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Low viral loads and lymphoid organ spheroids are associated with yellow head virus (YHV) tolerance in whiteleg shrimp Penaeus vannamei.

ABSTRACT: Yellow head virus (YHV) is an invertebrate nidovirus that has caused mass mortality in penaeid shrimp since 1990. Several YHV types are known, but only the original type (YHV-type 1 or YHV-1) is highly virulent. Most studies have focused on acute YHV-1 infections and there is limited work on YHV-1 survivors. We compared moribund and surviving (14%) whiteleg shrimp Penaeus (Litopenaeus) vannamei from an experimental challenge with YHV-1. Although grossly normal, all survivors were positive for YHV-1 by specific, reverse transcriptase polymerase chain reaction (RT-PCR) assays, histological analysis or transmission electron microscopy (TEM), indicating that they were not resistant but tolerant to YHV-1. On the other hand, real-time PCR analysis revealed that mean YHV-1 copies/ng total RNA for survivors (2.8x10(4) +/- 6.9x10(4)) were approximately 40 times lower (P<0.05) than those in moribund shrimp (1.2x10(6) +/- 6.7x10(5)copies/ng total RNA). This was confirmed by strong positive immunohistochemical and in situ hybridization (ISH) reactions for YHV-1 in lymphoid organ tubules (LOT) of moribund shrimp and weak positive reaction only in lymphoid organ spheroids (LOS) of survivors. TEM revealed morphologically complete YHV virions in both groups. Furthermore, immuno-TEM and Western blot analysis revealed that YHV-1 structural proteins gp116 and p20 were present at comparable reactive levels in each group. Thus, YHV-1 tolerance was not associated with absence of gp116 as previously reported for palaemonid shrimp. Instead, it was associated with the presence of YHV-positive LOS and a relatively low viral load.

SUBMITTER: Anantasomboon G

PROVIDER: S-EPMC7172694 | biostudies-literature | 2008

REPOSITORIES: biostudies-literature

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Low viral loads and lymphoid organ spheroids are associated with yellow head virus (YHV) tolerance in whiteleg shrimp Penaeus vannamei.

Anantasomboon Gun G Poonkhum Raksawan R Sittidilokratna Nusara N Flegel Timothy W TW Withyachumnarnkul Boonsirm B

Developmental and comparative immunology 20071106 6

Yellow head virus (YHV) is an invertebrate nidovirus that has caused mass mortality in penaeid shrimp since 1990. Several YHV types are known, but only the original type (YHV-type 1 or YHV-1) is highly virulent. Most studies have focused on acute YHV-1 infections and there is limited work on YHV-1 survivors. We compared moribund and surviving (14%) whiteleg shrimp Penaeus (Litopenaeus) vannamei from an experimental challenge with YHV-1. Although grossly normal, all survivors were positive for YH ...[more]

PMID: 18055012

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Project description:BACKGROUND: The microsporidian Enterocytozoon hepatopenaei was first described from Thailand in 2009 in farmed, indigenous giant tiger shrimp Penaeus (Penaeus) monodon. The natural reservoir for the parasite is still unknown. More recently, a microsporidian closely resembling it in morphology and tissue preference was found in Thai-farmed, exotic, whiteleg shrimp Penaeus (Litopenaeus) vannamei exhibiting white feces syndrome (WFS). Our objective was to compare the newly found pathogen with E. hepatopenaei and to determine its causal relationship with WFS. RESULTS: Generic primers used to amplify a fragment of the small subunit ribosomal RNA (ssu rRNA) gene for cloning and sequencing revealed that the new parasite from WFS ponds had 99% sequence identity to that of E. hepatopenaei, suggesting it was conspecific. Normal histological analysis using tissue sections stained with hematoxylin and eosin (H&E) revealed that relatively few tubule epithelial cells exhibited spores, suggesting that the infections were light. However, the H&E results were deceptive since nested PCR and in situ hybridization analysis based on the cloned ssu rRNA gene fragment revealed very heavy infections in tubule epithelial cells in the central region of the hepatopancreas in the absence of spores. Despite these results, high prevalence of E. hepatopenaei in shrimp from ponds not exhibiting WFS and a pond that had recovered from WFS indicated no direct causal association between these infections and WFS. This was supported by laboratory oral challenge trials that revealed direct horizontal transmission to uninfected shrimp but no signs of WFS. CONCLUSIONS: The microsporidian newly found in P. vannamei is conspecific with previously described E. hepatopenaei and it is not causally associated with WFS. However, the deceptive severity of infections (much greater than previously reported in P. monodon) would undoubtedly have a negative effect on whiteleg shrimp growth and production efficiency and this could be exacerbated by the possibility of horizontal transmission revealed by laboratory challenge tests. Thus, it is recommended that the PCR and in situ hybridization methods developed herein be used to identify the natural reservoir species so they can be eliminated from the shrimp rearing system.

Dataset Information

Low viral loads and lymphoid organ spheroids are associated with yellow head virus (YHV) tolerance in whiteleg shrimp Penaeus vannamei.

Publications

Low viral loads and lymphoid organ spheroids are associated with yellow head virus (YHV) tolerance in whiteleg shrimp Penaeus vannamei.

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