Outbreaks of Streptococcosis associated withStreptococcus iniaein Siberian sturgeon (Acipenser baerii) in China

Abstract

Streptococcus iniae has emerged as an important fish pathogen over the past few decades causing high losses in aquaculture farms all over the world. At least 27 species of fish have been documented to be infected by S. iniae, including cultured and wild populations. In August and October 2013, a serious infectious disease characterized by body ulcer, internal organs haemorrhages and nodules showing on epicardium occurred on the Acipenser baerii farms in Ya'an country, China. Histological examination revealed a multisystemic, necrotising inflammatory response that was particularly marked in liver, kidney, heart and brain. Mass mortality (>40%) was observed in infected fish and two Gram-positive cocci (Ab130920 and Ab131025) were obtained from kidneys and livers of diseased fish. Experimental infections with these two isolates resulted in marked symptoms in the sturgeons similar to those observed in natural outbreaks, and the LD 50 values of the two isolates were 5.1 9 10 5 and 6.4 9 10 5 cfu per fish respectively. The two microorganisms were identified as S. iniae through physiological and biochemical tests, 16S rRNA and lctO gene sequence analysis. Both two isolates showed a similar antibiotic susceptibility, which were sensitive to ampicillin, amoxicillin, cefazolin, amikacin, deoxycycline, florfenicol, azithromycin, ciprofloxacin, vancomycin and resistant to streptomycin, gentamicin, kanamycin, norfloxacin and sinomin (SMZ/TMP). Multiplex PCR assay for virulence genes showed both isolates possessed six main virulence genes: simA, scpI, pdi, pgm, cpsD and sagA genes. These results indicated that S. iniae could act as a pathogen of farmed A. baerii. This is the first report of S. iniae infection associated with mass mortality in A. baerii.

Outbreaks of severe myositis in cultured white sturgeon (Acipenser transmontanus L.) associated with Streptococcus iniae

“…Clinical signs characterized mainly by erratic swimming near the surface and arching of the back were similar to the clinical observations seen in both naturally and experimentally infected fish (Deng et al, ; Soto et al, ; Wang, Xu, Wang, Wang, & Cao, ). However, unlike previous cases, these signs were likely related to the epaxial muscle lesions, and not to neurological pathology (Soto et al, ), as no brain or spinal cord lesions were observed in the submitted fish in the current study.…”

“…Despite the unusual pathologic presentation of the cases, bacteriological tests, 16S rRNA and gyr B gene sequencing confirmed infection of the fish with S. iniae . These diagnostic cases highlight the emergence of streptococcosis in cultured sturgeon, adding to the initial reports from Asia and North America (Deng et al, ; Soto et al, ). These previous cases were associated with acute high mortalities of ~ 43% (Deng et al, ) in the farm and of 30% in a tank (Soto et al, ), respectively, similar to the mortality index observed in the second outbreak of this study, demonstrating the harmful potential of this agent for sturgeon.…”

“…In the Western United States, it has become a multi‐million dollar industry due to the commercialization of caviar, flesh, leather and cosmetics (Soto et al, ; Wei, Zou, Li, & Li, ). However, emerging infectious diseases pose a significant challenge to the industry and typically result in high morbidity and mortality (Deng et al, ).…”

“…(Agnew & Barnes, ), barramundi ( Lates calcalifera ) (Creeper & Buller, ), rainbow trout ( Onchorynchus mykiss ) (Lahav et al, ) and sturgeon ( Acipenser spp.) (Deng et al, ; Soto et al, ). The disease presentation is similar among the different susceptible fish species, including high levels of morbidity and mortality associated with septicaemia, meningitis and panophthalmitis (Agnew & Barnes, ).…”

“…The disease presentation is similar among the different susceptible fish species, including high levels of morbidity and mortality associated with septicaemia, meningitis and panophthalmitis (Agnew & Barnes, ). In sturgeons, reported cases of the disease are characterized mainly by a systemic inflammatory response that is particularly marked in the liver, kidney, heart and brain, associated with small foci of necrosis accompanied by fibrin deposition, minimal inflammatory response and small numbers of bacterial cocci (Deng et al, ; Soto et al, ). This report describes the pathological and molecular findings in two outbreaks of S. iniae infection in cultured white sturgeons, during 2018 and 2019, demonstrating an unusual gross and microscopic presentation characterized by necrotizing myositis and bacteraemia.…”