Many of these parasites do their dirty little business deep inside the body, so nobody needs to know that you’re infected. Not the Leishmania protozoa. If they set up shop, you’re going to let the whole world know. These microscopic parasites gain access to human bodies through sand flea bites, and immediately start reproducing in the host. As they grow, they cause an intense physical reaction around the bite issue, which grows larger and larger until it becomes a sore that can remain open for as long as a year. Once it heals, it turns into an unpleasant scar.
Photo credit: California Digital Library