Bovine spongiform encephalopathy (BSE), is not something you want to catch. Commonly known as ‘mad cow disease’, it's a progressive and fatal nervous disease found mainly in adult dairy cattle and caused by consuming abnormal prion protein. BSE is particularly worrisome because it can be transmitted to humans via meat-and-bone meal (MBM). The disease has a long incubation period, from 2-8 years with a 5 year average.
Japan is on high-alert for the disease. The first case of BSE in Japan was confirmed in September 2001, and ever since, all cattle slaughtered for human consumption have been tested for the disease. However, if a cow is infected, it cannot be detected unless it is just before the onset of the disease. The test cannot detect the infected cattle that are slaughtered or have died from other causes (“fallen stock”) before the end of the incubation period. Since the incubation period is long and varies between 2 and 8 years, the age of clinical onset is not fixed, and the age at which cattle may die or be slaughtered varies.
To improve the surveillance program for BSE in beef production, Professor Katsuaki Sugiura at the Laboratory of Global Animal Resource Science at the Graduate School of Agriculture and Life Sciences, the University of Tokyo, used Palisade’s @RISK to conduct Monte Carlo simulations and build stochastic models to conduct scenario analysis in predicting how changing the testing age of the cattle impacts the number of cattle tested and BSE infected cattle detected.
Four surveillance strategies were explored for beef cattle, with the minimum age at testing set at 0, 21, 31, or 41 months. Three surveillance strategies were explored for fallen stock, with the minimum age at testing set at 24, 31, or 41 months. Increasing the minimum age of testing from 0 to 21 months for both dairy cattle and Wagyu beef cattle had very little impact on the probability that a BSE-infected animal slaughtered for human consumption would be detected. Although increasing the minimum age at testing from 21 to 31 or 41 months would lead to fewer slaughtered animals being tested, the impact on the probability of detecting infected animals would be insignificant. The probability of infected Wagyu-Holstein crosses and Holstein steers being detected at slaughter or as fallen stock would be very low under all surveillance strategies.
Ultimately, thanks to Professor Sugiura’s work, the insights provided by @RISK enabled researchers to eliminate testing age as an important factor, which helped them focus on other, more effective factors in tracking BSE.