Although nearly 10 of the known shrimp viruses have been found in cultured penaeid
shrimp in the Western Hemisphere (Table 1), only four of these have caused panzootic disease
with serious economic consequences in the Americas (Lightner 1996a, 1996b, 2003) during the
past decade. These viruses, or perhaps more correctly groups of different strains of the same
virus species, are IHHNV, TSV, WSSV, and IMNV (Table 1; Figures 1-4 and 6). IMN
(infectious myonecrosis; Figure 5) recently emerged in 2002-2003 in shrimp farms in the
northeastern states of Brazil where it has caused serious mortality and production losses at
affected farms (Lightner et al. 2004).