Download Bacterial Cold Water Disease Salmonids

Bacterial Cold Water Disease
Salmonids
Regg Neiger DVM, PhD
Veterinary and Biomedical Sciences Department
South Dakota State University
Michael Barnes BS, MS
Hatchery Manager and Researcher
McNenny State Fish Hatchery
South Dakota Game Fish & Parks
Flavobacterium psychrophilum
cause of Cold Water Disease
• Important worldwide salmonid (trout and
salmon) disease
• Believed to be ubiquitous in freshwater
• Most severe in young fish (fry and
fingerlings)
• Older fish can be affected
Bacterial Cold Water Disease
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Typically occurs at low temp 39-50° F
Severity decreases with increased age of fish and temp
Gram negative bacterium
Affinity for skin and muscle causing deep ulceration.
Also can cause septicemia
Mortality rates from 1 to 70% varies due to water
temperature, inherent bacterial virulence, fish genetics
Pathogenesis
• Bacteria present in water or fish reservoir
• Enter via broken skin
• Vertical transmission via eggs is
suspected
• Spreads via fibrous connective tissue,
muscle, and internal organs. Produces
enzymes the degrade collagen etc.
Diagnosis
• Gross lesions: Skin and muscle ulcerations,
petechial hemorrhage in viscera, skeletal
deformities
• Microscopic lesions in skin, muscle, spleen,
kidney, skeletal system, with large numbers of
gram negative long thin bacterial rods
• Bacterial culture
• PCR examination
BCWD in Juvenile Steelhead Trout
Photograph from AFS Blue Book
Stumpy, peduncle ulcer, etc
Peduncle Lesion
Photograph from the
archive collection at the National Fish Health Research Laboratory, WV
Treatment and Prevention
Antibiotics
• Florfenicol effective but some resistance is
being reported. Need a Veterinary Feed
Directive to use this drug.
• Oxytetracycline is not as effective, VFD
not needed.
Role for Probiotics?
Compete and Inhibit F psychrophilium,
Stimulate Innate Immunity
Genetically Resistant Strains
BCWD Vaccine
Other treatments that may help
• Increasing Water temp above 20C
decreases disease
• Increase Salinity
• Both Are Expensive
Control of BCWD at
McNenny State Fish Hatchery
From Mike Barnes
Hatchery Manager and Researcher
Innovative Management Techniques
Management Techniques
1. Jar incubation (vs. trays). Trays need anti-fungal
treatment or remove dead eggs every couple of days – either one causes
stress.
Management Techniques
2. Reduce handling
• minimize routine inventories and fish movement
Netting < 75% at
McNenny Hatchery
Management Techniques
3. Reduce rearing densities
As low as 10% of
established norms
Downside
Because fish aren’t routinely moved to increase
screen sizes and reduce rearing densities:
1. More plugging risk
2. More time spent cleaning screens
3. More tanks to feed in early growth
(start at very low densities).
Result of McNenny Management Changes
• 2005-2009 – repeated BCWD outbreaks with
rainbow trout, high mortality, frequent antibiotic
use (even multiple times on the same fish).
• 2010, with these novel rearing strategies the
antibiotic use eliminated.
• Occasional BCWD outbreaks but mortality
minimal <1 to 2%.
June 2011
Fingerling McConaughy RBT tanks not cleaned –
screens plugged – tanks overflowed
June 2011
• 32,000 escaped, 10,000 recovered from drains
and put into one raceway unit (major stress).
• Fish left in tanks, 33,000, were inventoried
and put back into the tanks (less stress than
other fish)
July 2011
BCWD Outbreak in Raceway
• Mortality (0.15% per day) started in raceway 3 weeks
after moving. After 20 days total mortality of 2.5%.
• Symptoms typical of BCWD
• Flavobacterium psychrophilum diagnosed at SDSU.
• Treated with oxytetracycline, mortality dropped to
normal levels (0.1-0.2% over a 8 week period)
• Trout left in tank room experienced normal mortality
throughout this period.
Conclusions
1. F. psychrophilum always present at hatchery.
2. BCWD stress-induced at McNenny
3. Changes in management/rearing techniques to
reduce stress are likely responsible for the
decrease in BCWD outbreaks and severity.
4. Changes in management/rearing techniques have
eliminated the need for antibiotics – minimal
mortality associated with disease can easily be
accommodated with a small increase in
production.
F. psychrophilum
• Isolate cultured from this break was similar to
strain type 99/1A. Could have other types, only
this break had isolate available for typing.
• Neighboring hatchery has strain CSF259-93
which is more common than 99/1A
• Surprise, we assumed both hatcheries had
acquired disease from same source.
• McNenny has 1-2% loss when no major stress
event and Neighbor has up to 25% loss even
with use of antibiotics.
99/1A vs. CSF259-93
• Is 99/1A less virulent?
• Is low stress management keeping
immunity up?
• Is low density increasing growth rate and
moving fish through susceptible stage
faster? 4-5 inch fish resistant.
How do you handle prevention and treatment
of Flavobacterium psychrophilum?????
• What is the best treatment or combination of
treatments when there is a break?
• What is the order or timing of the different
treatment if combinations are used?
• Anyone using preventions such as probiotics,
vaccine, salt, water temperature, etc.
• Incorporation of stress management.