Prevalence of infectious hypodermal and hematopoietic necrosis virus (IHHNV) in Penaeus vannamei cultured in northeastern Brazil

Infectious hypodermal and hematopoietic necrosis virus (IHHNV) is a shrimp disease agent that causes mortalities of up to 90% in Penaeus stylirostris but does not cause lethal infections in Penaeus vannamei. The purpose of this study was to determine the prevalence of IHHNV in P. vannamei cultured in northeastern Brazil, the highest shrimp producing area in the country, by one-step polymerase chain reaction (PCR). Using one-step PCR, we amplified a 185 bp fragment of IHHNV genome and determined IHHNV prevalence on 26 rearing ponds of seven farms. Shrimp from all the ponds showed infection by IHHNV and the prevalence of the virus in the ponds ranged from 9.4% to 81%. Significant differences in IHHNV prevalence among rearing ponds from the same farm were found. These differences might be attributed to different larval origins, handling techniques and environmental factors. Despite the high IHHNV prevalence in shrimp populations, a relationship between cultivation time and gross signs of RDS were not observed. Our results showed that IHHNV infection was common in rearing ponds. but the clinical findings indicated no apparent impact of IHHNV disease on the shrimp, suggesting that P. vannamei reared in northeastern Brazil could have the so-called "non-infectious IHHNV form". (C) 2008 Elsevier B.V. All rights reserved.