Disease recovery in bats affected by white-nose syndrome

Abstract

Processes associated with recovery of survivors are understudied components of wildlife infectious diseases. White-nose syndrome (WNS) in bats provides an opportunity to study recovery of disease survivors, understand implications of recovery for individual energetics, and assess the role of survivors in pathogen transmission. We documented temporal patterns of recovery from WNS in little brown bats (Myotis lucifugus) following hibernation to test the hypotheses that: (1) recovery of wing structure from WNS matches a rapid time scale (i.e. approximately 30 days) suggested by data from free-ranging bats; (2) torpor expression plays a role in recovery; (3) wing physiological function returns to normal alongside structural recovery; and (4) pathogen loads decline quickly during recovery. We collected naturally infected bats at the end of hibernation, brought them into captivity, and quantified recovery over 40 days by monitoring body mass, wing damage, thermoregulation, histopathology of wing biopsies, skin surface lipids and fungal load. Most metrics returned to normal within 30 days, although wing damage was still detectable at the end of the study. Torpor expression declined overall throughout the study, but bats expressed relatively shallow torpor boutswith a plateau in minimum skin temperatureduring intensive healing between approximately days 8 and 15. Pathogen loads were nearly undetectable after the first week of the study, but some bats were still detectably infected at day 40. Our results suggest that healing bats face a severe energetic imbalance during early recovery from direct costs of healing and reduced foraging efficiency. Management of WNS should not rely solely on actions during winter, but should also aim to support energy balance of recovering bats during spring and summer.

Ecology and impacts of white-nose syndrome on bats

“…For bats that survive until spring, the return to euthermia can result in an intense inflammatory response in P. destructans-infected tissue, primarily in the wing and tail membranes 71,72 . This immune response can reduce fungal infection 73 but can also result in immune reconstitution inflammatory syndrome 71,74 , which causes severe immune-mediated tissue damage and can result in death for already compromised individuals 75 .…”

“…If bats survive through emergence from hibernation, they begin to clear infections within a few weeks 61,72,73,76 . Fungal loads drop significantly within 10 days following emergence and reach nearly undetectable levels (<1%) by mid summer 61,72,73 .…”

Continued preference for suboptimal habitat reduces bat survival with white-nose syndrome

“…Several bat species in North America have recently experienced severe population declines [22][23][24][25] due to a fungal pathogen introduced from Eurasia, Pseudogymnoascus destructans, which causes white-nose syndrome [26][27][28][29] . The fungus infects bats and grows into their epidermal tissue during hibernation, when bats cool their bodies down to near ambient hibernaculum temperatures.…”

Body mass and hibernation microclimate may predict bat susceptibility to white‐nose syndrome

“…Therefore, we cannot explicitly state that suboptimal environments for the fungus would result in higher rates of survival, but rather need to take a holistic approach to understanding the specific hibernation strategies of each bat species, recognizing that intraspecific differences can exist (e.g., Klüg‐Baerwald and Brigham, 2017). Additionally, our models only predict survival based on sufficient fat stores, but do not consider fat stores posthibernation, when remaining stores are necessary for flight and reproduction, nor the energy required for the costly inflammatory response to fight off infection (Fuller et al., 2020).…”