IHHNV or Infectious hypodermal and haematopoietic necrosis is a very small, very well characterized virus that is widely distributed and typically is not the cause of mass mortalities in the commonly farmed shrimp species, P. vannamei and P. monodon. For more information click OIE IHHNV. The virus, as with all viruses, mutates and several different variants have been isolated. It is endemic in many different populations of wild shrimp and while it causes what is typically referred to as the Runt Deformity Syndrome (RDS), slow growth and even low levels of mortality, there is no reason to believe that is has suddenly reverted to a high degree of virulence in Vietnam accounting for the 900 million deaths of PLs being reported. Because it is endemic it is highly likely that it will be present in all stocks derived from wild seed. Vietnam is still in the relatively early stages of shifting from reliance on wild adult broodstock for the source of eggs to specific pathogen free, captive and domesticated broodstock. Without the use of proper exclusion techniques at the time of broodstock collection (PCR and quarantine) it is highly probable that it will be present in all stocks farmed. While it is not impossible, it is improbable that the current disease problems widely coined as Early Mortality Syndrome (EMS) are due to IHHNV. Water quality is an essential component of sustainable aquaculture and pollution, when it is is rampant, even with steps being taken to sterilize the incoming water, can result in problems (such as algal toxins). Based upon what we know of this virus and the fact that it has been present in wild shrimp in Vietnam since testing for it began, it is highly unlikely that it would revert to high levels of virulence and be the sole agent responsible for killing large numbers of post larval shrimp within the first 30 days of stocking. While there is no doubt that it is present, there are other things going on.