Survey for the presence of White Spot Syndrome virus in Australian crustaceans

Abstract

Agriculture, Fisheries and Forestry - Australia, GPO Box 858, Canberra, Australian Capital Territory 2611.

Disease will limit future food supply from the global crustacean fishery and aquaculture sectors

“…Jones (2012) describes several instances where the translocation of important viral pathogens to new locations was not due to the movement of live animals. These include the outbreak of WSSV in Darwin, Australia in 2000 (East et al, 2004) and the outbreak of WSSV in Louisiana crawfish ponds in 2009 (Baumgartner et al, 2009). Furthermore, he states that in addition to the direct use of raw frozen products as aquarium/farm animal feeds, other potential pathways of introduction include discarded waste from crustacean processing plants, the use of commodity shrimp as angling baits, or even by industrial sabotage.…”

“…Furthermore, calculation of likelihood of passage of an established infection to other susceptible hosts within the population or an ecosystem is harder still. To this end, it was noted that even though WSSV was discovered in the Darwin aquarium facility in Australia in 2000 and the initial surveys of wild crustaceans at the facility outlet also tested positive for WSSV by PCR at the time, subsequent testing of animals at the site returned a negative result (East et al, 2004). Taken together, such evidence, and that arising from several other laboratory studies, appears to demonstrate that a pathogen with a wide host range (such as WSSV) present within commodity product can be passaged to naïve hosts via normal use pathways (feeding).…”

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“…Australian authorities considered one campaign as sufficient to determine disease freedom for WSSV (East et al, 2004;East et al, 2005). Here we consider a single campaign both sufficient and most desirable to determine a cost-effective surveillance strategy, given the contribution of both surveillance system components.…”

“…In the absence of positive findings, the surveillance system can be applied to determine that disease is absent at a level equal to or greater than that of the design prevalence (Cameron, 2009 Pu*: one where both took the fixed value of 10% and another where Ph* was set at 5% and Pu* was set at 10% (East et al, 2004;East et al, 2005). Keeping in mind the aforementioned values, for the worked example, the design prevalence was set at a value of 10% for Pu*, while the value of Ph* was kept conservatively lower, at 5%.…”

“…The OIE recommends the adoption of values of 1% to 5% for Pu* for slowmoving diseases and above 5% for highly contagious diseases, while values for Ph* should not exceed 2%, unless clearly justified (Corsin et al, 2009). However, published articles of Australian surveys, to determine country-level freedom from WSSV, used two sets of values for Ph* and Pu*: one where both took the fixed value of 10% and another where Ph* was set at 5% and Pu* was set at 10% (East et al, 2004;East et al, 2005). Keeping in mind the aforementioned values, for the worked example, the design prevalence was set at a value of 10% for Pu*, while the value of Ph* was kept conservatively lower, at 5%.…”