words, in possession of antibodies, which means that bats have survived the disease and developed an immune response," declared Weinberg. "After that, they overcame the virus altogether and disengaged from it; hence, they are no longer its carriers. Nevertheless, in many cases, a virus similar to a human pathogen is liable to be found in bats; however, it is not pathogenic to humans and is not sufficient to use bats as a reservoir."
"In general, bats are mistakenly conceived of as reservoirs of many contagious diseases, only due to their being positive serologically positive; in other words, in possession of antibodies, which means that bats have survived the disease and developed an immune response."
"To examine the overall situation, we conducted a meta-analysis of the literature and checked the finding for over 100 viruses for which bats are considered potential reservoirs; such as Ebola, SARS, and COVID," she went on. "We found that in a considerable number of cases (48%) this claim was based on the incidence of antibodies or PCR tests, rather than actual isolation of identical viruses. Moreover, many of the reported findings are not convincing."
The mere isolation of a virus is not enough to see an animal as a reservoir - since a minimum number of index cases is required in which the virus is isolated in order to be considered a reservoir animal, as well as the existence of an established path of transmission. Furthermore, the very detection of a particular virus in bats does not necessarily ensure further infection, and other biological, ecological and anthropogenic conditions must exist in order for such an event to occur," said Weinberg.
According to the researchers, in recent years evidence has been accumulating of the fact that bats are capable of coping with different viruses, including lethal ones, better than humans and most other mammals.
After over a century of focus on viruses carried by bats, it appears that bats' immune system is characterized by a restrained response during inflammatory processes.
As we see it, bats have developed an excellent balance between resistance and tolerance - an increased defense response of the host and immune tolerance through a number of different mechanisms. Moderate inflammatory pathways contribute to immune tolerance in bats, and a well-balanced response that prevents the virus from developing.
"The comprehensive study we've conducted raises serious doubts regarding the possibility of bats being the origin of the COVID-19 outbreak. The findings give rise to the opposite perspective, according to which we must study in-depth the immunological anti-viral capabilities of bats and thus obtain new and effective means of coping in humanity's struggle against contagious disease, aging and cancer," the researchers concluded.