Absence of inflammatory response by infectious hypodermal and hematopoietic necrosis virus (IHHNV) in Penaeus vannamei cultivated in northern Peru

Infectious hypodermal and hematopoietic necrosis virus (IHHNV) is a disease of penaeid shrimp caused by decapod Penstylhamaparvovirus 1, which infects both wild and cultured Penaeus vannamei shrimp and requires mandatory notification to the World Organization Animal Health (WOAH). This report presents the results of the molecular diagnosis of IHHNV and histopathological analysis of cultured P. vannamei specimens during the execution of the Pathogens Surveillance Plan (2022) on the Peruvian northern coast. Six epidemiological units located in Tumbes and Piura were sampled. Molecular diagnosis was performed by real- time PCR using a protocol recommended by the WOAH, and histopathological analysis was conducted using the hematoxylin and eosin H&E staining method. Overall, the prevalence of IHHNV-positive cases was 88.66%, with a prevalence greater than 75% per epidemiological unit. After histopathological analysis, all cases exhibited typical or IHHNV-related lesions, including mild nuclear alterations, presence of eosinophilic intranuclear inclusions of Cowdry type A or hypertrophied nuclei in cells of target tissues, such as cuticular, epicardial, and connective tissue. However, the severity of the lesions due to IHHNV infection was low, being categorized as grade 1. No evidence of an inflammatory response was observed, and no mortalities attributed to this pathogen were reported in the sampled epidemiological units. Our results are consistent with recent findings on the presence of endogenous viral elements in the shrimp genome as an adaptive response to IHHNV infections, resulting in no negative impact on P. vannamei culture.