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Shocking fish infections: Do you know which 27 fish species are threatened by S. iniae?
Since its isolation from freshwater dolphins in the Amazon in the 1970s, the Gram-positive cocci Streptococcus iniae, belonging to the genus Streptococcus, has become a major pathogen in the global aquaculture industry, causing economic losses of more than $100 million per year. Since this pathogen was first discovered, infections have been reported in at least 27 species of farmed or wild fish around the world, including carp, red drum, mixed striped bass and rainbow trout. Whether they are freshwater or saltwater fish, S. iniae poses an infection threat, and its infection can cause symptoms such as meningoencephalitis, skin lesions, and sepsis.
S. iniae not only poses a threat to fish, but also occasionally causes infections among fishmongers who handle fish in their hands, especially those of Asian descent. 【Notable】
History of infection
S. iniae was first isolated in 1972 from a subcutaneous abscess in an Amazon river dolphin suffering from "golf ball disease". The pathogen was susceptible to β-lactone antibiotics and was ultimately successfully treated with penicillin and tylosin. In 1976, the pathogen was officially named S. iniae. Over time, other streptococcal outbreaks emerged in Asia and the United States, some with symptoms similar to S. iniae.
"For the aquaculture industry, the economic impact of S. iniae cannot be underestimated."
Infected fish
S. iniae has been confirmed to affect 27 species of fish, including:
- Cyprinus carpio
- Rainbow trout (Oncorhynchus mykiss)
- Red Drum (Sciaenops ocellatus)
- Spotted fathead (Morone saxatilis)
- Baramundi fish (Lates calcarifer)
- Ctenopharyngodon idella
- Porcupine fish (Hypophthalmichthys molitrix)
- Oncorhynchus mykiss x Morone saxatilis
- Japanese anglerfish (Seriola quinqueradiata)
- Silver salmon (Oncorhynchus kisutch)
- Asian mud cat (Ictalurus punctatus)
- White-spotted individual (Carassius auratus)
Most of these fish species are most susceptible to S. iniae infection due to environmental stress (such as poor water quality, overcrowding, improper handling, etc.) during aquaculture.
"Today's aquaculture operations produce fish species that are highly susceptible to infection by S. iniae."
Infections in humans
Although S. iniae primarily causes infection in fish, in some cases it can also pose a threat to humans with weakened immune systems. The infection usually manifests as bacterial pyoderma, but may also cause symptoms such as endocarditis, meningitis, osteomyelitis, and septic arthritis. Cases of human infection were first reported in Texas and Ottawa in 1991 and 1994, all linked to the handling of raw fish.
Control and Treatment
To combat S. iniae infection, the aquaculture industry has several control measures. One study shows that reducing the amount of food fed to fish can reduce mortality because feeding speeds the spread of pathogens in the water. In addition, reducing fish density, adjusting water temperature and maintaining appropriate oxygen levels can also reduce fish stress and more effectively control the spread of infection.
"In some cases, S. iniae infections can be successfully treated with antibiotics, most commonly penicillin."
Aquaculture fields from small to large are threatened by S. iniae. This situation forces scientific researchers to develop new prevention and control programs and treatment methods. So, are we alert enough to face such an invisible threat and work hard to reduce the damage it brings?
