EDWARDSIELLA INFECTIONS

exp date isn't null, but text field is

Causative Agent(s)

 

There are 2 species of Edwardsiella that cause disease in fish. They are Edwardsiella tarda and Edwardsiella ictaluri. Both organisms are Gram negative rods, cytochrome oxidase negative, motile, glucose fermenters with production of acid and gas. These organisms could be isolated from diseased tissues (e.g., liver, kidney, spleen, brain) when inocula from organs are streaked on BHIA (Brain-heart infusion agar).

 

Clinical Presentation and Epidemiology

Edwardsiella tarda is the causative agent of Edwardsiellosis or Emphysematous putrefactive disease of catfish. This disease is global in occurrence and affects many species of fish.

 

Clinical singes include lethargy, ‘hanging’ at the water surface and swimming in a spiral manner are observed.

Gross lesions are variable and could include – small cutaneous lesions on the posterior portion of the body, later abscesses develop in the body musculature. These become larger and fill with gas and if these muscular lesions rupture, they emit a foul ‘rotten egg’ odour. Internally, small white nodules form on the liver, spleen, kidney, and intestine.

 

Edwarsiella tarda is ubiquitous in water and several animals (e.g., waterfowls) could serve as reservoirs of infection.

 

Edwardsiella ictaluri is the cause of Enteric septicaemia or ‘hole in the head disease’ of channel catfish. This disease affects mainly catfish.

Clinical signs and gross lesions include anorexia, hanging vertically at water surface and spiral swimming are often seen in sick fishes.

Grossly and externally, petechial haemorrhages are seen on the skin (near the mouth), exophthalmia, pale gills, ‘hole’ in the frontal bone between the eyes.

Internally swollen kidney and spleen, haemorrhage, and necrosis of the liver and serosanguinous fluid in the abdominal cavity. This infection usually occurs in catfish fingerlings and juveniles. Severity of infection could be high if organic load in pond is high and pond temperature also high.

 

Diagnostic Consideration

Edwardsiella infections may be suspected based on the classical lesions seen in either of them. For confirmatory diagnosis, affected organs (e.g., skeletal muscle, brain tissue, liver, kidney, and spleen) are subjected to microbial analysis. The organism grows well on tryptone soy agar, 5% blood agar and MacConkey agar. Edwardsiella ictaluri medium (EIM) can also be used as a selective culture medium (Emmett and Waltman, 1990). Isolated bacteria are further subjected to Gram staining and biochemical tests for confirmatory diagnosis.

 

Management and Treatment

This disease can be controlled by good biosecurity and proper use of antibiotic. The use of antibiotics should be based on outcome of antibiotic susceptibility test. For example, Amoxicillin could be administered via feed at 40mg/kg body weight for 5 to 7 consecutive days.