Investigating the origins of a BSE case and tracing the animal's contacts is...

• A. Is relatively straightforward, as long as the herd is closed.
• B. Can be difficult, because the incubation period is long, animal movements may be hard to trace over a period of years, and feed source records are often incomplete.
• C. Can be difficult, because the incubation period is long. Tracing the animal's contacts is nevertheless vital, because each infected cow may have infected a significant number of cattle during the incubation period.
• D. Is relatively straightforward due to a good animal identification program that was implemented in the mid-1980s, although the initial case may be difficult to diagnose.

Answer: (B)

Investigating origins and the set of animals that may have been exposed in a BSE case is challenging because the incubation period is long, animals can move across farms and markets over many years, and feed source records are often incomplete. BSE incubation can span multiple years, so the animal may become symptomatic long after the initial exposure, making it hard to identify the exact source. Herds are linked through purchases, auctions, and transfers, which means tracing all contacts over an extended time becomes a complex puzzle with many potential gaps. In addition, many animals were fed meat-and-bone meal or other contaminated feeds in the past, and historical feed records are frequently incomplete or unavailable, hindering the ability to pinpoint a contaminated batch or supplier. These factors together explain why origin tracing is difficult even in seemingly well-documented systems. While some situations may be easier—such as truly closed herds or excellent, contemporary identification and record-keeping—the general reality is that long incubation, extensive animal movement histories, and imperfect feed records make the task far from straightforward.