By: Ph.D Stephen G. Newman*
There can be no sustainable aquaculture without pathogen control. Members of the OIE are ethically obligated as a condition of their membership to submit relevant disease outbreak information in a timely and open manner. Still, shrimp pathogens’ movement across international borders has caused billions of dollars of losses to regional economies.
For three decades now I have been working with the international shrimp farming community. Prior to that I worked largely with farmed salmonids. My doctoral thesis identified the role of plasmid in the virulence of a vibrio species that affects many aquatic animals.
All animals have problems with diseases. The absence of disease is not natural; in fact, disease is a natural process that is an element of the recycling that all life is a part of. The impact of the diseases affected aquaculture is not inconsequential.
Controlling diseases through treatment of infected animals is much more challenging than prevention is in many instances. For most terrestrial agriculture vaccines are an important tool for this. Fish can be immunized and are routinely.
“Shrimp cannot be. Their immune systems have no memory function and they do not form antibodies. The most powerful tool available is to prohibit the movement of stocks carrying any pathogen into areas where these pathogens are not already endemic.”
Did you know that there is no AHPNS in Mexico? Or in India? And many other countries where it is endemic. The Office International des Epizooties (OIE) was founded as an independent inter-governmental international organization in 1924 well before the United Nations came into existence.
Its role is simple, to ensure that global agriculture is protected against domestic and international transmission of infectious diseases with the potential for serious impacts. If it was effective, in theory, many diseases that have the potential to cause significant economic damage would be contained as soon as they were observed.
This is a noble concept, but it turns out that it is largely impractical at least for shrimp farming. Focusing on farmed shrimp, typically when a disease is first discovered there are a series of steps that must be taken to establish that it is indeed due to a primary pathogen.
“The pathogen must be able to reproduce a specific disease when administered in pure culture. Typically, the portal of entry into the animals should be similar or identical to that of the pathogen in the environment.”
A pathogen that only kills when injected would not be considered an obligate pathogen unless it was endemic. The pathogen must be isolated and then used to re-infect animals with the same end result.
The DNA or RNA sequence must be determined so that a reliable and specific gene-based tool can be used to corroborate the presence of the pathogen when animals are tested.
At the same time as much information as can be readily gleaned about where the pathogen is in the environment, what carriers there may be, how infectious it is, etcetera is critical to understanding what one is dealing with.
“Once the pathogen has been characterized there is a process that allows for to be eventually added to the list of pathogens that OIE states are of serious concern. Unfortunately, this process is, much as with many things of this nature, convoluted and quite slow.”
It can take years from the time that a pathogen is first reported until it is listed. This is a huge loophole that must be plugged. Members of the OIE are ethically obligated as a condition of their membership to submit relevant disease outbreak information in a timely and open manner.
There are nine listed diseases for crustaceans, eight of which are for fresh and saltwater shrimp. The OIE Aquatic Animal Health Code 2019 (http://www.oie.int/en/international-standard-setting/aquatic-code/access-online/) details what actions importing and exporting countries should take to comply.
These are intended to prevent the movement of these pathogens into countries where they are not already present. The listed crustacean diseases include AHPNS, NHP, WSSV, TSV, YHV (I), IMNV, IHHNV and the nodavirus that causes white tail disease in M. rosenbergii.
The list does not (yet) include EHP, DIV1, any other YHV variant aside from Type I, LSNV, HPV, MBV, GAV or MOV and a myriad of other viral and bacterial pathogens that are known to cause serious losses in farmed shrimp. Many companies believe that they only need to test broodstock/ nauplii/ PLs for the listed diseases and all too often sell animals as SPF when they could easily contain any number of other potentially serious pathogens.
The movement of shrimp pathogens across international borders has caused billions of dollars of losses to regional economies. A notable example is of the White Spot Syndrome Virus (WSSV). Shrimp from Pakistan were rejected entry into the original country intending to import them and were subsequently reprocessed with the effluent from the plant entering untreated into the Gulf of Fonseca ecosystem.
“This ecosystem is central to the shrimp farming industries of Nicaragua and Honduras. The contamination of this ecosystem with the WSSV virus and the subsequent movement of infected animals spread the virus.”
The virus is now endemic in most areas in the Americas. As new diseases appear, an inevitable consequence of traditional farming practices, it is imperative that countries that are affected take responsibility and share this information with the international community.
Waiting till the pathogen has spread accomplishes little in the long run. One of the recent additions to the Aquatic Health code is the etiologic agent of AHPNS, a strain of Vibrio parahaemolyticus that contains a plasmid borne toxin complex (Pir A and Pir B) that is responsible for the observed pathology.
This plasmid has spread to several other vibrio strains and there is a good chance that it can move into non-vibrios species as well. To this day, there are instances where OIE has not been notified of its presence. The government denies its presence while researchers document it and farmers suffer from it presence.
“This has resulted in wide ranging adverse impacts that would not have occurred had the disease been reported as OIE requires.”
Recognizing that this can be a double-edged sword, responsible governments look to their scientists and animal health professionals to develop sensible approaches to containment where required and eradication where possible in order to mitigate some of the risks.
Unfortunately, this is not always the case. Almost every major shrimp producing nation is not revealing the extent of specific pathogens as their ethical obligations to OIE require.
Failure to comply with these ethical obligations could eventually force draconian approaches towards control of the movement of pathogens impacting the movement of farmed shrimp in the final market ready form as well as seed stocks and many of the important tools that are elements of production.
When countries are dependent on exports, protectionist policies may override concerns about pathogen movement. To some extent this is understandable when the presence of notifiable pathogens might limit the movement of consumer ready product into markets where these pathogens have not (yet) been reported.
“It is unfortunate that this fear has resulted in examples where the presence of a notifiable pathogen is common knowledge but not officially recognized by the government competent authorities.”
The perceived need to protect a local industry at the expense of others who would be buying animals that are carrying OIE notifiable (and for that matter any of the characterized pathogens) has caused untold amounts of suffering and economic damage.
This persists. While aquaculture is being actively promoted, hiding the presence of OIE pathogens is little more than hypocrisy and these actions strongly suggests that the concerns about aquaculture and the economic damage from preventable disease are words.
Their actions speak loudly. They do not care about the sustainability of aquaculture by their very actions. This is unfortunately compounded by any number of NGOs who tout themselves as being the standard bearers for sustainability.
Most of them know what is going on and choose to look the other way. There can be no sustainable aquaculture without pathogen control. The OIE has no teeth. They need to be able to police this, levying large fines for non-compliance and ensuring that those who choose to risk the livelihoods of others face the consequences.
Unfortunately there is no will to change this and those who have the greatest to lose are often those who refuse to acknowledge the presence of specific disease causing pathogens.
Stephen G. Newman has a bachelor’s degree from the University of Maryland in Conservation and Resource Management (ecology) and a Ph.D. from the University of Miami, in Marine Microbiology.
He has over 40 years of experience working within a range of topics and approaches on aquaculture such as water quality, animal health, biosecurity with special focus on shrimp and salmonids.
He founded Aquaintech in 1996 and continues to be CEO of this company to the present day.
It is heavily focused on providing consulting services around the world on microbial technologies and biosecurity issues.