National Wildlife Health Center

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Case Definitions for WNS


Updated May 18, 2012

White-nose syndrome (WNS) is a disease of bats infected with the fungus Geomyces destructans. The standard terminology that diagnostic laboratories and resource managers use to report WNS in bats, including identification of field signs suggestive of disease, detection of G. destructans by PCR, fungal tape strip and/or culture, and confirmation of WNS by histopathology has been simplified into 3 categories (Negative, Suspect, or Confirmed) described below. The former “Presumptive positive” classification has been eliminated. The criteria for confirming a diagnosis of WNS requires histopathological evidence of infection with G. destructans. “Suspect WNS” classification warrants testing additional submissions from the area to confirm WNS. For management purposes, hibernacula should be considered contaminated with G. destructans if they contain at least one bat (regardless of visible field signs) that tests positive for the fungus or WNS by any one or more diagnostic method. A contaminated hibernaculum retains this designation indefinitely.

Case Definitions for Bats

Negative:

  • No (or nonspecific) field signs are observed AND neither WNS nor G. destructans is detected by diagnostic tests (PCR, culture, fungal tape, and/or histopathology).

Suspect WNS:

To identify a bat as suspect for WNS, one of the following must be true:

  • Field signs are suggestive of WNS AND WNS was previously confirmed in the county or in an adjacent county. Further diagnostics (PCR, culture, fungal tape and histopathology) were not performed.
  • A bat is PCR positive meaning that DNA from G. destructans is present although the viability of the organism is unknown. Field signs are not required. No histopathology was performed or is negative.
  • A bat is culture positive meaning there is viable G. destructans present. Field signs are not required. No histopathology was performed or is negative.
  • Fungal tape strip of bat fur or skin is positive for G. destructans-like conidia. Visible fungus is required. No histopathology was performed or is negative.

Confirmed positive for WNS:

  • Confirmed positive bats are those that fulfill histopathologic criteria for the disease. These criteria require the identification of a specific pattern of fungal colonization in the epidermis which may extend to invasion of the dermis and connective tissue. Histopathology can also support the presence/identity of G. destructans if distinctive conidia are observed. Field signs, PCR, fungal tape strip, and culture can be negative for bats that fulfill the histopathologic criteria for confirmed WNS. Follow-up PCR/DNA sequencing or fungal culture should be considered to confirm the identity of the organism in geographic regions with no prior or unknown history of WNS.

Field Signs Associated with WNS in bats

NOTE - not all signs must be present but confidence levels improve with increasing number of signs observed

  • Winter/Spring - excessive or unexplained mortality at/near hibernaculum; visible fungus on flight membranes, muzzle, and/or ears of live or fresh dead bats; abnormal behaviors including daytime activity, population shift to entrance of the hibernaculum, decreased arousal with disturbance inside hibernaculum; moderate to severe wing damage in nontorpid bats*; thin body condition*
  • Summer/Fall - wing damage and depigmentation* through late May; bats with wing damage collected between June-October have tested negative for G. destructans and WNS.

* considered a nonspecific field sign when observed by itself

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