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Hawaiian Rickettsia –like Organism (HRLO). Allen C. Riggs DVM, MS Aquaculture Development Program- Disease Prevention (ADP-DP) Hawaii Department of Agriculture. Non-motile, Gram negative, non-sporeforming bacteria Pleomorphic shapes( cocci, rods or thread-like)

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hawaiian rickettsia like organism hrlo

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, non-sporeforming bacteria

Pleomorphic shapes( cocci, rods or thread-like)

Obligate intracellular parasite – must live inside cytoplasm of host cell

Rickettsia characterisitics
rickettsia characterisitics3
Rickettsia characterisitics
  • Cannot live in artificial nutrient environments – need tissue or embryo cultures
  • In the past positioned between viruses and bacteria
rlo history
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
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
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
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
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
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
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
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 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
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
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
Questions to be considered?
  • Is RLO/Francisella present on all of the Hawaiian 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?