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Infectious hypodermal and haematopoietic necrosis (IHHN) disease, Infectious hypodermal and haematopoietic necrosis virus, IHHNV, "runt-deformity syndrome" or RDS of P. vannamei.

Scientific name or taxonomic affiliation
IHHNV is a small (22 nm average diameter), single strand DNA-containing parvovirus. However, replication of this virus in the host cell cytoplasm has been used as evidence that IHHNV should be classified with the picornaviruses.

Geographic distribution
Enzootic in Taiwan, Singapore, Malaysia, Thailand, Indonesia, Australia and Philippines and possibly also enzootic in Ecuador, Peru, and Central America. Thought to have been introduced and now widely distributed in cultured penaeids in the southeast United States, Caribbean, Brazil, Hawaii, Guam, Tahiti, New Caledonia and Israel.

Host species
Considered highly contagious and infectious to many penaeids: Penaeus stylirostris, Penaeus vannamei, Penaeus monodon, Penaeus chinensis, Penaeus occidentalis, Penaeus californiensis, Penaeus semisulcatus and hybrids of Penaeus monodon and Penaeus esculentus. Experimentally transmitted to Penaeus setiferus, Penaeus japonicus, Penaeus aztecus, and Penaeus duorarum. Species like Penaeus indicus and Penaeus merguiensis seem to be refractory to IHHNV.

Impact on the host
Reduced food consumption, cannibalism, increased mortality. In some cases, shrimp repeatedly rise slowly to surface, roll over and sink to bottom. Disease particularly severe among juveniles in high density tank and raceway cultures. Some members of the population which survive IHHNV infection and/or epizootics apparently carry the virus for life and pass it onto their progeny and other populations by vertical and horizontal transmission. Although IHHNV may cause 80-90% cumulative mortalities in postlarvae and juveniles, the aetiological and economic significance in Asia remains unclear.

Diagnostic techniques
Gross Observations: White or buff coloured spots in the cuticular epidermis, especially at the junction of the tergal plates of the abdomen, giving the shrimp a mottled appearance.

Histology: Prominent eosinophilic (with haematoxylin and eosin stain of tissues preserved with fixatives containing acetic acid), Feulgen variable (depending on stage of virogenesis and amount of DNA present) intranuclear inclusion bodies in chromatin marginated hypertrophied nuclei of various tissues of ectodermal (i.e. gills, epidermis, hypodermal epithelium of foregut and hindgut, nerve cord, and nerve ganglia) and mesodermal origin (i.e. haematopoietic organs, gonads, antennal gland tubule epithelium, mandibular organ connective tissue and striated muscle). The inclusion bodies are common in acute infections, later decreasing in number and are followed by necrosis and infiltration of target tissues by haemocytes. Affected cells may also have highly vacuolated cytoplasm with cytoplasmic bodies that range from eosinophilic to basophilic. Usually the midgut, midgut caeca and the hepatopancreas (endodermal derived tissues) are unaffected, except in severe cases where hepatopancreatic involvement has been observed.

Electron Microscopy: Virus is un-enveloped, icosahedral, 17-26 nm in diameter in sections and 20-22 nm in purified preparations. Although there is nuclear involvement, the virus is assembled and replicates in the cytoplasm of the host cell. Chromatin strands (that may be visible as basophilic by light microscopy) are a prominent feature of IHHNV intranuclear inclusion bodies. Virions can occur in paracrystalline arrays that may be visible in histology as cytoplasmic bodies.

DNA Probes: Several probes including BS4.5 which is highly specific to IHHNV (Lightner et al. 1992) and BA402 (available in kit form from DiagXotics Inc., 27 Cannon Rd., Wilton, CT 06897, USA), have been identified. These probes have been developed into sensitive and specific diagnostic test based on in situ hybridization (preformed on Davidson's, AFA or formalin preserved histological samples and biopsied appendages), dot blot hybridization, and PCR (used on haemolymph or tissue homogenates).

Bioassay: Expose an indicator shrimp (0.1-4 gm juvenile Penaeus stylirostris) by cohabitation, feeding minced carcasses, or injecting cell-free homogenages of suspect shrimp (for details of procedure see Lightner (1996) Section 3: VIRUSES/IHHN/Page 5-6).

Methods of Control
No known treatment. However preventative measures well known within shrimp farming industry.




Variables to be used in health evaluation

Health evaluation tests
Wet Mount Procedure . PL visual examination . Stress test for post larva . Gill examination . Mid-gut Examination . Stomach Contents Analysis

Shrimp Diseases
Hepatopancreatic parvo-like virus (HPV) . Reo-like virus (REO) . Lymphoid organ vacuolization virus (LOVV) . Taura Syndrome Virus (TSV) . Rhabdovirus of Penaeid Shrimp (RPS) . White Spot Syndrome Virus (WSSV) . You are here . Baculovirus penaei (BP)
Bacterial Diseases
Vibriosis . Epicommensal fouling disease (filementous bacteria) . Necrotizing Hepatopancreatitis (NHP) . Black spot disease (BSD) . Mycobacteriosis
Fungal Diseases
Larval mycosis . Fusariosis
Haplosporidia . Gregarines . Cotton Disease
Black Gill Disease (BGD) Dissolved Oxygen Crisis Nitrogen Gas Bubble Disease

Disease control
Decreasing density, partial or early harvests . Drugs, chemicals and treatments . Sanitation