The term 'swerves at sea' can be solved by the four-letter word 'YAWS'. YAWS is a type of infectious disease caused by the bacterium Treponema pallidum, which is related to syphilis. It is characterized by skin lesions and joint pain, and is most common in tropical climates. It is spread through direct contact with an infected person's skin or mucous membranes. Treatment for YAWS includes antibiotics, and it can be prevented through good hygiene practices.