Evidence of existence of infectious hypodermal and hematopoietic necrosis virus in penaeid shrimp cultured in China

Infectious hypodermal and hematopoietic necrosis virus is the causative agent of a shrimp disease which causes economic losses on a global scale. A pair of primers, I2814F/I3516R, was designed from the IHHNV genomic sequence (GenBank) that encodes for structural protein corresponding to nucleotides 2814-3516, which amplifies a 703 base pair (bp) region from the virus genome. PCR amplification with the primers generated a product of the expected size from the purified IHHNV DNA of Litopenaeus vannamei and IHHNV-infected penaeid populations but not from the IHHNV-free shrimp, white spot syndrome virus (WSSV) and hepatopancreatic parvovirus (HPV). The PCR amplicon described above was labeled with digoxigenin (DIG)-11-dUTP as a probe used for dot blot hybridization and in situ hybridization test. Under the optimized PCR conditions, the primers were detected by as little as 20 fg of purified IHHNV DNA, which contained only 8.83 x 10(3) copies of IHHNV, a 1000-fold greater than using dot blot hybridization. Sections of histopathology showed eosinophilic intranuclear inclusions (Cowdry type A inclusions or CAIs) in infected tissues while in situ hybridization, cells displayed an intense reaction with the DIG-labeled probe. PCR assay was developed to detect IHHNV in penaeid shrimp and other crustaceans from the rearing ponds of China (March 2001-June 2004). The positive rate was 51.5% (154 out of 299) and 8.3% (2 out of 24) for penaeid shrimp and crab samples, respectively. The survey demonstrated the presence of IHHNV in China.