P. salmonis and piscrickettsiosis are present in various geographic regions from Europe to Oceania to South America, but the Chilean salmon farming industry has been particularly hard-hit.
[6] The disease caused by Piscirickettsia salmonis, piscirickettsiosis, was first identified in Chile in 1989 as coho salmon syndrome, although observations of the illness date to at least 1981.
It continues to present challenges today, and infected farms typically lose 30-35% of their stock, although that number can be as high as 90%.
In seawater, free-living P. salmonis can survive for at least 21 days under the right environmental conditions, and is capable of forming viable and mucus-tolerant biofilms on nonliving surfaces including glass, plastic, and mollusk shells.
[4] The type strain, LF-89, is from Chile, but isolates have been identified from multiple other localities including Norway, Canada, Scotland, Ireland, and possibly Tasmania.
[4] Although they belong to different classes, Piscirickettsia (Gammaproteobacteria) is morphologically similar to true Rickettsia bacteria (Alphaproteobacteria), for which it was named.
White or yellow lesions or ulcers, ranging from 1mm to 2cm in diameter, are often present in the liver, kidneys, spleen, intestine, and skeletal muscle.
[4] Although many fish do not display outward signs of illness even when the disease has progressed to the point of mortality, several indications of infection may be noted.
These include external symptoms such as lesions, ulcers, and darkening of the skin; abdominal swelling; and pale gills as a result of anemia.
[4] The anadromous life history of salmonids and the high population densities of farmed salmon make it difficult to effectively control piscirickettsiosis outbreaks, although early detection is crucial for successful management.
[4] Despite this, the Chilean salmon farming industry has one of the highest rates internationally of antibiotic consumption per ton of harvested fish.
[17] The use of florfenicol and oxytratracycline to treat piscirickettsiosis is still sometimes successful, especially if treatment is administered early in an outbreak when mortality is still low.
may provide a biodegradable, easy-to-administer alternative to vaccines and antibiotics, as they have been demonstrated to reduce the virulence of piscirickettsiosis outbreaks.
Salmon farming companies are also required to submit information about infectious diseases to the Chilean government to maintain their licenses.
[18] Peracetic acid, peroxides, and active and inactive chlorine dioxides are the most effective sanitizers at reducing P. salmonis prevalence.