Jesus Fever is, according to the narrator,
[…] a kind of gnomish little N**** whose primitive face was sharp against the drowning green sky. […H]is eyes, yellow feeble eyes dotted with milky specks, looked down on them with dreamy detachment. (1.1.104)
The adjectives "gnomish" and "primitive" make Jesus Fever seem less than human, while "feeble" and "milky" reveal that he's a very old man.
Jesus Fever has belonged to or at Skully's Landing his whole life. Randolph is already a middle-aged man, and Jesus Fever worked for his grandfather. In a way Jesus is like the consciousness of Skully's Landing. He's been a witness of its history for probably close to a century. When the house burned, according to Amy, "'there was no man on the place but Jesus Fever, and he was even then very old'" (1.2.37). And just like Jesus, the place is old and falling apart.
When Jesus dies, only Amy, Zoo, and Joel attend the burial. His funeral is not really serious:
It seemed odd to Joel nature did not reflect so solemn an event: flowers of cottonboll clouds within a sky as scandalously blue as kitten-eyes were offensive in their sweet disrespect: a resident of over a hundred years in so narrow a world deserved higher homage. The cedar chest capsized as they lowered it into the grave […] (2.10.1)
Just as the world seems to ignore Jesus Fever's life and death, it has also left Skully's Landing behind. The decadent old plantation doesn't have electricity or indoor plumbing, though the technology exists. Life is passing the plantation by, and Jesus, as almost the personification of the Landing, is left behind, too.