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Different responses to infectious hypodermal and hematopoietic necrosis virus (IHHNV) in Penaeus monodon and P.
Kanokporn Chayaburakul1, Donald V Lightner, Siriporn Sriurairattana
1Department of Anatomy, Faculty of Science, Mahidol University, Rama 6 Rd., Bangkok 10400, Thailand.
Abstract:
Infectious hypodermal and hematopoietic necrosis virus (IHHNV) is widespread in cultured Penaeus monodon and P. vannamei in Thailand. It causes runt-deformity syndrome that is characterized by physical abnormalities and stunted growth in P. vannamei, but causes no apparent disease in P. monodon. In both species, the virus may produce Cowdry Type A inclusions in tissues of ectodermal and mesodermal origin, but these are common in P. vannamei and rare in P. monodon. The virus can be more easily detected in both species by IHHNV-specific PCR primers. By in situ hybridization (ISH) using specific IHHNV probes, fixed phagocytes associated with myocardial cells tended to show strong positive reactions in both shrimp species. Ovarian and neural tissue (neurons in the nerve ganglia and glial cells in the nerve cord) were ISH positive for IHHNV only in P. vannamei. By transmission electron microscopy, necrotic cells were found in the gills of IHHNV-infected P. vannamei, while paracrystalline arrays of virions and apoptotic cells rather than necrotic cells were found in the lymphoid organ of IHHNV-infected P. monodon. Thus, it is possible that apoptosis in P. monodon contributes to the absence of clinical disease from IHHNV. These findings reveal different responses to IHHNV infection by the 2 shrimp species. A curious feature of IHHNV infection in P. monodon was inconsistency in the comparative viral load amongst tissues of different specimens, as detected by both ISH and real-time PCR. This inconsistency in apparent tissue preference and the reasons for different cellular responses between the 2 shrimp species remain unexplained.
Insights
Infectious hypodermal and hematopoietic necrosis virus (IHHNV) affects shrimp differently. Penaeus vannamei shows disease signs, while Penaeus monodon does not, suggesting apoptosis plays a role in resistance.
Area of Science:
- Aquaculture pathology
- Shrimp virology
- Infectious disease research
Background:
- Infectious hypodermal and hematopoietic necrosis virus (IHHNV) is prevalent in farmed shrimp in Thailand.
- IHHNV causes runt-deformity syndrome in Penaeus vannamei but is asymptomatic in Penaeus monodon.
- Differences in cellular responses and viral load distribution exist between these two shrimp species.
Purpose of the Study:
- To investigate the differential responses of Penaeus monodon and Penaeus vannamei to IHHNV infection.
- To elucidate the cellular mechanisms underlying disease manifestation or absence in the two shrimp species.
Main Methods:
- Polymerase Chain Reaction (PCR) for viral detection.
- In Situ Hybridization (ISH) to determine viral tissue distribution.
- Transmission Electron Microscopy (TEM) to examine cellular pathology.
Main Results:
- IHHNV PCR detected the virus in both shrimp species.
- ISH revealed viral presence in phagocytes of both species, but ovarian and neural tissues were positive only in P. vannamei.
- TEM showed necrotic cells in P. vannamei gills and apoptotic cells in P. monodon lymphoid organs, suggesting apoptosis as a resistance mechanism.
Conclusions:
- Penaeus monodon may resist IHHNV infection through apoptosis, explaining the absence of clinical signs.
- Significant differences in tissue tropism and cellular response to IHHNV exist between P. vannamei and P. monodon.
- The variable viral load in P. monodon tissues and the reasons for differential cellular responses require further investigation.
