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

• 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 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 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?