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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. Non-motile, Gram negative, non-sporeforming bacteria Pleomorphic shapes( cocci, rods or thread-like)

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Hawaiian Rickettsia –like Organism (HRLO)

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  1. Hawaiian Rickettsia –like Organism (HRLO) Allen C. Riggs DVM, MS Aquaculture Development Program- Disease Prevention (ADP-DP) Hawaii Department of Agriculture

  2. 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

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

  4. 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))

  5. 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

  6. 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

  7. 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

  8. 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

  9. 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

  10. 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

  11. 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

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

  13. 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

  14. 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?

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