YERSINIOSIS

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Causative Agent(s)

This is a severe bacterial disease of fish. It is also called ‘Enteric red mouth disease’. It could occur in acute or chronic form and is caused by a Gram-negative rod called Yersinia ruckeri. The bacterium is a slightly curved motile rod, oxidase negative, catalase positive organism. Crayfish are reported to be carriers of Enteric red mouth disease and they do not develop clinical signs of the disease.

Clinical Presentations and Epidemiology

Yersiniosis has been reported in the United States, Canada, Australia, Africa, and Europe.

Yersinia ruckeri is an important pathogen of fish (Tobback et al., 2007).

Transmission is by direct fish to fish contact or by exposure of susceptible fish to water borne bacteria. This bacterium causes sustained low-level mortality which could result in heavy losses when exacerbated by stress factors.

In acute outbreaks, affected fishes become darkened and lethargic, anorexia and isolating themselves from main population, occur. Affected fish could have exophthalmia or become blind in both or one eye. Small cutaneous haemorrhages occur in and around the gum line of the mouth and on the tongue, giving the area an inflamed reddish appearance. Also, abdominal distension with petechial haemorrhages on ventral surface and bases of fins are seen.

Internally, stomach is flaccid and filled with water (a common classical sign seen in ERM disease), enlarged dark spleen, petechial haemorrhage on swim bladder, gonads, and lateral musculature. Nephritis and enteritis will also be observed.

Diagnostic Considerations

Apart from the typical lesions seen in the mouth region, other affected organs like the spleen, liver, gonads, and kidney are harvested for microbial analysis. Inocula from affected organs are streaked on Shotts-Waltman medium which is selective for Yersinia ruckeri. It also grows well on tryptone soy agar.

Management and Treatment

This disease can be controlled by vaccination, use of resistant breed of fish 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