**1. Introduction**

Emerging infectious diseases (EIDs) remain a major threat to public health. Most EIDs described in humans have been shown to be of zoonotic origin. During the past decades, growing evidence that viruses causing EIDs in humans share identity or strong sequence homologies with viruses circulating in bats were reported; this result pushed the epidemiologist to focus their attention on these wild mammals in order to determine whether bats play a particular role as virus diversity reservoirs worldwide and to understand the state of the threat in a context of ecosystem change.

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Taxonomically, bats are grouped in the order *Chiroptera* (Gr. *cheir*, hand; *pteron*, wing) and they are the only mammals with adaptation for powered flight on long distance. Although bats are outnumbered by rodents in species richness, they represent the second species richness in the mammal world with 1230 species—more than 20% of all mammals on earth—inhabiting a multitude of ecological niches [1]. Bats are currently known as important reservoirs of zoonotic viruses worldwide [2] and factors underlying high viral diversity remain the subject of speculation. Bats have sometimes been considered as enigmatic mammals having a particularly effective immune system or antiviral activity [2, 3]. Obviously, bats are not very different from other mammals, and several bat viruses can cause disease and death of bats; in example, a study performed on 486 deceased bats of 19 European Vespertilionidae species showed that two thirds of mortality were due to trauma or disease and that at least 12% of these mammals had succumbed to infectious diseases (19 died from bacterial infections; 5 died from viral infections caused by bat adenovirus AdV-2 or bat lyssavirus EBLV-1; 2 died from parasitic infections) [4]. Yet, numerous viruses apparently remain non-pathogenic in bats, likely due to a long process of co-evolution; although most of these viruses apparently do not affect bats health, some of them have been shown to severely affect wild and domestic mammals, as well as humans.

populations and to analyze the diversity of viruses circulating in these populations. Although informative, the study of circulating viruses in a few specimens and a particular ecosystem cannot account for the global dynamics of viral populations present in the different families of bats on the planet. The isolation and sequencing of viruses was an important step, but not enough performing to capture the extent of the phenomenon. Polymerase chain reaction (PCR), when primers were available, have also contributed to a better characterization of bat-borne viruses being related to viruses that have already produced EIDs in humans. More recently, high-throughput sequencing and metagenomic approaches have led to a quantum leap in surveillance and the quest for knowledge [14–17]. However, a global vision remains indispensable and the initiatives, which make it possible to compile the data of the various laboratories and to catalog them as comprehensively as possible, are welcome [18] (http:// www.mgc.ac.cn/cgi-bin/DBatVir/main.cgi), in addition to other virus database such as the Virus-Host DB (http://www.genome.jp/virushostdb/; this database currently select 134/10028 items under "bat" query), the NCBI viral genome resources (https://www.ncbi.nlm.nih.gov/ genome/viruses/; this database currently select 84 items under "bat" query) or Virus Pathogen resource, VIPR (https://www.viprbrc.org/brc/home.spg?decorator=vipr). It is worth noting that although bats are found on all continents except Antarctica [19], the accumulation of results is very variable from one continent to another. As shown in **Figure 1**, Asia is largely in the lead for data accumulation ahead of North America and Africa and next Europe and South America (**Figure 1A**). The preponderance of Chinese results for Asia's contribution is even more impressive (**Figure 1B**). Almost 60% (58.9%) of Asian articles originate from China, followed by Vietnam at 16.8%. All other contributing countries are below 7%, i.e. 6.5% for both Thailand and Cambodia. It is quite interesting to highlight the correlation between the number of publications and the geographical origin of scientific teams who publish them, because Asia/Southeast Asia is considered as one of the hotspot on the planet for the emer-

Bats, Bat-Borne Viruses, and Environmental Changes http://dx.doi.org/10.5772/intechopen.74377 115

**Figure 1.** Data distribution. (A) Overall data distribution of bat-associated viruses by geographic region (Asia: 2274 publications; North America: 1772 publications; Africa: 1307 publications; Europe 891 publications; South America: 858 publications; Oceania: 142 publications; and unclassified: 47 publications). Adapted from the database of bat-associated viruses (http://www.mgc.ac.cn/cgi-bin/DBatVir/main.cgi). (B) Data distribution in Asia. China comes first with 1723 publications (58.9%), followed by Vietnam with 491 articles (16.8%), Thailand with 190 articles (6.5%) and Cambodia

with 189 articles (6.5%) (http://www.mgc.ac.cn/cgi-bin/DBatVir/main.cgi, updated February 18, 2018).

gence of new viruses.

#### **2. History**

The fact that bats play a role as reservoir of human viruses was recognized during the first half of the twentieth century, when rabies was found in South and Central America [5]. The hypothesis that bat may act as a reservoir of viruses causing EIDs in humans was next acknowledge several decades later, during the second half of the twentieth century. Most genotypes of rabies or rabies-related virus within the *Lyssavirus* genus of the Rhabdoviridae family have been documented in bats [6]. In the recent years, bats have gained notoriety after being implicated in numerous EIDs. Bat-borne viruses that can affect humans and have caused EIDs in humans fall into different families: paramyxoviruses including Hendra viruses [7] and Nipah viruses [8]; Ebola hemorrhagic fever filoviruses [9]; Marburg hemorrhagic fever filoviruses [10] and sudden acute respiratory syndrome-like coronaviruses (SARS-CoV) [11]. Their list is probably far from complete. Interestingly, the powerful retroviral hosting ability of bats had likely contributed to shape mammalian retroviruses [12]. Furthermore, sialic acid receptors for avian and human influenza virus are found in the North American little brown bats, which could potentially facilitate the emergence of novel zoonotic strains [13].

In this context, it becomes urgent to resolve, as soon as possible, three essential questions, namely: Will bats help to serve as a source of pathogenic viruses for animals and humans with regard to pathogens that have already caused EIDs in humans? Are bats reservoirs for viruses that have not yet infected humans but could be at the origin of EIDs in the future? Could bats be considered as "living test tubes" in which new viruses could be developed through genomic exchanges and genetic drift? To answer these questions, it is essential to monitor bat populations and to analyze the diversity of viruses circulating in these populations. Although informative, the study of circulating viruses in a few specimens and a particular ecosystem cannot account for the global dynamics of viral populations present in the different families of bats on the planet. The isolation and sequencing of viruses was an important step, but not enough performing to capture the extent of the phenomenon. Polymerase chain reaction (PCR), when primers were available, have also contributed to a better characterization of bat-borne viruses being related to viruses that have already produced EIDs in humans. More recently, high-throughput sequencing and metagenomic approaches have led to a quantum leap in surveillance and the quest for knowledge [14–17]. However, a global vision remains indispensable and the initiatives, which make it possible to compile the data of the various laboratories and to catalog them as comprehensively as possible, are welcome [18] (http:// www.mgc.ac.cn/cgi-bin/DBatVir/main.cgi), in addition to other virus database such as the Virus-Host DB (http://www.genome.jp/virushostdb/; this database currently select 134/10028 items under "bat" query), the NCBI viral genome resources (https://www.ncbi.nlm.nih.gov/ genome/viruses/; this database currently select 84 items under "bat" query) or Virus Pathogen resource, VIPR (https://www.viprbrc.org/brc/home.spg?decorator=vipr). It is worth noting that although bats are found on all continents except Antarctica [19], the accumulation of results is very variable from one continent to another. As shown in **Figure 1**, Asia is largely in the lead for data accumulation ahead of North America and Africa and next Europe and South America (**Figure 1A**). The preponderance of Chinese results for Asia's contribution is even more impressive (**Figure 1B**). Almost 60% (58.9%) of Asian articles originate from China, followed by Vietnam at 16.8%. All other contributing countries are below 7%, i.e. 6.5% for both Thailand and Cambodia. It is quite interesting to highlight the correlation between the number of publications and the geographical origin of scientific teams who publish them, because Asia/Southeast Asia is considered as one of the hotspot on the planet for the emergence of new viruses.

Taxonomically, bats are grouped in the order *Chiroptera* (Gr. *cheir*, hand; *pteron*, wing) and they are the only mammals with adaptation for powered flight on long distance. Although bats are outnumbered by rodents in species richness, they represent the second species richness in the mammal world with 1230 species—more than 20% of all mammals on earth—inhabiting a multitude of ecological niches [1]. Bats are currently known as important reservoirs of zoonotic viruses worldwide [2] and factors underlying high viral diversity remain the subject of speculation. Bats have sometimes been considered as enigmatic mammals having a particularly effective immune system or antiviral activity [2, 3]. Obviously, bats are not very different from other mammals, and several bat viruses can cause disease and death of bats; in example, a study performed on 486 deceased bats of 19 European Vespertilionidae species showed that two thirds of mortality were due to trauma or disease and that at least 12% of these mammals had succumbed to infectious diseases (19 died from bacterial infections; 5 died from viral infections caused by bat adenovirus AdV-2 or bat lyssavirus EBLV-1; 2 died from parasitic infections) [4]. Yet, numerous viruses apparently remain non-pathogenic in bats, likely due to a long process of co-evolution; although most of these viruses apparently do not affect bats health, some of them have been shown to severely affect wild and domestic

The fact that bats play a role as reservoir of human viruses was recognized during the first half of the twentieth century, when rabies was found in South and Central America [5]. The hypothesis that bat may act as a reservoir of viruses causing EIDs in humans was next acknowledge several decades later, during the second half of the twentieth century. Most genotypes of rabies or rabies-related virus within the *Lyssavirus* genus of the Rhabdoviridae family have been documented in bats [6]. In the recent years, bats have gained notoriety after being implicated in numerous EIDs. Bat-borne viruses that can affect humans and have caused EIDs in humans fall into different families: paramyxoviruses including Hendra viruses [7] and Nipah viruses [8]; Ebola hemorrhagic fever filoviruses [9]; Marburg hemorrhagic fever filoviruses [10] and sudden acute respiratory syndrome-like coronaviruses (SARS-CoV) [11]. Their list is probably far from complete. Interestingly, the powerful retroviral hosting ability of bats had likely contributed to shape mammalian retroviruses [12]. Furthermore, sialic acid receptors for avian and human influenza virus are found in the North American little brown bats, which could potentially facilitate the emergence of novel

In this context, it becomes urgent to resolve, as soon as possible, three essential questions, namely: Will bats help to serve as a source of pathogenic viruses for animals and humans with regard to pathogens that have already caused EIDs in humans? Are bats reservoirs for viruses that have not yet infected humans but could be at the origin of EIDs in the future? Could bats be considered as "living test tubes" in which new viruses could be developed through genomic exchanges and genetic drift? To answer these questions, it is essential to monitor bat

mammals, as well as humans.

**2. History**

114 Bats

zoonotic strains [13].

**Figure 1.** Data distribution. (A) Overall data distribution of bat-associated viruses by geographic region (Asia: 2274 publications; North America: 1772 publications; Africa: 1307 publications; Europe 891 publications; South America: 858 publications; Oceania: 142 publications; and unclassified: 47 publications). Adapted from the database of bat-associated viruses (http://www.mgc.ac.cn/cgi-bin/DBatVir/main.cgi). (B) Data distribution in Asia. China comes first with 1723 publications (58.9%), followed by Vietnam with 491 articles (16.8%), Thailand with 190 articles (6.5%) and Cambodia with 189 articles (6.5%) (http://www.mgc.ac.cn/cgi-bin/DBatVir/main.cgi, updated February 18, 2018).
