Epizootic ulcerative syndrome

Signs of disease

Important: animals with disease may show one or more of the signs below, but disease may still be present in the absence of any signs.

Disease signs at the farm level

• mass mortality

Disease signs at the tank and pond level

• mass mortality

Clinical signs of disease in an infected animal

• sores on body—red spots, black burn-like marks, or deeper ulcers with red centres and white rims
• ulcers on head often extend to skull erosion, exposing the brain

Gross signs of disease in an infected animal

• fungal hyphae (threads), sometimes extending into visceral organs
• liquefactive necrosis of muscle tissue

Disease agent

A fungus, Aphanomyces invadans, seems to be the primary cause of the disease, but other agents and water quality factors may also play a part in expression of the disease.

Host range

Presence in Australia

Epizootic ulcerative syndrome is endemic in many freshwater catchments and estuaries in Australia and has been officially reported from New South Wales, Northern Territory, Queensland, Victoria and Western Australia.

Epidemiology

• The disease is seen in over a hundred freshwater and estuarine species of fish.
• It has often been associated with acid water run-off and can appear after heavy rains, particularly after a long dry period.
• Disease transmission is through zoospore transfer in water, direct contact between fish, and skin contamination (penetration assisted by damage to skin).
• Secondary bacterial and viral infections are often associated with this condition.

Differential diagnosis

The differential diagnostic table and the list of similar diseases appearing at the bottom of each disease page refer only to the diseases covered by this field guide. Gross signs observed might well be representative of a wider range of diseases not included here. Therefore, these diagnostic aids should not be read as a guide to a definitive diagnosis, but rather as a tool to help identify the listed diseases that most closely account for the gross signs.

Sample collection

Because of uncertainty in differentiating diseases using only gross signs, and because some aquatic animal disease agents might pose a risk to humans, you should not try to collect samples unless you have been trained. Instead, you should phone your state or territory hotline number and report your observations. If samples have to be collected, the agency taking the call will advise you on what you need to do. Local or district fisheries/veterinary authorities could advise you on sampling.

Emergency disease hotline

For your state or territory emergency disease hotline number, see Whom to contact if you suspect a disease.

Further reading

library.enaca.org/Health/DiseaseLibrary/EpizooticUlcerativeSyndrome.pdf

The currently accepted procedures for a conclusive diagnosis of epizootic ulcerative syndrome are summarised at www.oie.int/eng/normes/fmanual/A_00027.htm