Settings:
Fast shamblers
Everyone's infected (the parasite just needs you dead)

Mod settings:

With "reanimating zeds" change it to 70% chance.
That way after awhile of killing the same zombie eventually it will be too destroyed for a new parasite to take over.

For "water goes bad" change it to instantly turn bad.

"Frighteningly fast crawlers" is here specifically because I think it adds to the parasite's creepy crawly nature.

"Where's my hazmat suit" is here because in lore there were hazmat units deployed all over the island
You can go into the mod file and change the numbers in the text file to have even more Hazmat suits around the island, for lore accuracy.
9 is a good max number I've found.
I use 9 for Military Zones, and Medical zones, and 2 for default zones.

Lore:

U.S. CENTER OF DISEASE CONTROL AND PREVENTION

This document is regarding the situation on Kingsmouth Island.
Redistribution of this document by or to unauthorized personnel, is a violation of federal law.

The "Rainworms" as we've come to call them are about the size of a small dog.
They have a 4 part mandible, 7 eyes, cerci, and a body divided into 5 segments. A very unconventional animal to say the least. Our researchers are still working on pinning down what family Rainworms belong to.
They are born as males in the water, using fish as their primary host. These males are very small and when consumed the male will begin to develop inside the host. If there is no female inside of the host already
The male develops into into a female Rainworm. The female will then hollow out the host. They eat their flesh laying multiple green egg sacks, and attach them to the body using a sticky mucus-like substance. The eggs are fertilized through the female piloting the corpse to a body of water a male Rainworm will the body of an already inhabited corpse, and the female will let the male fertilize the eggs, then she will eat him.
The egg sacks seem to need a dead body to help them get into a state where they are ready to return to the ocean, the reason isn't understood. While the eggs are developing the mother pilots the slow moving corpse to hunt down any more potential hosts.
Once they are dead a male Rainworm will crawl into their mouth and take the wheel.
When the eggs are ready the mother will pilot the corpse to the nearest body of water. The host will get down on their knees and the mother will rip her way out of the body.
Taking the eggs with her as she skitters into the water. The eggs then hatch, the mother dies, and the cycle continues.

When the female leaves the corpse a male will crawl into the uninhabited body and develop into a new female.
This reanimation can happen even if the corpse is in a massively decomposed or damaged state.
While the body has no nutrients or even warmth, the eggs will still develop, the only requirement for their growth is seemingly proximity to a corpse. Animals actively avoid the bodies, not even the birds are interested in the eggs.
Their origin is unknown, all that is known is that they came after the recent storm.

We don't fully know what we are dealing with yet, maintain the quarantine, re-direct fishing vessels, and confiscate anything they catch.