1. It is conventional to write the first letter of the generic name with a capital and the first letter of the specific name with a small letter.
2. Scientific names must be underlined separately when written by hand.
In printed matter, these names are printed in Italic and underlined when handwritten.
In option A, all the letters are capitalized.
In option B, all conventions are followed.
In option C, the generic name is wrongly capitalized and not written in italics.
In option D, the name is not written in italics.
So, the correct option is 'Trypanosoma gambiense'.