How did Canadian caribou become infected with CSE?

The correct answer highlights a specific pathway for the infection of Canadian caribou with chronic wasting disease (CSE), underscoring the role of local snails in the transmission of the parasite that causes the disease. This process typically involves the caribou ingesting these snails, which act as hosts for the pathogenic agents.

Understanding the transmission routes of diseases like CSE is crucial for wildlife management and conservation efforts. Unlike direct contact with infected individuals or human-related transmission, which are common in other disease contexts, the ingestion of snails provides a more indirect means of infection that is essential to recognize in epidemiological studies.

Other options involve direct interactions or consumption that do not accurately describe the unique mechanisms of CSE transmission in caribou. For example, while direct contact might lead to some infections in other animal species, it is not the primary route for this particular disease in caribou. Similarly, human travelers or contaminated feed are not implicated in the lifecycle of the parasite affecting caribou, making these routes less relevant in the context of CSE transmission.