Horses were reintroduced to the Americas by the Spanish in the 16th century, a pivotal moment in the Columbian Exchange. Domesticated in Eurasia, horses spread quickly once brought across the Atlantic, transforming travel, warfare, and economies across the New World. While other European powers later contributed, the initial introduction credited to the Spanish is the correct reflection. The idea that equines did not reach the Americas is incorrect.

Zoonosis means a disease that can be transmitted between animals and humans. The key idea is cross-species transmission—the illness can move from animals to people and, in some cases, from people back to animals. Pathogens involved can be viruses, bacteria, parasites, or fungi, so it’s not limited to viruses. It’s also not confined to transmission by insects; many zoonoses spread through direct contact with animals, contaminated food or water, or other routes. This definition explains why the concept fits best: the disease originates in animals and has the potential to affect humans as well. For example, rabies is a classic zoonosis transmitted through animal bites, while other zoonoses can come from contaminated animal products or environments.

In the Columbian Exchange, Europeans brought livestock to support exploration and settlement in the Americas. The Spanish were the ones who introduced sheep and goats to the New World, beginning with early voyages like those of Columbus, to provide wool, meat, and other resources for new colonies. Sheep offered wool for textiles and meat for food, while goats are hardy and adaptable, quickly establishing feral populations that continued to grow with colonization. Later, other nations did bring their own livestock, but the initial introduction of sheep and goats is attributed to the Spanish.

Bovine Spongiform Encephalopathy describes a fatal neurodegenerative disease in cattle caused by prions. “Bovine” denotes cattle, “Spongiform” refers to the sponge-like changes (vacuolation) seen in brain tissue, and “Encephalopathy” means a brain disease. This naming directly reflects the host, the characteristic brain lesions, and the disease process. Other options don’t fit standard terminology: epilepsy is a seizure disorder, not defined by spongiform brain changes; systemic encephalitis implies brain inflammation with systemic illness; severe encephalopathy isn’t a recognized disease name. This is the established term used in veterinary and public health contexts (also known as mad cow disease).