Discovery of a novel Picornavirales, Chequa iflavirus, from stressed redclaw crayfish (Cherax quadricarinatus) from farms in northern Queensland, Australia.

In 2014, northern Queensland crayfish from farms affected by particularly transportation and translocation stress, started to die with mortality reaching 20-40% after about three weeks and then mortalities subsided. Crayfish from 1 farm had 65% mortalities within 11 weeks. With histological examination of broodstock and juveniles, the muscle fibres were fractured with haemocytic infiltration reminiscent of viral infection or vitamin E/selenium deficiencies. Sequence dependent and independent PCRs failed to identify a viral aetiology. However, the whole transcriptomes of a case crayfish and an unaffected crayfish from a different population were assembled producing over 500,000 contigs. The complete sequence of a positive sense, single stranded RNA virus (+ve ssRNA virus; 9933bp) and the large and medium segments of a bunya-like virus were detected. Transcript back-mapping and newly developed PCRs indicated that the viruses were in the case crayfish but not the control crayfish. The +ve ssRNA virus is clearly in the order Picornavirales, marginally in the genus Iflavirus in a clade of Chinese and Northern American terrestrial arthropod viruses. The internal Picornavirales motifs; RNA-dependent RNA polymerase, helicase (P-loop) and 2 viral capsids genes were easily identified. This is the first iflavirus identified from crustacea and is named Chequa iflavirus. Whether these viruses are responsible for the stress-related mortalities is unproven but the Chequa virus' role seems limited as it appears it has been present in crayfish from at least the early 1990s; unless low-grade, chronic mortalities have been largely unnoticed.