Abstract
Infectious hypodermal and hematopoietic necrosis virus (IHHNV) is a widely distributed single-stranded DNA parvovirus that has been responsible for major losses in wild and farmed penaeid shrimp populations on the northwestern Pacific coast of Mexico since the early 1990's. IHHNV has been considered a slow-evolving, stable virus because shrimp populations in this region have recovered to pre-epizootic levels, and limited nucleotide variation has been found in a small number of IHHNV isolates studied from this region. To gain insight into IHHNV evolutionary and population dynamics, we analyzed IHHNV capsid protein gene sequences from 89 Penaeus shrimp, along with 14 previously published sequences. Using Bayesian coalescent approaches, we calculated a mean rate of nucleotide substitution for IHHNV that was unexpectedly high (1.39×10−4 substitutions/site/year) and comparable to that reported for RNA viruses. We found more genetic diversity than previously reported for IHHNV isolates and highly significant subdivision among the viral populations in Mexican waters. Past changes in effective number of infections that we infer from Bayesian skyline plots closely correspond to IHHNV epizootiological historical records. Given the high evolutionary rate and the observed regional isolation of IHHNV in shrimp populations in the Gulf of California, we suggest regular monitoring of wild and farmed shrimp and restriction of shrimp movement as preventative measures for future viral outbreaks.
Highlights
Effective implementation of monitoring and control measures for viral epizootic outbreaks requires an understanding of the factors that underlie molecular evolution and population dynamics
The majority of the infectious hypodermal and hematopoietic necrosis virus (IHHNV) sequences were amplified from L. stylirostris (n = 83) followed by L. vannamei (n = 5) and one from F. californiensis (Table 1)
Our analysis suggests that the common ancestor of the sampled IHHNV isolates dates to the early 1970’s, which coincides with the assumed time of IHHNV introduction into the region [39]
Summary
Effective implementation of monitoring and control measures for viral epizootic outbreaks requires an understanding of the factors that underlie molecular evolution and population dynamics. This is true for introduction of the infectious hypodermal and hematopoietic necrosis virus (IHHNV) into shrimp populations of the northern Pacific coast of Mexico. In the northwestern coast of Mexico, IHHNV affects two of the most economically important shrimp species, Litopenaeus stylirostris and L. vannamei This viral pathogen is known to cause mortalities of up to 90% in juvenile and subadult individuals of L. stylirostris [5], and growth reduction and cuticular deformities in L. vannamei [6]. In 1990, IHHNV caused major epizootics in farmed and wild
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