Grass Carp Hemorrhagic Disease - Viral Infections In Fish

Grass Carp Hemorrhagic Disease

CAUSATIVE AGENT:

Aquareovirus (60 to 80 nm)

SPECIES AFFECTED:

Grass carp (Ctenopharyngodon idellus), black carp (Mylopharyngodon piceus), topmouth gudgeon (Pseudorasbora parva), silver carp (Hypophthalmichthysmolitrix), Chinese minnow (Hemiculter bleekeri) and rare minnow (Gobiocypris rarus)

GROSS SIGNS:

Clinical signs include exophthalmia, hemorrhagic or pale gills and hemor-rhagic fin bases or gill covers.

EFFECT ON HOST:

This disease was first observed in China more than 20 years ago. Outbreaks occured in Southern China during the summer at temperatures of 24-30°C. Acute infections cause significant mortalities of up to 80% among fingerlings and sometimes among yearlings. Internally, hemorrhages occur in the muscu-lature, oral cavity, intestinal tract, liver, spleen and kidneys. Naturally and ex-perimentally infected fish manifest reduced erythrocytes, plasma protein, cal-cium and urea nitrogen. Serum potassium elevated. Signs of disease and mor-tality are observed within 1 to 2 weeks of exposure of fish in water at tempera-tures of 25°C or higher. Experimental vaccination induced 80% level of immu-nity by day 4 at temperatures above 20°C.

DIAGNOSIS:

The virus can be propagated in cell cultures of GCK-84, GCG and GCF yielding titers as high as 108 to 109TCID50 per ml. In vitro replication is considered opti-mum between 28 and 30°C inducing CPE in 3 to 4 days post inoculation. Re-verse transcription-polymerase chain reaction (RT-PCR) and electron micros-copy are also used for detecting the virus.