Question

What agents of transmission have taken the place of nomadic peoples in recent centuries?

Answer 1

Nomadic people have served as agents for the transfer of food crops, and nomadic warriors have played key roles on transmitting diseases.
For example, when the mongol soldiers tried to expand their influence, they brought the bacteria that known as the black death which eventually wiped almost 100 millions of people around the world. They also were agent of transmission in cultures atechnologyogy.

Answer 2

People continued to make the transmission of diseases happen, even though that's does not happen mainly by nomadic people's hands anymore. Now, with more integrated economy and faster ways of travel, its way easier for travelling people and the carrier animals transmit disease to more people in vastly different places.