Bats and Viruses. Current Research and Future Trends.

When I encountered the first mention of this publication, I was quite intrigued because a book with a similar title, Bats and Viruses. A New Frontier of Emerging Infectious Diseases (Wang and Cowled 2015) had appeared relatively recently. Of course, five years present a substantial timespan to update previous information with new data, even if focused on the same topic. However, upon comparison of the contents, I realized that the new book is quite different. The major distinction is that it is not focused on bats as a source of zoonotic diseases, related mechanisms of host shifts, or implementation of prevention and control measures, as might be expected by members of the Wildlife Disease Association. Rather, this new book concentrates more on bat viruses per se, and methods for their study.

Instead of parsing a direct comparison between these two different approaches, I will provide my impressions of the material provided in this new book, with 13 chapters and more than 25 authors. The overall breadth of provided information is quite wide, raising a question of balance. For example, the last chapter “Are Bats ‘Special?”' and the “Introduction” on bats and viruses do not really correspond to the majority of the other chapters, which describe viruses found in bats, almost divorced from any specific attention to the so-called “uniqueness” of bats.

Relatively comprehensive chapters dedicated to flaviviruses and alphaviruses provide a rather large body of information on the ecology of these agents in other mammals, but only relatively tiny pieces describing surveillance findings in bats. I agree with the generic statement that the role of bats in flavivirus and alphavirus circulation is unclear, but this being the case, I do not see any substantial rationale to include such large sections on alphaviruses and flaviviruses in a book dedicated to bat viruses (and to the exclusion of other significant pathogens).

The chapter on hantaviruses is substantially different. Although the authors indicate that only a limited number of studies have been focused on attempts to identify bat hantaviruses, and findings of these studies are limited as well, they describe hantaviruses more broadly and in depth, discussing novel aspects of hantavirus evolution, distribution, and ecology in light of the findings made in bats during recent decades. I am sure that any scientist studying hantaviruses will enjoy reading this part and come away with new ideas (and this chapter seems to be the only one available in an open access format).

The chapter dedicated to bat influenza-like viruses is full of ‘high-tech’ influenza virology. This is not surprising, given the true scarcity of findings in bats. Any influenza virologist will find plenty of useful information on viral genetics, pathobiology, and virus-host interactions. However, what really brings this chapter to another level of significance for the broader audience interested in public health, emerging wildlife and zoonotic diseases, and so on is the discussion of the rather low zoonotic potential of bat influenza-like viruses, with relevant argumentation and qualified explanations, just as a well-balanced offering should provide.

The chapter on polyomaviruses is comprehensive in the amount of basic information about these viruses, their host range and pathobiology, and inclusion of details directly related to bat polyomaviruses. This is a fine basic read for those who study not only polyomaviruses but also other DNA viruses (e.g., herpesviruses), their host associations, and potential for crossing species barriers.

Perhaps the chapter on bat coronaviruses deserves the most attention, given the ongoing devastating pandemic of COVID-19. Of course, preparation of a book is a long process, and this one is not an exception. It was published right at the rise of the pandemic, but most authors would have completed writing their chapters 1–2 years before (considering that most references in this chapter are from no later than 2018), when no one knew about SARS-Cov-2. With all due respect to the authors, who performed outstanding studies of bat coronaviruses, I am not overly impressed by this chapter. About 90% of the text is actually a listing of surveillance records, subdivided into sections dedicated to SARS-related, MERS-related, and other bat coronaviruses, some of which caused outbreaks in different species via host shifts. The information also addresses genomic characteristics of various bat coronaviruses including recombination, structures of receptor-binding domains, and other important parts of viral genes that may influence host range or provide insights into historical host shifts. I would like to reiterate that I understand this book is neither about emerging zoonotic diseases nor about their prevention and control. Therefore, I did not expect to find information on the development of experimental vaccines, immunoglobulins, and antivirals which were initiated during SARS and MERS outbreaks and which are now resurrected in the battle against COVID-19. Additionally, I was not looking for a broader description (i.e., of experimental findings) or a discussion (i.e., based on the receptor structure) of potential susceptibility of non-chiropteran animals to bat-borne coronaviruses. However, I really missed a frank discussion on viral and host properties that might facilitate host shifts of a variety of bat-borne coronaviruses or evolutionary traits of coronaviruses supporting their adaptations to a new host. Such an inclusion would have been appreciated given past events and current circumstances.

Two chapters are dedicated to bat immunity. The chapter on the innate immune response provides solid basic information on the mechanisms and pathways of the mammalian innate immune response, further focusing on findings in bats. As the author reasonably indicates, bats are numerous and divergent, as well as are their pathogens. Therefore, there is no surprise that, in this area, which is at an early state of research, different findings were published for different bat species infected by distinct pathogens. There is no single “magic recipe” that helps bats to survive and clear pathogens that cause severe diseases in other mammals, including humans. Rather, bats of different taxa developed different mechanisms to counteract their specific pathogens. The chapter describing the adaptive immune response is shorter by comparison. The author provides evidence suggesting that antibody responses do not play a significant role in the protection of bats from pathogens (if this is true, then I am curious about why did bats retain all these functional classes of antibodies during their evolution?!), and that cell-mediated responses may be the major protective mechanism. As the author indicates, this aspect has not been studied sufficiently because of the general lack of bat-specific reagents and methodology. Although some available data on bat cell-mediated response are provided, the findings cannot be interpreted with any substantial degree of confidence.

Three following chapters describe methods of virus isolation, genetic approaches for virus detection, and in vivo models of bat infections. These are very much descriptive but provide quite detailed information on various operational procedures, their advantages, and shortcomings. It is hard to disagree that all such methods are in a developmental state today; therefore, further improvement and accumulation of data are expected soon. However, I would have liked to see a discussion in line with a broader generalization, method comparisons, and author opinions on the same. One of the advantages of a book chapter over a stricter research article is that it provides such explorative opportunities for more diverse audiences, particularly for the training of scientists early in their careers.

As mentioned at the outset, the book ends with the chapter “Are Bats ‘Special?'” and provides a brief but insightful opinion (supported by data) on specific bat-pathogen interactions. As an informed opinion, this is a remarkably interesting read where the header of almost every subsection ends with a question mark.

I now would like to indicate the most striking reservations about this book (from my subjective perspective). The book is completely lacking chapters on such important bat pathogens as lyssaviruses, paramyxoviruses, and filoviruses. Lyssaviruses (particularly rabies virus) represent some of the best-studied bat pathogens. There have been many peer-reviewed papers and chapters describing bat lyssaviruses; however, as with any pathogen, the knowledge is cumulative in time, old paradigms are challenged by new findings and ideas, and therefore I do not see any objective explanation for excluding lyssaviruses from a book dedicated to bat viruses. Paramyxoviruses represent another example, not only because some of these pose a substantial threat in veterinary medicine and public health alike (such as henipaviruses) but also because, as in the case of lyssaviruses, the information on bat paramyxoviruses is aging and deserves a modern update. Finally, to filoviruses: with the recent surge of Ebola outbreaks in Africa, together with recent discoveries of novel bat filoviruses, experimental studies of filovirus infections in bats, and so on, this group should be a “must” for such an ensemble. Curiously, viruses from these taxa are mentioned repeatedly in various other chapters, and Ebola (together with rabies) is listed as an example of an important life-threatening disease in the advertisement blurb, suggesting that authors and editors recognize the significance of these pathogens.

One additional drawback in my view is the absence of a standalone chapter dedicated to the ecology of individual bat-virus interactions or the circulation of viruses in bat populations. Quite substantial amounts of data and extensive modeling efforts on these aspects have been published recently but, unfortunately, they are not present in this book, which could have benefited from a greater One Health contextual wrap.

Despite these limitations, the subject matter available in this book contains a solid body of work, which should prove quite useful for the comparative virologists focused upon certain viral families and those who are more broadly interested in bat pathogens and bat immune systems, particularly in this challenging age in which we find ourselves today.