Histopathologic Criteria to Confirm White-nose Syndrome in Bats

Abstract

White-nose syndrome (WNS) is a cutaneous fungal disease of hibernating bats associated with a novel Geomyces sp. fungus. Currently, confirmation of WNS requires histopathologic examination. Invasion of living tissue distinguishes this fungal infection from those caused by conventional transmissible dermatophytes. Although fungal hyphae penetrate the connective tissue of glabrous skin and muzzle, there is typically no cellular inflammatory response in hibernating bats. Preferred tissue samples to diagnose this fungal infection are rostral muzzle with nose and wing membrane fixed in 10% neutral buffered formalin. To optimize detection, the muzzle is trimmed longitudinally, the wing membrane is rolled, and multiple cross-sections are embedded to increase the surface area examined. Periodic acid-Schiff stain is essential to discriminate the nonpigmented fungal hyphae and conidia. Fungal hyphae form cup-like epidermal erosions and ulcers in the wing membrane and pinna with involvement of underlying connective tissue. In addition, fungal hyphae are present in hair follicles and in sebaceous and apocrine glands of the muzzle with invasion of tissue surrounding adnexa. Fungal hyphae in tissues are branching and septate, but the diameter and shape of the hyphae may vary from parallel walls measuring 2 microm in diameter to irregular walls measuring 3-5 microm in diameter. When present on short aerial hyphae, curved conidia are approximately 2.5 microm wide and 7.5 microm in curved length. Conidia have a more deeply basophilic center, and one or both ends are usually blunt. Although WNS is a disease of hibernating bats, severe wing damage due to fungal hyphae may be seen in bats that have recently emerged from hibernation. These recently emerged bats also have a robust suppurative inflammatory response.

Living strategy of cold-adapted fungi with the reference to several representative species

“…destructans (formerly known as Geomyces destructans ) is a psychrophilic fungus that causes white-nose syndrome (WNS) of hibernating and cave-roosting bats, a fatal disease that has devastated bat populations in parts of the United States and Canada. A visually conspicuous white fungus grows on the face, ears or wings of stricken bats; infiltration of the hyphae into membranes and tissues leads to severe damage (Meteyer et al 2009). Bats that exhibit WNS have little or no fat reserves, which are essential for their survival throughout and after hibernation (Blehert et al 2009).…”

Space-Time Models for a Panzootic in Bats, With a Focus on the Endangered Indiana Bat

“…White-nose syndrome is characterized by the presence of profuse but delicate hyphae and conidia produced by the fungus on the muzzles, wing membranes, and pinnae of infected hibernating bats; the fungal hyphae pervade the living skin tissues of infected bats, with hair follicles and sebaceous glands being effaced Meteyer et al, 2009). Severe wing damage associated with fungal invasion may be seen in bats that have recently emerged from hibernation (Meteyer et al, 2009;Cryan et al, 2010).…”

Editorial: What is in a Name? A Proposal to Use Geomycosis Instead of White Nose Syndrome (WNS) to Describe Bat Infection Caused by Geomyces Destructans

“…Subsequent studies indicated that the cottony appearance was due to fungal growth. The extensive fungal colonization of bat skin and hair, characteristic histopathological appearance, and exclusive presence of a specific fungal DNA in the animals' tissues led to the discovery of the causal agent-a newly described species called Geomyces destructans [2][3][4][5][6]. Subsequent studies revealed that this condition has caused the deaths of nearly a million bats in the Northeast and it has rapidly spread to other parts of the country [7].…”

“…Bats afflicted with WNS have many symptoms, such as, emaciation, epidermal erosion and ulcers, and extensive wing damage [4,10]. Accordingly, this disease can be confirmed by the morphological appearance of the fungus on any part of the body, histopathology of affected tissues with demonstration of hyphae-conidia, or demonstration of G. destructans by PCR-nucleotide sequencing [3,4,6,11].…”

“…Accordingly, this disease can be confirmed by the morphological appearance of the fungus on any part of the body, histopathology of affected tissues with demonstration of hyphae-conidia, or demonstration of G. destructans by PCR-nucleotide sequencing [3,4,6,11]. Thus, it is reasonable to conclude that WNS is neither an exclusive presentation nor an all-encompassing description of G. destructans infections in bats.…”