Whirling Disease: Reviews and Current Topics

Efficacy of Fumagillin and TNP-470 to Prevent Experimentally Induced Whirling Disease in Rainbow Trout Oncorhynchus mykiss

Linda Staton, Dave Erdahl, and Mansour El-Matbouli

doi: https://doi.org/10.47886/9781888569377.ch21

ABSTRACT Two potential therapeutants, fumagillin, an antibiotic derived from the fungus Aspergillus fumagatus, and TNP-470, a superactive analog of fumagillin, were tested for efficacy to prevent Myxobolus cerebralis infection in rainbow trout. The study was conducted at the Wild Trout Research Laboratory in Bozeman, Montana utilizing rainbow trout Oncorhynchus mykiss fry (~2.0 g). Treatment groups included negative controls (no treatment, no exposure), positive controls (no treatment, exposure), fumagillin top-dressed on feed, fumagillin incorporated in feed, and TNP-470 incorporated in feed. The exposure dose was 1000 triactinomyxons (TAMs) per fish for 2 h. Medicated feed treatment was initiated 24 h after exposure to TAMs. All treated groups received medicated feed for 10 d, with the exception of a single TNP-470 treatment group that was fed for 26 d. Five replicate tanks of fish were used for each treatment group. Presence and level of Myxobolus cerebralis infection were determined by histology, spore counts, and electron microscopy evaluation conducted 150 d postexposure. Hematology samples were also collected to evaluate potential toxic effects of treatment. Spore count and histological evaluation indicated that fumagillin and TNP-470 treatment was not efficacious in preventing or reducing Myxobolus cerebralis infection. Although fumagillin and TNP-470 administered for 10 d or 26 d did result in a reduction in spore numbers, results were not significantly different than observed in positive controls. Furthermore, histological scores were similar for all treatment groups and the positive controls. Although electron microscopy revealed spore deformation in both fumagillin and TNP-470 treated groups, no treatment group was effective in preventing Myxobolus cerebralis infection. Fumagillin treatment and TNP-470 fed for 10 d did not appear to negatively impact fish performance. However, toxicity was observed in fish fed TNP-470 for 26 d. These fish were observed to be lethargic 30 d pe, and blood samples revealed low hematocrits, severely decreased lymphocytes, and reduced numbers of blast cells. Histological evaluation revealed abnormal cytology in both the kidney and thymus. Based on study results, fumagillin and TNP-470 did not appear to be effective therapeutants for use in the prevention or control of Myxobolus cerebralis infection in rainbow trout.