The lymphoid organ (LO) is an additional, prime target for decapod iridescent virus 1 (DIV1) in Penaeus vannamei

Detailed histopathological analysis (HA) and in situ DNA hybridization assays (ISH) were carried out with adjacent tissue sections from the whiteleg shrimp Penaeus vannamei that had been infected with decapod iridescent virus 1 (DIV1) in the laboratory. Results with two ISH methods confirmed those recently published in China indicating that unique, basophilic, cytoplasmic lesions pathognomonic for DIV1 disease were produced in the hematopoietic tissue (HPT). In addition, both methods revealed that the lymphoid organ (LO) was also a prime target for DIV1, although the lesions produced in the LO were not sufficiently unique to be considered pathognomonic for DIV1 infection. However, the HPT lesions of DIV1 often require use of a 100× objective lens to confirm their presence. In contrast, the LO can be quickly located and lesions can be recognized using a 10× objective lens and confirmed with a 40× objective lens. Once confirmed, a diagnostician can switch to the HPT (usually relatively nearby) to search for pathognomonic lesions with 40× and 100× objective lenses. This will speed up histological screening for DIV1 infections. However, the LO is unique to penaeid shrimp, so this approach would not be applicable to the many other species of crustaceans that are susceptible to DIV1 infection. •Lesions in hematopoietic tissue (HPT) are used for histological diagnosis of DIV1 infection.•Discerning these lesions often requires use of a 100× microscope objective.•We reveal severe DIV1 lesions in the lymphoid organ (LO) visible with a 10× objective.•This can speed up preliminary screening for DIV1 infections in penaeid shrimp.