These posters were found in the Otis Historical Archives National Museum of Health & Medicine flicker site housing photos and graphics from the National Museum of Health and Medicine in Washington, DC. These government produced World War II images are now public domain.
If you look closely at the faces on the fleas, the poster to the left appears Japanese and the flea below resembles Hitler. These posters must reflect an unease that biological warfare was possible on all fronts. By placing the face of the enemy on disease vectors, the military wants the soldiers to associate disease with biological warfare rather than natural sources.