Could Thrax from Osmosis Jones have caused that high fever in reality?

Would a real virus cause such symptons (and sudden death) if it were to do the same thing as Thrax did in the film?

It's too difficult to say, mostly because we don't know what Thrax actually removed from the DNA.

In short, there are too many inconsistencies between how the film depicts DNA and how real world DNA actually is, to make a suggestion as to how the human body would react should Thrax be real and remove said part of DNA from a single cell in the hypothalamus.

DNA being depicted in Osmosis Jones.

Real world DNA.

In general though, cells in the body that have DNA also has an enzyme (DNA polymerase) that constantly scans the DNA for errors/damage, and will repair specific errors/damages should they occur.

Depending on what Thrax took from the DNA, the damage could be:

• Repaired by DNA polymerase, and nothing would happen to the person.
• Irreparable and cause apoptosis (programmed cell death), leading to the cell then being collected by a lysosome, which would still have no larger affect on the person.
• Irreparable and cause life-threatening cancer.

The chances that a single cell would cause the hypothalamus as a whole to dysfunction is probably unlikely. I am however not an endocrinologist, nor am I a neuroscientist, so it's possible that I'm overlooking something. (But I am a bioinformatician, so I do know something!)

I will say though that, with Thrax being a virus and having the ability to access host DNA, Thrax would be considered a retrovirus, and those are very dangerous. Thrax however removes genetic material in the film, whereas a typical retrovirus will add genetic material, so, even in this regard it's not possible to speak so definitively.