Piscirickettsiosis is a bacterial disease caused by Piscirickettsia salmonis causing high mortality and huge losses in salmonid and non-salmonid fish such as European sea bass (Dicentrarchus labrax), in which disease outbreaks caused by Rickettsia-like Organisms (RlO) then identified as Piscirickettsia salmonis, were reported during the winter in the Mediterranean, in particular in France, Greece and Croatia (Zrnčić et al., 2021). Typical clinical sign is an abnormal swimming behaviour with internal signs such as swollen kidney and pale liver, among others. In February and April 2023, two outbreaks of P. salmonis infection were diagnosed in cage-reared European sea bass in Southern Italy. The mean weight of fish from the two batches (0+ and 1+), was 35 gr and 170 gr, respectively. Cumulative mortality of 6% was recorded in the two batches during the 3-months observation period. Water temperature range was 13.5-19°C. The fish showed nervous symptoms and appeared thin, with haemorrhagic suffusions in the skin, gill necrosis, marbled liver with focal necrosis, brain congestion, splenomegaly, visceral haemorrhages and catarrhal enteritis. Parasitological, bacteriological, histological analyses and RT-PCR for Betanodavirus were performed according standard lab protocols. The monogenean Diplectanum aequans in the gills and a massive infection by the myxozoan Sphaerospora dicentrarchi in the gut were detected, while cultural exam for bacteria on standard media and PCR for Betanodavirus were negative. At histology diffuse necrosis of brain, liver, spleen and kidney was observed in association with intracellular coccoid structures referable to rickettsiae. The identification of the pathogen was achieved by molecular analysis through 16 S EubB and EubA PCR and Nested PCR with PS2S and PS2AS primers (Manuel et al., 1996). In European sea bass some cases were reported a decade ago in Italy as a disease caused by Rickettsia-Like-Organisms (RLO). The occurrence of further outbreaks of piscirickettsiosis indicates that the infection circulates in Italian sea bass farms, promoting the necessity to improve specific diagnostic capacity, including culture-based tools, and to carry out epidemiological studies aimed to identify main risk factors.
Mortalities outbreaks by Piscirickettsia salmonis in European sea bass (Dicentrarchus labrax) farmed in Italy.
Quaglio, Francesco;
2023
Abstract
Piscirickettsiosis is a bacterial disease caused by Piscirickettsia salmonis causing high mortality and huge losses in salmonid and non-salmonid fish such as European sea bass (Dicentrarchus labrax), in which disease outbreaks caused by Rickettsia-like Organisms (RlO) then identified as Piscirickettsia salmonis, were reported during the winter in the Mediterranean, in particular in France, Greece and Croatia (Zrnčić et al., 2021). Typical clinical sign is an abnormal swimming behaviour with internal signs such as swollen kidney and pale liver, among others. In February and April 2023, two outbreaks of P. salmonis infection were diagnosed in cage-reared European sea bass in Southern Italy. The mean weight of fish from the two batches (0+ and 1+), was 35 gr and 170 gr, respectively. Cumulative mortality of 6% was recorded in the two batches during the 3-months observation period. Water temperature range was 13.5-19°C. The fish showed nervous symptoms and appeared thin, with haemorrhagic suffusions in the skin, gill necrosis, marbled liver with focal necrosis, brain congestion, splenomegaly, visceral haemorrhages and catarrhal enteritis. Parasitological, bacteriological, histological analyses and RT-PCR for Betanodavirus were performed according standard lab protocols. The monogenean Diplectanum aequans in the gills and a massive infection by the myxozoan Sphaerospora dicentrarchi in the gut were detected, while cultural exam for bacteria on standard media and PCR for Betanodavirus were negative. At histology diffuse necrosis of brain, liver, spleen and kidney was observed in association with intracellular coccoid structures referable to rickettsiae. The identification of the pathogen was achieved by molecular analysis through 16 S EubB and EubA PCR and Nested PCR with PS2S and PS2AS primers (Manuel et al., 1996). In European sea bass some cases were reported a decade ago in Italy as a disease caused by Rickettsia-Like-Organisms (RLO). The occurrence of further outbreaks of piscirickettsiosis indicates that the infection circulates in Italian sea bass farms, promoting the necessity to improve specific diagnostic capacity, including culture-based tools, and to carry out epidemiological studies aimed to identify main risk factors.
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