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CASE STUDY
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Let ’ s go back to our farm “ Happy Abs ”
We are now 20 days into the event and have a laboratory confirmed diagnosis of sleepy abalone disease ( SAD – a fictitious disease ) caused by sleepy abalone disease virus ( SADV ).
We can now refine our case definition “ A deceased abalone displaying a curled foot , enlarged mouthparts and protruding radula for which the SAD virus has been detected by qPCR ” ( a specific molecular test ).
Usually , we would have positive qPCR results prior to clinical signs as the test is very sensitive . If we wanted to increase the chance of including subclinical animals in our diagnosis , we could incorporate any positive laboratory result ( even without clinical signs ) into our case definition .
We collect data from all the tanks ( Table 2 ) and construct an epidemic curve ( Figure 12 ). We know from previous outbreaks that this disease is water borne , highly virulent and difficult to kill using standard disinfectants . The disease has a short incubation period of around three days . We had already instituted quarantine of infected tanks based on the rapid spread of the disease . Once we had the diagnosis confirmed by the laboratory , we commenced an emergency harvest of infected tanks which will take some time to complete .
From the epidemic curve we can see that the index case was on 12 June , the peak of the outbreak was 19 June with 14 cases . The shape of this curve is suggestive of a propagating epidemic and the duration of the outbreak was 19 days . The long tail of the curve may imply that there was a lot of movement of abalone prior to quarantine being instituted or the control measures were slow to take effect .
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