Hawaiian Rickettsia

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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

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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

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Rickettsia characterisitics

• Cannot live in artificial nutrient environments
  need tissue or embryo cultures
• In the past positioned between viruses and
  bacteria

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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))

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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

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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

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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

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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

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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

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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

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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

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Secondary stressors

• Overcrowding
• Sub-optimum water quality
• Inadequate nutrition
• Presence of ectoparasites
• Combination of many or all is worst case scenario

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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

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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?