A High Throughput Viability Screening Method for the Marine Ectoparasite Neoparamoeba perurans

Area of Science:

• Aquatic animal health
• Parasitology
• Fish disease research

Background:

• Amoebic gill disease (AGD) in Atlantic salmon (Salmo salar) is caused by the marine protozoan Neoparamoeba perurans.
• Current treatments include freshwater bathing (Australia) and hydrogen peroxide (H₂O₂) (cooler climates), but novel therapies are needed.
• Lack of established in vitro high-throughput screening methods hinders the discovery of new antiparasitic compounds for AGD.

Purpose of the Study:

• To develop and evaluate two in vitro bioassays for screening antiparasitic compounds against Neoparamoeba perurans.
• To differentiate between amoebistatic and amoebicidal activity of potential AGD treatments.
• To provide a critical tool for high-throughput screening of novel and effective AGD therapies.

Main Methods:

• Two in vitro bioassays were evaluated, focusing on metabolic energy production and cellular membrane integrity.
• Neoparamoeba perurans were treated with freshwater, hydrogen peroxide (H₂O₂), or chloramine-T for 4 hours.
• Parasite viability and recovery were assessed 24 hours post-treatment using microscopy and bioassay measurements.

Main Results:

• Both H₂O₂ and freshwater demonstrated 95% amoebicidal activity, though via distinct mechanisms.
• The bioassays successfully distinguished between amoebistatic (reversible inhibition) and amoebicidal (cell death) effects.
• A crucial recovery period post-treatment was identified for accurately differentiating treatment mechanisms.

Conclusions:

• The developed in vitro bioassays are effective for assessing the activity of potential AGD treatments.
• These assays provide a foundation for high-throughput screening, accelerating the search for new AGD therapies.
• The findings support the inclusion of a recovery assessment to accurately characterize antiparasitic compound efficacy.