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The Aquarium's Deadly Enemy: How S. iniae Caused Millions of Dollars in Damage
Since its first isolation from freshwater dolphins in the Amazon in the 1970s, Streptococcus iniae, a Gram-positive spherical bacterium, has become an important pathogen in the global aquaculture industry, causing losses of up to $100 million per year. This bacterium has been detected in at least 27 species of fish. The infection situation in many fresh fish species including carp, fresh fish and rainbow trout is becoming increasingly serious, causing aquariums everywhere to face huge economic losses.
To date, S. iniae infection has caused annual losses of more than US$100 million to the global aquaculture industry.
Infections with S. iniae commonly manifest as meningoencephalitis, skin lesions, and sepsis, and pose a threat to aquatic life including bass and bream. In addition, this bacterium occasionally infects humans, especially workers who frequently come into contact with fish, and can cause serious illnesses such as sepsis and toxic shock syndrome.
The history of germs
In 1972, S. iniae was first isolated from an Amazon dolphin infected with golf ball disease. At that time, the dolphin was successfully treated with penicillin and mezlocillin. The bacterium was subsequently recognized as a new species and officially named S. iniae in 1976. Over time, S. iniae infections spread further in aquaculture in Asia and the United States, and researchers discovered similarities with other streptococcal pathogens, raising further concerns.
How to identify an infection
Determining the presence of S. iniae in the laboratory is challenging, especially as traditional methods often fail to provide accurate results. While molecular genetic methods such as DNA sequencing can provide identification, CDC research shows that in the vast majority of cases, these methods are not necessary. Therefore, rapid and accurate detection of S. iniae becomes crucial.
S. iniae may be misidentified or not identified by many traditional automated microbiology systems.
Effects on fish
S. iniae is highly pathogenic in freshwater, marine and metastable haloline fishes and can be lethal up to 30-50%. If left unchecked, it could have serious consequences for the aquaculture community. According to a 1997 report, the global economic losses caused by S. iniae infection reached US$100 million that year, with the United States being particularly affected.
Fish infected by S. iniae will show various symptoms that vary depending on the species, for example: in Terrapia, it causes damage to the nervous system, as well as weakness and erratic swimming. Such situations often lead to death within a few days. In rainbow trout, it is often associated with sepsis and central nervous system damage, with symptoms including weakness, disorientation, and external and internal bleeding.
Human infection with S. iniae
Although S. iniae primarily affects fish, it can also cause opportunistic infections in humans who are vulnerable or have compromised immune systems. Although cases of infection are relatively rare, the bacterium has been confirmed to cause infection in humans in a few cases in the United States and Canada since 1991. Most of the patients are of Asian descent, and whether this implies a genetic factor requires further research.
Control and Treatment
To control the spread of S. iniae in aquaculture, researchers have taken a variety of measures. Reducing the amount of fish feed can reduce mortality because fish accelerate the spread of bacteria in the water when eating. In addition, reducing the survival density of fish and maintaining suitable water quality are equally effective. Research shows that adding certain probiotics can also control S. iniae infection to a certain extent.
Controlling S. iniae infection can significantly reduce economic losses in aquaculture.
Overall, the impact of S. iniae cannot be underestimated, and research continues even in the medical and aquaculture industries. Faced with this threat, should we rethink the operating model of aquaculture to ensure the sustainable development of the industry?
