Epizootic Ulcerative Syndrome (EUS)
This is a complex disease attributed to a combination of rhabdovirus (65x175 nm) (Fig. 2-2), the bacterium Aeromonas hydrophila, and the fungus Aphanomyces invadans.
A wide range of cultured and wild fish species are affected namely: snakehead (Ophicephalus striatus), catfish (Clarias sp.), climbing perch (Anabas spp.), spiny eel (Mastamcembelus armatus), gourami (Trichogaster spp.), barbs (Puntius spp.), serpent fish (Channamicropeltes), sand goby (Oxyeleotris marmoratus), barbs, three-spotgourami (T. trichopterus), striped croaking gourami (Trichopsisvittatus), siamese fighting fish (Betta splendens), wrestling half-beak(Dermogenus pustillus), swamp eels (Fluta alba). EUS has occurred in Australia, Malaysia, Indonesia, Thailand, Myanmar, Kampuchea, Lao PDR, Philippines, Sri Lanka, Bangladesh, Nepal, Bhutan, Singapore, Vietnam and Pakistan.
EUS lesions are characterized by severe, ulcerative, dermal necrosis with extensive erosion/sloughing of the underlying musculature (Fig. 2-3). The necrotic muscular tissue emits a foul odor. Fish manifest frank ulcers consisting of eroded dermal layer, exposing the underly-ing musculature, which may be hemorrhagic. Fish with less severe lesions exhibit scale loss with erosion of the skin surface with or with-out hemorrhagic signs.
EFFECT ON HOST:
The histopathological profile of the disease consists of a chronic, ne-crotic, and mycotic granulomatous inflammatory response.
Outbreaks are observed annually between November to February when the water temperature is at its lowest. EUS is transmitted by cohabitation with diseased fish or exposure to contaminated waters. The virus replicates at 15~25°C in 2-3 days to 107 TCID50/ml in SHS cells and in SSN-1 cells. The virus experimentally induced dermal lesions and mass mortalities of snakehead fry and fingerlings.
Signs of disease and isolation/identification of the associated virus, Aeromonashydrophila/Aphanomyces sp., histopathology and electron microscopy.