Protozoan infections are most prevalent in Asia, Africa and South America.
Step-by-step explanation:
Infections caused by protozoans in humans include severe diseases like African sleeping sickness, malaria, amoebic dysentery, giardiasis etc.
These infections are transmitted through arthropod vectors mostly through their bite. Protozoan parasitic infections are common in tropical developing countries than in the developed nations.
When travelers from non-prevalent countries like the United States travel to countries which are prone to protozoan infections, they also become susceptible and get infected when their own immune system is weakened. They become potential carriers when they travel back to their country.