**7. Deforestation trends and increased risk of emergence**

of ubiquity bat species, whereas natural environments might be more selective and suited for species with stricter ecological requirements. Anthropized environment displaying a higher biodiversity, the risk of virus transmission is therefore increased [41]. The impact of land use change on the emergence of diseases has been modeled to two main processes: (1) the perturbation hypothesis in which "land use change perturbs disease dynamics in multihost disease systems by disrupting the cross-species transmission rate" and (2) the pathogen pool hypothesis in which "land use change allows exposure of novel hosts to a rich pool of pathogen diversity, influencing the cross-species transmission rate" [66]. However, the same authors stated that these hypotheses tend to be vague or case specific with lack of theoretical foundation. This makes sense since the emergence of an infectious disease is an accidental process or in other words a very low probability event resulting from the sum of low probability independent events. According to this accidental process, an emergence cannot be predicted and will always appear as case specific. In the case of bats, numerous viruses have been found in bats but no direct transmission to humans has been formerly described. Emergence of bat-borne viruses is therefore most likely the consequence of the accidental association of a chain of events favored by structural elements from the human society. Although traced as a bat-borne virus, the coronavirus responsible for SARS seems to have been initially transmitted by civet meat to humans [31]. The outbreak itself was most likely triggered by human-to-human transmission through aerosols. The epidemic of SARS in 2003 was limited to hotels, high population density areas, and hospitals. No direct contact with bats was involved in the outbreak. Similarly, the MERS epidemic in the Arabic Peninsula was attributed to a coronavirus probably initially present in bats but transmitted to humans by dromedaries [34]. MERS was also involved, like SARS previously, in major nosocomial outbreaks [67]. In this case, also the trigger for the epidemic was not a direct contact with bats but the human society organization, close proximity with

The main risk for emergence of bat-borne diseases is directly linked to the development of anthropized environment and reduction of natural environments. It is often understood that deforestation and anthropization will lead to the disappearance of species. This is not always true and anthropized environments can provide an acceptable habitat for a large range of bat species, generating thus a higher diversity of bats and in turn of bat-borne viruses next to human dwellings. Anthropization generates a highly diverse environment in the vicinity of human, characterized by differing forest densities. Bats of differing ecology can find in anthropized environments niches compatible with their roosting and hunting needs. Natural environments are highly selective and compatible only with adapted species over a large surface, usually away from human settlements. In the exact contrary, anthropized environments provide a mosaic of ecosystems, very close to each other, each one corresponding to the needs of a given group of bat host. Insectivorous bats will find large populations of insects due to the presence of water, animals, and humans. Furthermore, house lights attract large number of insects at night. Houses and barns offer shelter for cave-dwelling bats while orchard and field can attract frugivorous bats. This environment is favorable to the occurrence of key parameters identified for virus transmission in large colonies of cave bats, i.e. shared roosting areas, close contact of different species, and regular introduction of infected individuals [45, 58]. However, in this specific environment, there is an additional aspect, the proximity of humans

domestic animals, and nosocomial transmission.

124 Bats

Bats have long rendered great services to mankind by acting positively on its environment and without living in a too close vicinity of human populations. However, by increasing the surface of cultivated areas and through the rapid growth of cities in the recent decades, men have drastically modified ecosystems which had remained in equilibrium for millennia. This evolution of ecosystems is even faster in Asia than in the rest of the world. Southeast Asia (SEA) is the region in the world that suffered the largest deforestation with a loss of 30% of forest surface over the last 40 years. In Thailand, agricultural lands represented 23% in 1960 and 40% since 1985 [69]. Similar trends were observed in other Southeast Asian countries [69]. In Cambodia, agricultural surfaces doubled from 15% in the 1980s to 30% in 2000. A similar trend was observed in Vietnam with an increase from 20% in 1990 to 35% today. In Indonesia, the growth was from 21% in the 1980s to 31.5% today. Deforestation is today linked to increased agricultural surfaces and to poorly managed urban growth. Owing to evolving land use, bat populations are setting in area closer to human dwellings [70]. Anthropized rural environments are characterized by a wide diversity of landscapes comprising houses, barns, fields, orchards, and woods of differing density. Human dwellings are also established close to water which along with the presence of animals is favorable for insects and insectivorous bats. Unlike natural environment which are highly selective, these altered landscapes are acceptable by a wide range of bat species, usually not encountered together, which establish close to human dwellings. This results in a higher density of bat-borne CoVs in the close vicinity of human dwellings [70–72], and thus a higher risk of human infection through direct contact or contamination by urine or feces. An aggravating factor is that the human population growth is higher in suburban and rural areas generating thus a higher pressure on land use, agricultural land, and deforestation with the most common activities being farming, logging, and hunting. The recent acceleration of deforestation in Southeast Asia and all predictions based on demographic burden on land use clearly indicate that the risk of contact and of transmission of new microorganisms which could turn pathogenic for humans will increase. It is thus just a matter of time, chance to encounter appropriated targets (human or animal in close contact with humans) and viral mutations to adapt to new hosts. Similar trends of deforestation are occurring in South America, but landscape organization is different, and the human population density is far lower than in SEA making thus the risk perhaps lower. If the exact time and nature of the emergence cannot be predicted, the increased probability of encounter and occurrence of emergence-leading chain of events yielded by anthropized environment must be considered seriously.
