Syndromes and Aquaculture

Not being an expert in white spot virus, I was digging a little deeper into this virus commonly found in shrimp, especially in shrimp farms.  While we commonly call this white spot, others call it white spot syndrome virus.  This makes me recall another virus found in pigs known as PRRSV or porcine reproductive and respiratory syndrome virus.  Even though the virus has been isolated from both, they are known as syndromes.   Wikipedia defines syndrome as,” as the association of SEVERAL clinically recognizable features, signs (observed by a physician), symptoms (reported by the patient), phenomena or characteristics that often occur TOGETHER, so that the presence of one or more features alerts the physician to the possible presence of the others.  PRRS for instance is a virus that infects pigs, but doesn’t always cause the manifestation of the disease.  In fact other pathogens seem to open the door for PRRS.  Mycoplasma and Salmonella for instance in pigs.  However, this is still a syndrome as a number of other occurrences such as stress can increase the opportunity for PRRS to cause disease.  Viruses are all around us folks, so we have to be aware of the other pieces that open the door to these viruses.  Stress and other pathogens for instance.  In one paper, they researchers had found that in 200 shrimp tested, 2% had the signs of the virus, but PCR methods demonstrated 92% of the shrimp were positive for white spot (http://www.raisaquaculture.net/uploads/media/prevalance_of_WSSV-1_1.pdf). So the viruses are there, they are just waiting for a formal introduction. 

What are the other pieces of the syndrome that open the door for the virus?  The common theme I find is poor water quality which leads to stress.  Poor water quality seems to mean a number of issues including high alkalinity (by the way the white spots are from calcium deposits so maybe this makes sense), but also poor aeration, low water changeover and of course the fact they are swimming in their own waste.  I also see vibriosis commonly associated with white spot virus.  Vibriosis is the presence of aquatic Vibrios many of which are pathogens to shrimp.

Beyond vibrios I also wonder about the other pathogens that may be inviting the virus.  Do Aeromonas, Strep and Pasteurella open the doors for white spot?   It is real tempting to try to solve these problems by adding microbes.  We have many strains in our library that have unique properties relating to Vibrios.  However, you can’t help to think you are providing the aspirin for the headache, rather than solving the health problem that leads to the vibriosis and the virus, meaning poor water quality and most likely the balance of nature and ecology that occurs in these shrimp rearing environments.  Judging from the websites, having good water quality is the first step.  But yet I still see white spot everywhere and I still here of high antibiotic usage to deal with the pathogens, so some aren’t getting the message.  Our focus on returning wastewater and bioremediation to the proper balance and in turn microbial ecology has lead to some very interesting breakthroughs in our lab and in the field.

Let’s solve the problem rather than the symptom, which is counterintuitive as I make a living being a symptom solver.  When we start at the root, everyone wins.

Michael King, Ph.D.

mike.king@mdgbio.com
http://www.linkedin.com/in/mikekingmdg
http://www.mdgbio.com/