ELECTRON-MICROSCOPIC EVIDENCE OF BACILLIFORM VIRUS-INFECTION IN KURUMA SHRIMP (PENAEUS-JAPONICUS)

Beginning in the spring of 1993, a serious mortality among cultured ku ruma shrimp, Penaeus japonicus occurred in Japan. The typical sign of this disease was white spots on the inside surface of the carapace. Ch allenge tests demonstrated that the causative agent was highly virulen t. This was demonstrated by injection of a filtrered homogenate of the lymphoid organ obtained from diseased shrimp. A non-occluded bacillif orm virus was found by electron microscopy in the lymphoid organ of bo th naturally and experimentally infected shrimps. The virion was bacil liform and surrounded by a virion envelope (a lipid bilayer membrane). The dimension of the virion was 83 nm in diameter and 275 nm in lengt h. From these results, the bacilliform virus is considered to be the c ausative agent of the disease.