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.
Abstract:
Naive channel catfish Ictalurus punctatus were infected by 2 isolates of the parasitic ciliate Ichthyophthirius multifiliis that differed in virulence. The isolates, NY1 and G5, Serotypes A and D, respectively, express different surface immobilization-antigens. The virulence of the 2 isolates was compared using tail-fin infections to quantitate parasite numbers and by analysis of the survival of infected fish. Although NY1 infected fish at a lower level than G5, all NY1-infected fish died, but 51% of G5-infected fish survived. The greater virulence of NY1 is apparently a consequence of its shorter life cycle, which results in overwhelming reinfection of fish before they can develop a protective immune response. This report represents the first experimental evidence for differences in virulence between serotypes of I. multifiliis.
Insights
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.
