First report of myiasis caused by Cochliomyia hominivorax in free-ranging giant otter (Pteronura brasiliensis).

Giant otters are territorial semi-aquatic mammals. It is common to find several individuals exhibiting wounds and scars due to intraspecific conflicts. Myiasis is a parasitic infestation on living tissues of vertebrates caused by dipterous larvae, that usually develops in freshly open wounds and can seriously threaten the host's health. Ectoparasites seem to be rare among giant otters and myiasis had not been recorded in this species until now. Here, is presented one record of myiasis in a free-ranging giant otter found dead in the Pantanal, Brazil. An ulcerative lesion was found in the frontoparietal region, from which 22 larvae were recovered and identified as Cochliomyia hominivorax. The low occurrence of ectoparasites in giant otters might reflect their semi-aquatic habits and their grooming behavior, which makes it difficult for parasites to remain on the skin. The injured otter probably got the larvae after an intraspecific fight. Agonistic encounters between groups of giant otters have been reported before and these fights can result in serious wounds or even death. It was hypothesized that the myiasis caused by C. hominivorax deteriorated the health of the infested giant otter, which prevented recovery and accelerated its death.