Download Health Care for Koi - University of Hawaii

Hawaiian Rickettsia –like
Organism (HRLO)
Allen C. Riggs DVM, MS
Aquaculture Development Program- Disease
Prevention (ADP-DP)
Hawaii Department of Agriculture
Rickettsia characterisitics
• Non-motile, Gram negative, nonsporeforming bacteria
• Pleomorphic shapes( cocci, rods or threadlike)
• Obligate intracellular parasite – must live
inside cytoplasm of host cell
Rickettsia characterisitics
• Cannot live in artificial nutrient
environments – need tissue or embryo
cultures
• In the past positioned between viruses
and bacteria
RLO History
• Piscirickettsia salmonis – first RLO fish
pathogen from coho salmon from Chile in
the 1980s
• Now numerous freshwater and saltwater
species affected ( salmon, seabass,
grouper, tilapia and several ornamentals))
RLO in tilapia
• First reported case in Taiwan - 1992
• Epizootic affecting six species of tilapia
• FW and SW
• Originated in 1 farm and eventually spread
to 37 facilities
• Mortality 75%+ in severe cases – 30%
average
RLO in Hawaii
• Initial cases in mid 1990s on Oahu
• Oreochromis mossambicus and
Sarotherodon melanotheron (black
chinned tilapia)
• Farmed and wild populations affected
• Farmed mortalities exceeding 60%
resulting in major financial losses
New name and culture conditions
for RLO
• In 2007 researchers determined that the
agent responsible for RLO is a Francisella
sp. bacteria – not a rickettsia
• They were also able to culture the bacteria
on modified artificial media – but difficult
and not always successful
• PCR assay was developed which is now
the preferred method of confirmation
Clinical signs of RLO/Francisella sp.
• Dark in color
• Emaciation
• Abnormal swimming behavior
• Eye lesions
• Enlarged spleen
• White nodules in many visceral organs but
NOT liver
What are these white nodules?
• Granulomas – groups of inflammatory cells
around a focus of infection
• Typically chronic or slow, occurring over a
long period of time
• NOT specific to any one disease – other
steps needed to ID cause
How to ID cause of granulomas?
• Routine H & E histology to confirm that
the structure is a granuloma
• Special stain to rule-out acid fast bacteria
( Mycobacterium sp.)
• Lowenstein-Jensen culture to rule-out
Mycobacterium sp.
• PCR test for specific agent - Francisella
What factors lead to clinical
outbreaks?
• Low water temperatures for longer than 7 days
– most Hawaii outbreaks occur October - April
• Optimum temperature for tilapia is 29 – 31C or
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85-88F
Increased mortalities from all infectious diseases
including RLO at temperatures below 19C or 66F
Tilapia often stop feeding below 17C or 63F
Lower lethal temperature in normal non-infected
tilapia typically 10 -11C or 50-52F
Secondary stressors:
• Overcrowding
• Sub-optimum water quality
• Inadequate nutrition
• Presence of ectoparasites
• Combination of many or all is worst case
scenario
Can it be treated ?
• Mortalities decreased with oxytetracycline
medicated foods during the early cases in
the 1990s
• Alternative treatment methods are being
used/developed internationally but not
available yet in the US
Questions to be considered?
• Is RLO/Francisella present on all of the Hawaiian
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•
•
•
•
islands?
Is it present in both wild and farmed stocks?
Can other important Hawaiian aquaculture
species be affected?
What can we do with infected stocks?
Is the bacteria endemic in the environment?
Is there a industry need for clean stocks?