Biodiversity loss and COVID-19 pandemic: The role of bats in the origin and the spreading of the disease

Abstract

The loss of biodiversity in the ecosystems has created the general conditions that have favored and, in fact, made possible, the insurgence of the COVID-19 pandemic. A lot of factors have contributed to it: deforestation, changes in forest habitats, poorly regulated agricultural surfaces, mismanaged urban growth. They have altered the composition of wildlife communities, greatly increased the contacts of humans with wildlife, and altered niches that harbor pathogens, increasing their chances to come in contact with humans. Among the wildlife, bats have adapted easily to anthropized environments such as houses, barns, cultivated fields, orchards, where they found the suitable ecosystem to prosper. Bats are major hosts for αCoV and βCoV: evolution has shaped their peculiar physiology and their immune system in a way that makes them resistant to viral pathogens that would instead successfully attack other species, including humans. In time, the coronaviruses that bats host as reservoirs have undergone recombination and other modifications that have increased their ability for inter-species transmission: one modification of particular importance has been the development of the ability to use ACE2 as a receptor in host cells. This particular development in CoVs has been responsible for the serious outbreaks in the last two decades, and for the present COVID-19 pandemic.

History of the COVID-19 pandemic: Origin, explosion, worldwide spreading

“…However, subsequent extensive epidemiology studies had failed to find SARS-CoV in farmed and wild-caught civet cats, indicating that other animal(s) might have been the natural virus reservoir of SARS-CoV [ 26 , 27 ]. It was also found that strains of SARS-CoV isolated from palm civets in 2002–2003 and 2005, had low affinity for human ACE2 receptors and low infectivity in human cells, but had high affinity for civet cat ACE2 receptors and high infectivity in civet cat cells [ 25 ],Therefore, there is a strong possibility that these animals were only incidental hosts for the SARS-CoV [ 1 , 3 ]. In fact, no intermediate host has yet been established for SARS-CoV [ 28 ].…”

“…Macaques are widely traded for consumption in South East Asia, and are frequently found in markets where they are kept together with other animals, including bats. Considering macaques’ close phylogenetic relationship to humans, the possibility of the transfer of SARS-CoV-2 from bats to them as intermediate hosts for the spillover to humans seems plausible [ 3 ].…”

“…In the wet markets, live animals are promiscuously crowded in cages in non-existing hygienic conditions with dispersal of dangerous excrement [ 1 ]. These are conditions that obviously abolish the dilution effect of the biodiversity, and creating instead an amplification zone, where the high density of pathogen’s reservoirs and of susceptible hosts can interact optimally, greatly increasing the chances of outbreaks [ 1 , 3 ]. Humans entering in contact with this amplified zone also represent susceptible hosts, who can be infected indirectly through an intermediate host or directly by the animal reservoir.…”

“…Gradually, however, in the last decades of past century conditions have matured that have favored the chances of all sorts of pathogens, including viruses like SARS-CoV-2, to become dangerous and even lethal to animals and humans. These conditions have been described in detail in an accompanying contribution in this Special Issue [ 3 ]. They are essentially related to the loss of ecosystem biodiversity caused by the conversion of natural habitats to agricultural and/or urban ecosystems, that have increased the contacts between humans and wildlife, and among it, reservoirs of potential zoonoses.…”

“…They adapt easily to anthropized environments, and the anthropogenic ecosystem changes mentioned above have greatly increased their promiscuity with domestic animals and humans. Evolution has gradually shaped their metabolism and their immunological system to make them insensitive to the dangerous weapons of pathogenic coronaviruses, making them important reservoirs of them [ 3 ]. Importantly, bats are also a locus for coronavirus evolution, as the recombination frequency of coronavirus is high.…”