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Yellowhead Virus (YHV)

Six known genotypes in yellowhead complex. Family Roniviridae, genus Okavirus. Virions measure 200nm, rod-shaped with prominent projections at surface Affected countries: China, India, Indonesia, Malaysia, Philippines, Sri Lanka, Thailand, Vietnam, Australia, Mozambique

Up to 100% mortalities in affected farm ponds. YHV can infect all cultured Penaeids, both wild and cultured Palemonids and other species (e.g. krill) Euphausia superba. Gross symptoms - Very high feeding rates followed by sudden cessation. Moribund shrimp at pond edge, bleached or yellow appearance of cephalothorax

Ectodermal and mesodermal tissues incl. lymphoid organ, haemocytes, haemopoietic tissue, gills and connective tissues. Loss of cuboidal structure to epithelial cells, infected cells are rounded with pyknotic nuclei. Loss of tissue structure within lymphoid organ, stromal matrix cells that comprise tubules become infected leading to loss of tubular structure, tubules appear degenerate. Lymphoid organ spheroids (LOS) develop during infection. Ectopic spheroids can be found in other tissues such as heart and gill.

University of Arizona

Tucson, Arizona

USA