How was cerebrospinal elaphostrongylosis (CSE) likely introduced to Canadian caribou?

Cerebrospinal elaphostrongylosis (CSE) is a disease caused by a parasite known to primarily affect cervids, including caribou and reindeer. The introduction of CSE to Canadian caribou is most likely attributed to the interaction with infected reindeer that were shedding the parasite. This is significant because reindeer and caribou are closely related species, and cross-species transmission can occur, especially in regions where their habitats overlap or where they come into contact due to migration patterns or other movements.

The transmission of the parasite through infected reindeer is a critical factor, as it illustrates the dynamics of wildlife diseases and how they can transfer from one species to another. In this context, mobile wildlife populations can play a key role in the spread of infectious agents, emphasizing the importance of understanding ecological interactions in disease management.

The other options explore potential transmission routes, but they lack the direct link established between infected reindeer and the caribou population concerning this specific disease. Contaminated water, direct contact with horses, and feeding on contaminated vegetation are less likely pathways for the introduction of CSE to Canadian caribou compared to the definitive role that infected reindeer would have played.