Plant pathogens provide clues to the potential origin of bat white-nose syndrome Pseudogymnoascus destructans.

White-nose syndrome has killed millions of bats, yet both the origins and infection strategy of the causative fungus, Pseudogymnoascus destructans, remain elusive. We provide evidence for a novel hypothesis that P. destructans emerged from plant-associated fungi and retained invasion strategies affiliated with fungal pathogens of plants. We demonstrate that P. destructans invades bat skin in successive biotrophic and necrotrophic stages (hemibiotrophic infection), a mechanism previously only described in plant fungal pathogens. Further, the convergence of hyphae at hair follicles suggests nutrient tropism. Tropism, biotrophy, and necrotrophy are often associated with structures termed appressoria in plant fungal pathogens; the penetrating hyphae produced by P. destructans resemble appressoria. Finally, we conducted a phylogenomic analysis of a taxonomically diverse collection of fungi. Despite gaps in genetic sampling of prehistoric and contemporary fungal species, we estimate an 88% probability the ancestral state of the clade containing P. destructans was a plant-associated fungus.

Wing pathology of white-nose syndrome in bats suggests life-threatening disruption of physiology.

White-nose syndrome (WNS) is causing unprecedented declines in several species of North American bats. The characteristic lesions of WNS are caused by the fungus Geomyces destructans, which erodes and replaces the living skin of bats while they hibernate. It is unknown how this infection kills the bats. We review here the unique physiological importance of wings to hibernating bats in relation to the damage caused by G. destructans and propose that mortality is caused by catastrophic disruption of wing-dependent physiological functions. Mechanisms of disease associated with G. destructans seem specific to hibernating bats and are most analogous to disease caused by chytrid fungus in amphibians.

Rapid polymerase chain reaction diagnosis of white-nose syndrome in bats.

A newly developed polymerase chain reaction (PCR)-based method to rapidly and specifically detect Geomyces destructans on the wings of infected bats from small quantities (1-2 mg) of tissue is described in the current study (methods for culturing and isolating G. destructans from bat skin are also described). The lower limits of detection for PCR were 5 fg of purified fungal DNA or 100 conidia per 2 mg of wing tissue. By using histology as the standard, the PCR had a diagnostic specificity of 100% and a diagnostic sensitivity of 96%, whereas the diagnostic sensitivity of culture techniques was only 54%. The accuracy and fast turnaround time of PCR provides field biologists with valuable information on infection status more rapidly than traditional methods, and the small amount of tissue required for the test would allow diagnosis of white-nose syndrome in live animals.

Histopathologic criteria to confirm white-nose syndrome in bats.

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.

Pathology and proposed pathophysiology of diclofenac poisoning in free-living and experimentally exposed oriental white-backed vultures (Gyps bengalensis).

Oriental white-backed vultures (Gyps bengalensis; OWBVs) died of renal failure when they ingested diclofenac, a nonsteroidal anti-inflammatory drug (NSAID), in tissues of domestic livestock. Acute necrosis of proximal convoluted tubules in these vultures was severe. Glomeruli, distal convoluted tubules, and collecting tubules were relatively spared in the vultures that had early lesions. In most vultures, however, lesions became extensive with large urate aggregates obscuring renal architecture. Inflammation was minimal. Extensive urate precipitation on the surface and within organ parenchyma (visceral gout) was consistently found in vultures with renal failure. Very little is known about the physiologic effect of NSAIDs in birds. Research in mammals has shown that diclofenac inhibits formation of prostaglandins. We propose that the mechanism by which diclofenac induces renal failure in the OWBV is through the inhibition of the modulating effect of prostaglandin on angiotensin II-mediated adrenergic stimulation. Renal portal valves open in response to adrenergic stimulation, redirecting portal blood to the caudal vena cava and bypassing the kidney. If diclofenac removes a modulating effect of prostaglandins on the renal portal valves, indiscriminant activation of these valves would redirect the primary nutrient blood supply away from the renal cortex. Resulting ischemic necrosis of the cortical proximal convoluted tubules would be consistent with our histologic findings in these OWBVs.

Nonlethal screening of bat-wing skin with the use of ultraviolet fluorescence to detect lesions indicative of white-nose syndrome.

Definitive diagnosis of the bat disease white-nose syndrome (WNS) requires histologic analysis to identify the cutaneous erosions caused by the fungal pathogen Pseudogymnoascus [formerly Geomyces] destructans (Pd). Gross visual inspection does not distinguish bats with or without WNS, and no nonlethal, on-site, preliminary screening methods are available for WNS in bats. We demonstrate that long-wave ultraviolet (UV) light (wavelength 366-385 nm) elicits a distinct orange-yellow fluorescence in bat-wing membranes (skin) that corresponds directly with the fungal cupping erosions in histologic sections of skin that are the current gold standard for diagnosis of WNS. Between March 2009 and April 2012, wing membranes from 168 North American bat carcasses submitted to the US Geological Survey National Wildlife Health Center were examined with the use of both UV light and histology. Comparison of these techniques showed that 98.8% of the bats with foci of orange-yellow wing fluorescence (n=80) were WNS-positive based on histologic diagnosis; bat wings that did not fluoresce under UV light (n=88) were all histologically negative for WNS lesions. Punch biopsy samples as small as 3 mm taken from areas of wing with UV fluorescence were effective for identifying lesions diagnostic for WNS by histopathology. In a nonlethal biopsy-based study of 62 bats sampled (4-mm diameter) in hibernacula of the Czech Republic during 2012, 95.5% of fluorescent (n=22) and 100% of nonfluorescent (n=40) wing samples were confirmed by histopathology to be WNS positive and negative, respectively. This evidence supports use of long-wave UV light as a nonlethal and field-applicable method to screen bats for lesions indicative of WNS. Further, UV fluorescence can be used to guide targeted, nonlethal biopsy sampling for follow-up molecular testing, fungal culture analysis, and histologic confirmation of WNS.

Electrolyte depletion in white-nose syndrome bats.

The emerging wildlife disease white-nose syndrome is causing widespread mortality in hibernating North American bats. White-nose syndrome occurs when the fungus Geomyces destructans infects the living skin of bats during hibernation, but links between infection and mortality are underexplored. We analyzed blood from hibernating bats and compared blood electrolyte levels to wing damage caused by the fungus. Sodium and chloride tended to decrease as wing damage increased in severity. Depletion of these electrolytes suggests that infected bats may become hypotonically dehydrated during winter. Although bats regularly arouse from hibernation to drink during winter, water available in hibernacula may not contain sufficient electrolytes to offset winter losses caused by disease. Damage to bat wings from G. destructans may cause life-threatening electrolyte imbalances.

Recovery of little brown bats (Myotis lucifugus) from natural infection with Geomyces destructans, white-nose syndrome.

Geomyces destructans produces the white fungal growth on the muzzle and the tacky white discoloration on wings and ears that characterize white-nose syndrome (WNS) in cave-hibernating bats. To test the hypothesis that postemergent WNS-infected bats recover from infection with G. destructans, 30 little brown bats (Myotis lucifugus) were collected in May 2009 from a WNS-affected hibernation site in New Jersey. All bats were confirmed to be infected with G. destructans using a noninvasive fungal tape method to identify the conidia of G. destructans and polymerase chain reaction (PCR). The bats were then held in captivity and given supportive care for 70 days. Of the 26 bats that survived and were humanely killed after 70 days, 25 showed significant improvement in the external appearance of wing membranes, had no microscopic evidence of infection by G. destructans, and had wing tissue samples that were negative for G. destructans by PCR. A subset of the bats was treated topically at the beginning of the rehabilitation study with a dilute vinegar solution, but treatment with vinegar provided no added advantage to recovery. Provision of supportive care to homeothermic bats was sufficient for full recovery from WNS. One bat at day 70 still had both gross pathology and microscopic evidence of WNS in wing membranes and was PCR-positive for G. destructans. Dense aggregates of neutrophils surrounded the hyphae that remained in the wing membrane of this bat.