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IHHNV and WSSV, two viral pathogens of interest in Thai aquaculture Diva January Aldama Cano, PhD Postdoctoral researcher, Centex Shrimp

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Page 1: IHHNV and WSSV, two viral pathogens of interest in Thai …aquaexpoguayaquil.cna-ecuador.com/wp-content/uploads/... · 2019-11-05 · Talk overview •General introduction •Infectious

IHHNV and WSSV, two viral pathogens of interest in Thai aquaculture

Diva January Aldama Cano, PhDPostdoctoral researcher, Centex Shrimp

Page 2: IHHNV and WSSV, two viral pathogens of interest in Thai …aquaexpoguayaquil.cna-ecuador.com/wp-content/uploads/... · 2019-11-05 · Talk overview •General introduction •Infectious

Talk overview• General introduction

• Infectious hypodermal and hematopoietic necrosis virus (IHHNV)• Background

• Current situation

• White-spot syndrome virus (WSSV)• Background

• Detection and preventive measures

• Guidelines for WSSV control based on our research findings

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Viral diseases in Thai shrimp farming

• Major source of economic loss

• YHV (1995)• 40 million USD (lost in export

revenue)

• WSSV (1996-1997)• 1 billion USD (estimated)

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Flegel, 2019

• E H P• W F S

Thai shrimp production over the years

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Infectious hypodermal and hematopoietic necrosis virus (IHHNV)

• First discovered in blue shrimp P. stylirostrisand white shrimp P. vannamei in the Americas in the early 1980's

• Believed to have been introduced by live experimental stock of P. monodon from Asia

• Densovirus with non-enveloped icosahedral virions averaging 22–23 nm in diameter and containing linear ssDNA of 4.1 kb

Picture: Bonami et al.,1990

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• IHHNV has been reported in several species

• Known to cause mortalities in P. stylirostris juveniles and sub-adults

• In P. vannamei• No mortality

• Reduced growth

• Cuticular deformity known as “runt-deformity syndrome” (RDS)

• Can be passed by vertical and horizontal transmission

• P. monodon• Seems to be unnafected

• P. merguiensis and P. indicus• Refractory to infection (resistant)

(Brock and Main, 1994; Lightner, 1993, 1996; Flegel, 2009)

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Actual status of IHHNV in Asia• This disease is of little concern to the shrimp industry

• No significant loss related to IHHNV episodes in Thailand or in Asia in general in the past 10 years or so after the development and use of SPF shrimp

• Some shrimp carry IHHNV viral fragments inserted into theirgenome (P. stylirostris, P. monodon and P. vannamei)

• Possibility of false positives by following OIE detection methods

Flegel, 2009; Cowley et al ,2018; Tang et al,2006

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OIE- Diagnostic manual for aquaticanimal disease

Is it appropriate to still keepIHHNV as an OIE listed

disease?

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• IHHNV has no longer any significant negative economic impact on aquaculture after the introduction and development of SPF resistant shrimp lines.

• Should it be removed from the OIE list of reportable diseases for the same reason as other disease that are no longer a threat?

As long as they remain on the list they can be used as unjustified barriers to international trade in shrimp and shrimp products

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• Trading difficulties and bannedexports due to presence of disease

• Problems are not based on the detection of the disease itself buta problem with trading, politicaland economical underlines

• No risk of disease transmission to shrimp farms from shrimp thathave been prepared for human consumption

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White spot syndrome virus (WSSV)

•#1 viral treat and major source of concern forshrimp industry worldwide

• It has been extensely reviewed

•Wide host range (>100 species)

•Major threat for P. monodon and P. vannamei

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Pathology• Lead to mortality rate of 100% within days

• Clinical: reduction in food consumption, lethargy, loose cuticle and reddish discolouration, white spots on the inside surface

• The most convenient tissue for histological diagnosis is the subcuticular epithelium

Distinctive white

inclusions INthe cuticle;cannot be

scraped off with

thumbnail

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• infects a wide variety of cells from ectodermal and mesodermal origin

•Gill epithelium, nervous tissue, connective tissueand intestinal epithelial tissue

•Pathogenesis involves widespread tissue necrosis and disintegration

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Transmission• Principle transmission mode is vertical from grossly normal broodstock

carriers

• Most viral particles in supporting tissues of ovary and not in eggs

• Washing of eggs and nauplii: effective in reducing transmission probability

• Screening of broodstock recommended so infected carriers can be eliminated

Broodstock → Nauplii → Post-larvae

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Bird droppings

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Roof netting

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Example of biosecure farm in the south of Thailand

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WSSV detection• The OIE recommended method for diagnosis of WSD is by the use of a

nested PCR method

• A Recent modification has been proposed to OIE recommended method which is a single step method and has equal sensitivity and specificity

WSSVShrimp DNA

Lo et al., 1996

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IQ2000™ WSSV

• Yun-Long Tsai , Yu-Chan Lin , Pin-HsingChou , Ping-Hua Teng , Pei-Yu Lee.Detection of white spot syndrome virus by polymerase chain reaction performed under insulated isothermal conditions

• Journal of Virological Methods Volume 181, Issue 1 2012 134 - 137

• http://dx.doi.org/10.1016/j.jviromet.2012.01.017

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WSSV therapeutic measures

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Strategies are based onthe viral bindingproteins (VBP) fromshrimp that can be used to study host-pathogen interactionsin vivo

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Vaccinations

Delivery of recombinantproteins as a vaccine that can protect against the virus in P. monodon

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Control guidelines for WSSV

•Based on preventive measures• Adequate monitoring of broodstock and PL • Use of domesticated genetically improved SPF

stock• Elimination of potential carriers in the farm• Appropriate treatment of the pond, equipment

and pond water before cultivation

•Biosecurity is still a major problems when itcomes to WSSV outbreaks and control

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• Most of therapeutic measures are successful at laboratory level but hard to implement in a farming setting due to the high cost

• Practical measures• A lot of farmers have opted to avoid shrimp culture during Thai winter time

(oct-feb)

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Acknowledgements

Email

[email protected]

Dr. Kallaya Sritunyalucksana

Dr. Ornchuma Itsathitphaisarn

Prof. Dr. Tim W. Flegel

Centex Shrimp, Mahidol University

Aquatic Animal Health Research Team, BIOTEC

Aqua Expo 2019