Abstract

The postmortem diagnosis of dermatophytosis in a short-nosed echidna (Tachyglossus aculeatus) prompted the clinical investigation of Perth Zoo’s remaining echidnas. All presented with dermatopathy of varying severity. The lesions were diagnosed histologically as dermatophytosis, probably caused by Microsporum gypseum, with secondary pyoderma. All clinical cases responded to a combination of systemic antibiotics, topical treatment and bathing, and environmental change.

Case Study

Case 1. Detection of Dermatophytosis in an Echidna at Necropsy

An individual from Perth Zoo’s collection of short-nosed echidnas (Tachyglossus aculeatus) was submitted for veterinary examination after being found laterally recumbent and severely depressed. Traumatic excoriations on the snout and forelimbs suggested that the animal had become entrapped while burrowing and produced the injuries when attempting to struggle free. Almost all the spines on the cranial third of the body were broken, and remaining spines were friable and easily damaged. Although hospitalized and given subcutaneous fluids in 20 ml boluses throughout the afternoon, the echidna was found dead the following day.

At postmortem examination, the echidna (Echidna 1) was found with very brittle spines, marked ventral alopecia, and excessive waxy exudate on the ventral skin and in the ears. Histopathologic examination of the skin revealed a severe pyoderma and marked dermatophytosis. Fungal hyphae were evident within the superficial keratin and serocellular crust, and the surface keratin was also heavily infested with bacteria, including gram-positive cocci and bacilli and some gram-negative bacilli. The skin pathology was characterised by parakeratotic and hyperkeratotic hyperkeratosis, dermal infiltration with polymorphonuclear cells, and pustules.

Case 2. Physical Examination and Diagnostic Sampling of Echidna Collection

The findings of Echidna 1 prompted the veterinary examination of the five remaining echidnas in the collection. Although the echidnas were routinely examined by keepers every 4–6 weeks, close inspection of the skin was made difficult by the accumulation of soil and debris in the spines, and the echidnas’ tendency to curl up when restrained. Veterinary examination necessitated manual restraint after removal from their burrows. All five were found to have varying degrees of dermatitis, characterized by alopecia, fragile and broken spines, and dark, waxy exudate on the ventral skin and in the ears. Due to the possibility of dermatophytosis, all the animals were transferred from their heavily mulched outdoor enclosure to a dry, lightly mulched, indoor enclosure. At transfer, skin scrapes and swabs were collected from all individuals for microscopy, fungal and bacterial culture and sensitivity. Spines and hairs from the most affected individuals were submitted for potassium hydroxide examination and histopathology.

Microscopy of skin scrapes and potassium hydroxide examination of hair shafts in affected individuals revealed a few fungal hyphae, not infecting hair shafts. The absence of hair shaft involvement suggested that the hyphae were soil contaminants, rather than pathogens. No ectoparasites were detected on skin scrapes. Wet microscopy and gram stains were characterised by occasional fungal hyphae, with some gram-negative bacilli and gram-positive cocci. Culture from four individuals (Echidnas 2, 3, 4 and 5) grew a moderate to heavy mixed growth of a number of organisms, including Enterobacter spp., Klebsiella spp., coagulase negative Staphylococcus, non-hemolytic Streptococcus, and non-hemolytic E. coli.

Fungal culture of spines and skin scrapings was undertaken for the three most affected individuals (Echidnas 2, 3, and 5). Echidna 5 grew Mucor spp., Echidna 3 grew Aspergillus fumigatus and Penicillium spp., and Echidna 2 grew Microsporum gypseum. Given the histopathologic finding of dermatophytosis in Echidna 1, it was suspected that Microsporum gypseum was the primary pathogen in all the echidnas, and that opportunistic bacterial infection with commensal organisms resulted in the secondary pyoderma.

Initial Treatment of Echidna Group

Topical treatment of echidnas is made difficult by their spines, burrowing behaviour and physical strength. A manual restraint technique of suspending them by their hind feet causes them to uncurl, exposing the head, ventral region and the non-spiny parts of the limbs. While waiting for results of diagnostic sampling, each animal was restrained in this manner every 3 days for IM long-acting penicillin injection (Norocillin LA Injection: procaine penicillin 150 mg/ml, benzathine penicillin G 112.5 mg/ml: Norbrook Laboratories Australia Pty. Ltd., 1 ml/10 kg body weight). At each treatment, the animal was also sprayed topically with oxytetracycline (Terramycin Pinkeye Aerosol: oxytetracycline hydrochloride 2 mg/g, Pfizer Animal Health, West Ryde, New South Wales). Although cultured Enterobacter and Staphylococcus species were resistant to the penicillin, treatments were continued for 2 weeks due to concerns of stress related to more frequent treatment modalities.

Because the animals were otherwise in good health and of good general body condition, specific antifungal treatment was not performed. It was hoped that the condition would be self-limiting if the echidnas were removed to another enclosure and secondary bacterial infection was controlled. Manual restraint and veterinary examinations were scheduled once every 3 weeks to monitor the progress of alopecia and damage to spines.

Examination, Sampling and Treatment Under Anaesthesia

Over the ensuing month, the skin condition of the worst affected echidna (Echidna 2) deteriorated further, so it was anesthetized for a more detailed workup and treatment. The animal was induced in an induction chamber using isoflurane (Isoflurane Inhalation Anaesthetic, David Bull Laboratories, Mulgrave, Victoria) then maintained by facemask.

Skin lesions were characterised by generalized alopecia, with scaling on the ventral mandible and accumulation of skin debris and crusting at the base of the spines. Many spines were broken, and the shafts of the broken spines were hollow, rather than being solid keratin. Waxy seborrheic discharge was present around the head and in the external ear canals.

Wedge skin biopsies were taken for bacterial and fungal culture, and histopathology. The echidna appeared to be in good body condition, and no other abnormalities were found on physical examination. Hematology and serum biochemistry parameters were within ISIS reference ranges for the species.

After diagnostic samples were taken, the echidna was placed in dorsal recumbency in a warm water bath, to which an antibacterial, keratolytic, antifungal shampoo was added (Sebolyse Medicated Foam: miconazole nitrate 20 mg/ml, chlorhexidine gluconate 20 mg/ml, selenium sulfide 2.5 mg/ml; Dermcare-Vet Pty. Ltd., Springwood, Queensland). A long-handled dishwashing brush was used to scrub the skin and the spines. This process was effective in removing scurf, dirt and seborrheic debris. Topical treatment with miconazole aerosol powder (Daktarin, 2% miconazole nitrate; Janssen-Cilag Pty. Ltd., North Ryde, New South Wales) was initiated following the bath. This product was sprayed over the spines and ventrum at a distance of 15 cm from the animal, once daily for 3 weeks. Sebolyse baths were given every 2 weeks for a total of four treatments.

Histopathology of the skin biopsy from Echidna 2 showed evidence of heavy fungal infection and secondary pyoderma. Bacterial culture of the skin biopsy once again demonstrated a heavy mixed growth. No pathogenic fungal species were detected on culture of the skin biopsies, although soil commensal species of Fusarium and Rhizopus were identified.

Two of the remaining four echidnas (Echidnas 3 and 4) developed signs that warranted bathing under anesthesia, but the Echidnas 5 and 6 resolved without further treatment. Only Echidna 2 was treated with topical miconazole spray. Manual restraint and veterinary examination of all echidnas was continued every 4–6 weeks for 6 months, to assess the need for further bathing. Echidna 2 underwent Sebolyse baths on another two occasions during the 6 months, but all the others continued to improve without further topical treatment.

Discussion

The monitoring, diagnosis and treatment of disease in echidnas is a challenge. Conscious manual restraint is difficult and potentially stressful to the animal. Echidna which are not restrained appropriately assume a defensive posture; in these cases, this caused keepers to underestimate the extent and severity of skin lesions during routine weighing and handling, prior to the death of Echidna 1.

There is limited information in the literature regarding pathologic skin conditions in echidnas.^1-3,5-7 A hyperkeratotic condition is described in juvenile echidnas, which has been associated with the presence of pox virus particles.^1,3,5,7 Staphylococcus granulomata,⁵ and nodular masses caused by plerocercoids of Spirometra erinacei,⁷ are also reported. There is one report of Microsporum gypseum being isolated from the skin of a captive echidna with fractured, friable spines, but there are few published details of this case.^1-3,6,7

Histopathologic examination of biopsies Echidnas 1 and 2 confirmed the diagnosis of dermatophytosis. It seems likely that the causative agent was Microsporum gypseum, given that this organism was grown from one of the quill samples taken from Echidna 2. The failure to isolate M. gypseum from the other cases is not surprising, since saprophytic fungal overgrowths are a common complication of dermatophyte culture.⁴ Fungal soil commensals were detected on skin scrapings and fungal culture from several individuals. Mucor sp., which were cultured from Echidna 5, are also known to be potentially pathogenic, and have been known to cause systemic disease and ulcerative dermatitis in platypuses.^1,3,6 However, the non-ulcerative nature of the echidnas’ skin lesions, the histopathologic appearance, and the lack of systemic illness, were more consistent with dermatophytosis than mucormycosis.

The secondary pyoderma was responsive to long-acting antibiotics in most cases, but the most severely affected animals required regular topical treatment under anesthesia to resolve the problem. The baths were highly successful in removing debris and seborrheic buildup, as well as providing a means of medicating the skin with antibacterial and antifungal compounds.

The use of antibiotic and antifungal drugs in echidnas is limited by the lack of reliable pharmacokinetic data. In this case study, no adverse effects were seen with the use of long-acting penicillin, topical miconazole, topical Sebolyse or topical oxytetracycline spray.

Eighteen months after the death of Echidna 1, the entire echidna group was moved from their temporary holding enclosures into a new outdoor display enclosure. The new enclosure features a sand and leaf litter substrate, and custom built, easily cleaned burrows containing jarrah sawdust as bedding. There have been no relapses since the echidnas were removed from their original enclosure. It seems likely that the origin of the skin condition was environmental and may have been linked to the use of a new type of soil substrate that was put in the enclosure about 10 weeks prior to the death of Echidna 1. M. gypseum is known to survive for long periods in soil,⁴ and the echidnas burrowed extensively in the soil of their old exhibit, only emerging from their diggings to feed. In the new enclosure, they are inclined to use the pre-built burrows rather than digging their own, and this is likely to contribute significantly to the persisting good condition of their skin and spines.

Acknowledgments

The authors would like to thank the staff of the Perth Zoo Veterinary Department and Australian Section for their dedication in the management of these cases. Thanks also to Dr. John Jardine of Vetpath Laboratory Services for his comments on the histopathology and culture results.

Literature Cited

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2.  Booth, R.J. 1999. Care and medical management of monotremes. In: Wildlife in Australia Healthcare and Management, Proceedings 327 of the Post Graduate Foundation in Veterinary Science, 1999, University of Sydney, Dubbo: 41–47.

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7.  Whittington, R.J. 1993. Diseases of monotremes. In: Fowler, M.E. (ed.), Zoo and Wild Animal Medicine, 3rd ed. W.B. Saunders, Philadelphia, Pennsylvania. Pp. 269–276.