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Differences in virulence between two serotypes of Ichthyophthirius multifiliis.
Alton G Swennes1, Jane G Noe, R Craig Findly
1Department of Infectious Diseases, College of Veterinary Medicine, University of Georgia, Athens 30602, USA.
Diseases of Aquatic Organisms
|May 27, 2006
Summary
Two Ichthyophthirius multifiliis (I. multifiliis) isolates showed different virulence in channel catfish. One isolate, NY1, caused higher mortality despite lower initial infection levels, indicating faster parasite life cycles impact fish survival.
Area of Science:
- Aquatic Animal Health
- Parasitology
- Fish Immunology
Background:
- Ichthyophthirius multifiliis is a parasitic ciliate causing significant disease in freshwater fish.
- Different isolates of I. multifiliis may exhibit varying levels of virulence.
- Surface immobilization-antigens (i-antigens) can differentiate I. multifiliis serotypes.
Purpose of the Study:
- To compare the virulence of two I. multifiliis isolates (NY1 and G5) in channel catfish.
- To investigate the relationship between parasite life cycle, serotype, and disease outcome.
- To provide experimental evidence for virulence differences among I. multifiliis serotypes.
Main Methods:
- Channel catfish were infected with two distinct I. multifiliis isolates (NY1 - Serotype A, G5 - Serotype D).
- Tail-fin infections were used to quantify parasite load.
- Fish survival rates were monitored to assess virulence.
Main Results:
- NY1 isolate infected fish at a lower level compared to the G5 isolate.
- Despite lower initial infection, all fish infected with NY1 died.
- 51% of fish infected with the G5 isolate survived.
Conclusions:
- The NY1 isolate of I. multifiliis demonstrated greater virulence than the G5 isolate.
- A shorter parasite life cycle in the NY1 isolate likely leads to overwhelming reinfection before an immune response can develop.
- This study provides the first experimental evidence of virulence variation between I. multifiliis serotypes.