Metarhizium anisopliae infection of an adult wētāpunga (Deinacrida heteracantha).

Abstract

Case history: An adult male wētāpunga (Deinacrida heteracantha), wild-caught under permit in May 2024 as part of a group collected for conservation breeding purposes, presented in mid-August 2024 with a month-long history of gradually worsening discolouration of the left eye and periocular region of the gena.

Clinical findings: The left eye was internally discoloured a blotchy yellow colour with a metallic bronze-gold sheen, while the periocular region was discoloured dark brown, radiating approximately 5 mm circumferentially from the eye. No samples from affected tissues were able to be taken ante-mortem for diagnostics. Fungal infection was suspected, and empirical treatment was started using once daily application of a topical ointment of povidone-iodine 10% w/w, equivalent to 1% w/w available iodine. Within 24 hours, discolouration of the eye, but not the periocular region, temporarily resolved during treatment and with no obvious adverse effects. The animal died 1 month after presentation, despite ongoing treatment.Gross necropsy showed focally extensive black discolouration of tissues deep to the left eye. Histopathology revealed extensive keratitis, rhabdomyositis and steatitis with multisystemic fungal infection. Fungal culture and phenotypic assessment were consistent with Metarhizium species, and genomic sequencing confirmed M. anisopliae as the causative agent. Retrospective evaluation of six previous cases of integumentary lesions in wētāpunga revealed some similarities in case presentation but key differences in the severity of infection.

Diagnosis: Multisystemic fungal infection due to Metarhizium anisopliae.

Clinical relevance: Metarhizium species are ubiquitous in the environment, and M. anisopliae is a known keratophilic pathogen of insects with application as a biologic pest control agent. While empirical topical treatment appeared to alleviate the external clinical signs of the ocular infection, the severity of infection was difficult to determine ante-mortem. Here, through retrospective analyses of this and similar cases at Auckland Zoo, we show that fungal integumentary and/or ophthalmic disease in wētāpunga may present as focal darkening of the exoskeleton and pallor of the affected eye(s). Given the limitations for ante-mortem diagnostics and treatment options in invertebrates, and the unknown capacity for these animals to perceive pain, subsequently making it more challenging to assess their welfare while diseased, euthanasia remains an important treatment option in invertebrate medicine.