Infectious Myonecrosis (IMN):Status and Threat

DISEASE ADVISORY

Status and Threat

Infectious myonecrosis (IMN) is a viral disease caused by infectiousmyonecrosis virus (IMNV), a putative totivirus. IMNV particles areicosahedral in shape and 40 nm in diameter.

H t R HistopathologyHost Range Histopathology

AB

• Pacific white shrimp, Penaeusvannamei (principal host);

• Tiger prawn, P. monodon and blueshrimp, P. stylirostris (experimentalinfection).

Source: Pouloset al., 2006

Disease SignsMyonecrososis dueto IMNV infection in P. vannamei, H&Estain:A) Coagulative necrosis of skeletal muscle by

haemocytic infiltration and fibrosis, incontrast to normal skeletal muscle which

20 μmFarm Level:• Large numbers of sick animals and

significant mortalities in pond-reared P.vannamei (juveniles and adults);

• Losses due to mortality range from 40

Source: DV Lightner

contrast to normal skeletal muscle whichcan be observed at the upper right corner.

B) Perinuclear pale basophilic to darkbasophilic inclusion bodies (arrows)observed in striated muscle cells.

In-situ hybridisation ofskeletal muscle tissueusing a digoxigenin-

to 70 %.

using a digoxigenin-labelled IMNV probe. Ablack precipitate ispresent in areas wherethe probe has hybridisedwith the target virus.

Diagnostic MethodsSource: DV Lightner

Source: DV Lightner

Clinical:• Presence of focal to extensive white

necrotic areas in striated (skeletal)muscles, especially in the distalabdominal segment and tail fan, whichcan become necrotic and reddened insome affected shrimp

Diagnostic Methods

• Tentative diagnosis by histology (acuteand chronic phases);

• Molecular detection of IMNV by in-situhybridisation, nested RT-PCR and realtime RT-PCR;

• RT PCR recommended for targetedsome affected shrimp.• These signs may have sudden onset

following stresses (e.g. capture by castnet, feeding, sudden change intemperature or salinity).

• RT-PCR recommended for targetedsurveillance. Diagnostic kits arecommercially available (e.g.GeneReach Biotechnology Corporation,http://genereach.com/about1.html).

Infectious Myonecrosis (IMN)

Presence in the Asia-Pacific• Originally reported from north-easternOriginally reported from north eastern

Brazil, the first outbreak in Asia-Pacificwas reported in East Java (SitubondoDistrict), Indonesia in May 2006. It wascontained in this area until 2008.

• In 2009, however, more districts in EastJava were affected including Situ,Banyuwangi Blitar and Malang as well What to do when there is

Source: DV Lightner

Banyuwangi, Blitar and Malang, as wellas some districts in the provinces ofBali, Lampung, West Nusa Tenggaraand Central Java.

• Based on Quarterly Aquatic AnimalDisease (QAAD) reports submitted toNACA, the following Indonesian

i ff t d b IMNV

What to do when there is (suspected) Outbreak?

• Report immediately to CompetentAuthorities in respective countries, andto regional and internationalorganizations involved in aquatic animalhealth: NACA (www enaca org); Worldprovinces are now affected by IMNV:

o East Javao Balio Lampungo Central Java (Jepara, Blora,

Kendal and Rembang)o West Kalimantan (Bengkayang)

health: NACA (www.enaca.org); WorldOrganisation for Animal Health (OIE,www.oie.int); Food and AgricultureOrganization of the United Nations(FAO; www.fao.org)

• Collect tissue samples with guidancefrom Fish Health experts, for

b i i di d i lo West Nusa Tenggara (WestSumbawa)

Current Threat• With the current spread of the disease

to other provinces in Indonesia, there isa high threat of spreading the disease to

submission to accredited national orregional laboratories:o Best tissue samples for IMNV

detection include striated (skeletal)muscle, connective tissues,haemocytes, and lymphoid organ;

o For non-lethal testing (can be useda high threat of spreading the disease toneighboring P. vannamei-producingcountries;

• P. vannamei is now the most popularlycultured shrimp species in many Asiancountries, including Malaysia, Thailand,the Philippines, Vietnam and China

for surveillance), haemolymph orexcised pleopods may becollected.

Prevention and Control• Better husbandry practices and use of

specific pathogen free (SPF)among others;

• Increased awareness and preparednesson IMN disease and outbreak areneeded in these countries.

p p g ( )broodstock have been proven to be themost successful methods to preventinfection;

• There are no reported control measuresfor IMNV.

Key ReferencesAGDAFF-NACA (2007). Infectious myonecrosis. Aquatic Animal Diseases Significant to Asia-Pacific Region: Identification Field Guide,

@ Network of Aquaculture Centres in Asia-Pacific, Bangkok, Thailand. December 2010

Autralian Government of Agriculture, Fisheries and Forestry, Canberra, Australia.OIE (2010). Chapter 2.2.3 – Infectious myonecrosis. Manual of Diagnostic Tests for Aquatic Animals 2010. World Organisation for AnimalHealth, Paris, France.Poulos, B.T., Tang, K.F.J., Pantoja, C.R., Bonami, J.R., Lightner, D.V. (2006). Purification and characterization of infectiousmyonecrosis virus of penaeid shrimp. J. Gen. Virol., 87: 987-996.Saengchan, S., Phewsaiya, K., Briggs, M., Flegel T.W. (2007). Outbreaks of infectious myonecrosis virus (IMNV) in Indonesiaconfirmed by genome sequencing and use of an alternative RT-PCR detection method. Aquaculture, 226: 32-38.