How did Canadian caribou likely become infected with Elaphostrongylus rangiferi?

The correct response highlights the role of environmental interactions in the transmission of Elaphostrongylus rangiferi, a parasite that typically affects caribou and reindeer. Caribou can become infected by ingesting snails that have consumed larval stages of the parasite found in reindeer feces. This process illustrates the complex relationship between wildlife, their habitats, and the ecosystems in which they live.

In this case, the snails act as intermediate hosts for the parasite. When caribou consume these infected snails, they inadvertently acquire the parasite, leading to infection. This demonstrates how the life cycle of E. rangiferi is closely tied to various environmental factors, including the presence of other species, such as reindeer, and how feces can contaminate the habitat with infectious stages of the parasite.

In contrast, other options, like direct contact with infected reindeer or aerial transmission, do not align with the established transmission routes for this specific parasite. Environmental contamination may contribute to overall disease dynamics but does not specifically account for the mechanism by which caribou ingest the parasite. By identifying the route through which the infected snails facilitate the transmission, one identifies a critical link in the life cycle of the parasite and the epidemi