Current situation of emerging shrimp diseases in Asia and...
Transcript of Current situation of emerging shrimp diseases in Asia and...
Current situation of emerging shrimp diseases in Asia and some recommendations to prevent
their arrival and spread
Dr. Celia R. [email protected]
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.