Current situation of emerging shrimp diseases in Asia and some recommendations to prevent

their arrival and spread

Dr. Celia R. Lavilla-Pitogocelia.pitogo@fulbrightmail.org

Hilton Hotel, Guayaquil, EcuadorSeptember 25-28, 2017

Penaeus vannamei is native to the Western Pacific coast of Latin America from Peru in the south to Mexico in the north

1970s

1980s

1978-79

1996

2000It’s a vannamei world!

Dangerous exchanges

YHVWSSVIHHNVMOV?

LOVV?TSVBP?Reo?

P. monodon P. vannamei

Slide from Dr Tim Flegel

Lessons from the hypothetical “exotic shrimp transfer network”

Rapid and widespread distribution of shrimps and their hitch-hikers!

Can we stop it? When?

It’s a risky and fast-changing world!

Our shrimp world is full of acronyms!It was EMS before it became AHPNS, then AHPND.

The Many Faces and Phases of Biosecurity

Requirements for successful implementation:▪ knowledge of the enemy▪ where and how to find it

Has this been effective?

The Many Faces and Phases of Biosecurity

Does this help?

What are the shrimp’s enemies?

1. Acute hepatopancreatic necrosis disease (AHPND)2. Hepatopancreatic microsporidiosis (HPM) due to EHP

1. Hepatopancreatic haplosporidiosis (HPH)2. Aggregated transformed microvilli (ATM)

1. Covert mortality disease (CMD)2. White spot disease (WSD)3. Yellow head disease (YHD) 4. Infectious myonecrosis (IMN)

5. Taura syndrome virus (TSV) and infectious hypodermal and hematopoietic necrosis virus (IHHNV) have become innocuous due to the widespread use of highly tolerant specific pathogen free (SPF) stocks of Penaeus vannamei that dominate production.

We can only detect what we know.

Symposium on Diseases in Asian Aquaculture August 28 - September 1, 2017 in Bali, Indonesia

WSSV = 7 oral presentationsAPHND = 7 oral presentations

EHP = 4 oral presentations

Biosecurity Levels: NationalWhat to keep out?

1. IMNV?2. EMS/

AHPND?3. EHP?

Agreement on disease list is important.

Be aware of what is already at home.

Biosecurity Levels: Regional or Ecological

Biosecurity Level: FarmsWhich

diseases are potential hazards?

• Identify and prioritize

How much risk it is to the

farm?

• Evaluate disease impact

How and where can

disease enter?

• Identify control points

Biosecurity Level: Farms

How much will exclusion cost?

• Know the economic impact of disease occurrence, diagnosis and prevention

Is it practical?• Evaluate farm

location vis-à-vis planned actions

Pathogen “Jumps”: IMNV

IMNV in Indonesia (2006) IMNV in Brazil (2004)

How did IMNV travel from Brazil to Indonesia?

Pathogen “Jumps”: EHP

EHP in Asia (2014)

EHP in South America (2017)

How did EHP travel from Asia to Latin America?

Pathogen “Jumps” or pathogens in flight?

Givens:

1. A virus like IMNV is an obligate pathogen and ALWAYS travels WITH SHRIMP or other hosts

2. An obligate parasite like EHP ALWAYS travels WITH SHRIMP or other hosts

“Traditional” BIOSECURITY in Shrimp

• Focused on viruses

• Systems were not prepared for bacteria or parasites

• AHPND is not a case of simple vibriosis, but some “traditional” control measures could work

Biosecurity for vibrios

• Unheard of before the advent of AHPND because vibrios are ubiquitous in the environment

• Difficult because vibrios:

– form biofilms and adhere to particles

– have positive affinity to chitin, an abundant material ON and IN shrimps

– grow on organic material, including feeds

– exchange genetic material with other vibrios or bacteria

• Microbial ecological management is key to control of vibriosis

Sources of Vibrio harveyi in Penaeus monodon hatcheries:Spawners release fecal material in spawning water; adherence resulted

to biofilm formation on egg surface

Penaeus monodon egg with bacterial plaques on the surface

The bacterial plaques are composed of actively dividing cells similar to Vibrio harveyi

This proves that eggs are colonized by V. harveyi before hatching and this pathogen route can be disrupted by spawner removal and

egg rinsing.

Vibriosis in shrimp grow-out cultureThe shrimp pond is like a bank!

A lot is deposited; very little is withdrawn.

Rearing pondFeeds Fertilizers

Shrimp

Algae and zooplankton grow and dieOrganic matter builds-up

Water quality changesMicroorganisms grow

Biofilms form

Feces, metabolites, old exoskeleton,mortalities

Vitamins, additives, binders, uneaten pellets

Probiotics, lime and otherchemicals

Thousands of postlarvae withassociated bacteria + vibrios

+ vibrios

+ vibrios

+ vibrios ?Fertilizers ✔

+ vibrios

Avoiding too much deposits in the shrimp farm bank through Best Management Practices

Reference: INFOTIP by ASEAN-SEAFDEC

Shrimp toilet!!!

Then came EHP!

EHP Disease Card:- a 5-page document that can be downloaded from the NACA website at www.enaca.org

EHP – Advisory from Thailand

We have data indicating that most SPF stocks of P.vannamei imported to Thailand are negative for EHP, butthey often become contaminated in recipient maturationfacilities and hatcheries because of poor biosecurity.

What kind of biosecurity works for a pathogen than came in unnoticed?

• Although EHP does not appear to cause mortality, it is associated with severe growth retardation in P. vannamei.

• Management options are available.

Diagnostic Methods:

• PCR = limited information!

• Wet mount of fresh samples

• Histopathology

Let’s befriend that microscope once again.

EHP spores form clusters in the cytoplasm of infected cells (arrows)

Smear of shrimp hepatopancreas heavily-infected with EHP; spores form clusters in the cytoplasm (arrows)

EHP spores in histo slides (arrows)

SEVERITY GRADE TABLE FOR VARIOUS CLINICAL FINDINGS IN SHRIMP TISSUES

from Dr. Lightner

Effect of EHP: Wide size variation during harvest

Size distribution of shrimps during harvest can be a reflection of the effect of high Coefficient of Variation in postlarvae during stocking

-50

0

50

100

150

200

250

0 5 10 15 20 25 30 35

Pcs

grams

Size distribution during harvest

Uniform size of postlarvae is important Size distribution during harvest

EHP and biosecurity

– Reduction of infectious spores in the environment• Very challenging because spores are RESISTANT to

routine chlorine levels used by the farm

• Spores are not deactivated by drying

• Billions of spores may have been released in the environment through hundreds of pond growoutactivities with EHP-infected shrimp

– PL selection• Use PCR

• Where EHP is present, compare production and profit data of EHP-negative and positive PLs during stocking

• What management strategies will improve it?

Prevention of EHP in Hatcheries

Nauplii mouths are closed; transfer to tanks with minimum

water from spawning tank

Zoeae produce large amount of feces; hygiene, feeding strategy and stocking density should be reviewed

Use spawning tanks; avoid ”straight” hatchery runs

Prevention of EHP in growout ponds

Why should we use extremely high or low pH for clean up?

Microsporidian Spore StructureThe polar tube acts like a harpoon or missile that perforates host cells.

Chitin surrounding the spore wall makes it resistant to harsh environments.

http://web.stanford.edu/group/parasites/ParaSites2006/Microsporidiosis/microsporidia1.html

What will make the spore eject its polar tubule, a single-use ammunition?

There is more to slow growth than EHP

Strangulated HP tubules

Granulomas in HP tubules

What are meaningful strategies for biosecurity?• WSSV

– Carrier-eradication through filtration, application of crustacicide, disinfection of water, bird-nets, control of staff and equipment movement, etc.

– Stock SPF/SPR• PL selection

• EMS/AHPND– Disinfection of water by chlorination, microbially-mature water via

ageing or application of probiotics, control of feeding and prevention of sludge accumulation, etc.

– Stock SPF• PL selection

• EHP– Disinfection of pond bottom by use of lime or acid; prevention of

sludge accumulation, etc.– Stock SPF

• PL selection

Biosecurity strategies should match pathogen biology.

How about unknown pathogens?

Thank you for your attention!

We can only detect what we know.

Let’s take care of shrimps we have.