The Eki Eki no Mi is a Paramecia-type Devil Fruit that allows the user's to manipulate, create, and modify any form of disease or malady, making the user a plague Human (疫癘の人間Ekirei Ningen). It was eaten by Salazar Poveglia
Eki comes from Ekirei meaning plague
Strength and Weaknesses
this Devil Fruit allowed the user immunity to all diseases. the user can generate any disease in existence or bioengineer new one by cross fusing ones in existence. Diseases can then be spread by touch, breath, blood(unless the blood type of the victim is the same as the user; it grants the same level of immunity), saliva and worst of all, hypodermic needle-like fingers. It seems however that non-human Zoan Devil fruit users have an unnatural resistance to this fruit disease based attacks as those with Devil Fruits are able to survive longer and resist longer. This is potentially the most dangerous fruit in existence as not even darkness can drag down disease.
The user can also synthesize different strains of a disease, alter it to make it airborne, speed up how fast it kills someone, etc.
Non-human Zoan Devil fruit users have an unnatural resistance to this fruit's disease based attacks along with those with certain Paramecia and Logia Devil Fruits are able to survive longer and resist longer
Standard Devil Fruit Weaknesses