Overview of major diseases (possibly) affecting Vietnam

shrimp farmsStephen G. Newman Ph.D.

CEO

Aquaintech Inc.

Biotechnology Benefiting Aquaculture

Disease is complex

Disease

Pathogen

Environment

Host

Disease

Biosecurity

Good-less disease

Poor-more disease

Disease is an outcome of the relationship between the host, the pathogen and the environment.

Using appropriate biosecurity strategies can result in a shift in this dynamic in favor of the shrimp. Less disease.

Obligate Causes diseases because it is present in healthy animals versusOpportunistic Causes disease in weakened animals

What are primary diseases?

• Vibriosis• Early Mortality Syndrome

• Non specific largest cause of mortality in shrimp farms

• Viral Infections• WSSV, CMNV, others?

• Protozoan/Fungi• Microsporidians Enterocytozoon hepatopenaei

Single or multiple pathogens

• Where do these problems start?• In the hatchery because of poor or no biosecurity

• Moved into the farm

• Continue on the farm by• Improper filtration of water

• Failure to lessen load of vectors

• Inadequate pond preparation

• Poor biosecurity

• Failure to control stressors

Bacterial Pathogens

• Vibrios• Mostly opportunistic

• Number one cause of mortality

• Often secondary not primary; animals are weakened by stress • Low dissolved oxygen levels

• High ammonia levels

• Hydrogen sulfide from anaerobic bottoms

• Poor quality feed

• Poor biosecurity allows potential pathogens to move through the production cascade

Many vibrios cause disease direct and indirect

Partial List of vibrio species reported to cause disease in shrimp

(To date > 120 named species and counting with thousands of strains)

Vibrio parahaemolyticus Vibrio orientalis

Vibrio alginolyticus Vibrio ordalii

Vibrio anguillarum Vibrio mediterrani

Vibrio damsela Vibrio logei

Vibrio vulnificus

Vibrio penaeicida

Vibrio harveyi

Vibrio owensii

Vibrio nigropulchritudo

Vibrio campbellii

Vibrio splendidus

Vibrio fischeri

Vibrio pelagicus

Most are opportunistic

Vibriosis

Many pathogenic vibrios are yellow in TCBS

Many other bacteria grow on TCBS-not just vibrios

Biosecurity starts in maturation and the hatchery

The vibrio that is causing the most problems today

• Etiologic agent of EMS• A unique strain of a common vibrio species Vibrio parahaemolyticus

• Contains genes that produce a powerful toxin that damages the HP

• Shrimp are affected according to the level of toxin ingested

• Can be present with no disease

• Current theory is that these bacteria colonize uneaten feed and the pond bottoms and as shrimp forage they ingest a large dose of the toxin

• Control-minimization of loads, management of stress

• Likely impacted by other pathogens being present

Control of vibrios (I)

• Minimize the load of the pathogen entering the system through effective biosecurity protocols in the hatchery and on the farm

Etiologic agent of EMS Flegel et al. GOAL 2014

Biosecurity failures in hatchery spread the disease from broodstock to the farm

Contaminated feeds are an important source of the bacteria

Infected with E. hepatopenaei (EHP) 72/148 = 49%

Mortality <35 days, i.e. the classic definition of EMS 21/148 = 14%

Infected with white spot syndrome virus (WSSV) 8/148 = 5%

Covert mortality nodavirus (CMNV) 64/148 = 43%

Early mortality with no HP lesions 5/148 = 3%

Examined 200 Thai ponds at random for prevalence GOAL 2014 Flegel et al

Serious problem with infections with multiple pathogens?

Could this be what is happening everywhere? RMS in India

Three pathogens…

Vibriosis is being reported everywhere

Control of vibrios (I)

• Use of PRO 4000X• Field trials have shown that proper use can lower loads of vibrios

• Competitive exclusion-not elimination

• Acts on sediments to start –high nutrient loads allow bacteria to proliferate inhibiting vibrio growth

• Not elimination

• Not possible under most circumstances CONTROL

India Field Trial with PR0 4000X

One ha ponds35 per meter square8 kgs/ha/cycleP. vannamei

Control pond open due to high ammonia levels

Experimental ponds closed due to ammonia control

TCBS green vibrio loads dropped with PRO4000X application

Other tools for controlling vibrios

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CFU/ml of presumptive Vibrios

Compound L top dressed on the feedSafe, cheap and effectiveCommon component in human food

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Experimental

MEGAX Field proven tool for increasing survivalUsed in the hatchery, acclimation, etc.Results are based on challenge with virulent VP

MEGA X (1:500 dilution for 6 hrs) results in increased survival against EMS (triplicate)

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Control of vibrios (I)

• PRO 4000X bioremediation and competition

• Compound L direct inhibition

• Mega X Affects animals ability to withstand exposure

• Environmental management –biosecurity in hatchery and on farm can inhibit specific loads of vibrios

Control of vibrios (II)• Environment –high water exchange rates, well water, very low salinity water,

lined ponds (no sediment), highly controlled production systems, high quality water, biofloc (sometimes), others?

Biofloc indoors (Mexico)

Indonesia high water exchange with very clean seawater

Viral Diseases

• Many affect shrimp farmers in Vietnam• Many likely not characterized

• PROACTIVE disease management is critical

• White Spot Syndrome Virus (vibriosis)

• IHHNV Infectious hypodermal and hematopoietic necrosis virus Minimal impact

• Covert Mortality Nodavirus (CMNV)

Many other viruses > 20 in total to date

• IMNV Infectious myonecrosis virus (Indonesia)

• TSV Taura Syndrome Virus (Latin America)

• YHV Yellow Head Virus (Thailand)

• MrNV Macrobrachium rosenbergii nodavirus (India)

• ASDD Abdominal segment deformity disease

• HPV Hepatopancreatic Virus

• LSNV Laem Singh Virus (Thailand in P. monodon)

• MBV Monodon Baculo Virus

Not new. Chinese coined the term “bottom death”. It has been around for more than a decade.

Shrimp die on the bottom. Kills at temps above 28 C. The mortality appears at about 1 month

post-stocking and increased after 60–80 days post-stocking, accompanied by an increase of nitrite nitrogen.

Can see a cumulative mortality up to 80 % Possibly more than virus involved Some researchers report that this virus is

not very pathogenic and may be involved in weakening animals making them more susceptible to other pathogens (vibriosis).

Control of viral diseases

• Exclusion• Prevention of entry into the production system they are everywhere

• Biosecurity in the hatchery

• Complicated by failure to test for the virus (not OIE)

• Role in acute mortality not well understood

• Likely weakens animals and contributes to susceptibility (Running mortality syndrome?)

• Use of Chinese frozen feeds in broodstock likely contaminated shrimp in VN and elsewhere

• Synergistic

Parasites (fungal/protozoan) Enterocytozoon hepatopenaei (EHP)

Enterocytozoon hepatopenaei (EHP)

Microsporidian >130 genera identified

approximately 25 affect crustaceans

Parasites with complex life cycle

• Widely spread throughout SE Asia (reported in late 1990’s in Malaysia?)

• Possibly associated with white feces• i.e. EHP positive with white feces EHP negative no reports of white feces

Tissue specific for HP unlike most other microsporidians which affect muscle

Transmitted orally between shrimp with no need for an intermediate vector very unusual and very worrisome?

EHP control

• Cannot be eradicated using traditional approaches

• Resistant to all known drugs

• Very difficult to eradicate• Broodstock biosecurity (in feces?)

• Environmental management • Sludge reduction

• Proper pond preparation

Conclusions

• Essential that hatcheries wash and surface disinfect eggs and nauplii

• Limit movement of broodstock between countries

• Implement proactive disease management strategies• Stress reduction

• Environmental improvement (PRO 4000X, Aquapro EZ)

• Competitive exclusion

• Strengthening animal (Mega X)

• Elimination of carriers, vectors, etc. (proper pond preparation)• Avoid the use of chlorine and other chemicals that destroy pond ecology and allow

bacteria like the causative agent of EMS to proliferate