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

Beginning in the spring of 1993, a serious mortality among cultured kuruma shrimp, Penaeus japonicus occurred in Japan. The typical sign of this disease was white spots on the inside surface of the carapace. Challenge tests demonstrated that the causative agent was highly virulent. This was demonstrated by injection of a filtrered homogenate of the lymphoid organ obtained from diseased shrimp. A non-occluded bacilliform virus was found by electron microscopy in the lymphoid organ of both naturally and experimentally infected shrimps. The virion was bacilliform and surrounded by a virion envelope (a lipid bilayer membrane). The dimension of the virion was 83 nm in diameter and 275 nm in length. From these results, the bacilliform virus is considered to be the causative agent of the disease.