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Rapportserie 2010

15-2010: Evaluation of the surveillance and control programme for VHS and IHN

The National Veterinary Institute has evaluated the surveillance and control programme for viral haemorrhagic septicemia (VHS) and infectious haematopoietic necrosis (IHN). The methodology used is a quantitative analysis of multiple complex data sources, and is based on scenario tree analysis and stochastic simulation. By evaluating the surveillance programme according to this method, we will have quantitative estimates for the probability of detecting disease (the system surveillance component sensitivity, SSCSe) for the various surveillance strategies. The most cost-effective surveillance strategy is the strategy that yields at least 95% SSCSe with lowest cost.

The present model shows that if surveillance is risk-based we have a high probability of detecting disease. However, the surveillance system component sensitivity is dependent on the number of samples taken within farms, and the design prevalence (i.e. the hypothetical prevalence of disease that the surveillance program is assessed against).

If the surveillance is targeted towards farms with rainbow trout, a minimum of 20 samples per farm from fish with disease signs will be needed for the detection of VHS given the farm is infected with a within-farm prevalence of 5 %. Furthermore, a number of 487 farms (a total of 9740 samples) will be needed to achieve a 95 % certainty that the programme will detect a VHS-infected farms assuming that there is at least 2 infected farms in the whole salmon farm population (design prevalence of 0.2 %). Because there are not that many farms with rainbow trout, 20% of the salmon farms have to be added in the strategy to achieve at least 95% sensitivity.

Cost considerations indicate that running PCR for VHS virus on few, large batches of samples will be more cost effective than the present programme using cell culture. However, rapid reply is not possible if samples are collected over a period of time, so the need for early detection must be considered in relation to response time.

The model presented is targeted towards VHS. Historically, IHN has been included as part of the same sampling regime as VHS. The results and conclusions in this model may therefore be relevant also for IHN but needs to be validated.

7b-2010: The presence of pinnatoxins in Norwegian mussels

Naturally occurring algal toxins can cause poisoning in humans when they accumulate in shellfish destined for consumption.The National Veterinary Institute now identified a hitherto unknown algal toxin in Norwegian waters that could pose a potential problem.

Pinnatoxins and pteriatoxins are toxins that were first identified by Japanese researchers in 1995, after a poisoning incident in China in 1990. It is still uncertain whether these toxins were the cause of this episode, and toxic effects on humans are unknown. These substances are structurally similar to the more familiar spirolides, produced by dinoflagellates including Alexandrium ostenfeldii that is frequently detected in Norwegian waters.

The National Veterinary Institute has established a sensitive analytical method for determination of pinnatoxins and spirolides. After chemical analysis of shellfish and algal extracts, toxins of the pinnatoxin group were found in shellfish and algal samples along the whole of the Norwegian coast. This is the first time that pinnatoxins has been detected in Europe.

Pinnatoxins give high mortality at low doses, not just by intraperitoneal (ip) injection, but also when mice eat the toxin.

The alga that produces pinnatoxin G is still unknown, but researchers in New Zealand have managed to culture a new type of dinoflagellate that produces pinnatoxin F.

There is no knowledge about the metabolism and detoxification of pinnatoxins in various species of shellfish in Norway, and it is also important to establish knowledge on its mechanisms of action, how dangerous pinnatoxins are in seafood, and the possible limits.