EFFECT OF HYPERTHERMIA ON A NATURAL INFECTIOUS HYPODERMAL AND HAEMATOPOIETICAL NECROSIS VIRUS (IHHNV) INFECTION IN Litopenaeus vannamei UNDER EXPERIMENTAL CONDITIONS
The IHHNV virus causes growth stunt and the runt deformity syndrome without mortalities in the Pacific shrimp, Litopenaeus vannamei. The prevalence of IHHNV has increased in hatcheries and farms in México, from 31 % in 2011 to 63 % in 2014. This trend may be caused by the importation of shrimp batches allegedly resistant to the Acute Hepatopancreas Necrosis Disease (AHPND) bacteria. Hyperthermia can be an effective control method against IHHNV since it inhibits virus replication as it was reported in an experimental IHHNV inoculation where hyperthermia reduced over 100 times the virus load compared to controls at 6 days after treatment (1.44 × 103 vs 2.25 x 105, respectively). The aim of the present study was to determine the antiviral efficacy of hyperthermia to inhibit a natural IHHNV infection in a batch of Pacific shrimp L. vannamei and how long it takes to IHHNV to become again detectable in pleopods.
Shrimp L. vannamei (2 ± 0.3 g) naturally infected with IHHNV were treated with hyperthermia in 80 l plastic tanks filled with water at ≥ 32.5 ± 0.5 °C. Treatments were hyperthermia (≥ 32.5 °C) with salinity of 25 g/l for (1) 14, (2) 21 or (3) 28 days, respectively. For each treatment, three tanks with 10 shrimp each were used. At the end of the experiments, shrimp were placed in tanks with water at 27 ± 1 °C and a pleopod was drawn from three shrimp per treatment at 0, 1, 3, 7, 10, 15 y 25 days post treatment. The DNA was extracted and the presence of IHHNV DNA was determined by PCR. Also, the time that took to the virus to become detectable at each treatment was recorded.
The results are presented in table 1.
The hyperthermia treatments were effective to inhibit IHHNV replication in naturally infected shrimp. The treatments had a time-dependent effect, where the longer the time of treatment, the longer the inhibition of virus replication. It was also observed that the longer the hyperthermia treatment lasted, the longer it took to IHHNV to become detected again in pleopod tissues.
It is concluded that hyperthermia is effective to inhibit IHHNV replcation in a time-dependent manner and it took IHHNV between 7 - 15 days to become detectable again by PCR in shrimp tissues depending on the intensity of hyperthermia treatment.
