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Diseases of Aquatic Organisms

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DAO 74:85-94 (2007)  -  doi:10.3354/dao074085

Pathogenesis of a Thai strain of white spot syndrome virus (WSSV) in juvenile, specific pathogen-free Litopenaeus vannamei

C. M. Escobedo-Bonilla1,2, M. Wille1, V. Alday Sanz3, P. Sorgeloos1, M. B. Pensaert2, H. J. Nauwynck2,*

1Laboratory of Aquaculture & Artemia Reference Center, Faculty of Bioscience Engineering, Ghent University, Rozier 44, 9000 Ghent, Belgium
2Laboratory of Virology, Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, 9820 Merelbeke, Belgium
3INVE Technologies, Hoogveld 93, 9200 Dendermonde, Belgium
*Corresponding author. Email:

ABSTRACT: White spot syndrome virus (WSSV) causes disease and mortality in cultured and wild shrimp. A standardized WSSV oral inoculation procedure was used in specific pathogen-free (SPF) Litopenaeus vannamei (also called Penaeus vannamei) to determine the primary sites of replication (portal of entry), to analyze the viral spread and to propose the cause of death. Shrimp were inoculated orally with a low (101.5 shrimp infectious dose 50% endpoint [SID50]) or a high (104 SID50) dose. Per dose, 6 shrimp were collected at 0, 6, 12, 18, 24, 36, 48 and 60 h post inoculation (hpi). WSSV-infected cells were located in tissues by immunohistochemistry and in hemolymph by indirect immunofluorescence. Cell-free hemolymph was examined for WSSV DNA using 1-step PCR. Tissues and cell-free hemolymph were first positive at 18 hpi (low dose) or at 12 hpi (high dose). With the 2 doses, primary replication was found in cells of the foregut and gills. The antennal gland was an additional primary replication site at the high dose. WSSV-infected cells were found in the hemolymph starting from 36 hpi. At 60 hpi, the percentage of WSSV-infected cells was 36 for the epithelial cells of the foregut and 27 for the epithelial cells of the integument; the number of WSSV-infected cells per mm2 was 98 for the gills, 26 for the antennal gland, 78 for the hematopoietic tissue and 49 for the lymphoid organ. Areas of necrosis were observed in infected tissues starting from 48 hpi (low dose) or 36 hpi (high dose). Since the foregut, gills, antennal gland and integument are essential for the maintenance of shrimp homeostasis, it is likely that WSSV infection leads to death due to their dysfunction.

KEY WORDS: WSSV · Specific pathogen-free Litopenaeus vannamei · Pathogenesis · Oral inoculation · Immunohistochemistry · Indirect immunofluorescence · PCR

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