American horseshoe crabs (Limulus polyphemus) developed white, proliferative soft tissue lesions affecting the gills, legs, and tail as well as ulcerative lesions affecting the ventral shell. On physical examination 39/46 crabs of all age groups were affected with one or both of the described lesions and their severity increased with age. Lesions were of un-speciated fungal etiology based on culture, cytology, histopathology, and PCR. In order to establish an antifungal protocol for treatment of infected crabs, a pharmacokinetic study using itraconazole was performed. Itraconazole was administered intravenously at 10 mg/kg to 10 adult, healthy American horseshoe crabs. Hemolymph samples were collected via cardiocentesis at 0, 0.5, 1, 2, 4, 6, 24, 48 and 72 h following administration of itraconazole. The concentrations of itraconazole and its most active metabolite, hydroxyitraconazole were determined using high performance liquid chromatography. The t½, volume of distribution, and clearance were 25.78 h, 10.95 L/kg, and 0.31 L/h∗kg, respectively. The AUC0-∞ and C0 were 49.93±36.49 mg∗h/L and 9.73 mg/L, respectively. The active metabolite hydroxyitraconazole had a Cmax and AUC0-last of 0.08 mg/L and 2.23 mg∗h/L, respectively. Therapeutic levels (500 ng/ml) of itraconazole were attained in the hemolymph of all study animals. Results of this study conclude that itraconazole administered intravenously at 10 mg/kg every 24 h should be effective in the treatment of susceptible fungal infections in the American horseshoe crab. Further studies are indicated to establish potential toxicities of itraconazole, as well as sensitivities of common fungal pathogens to itraconazole in the horseshoe crab.
The authors thank the staff at Ripley’s Aquarium of the Smokies for their assistance and support during the study. This project was funded by a grant from the Companion Animal Fund, Department of Small Animal Clinical Sciences, College of Veterinary Medicine, The University of Tennessee, Knoxville, TN, USA.