Dose Titration of Walleye Dermal Sarcoma (WDS) Tumor Filtrate

Area of Science:

• Ichthyology and Aquatic Animal Health
• Virology and Molecular Biology
• Fish Pathology

Background:

• Walleye dermal sarcoma is a neoplastic disease affecting walleye (Stizostedion vitreum).
• The causative agent is a virus, but the precise infectious dose for tumor induction via topical application is not well-defined.

Purpose of the Study:

• To determine the minimum infectious dose of walleye dermal sarcoma virus required to induce tumors.
• To establish a quantitative baseline for viral RNA copies in tumor filtrates.

Main Methods:

• Cell-free dermal sarcoma tumor filtrates were serially diluted (10-fold).
• Fish were challenged topically with diluted filtrates and incubated at 15°C for 20 weeks.
• Viral RNA quantification in filtrates was performed using quantitative (real-time) reverse transcriptase-polymerase chain reaction.

Main Results:

• The initial walleye dermal sarcoma inoculum contained approximately 10¹⁰ viral RNA copies per 100 μL.
• The minimum dose that induced grossly visible tumors via topical challenge was a 1,000-fold dilution.
• This corresponds to approximately 10⁷ viral RNA copies.

Conclusions:

• Topical application of walleye dermal sarcoma virus can induce tumors in susceptible fish.
• Approximately 10⁷ viral RNA copies represent the minimum dose for tumor induction under experimental conditions.
• This study provides a quantitative measure for the infectivity of walleye dermal sarcoma virus.