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Comments to “Detection and phylogenetic characterization of astroviruses in insectivorous bats from Central‐Southern Italy”

We have read with interest the manuscript by Maria Grazia Amoroso et al., which provides an interesting and potentially important per‐ spective into astrovirus infections in insectivorous bats from Central and Southern Italy (Amoroso et al., 2018). Interestingly, the paper revealed that the authors had randomly selected some bats to be screened for rabies virus as well. In this respect, we have some concerns that we would like to share with the readers. The data presented by Amoroso et al. should be care‐ fully interpreted, given (a) the very limited number of bats collected during this active surveillance plan (only 147 bats), (b) the approach to rather randomly selected bat species, (c) the lack of sensitivity of the sampling method used, (d) the absence of validation of the applied diagnostic test and (e) the conclusions raised by the authors considering all the limitations of the study. Due to the pathobiology of the aetiological agents of rabies, that is, lyssaviruses, the active search for shedding in saliva in free‐living bats in the absence of neurological signs is per se challenging. Except for fortuitous cases, attempts to detect lyssaviral RNA or viable virus in saliva samples from bats were of very limited success (Brookes et al., 2005; Hammarin et al., 2016; Nokireki et al., 2013; Picard‐Meyer et al., 2014; Robardet et al., 2017; Schatz, Ohlendorf, et al., 2014; Schatz, Freuling, et al., 2014; Vázquez‐Morón et al., 2008). This low level of detection was corroborated by experimental studies in bats (Freuling et al., 2009; Johnson et al., 2008). Thus, while eventual positive results would confirm the presence of circulating virus, the absence of evidence is not evidence of absence, even if larger num‐ bers of bat saliva samples had been collected and tested. Therefore, enhanced passive surveillance targeting dead, sick or impaired ani‐ mals displaying neurologic disease is recognized as the most suitable approach for bat rabies surveillance to gain knowledge on the possi‐ ble circulation of lyssaviruses in indigenous bat populations (Cliquet et al., 2010; Leopardi et al., 2018; Schatz, Freuling, et al., 2014; Wise et al., 2017). Secondly, against the backdrop that known reservoir bat spe‐ cies for lyssaviruses in Europe were not targeted in the study, the sampling pattern reported by the authors is absolutely inadequate to draw conclusions about non‐occurrence of lyssavirus infections in Italian bats. While rabies virus (RABV), the prototype of lyssaviruses, cir‐ culates in insectivorous and vampire bats in the Americas only, European bats act as reservoirs for at least five distinct lyssaviruses, which have been recognized as autonomous virus species within the genus lyssavirus (Walker et al., 2018). Despite evidence for as‐ ymptomatic circulation in different bat species (Amengual, Bourhy, López‐Roíg, & Serra‐Cobo, 2007; Leopardi et al., 2018; Schatz, Ohlendorf, et al., 2014; Schatz, Freuling, et al., 2014; Serra‐Cobo, Amengual, Carlos Abellán, & Bourhy, 2002), each of these five lys‐ saviruses is associated with mortality in specific bat hosts (Banyard, Evans, Luo, & Fooks, 2014; Nokireki, Tammiranta, Kokkonen, Kantala, & Gadd, 2018). These include the following: