Detection and Quantification of Infectious Hypodermal and Hematopoietic Necrosis Virus (IHHNV) and Enterocytozoon hepatopenaei (EHP) of Litopenaeus vannamei by Real-Time PCR

Abstract:

Infectious hypodermal and hematopoietic necrosis virus (IHHNV) is one of the pathogens causing the significant diseases of crustaceans listed by the OIE (Office internaptional despizooties) Manual of Diagnostic Tests for Aquatic Animals. Infection with IHHNV does not produce any pathognomonic gross clinical signs, although runt-deformity syndrome (RDS) has been noted in infected juvenile Litopenaeus vannamei and Penaeus monodon. Enterocytozoon hepatopenaei (EHP) was first found and isolated in Thailand in 2009, which caused slow growth of P. monodon. IHHNV and EHP were found in the samples of L. vannamei postlarvae which were collected from hatchery farms in Tianjin and Hebei Province in 2013. The diseased shrimps showed some clinical signs with high mortality, slow growth and difference of individual growth rate. The IHHNV and EHP individual detection was conducted on these samples using the real-time PCR technique. In total, 108 out of 108 (100%) L. vannamei postlarvae samples were IHHNV positive, and 53 out of 108 (49.1%) L. vannamei postlarvae samples were EHP positive. Positive samples contained approximately 103–107 copies/(μg DNA) of IHHNV and big size of individual shrimp carried higher number of virus copies. Positive samples contained approximately 103–105 copies/(μg DNA) of EHP and mainly the small sized individual shrimp. The analysis showed that the IHHNV loads were positively correlated with the shrimp growth rate. IHHNV loads above 8.51×104 copies/μg DNA represented a high risk level. EHP loads were negatively correlated with the shrimp growth rate. EHP loads above 2.19×104 copies/μg DNA represented a high risk level. Our study showed that the diseased L. vannamei postlarvae samples occurred in the hatchery farms of Tianjin and Hebai Province infected with shrimp pathogens of IHHNV and EHP. Data provides scientific basis on the effects of pathogens infection on the growth of cultured penaeid shrimp.