A 25-year-old man presents with a painless, non-healing ulcer on his left thumb for six weeks. This commenced as a small papule which progressively grew larger and then ulcerated. There is no bleeding or discharge.

He is otherwise healthy, and reports no previous injuries to his hand. His medical, surgical, and family histories are unremarkable, and he is not on any medications, or over-the-counter supplements. There is no history of recreational drug use.

He works as a gardener, only drinks socially, and does not smoke. Close questioning reveals that he traveled to Brazil for a two-week long holiday around three months ago, although he denies experiencing any insect bites.

A complete blood count is found to be within normal parameters.