The Parasite is a plague unlocked after completing the Fungus on Normal (similar to Neurax Worm (on Plague Inc: Evolved (only))). As usual, the guide is below.
https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=2352145422

Unlike the norm, almost all of your DNA will come from red and orange bubbles. This is because the Parasite doesn't get DNA for infections or deaths. To make up for this, Orange bubbles will grant extra DNA. The Parasite also starts with a severity of 7 and has the unique ability Symbiosis, which lowers severity and decreases the severity of symptoms.

There is one continuity error with the parasite. Parasites are creatures that nest inside a host organism and simply live off of it as long as possible. The Parasite you will (indirectly) control is more similar to a Parasitoid, a parasite that lives off of its host at the host's expense, eventually leading to the host's death.

Since the Parasite is an unusual game mode, normal genes are of different value.

Since you get a bonus from Orange Bubbles, use Cytochrome Surge for a larger bonus from orange bubbles.

While Creationist is useful, use Genetic Mimic if possible.

Use Teracyte, Aerocyte, or Aquacyte.

Use Extremophile or Xerophile.

Ionised Helix, obviously.

Allow any non-lethal symptoms.

Start in any hot country (list time - Algeria, Angola, Australia, Botswana, Brazil, Central America (C. America), Caribbean, Central Africa, Colombia, East Africa, Egypt, India, Indonesia, Iran, Iraq, Libya, Mexico, Middle East, Morocco, New Guinea, Pakistan, Philippine Islands (Philippines), Southeast Asia (S.E Asia), Saudi Arabia, South Africa, Spain, Sudan, West Africa, or Zimbabwe). South Africa is preferred (specifically South Africa, Namibia, Eswatini, and Lesotho).

Save up for 30 DNA. Remember to pop all orange bubbles.
Under Transmissions, get Water I and Water II.

Save up for 30 DNA.
Under Abilities, get Symbiosis I and Symbiosis II. Symbiosis will reduce severity and reduce the severity increase of symptoms.

Save up for 30 DNA.
Under Transmissions, get Air I and Air II.

Save up for about 80 DNA.
Under Abilities, get Drug Resistance I, Cold Resistance I, Cold Resistance II, Heat Resistance I, and Heat Resistance II.

OPTIONAL:
Save up for 50 DNA.
Under Abilities, get Drug Resistance II.

Save up at least 100 DNA. Wait until there are no blue or pink countries in the World Menu and/or get the message "THERE ARE NO HEALTHY PEOPLE LEFT IN THE WORLD."
Under Symptoms, get Insomnia, Paranoia, Inflammation, Paralysis, Coma, Total Organ Failure, and any other lethal symptoms afterward.

You win!