Life cycle of fish parasite
Parvicapsula minibicornis
Christopher Zielinski, Stephen Atkinson,
Dr. Sascha Hallett, & Dr. Jerri
Bartholomew
Center for Fish Disease Research
Department of Microbiology
Oregon State University

Parvicapsula minibicornis is a myxozoan
What are Myxozoans?
-Mostly fish parasites
-Multicellular organisms
-Over 1350 described species
-Infection of commercially important species is of most concern
Salmon

Myxospore stage
Develops in fish
Actinospore stage
Develops in Aquatic worms
Myxobolus cerebralis
Myxobolus cerebralis

Spore valve
Polar filament
Sporoplasm
Polar Capsule

Valves
Sporoplasm
Polar capsules

P. minibicornis uncompleted lifecycle
?
Actinospore
?
Aquatic invertebrate
Myxospore

Lifecycles
Described species
27 Known freshwater life cycles
1 Known saltwater life cycles
Of the 1350 myxosporean species (fish stage) described:
 28 myxozoan life cycles are known
 26 are freshwater and involve an oligochaete worm
 1 is freshwater and involves a polychaete worm
 1 marine life cycle involves a polychaete worm

 First described from sockeye salmon from
British Columbia
(Kent et al. 1997)
 Infect kidney or urinary bladder
Myxospores

Clinical signs of infection
- swollen kidney
- anemia

Parvicapsula minibicornis in the
Klamath River
 Detected in juvenile
Chinook in Klamath
River since 1992
 Prevalence 80 -
100% during May -
July 2005

Parvicapsula minibicornis unknowns
 What is the parasite life cycle?
 Is kidney damage likely to impact juvenile
Chinook salmon survival?
 Where are sites of parasite transmission?

• Samples of sediment and periphyton were collected from the
Klamath River
• Oligochaetes and polychaetes were sorted and examined for actinospores

Developing actinospore stages seen in polychaetes
Early actinospore stages
(multinucleated cells)
Developing actinospores

Released mature actinospores
Polychaetes infected with thousands of mature actinospores
Actinospore characteristics
- nearly spherical
- 3 polar capsules
- 4-5 microns

P. minibicornis -specific primers (St. Hilaire et al. 2002) amplified DNA from:
Actinospore from
Klamath River polychaete
Myxospore from
Fraser River adult sockeye salmon
Myxospore from
Klamath River
Chinook salmon negative control

• The 18S rDNA sequence of the mature actinospore from the Klamath River polychaete was compared with the published sequence of P. minibicornis from the Fraser
River adult sockeye salmon
– 1710 bases sequenced
– 6 bp difference
– 99% similarity

• 10 juvenile Chinook salmon were exposed in the laboratory to actinospores from infected polychaetes.
– Dosage of 1000 actinospores per fish in static water for 24 hours
• Tissue was assayed by QPCR.
• Kidneys from 3 out of 10 fish were positive for P. minibicornis

Prevalence of
in Polychaetes
• Collected polychaetes from one location
• Pooled in groups of 5, 10, and 1 worm each
• Assayed worms by PCR
• Prevalence of infection is 1.8%
• Polychaete densities at collection location are 60,000-
100,000/mˆ2
• With a prevalence of 1.8%, 100,000 polychaetes could produce millions of actinospores

Lifecycle of Parvicapsula minibicornis
?
Actinospore ?
myxospore polychaete

Special Thanks To: Howard Hughes Medical
Institute for their support. Also thank you to Dr. Sascha Hallett, Stephen Atkinson, Dr.
Kevin Ahern and Dr Jerri Bartholomew for their guidance.