Final Report - 2016-064 - Field observations and assessment of the response to an outbreak of White Spot Disease (WSD) in Black Tiger Prawns (Penaeus monodon) farmed on the Logan River in November 2016
White spot disease (WSD) is an internationally notifiable disease of crustaceans caused by White Spot Syndrome Virus (WSSV). In November 2016 a WSSV incursion was first reported in Black Tiger Prawns (Penaeus monodon).
Principle Investigator: Ben Diggles
Key Words: White spot disease (WSD); White Spot Syndrome Virus (WSSV); Penaeus monodon; Black Tiger Prawns; Prawn Farming; disease outbreak; biosecurity
White spot disease (WSD) is an internationally notifiable disease of crustaceans caused by White Spot Syndrome Virus (WSSV), a double-stranded DNA virus of the genus Whispovirus within the family Nimaviridea (OIE 2016). Previous WSSV incursions into Australia include its detection in broodstock prawns (Penaeus monodon) and mud crabs (Scylla serrata) fed frozen imported prawns at an aquaculture hatchery in Darwin Harbour in December 2000. In that case wild mud crabs and prawns adjacent to the hatchery outlet were also transiently infected with WSSV, but over time this infection fizzled out and subsequent testing indicated that the virus did not become established in Darwin Harbour (East et al. 2004, 2005).
The current WSSV incursion was first reported in Black Tiger Prawns (Penaeus monodon) cultured on a prawn farm (1IP) taking water from the Logan River, SE QLD on 22rd November 2016. Biosecurity Queensland (BQ) was alerted, obtained diagnostic samples, and a confirmed diagnosis of White Spot Disease (WSD) was obtained from the Australian Animal Health Laboratory (AAHL) on 1 December 2016. The Office International des Epizooties (OIE) was provided with an immediate notification on the same day, and on the morning of 2 Dec 2016, DigsFish Services was engaged with the objective of visiting the affected farm to document proceedings and provide updates to the fisheries and aquaculture industries regarding what was happening on the ground. At the same time information on the response was recorded with the objective of updating industry resources and the relevant Aquavetplan manuals at a future date, samples were taken for storage onsite for future industry based research and biosecurity advice and assistance was provided to farm staff, the prawn farming industry, and Government authorities upon request.
Upon confirmation of WSD at the first farm, BQ immediately enacted an eradication program based on Aquavetplan (D epartment of Agriculture 2013) involving destruction and decontamination of affected farms, a program that is ongoing at the time of publication. The virus proved to be highly contagious for P. monodon. By Monday 5th Dec disease had spread to a second farm (3IP), 1 km north of the index farm and the virus was also detected in a small number of wild prawns from the Logan River (Metapenaeus spp., n = 5, Acetes spp. n = 1). Disease subsequently spread in a non-random fashion to a fourth farm (4IP, clinical disease 8th December), a separate compartment of the first farm (2IP, clinical disease 12th Dec) and a fifth farm c. 5 km downstream (5IP, clinical disease 28th Dec 2016), all of which were drawing water from the Logan River (Figure 1). Infection of Mud Crabs (Scylla serrata) was also confirmed in drains of several infected farms, as well as an anomalous detection of one mud crab sampled on 23 rd Dec 2016 in the outlet canal of a seventh uninfected farm (7ARP) around 7.3 km east of the index farm (Figure 2). A sixth farm (8IP) was positive for WSSV in samples taken on 24th Jan 2017 during the later stages of harvest, and clinically diseased prawns were noticed on the last remaining farm (formerly 7ARP, now 7IP) on 11 Feb 2017. On-farm activities undertaken by DigsFish Services director Dr Ben Diggles (BKD) from 2 Dec 2016 were documented at the time in field notes that formed the basis of a series of nine Industry Situation Reports (Appendices 1-9) that were published on a near immediate basis in order to facilitate rapid flow of information from the on-farm situation to the wider prawn farming and fishing industries. The present report summarises the field observations and analyses outcomes from those Industry Situation Reports, and provides some suggestions for consideration when updating the relevant Aquavetplans and the Import Risk Analysis for prawn products.