Her body refused to die.
Her cells were resilient. They formed tumours which killed her system but it turned out they didn't actually need it to survive.
They were biologically immortal now, and they could reproduce on their own for years after the death of their host.
The doctors kept them for analysis, and before long her resilient body became the subject of worldwide research.
*She contaminated other samples.*
A single cell of her was enough to expand into a whole strain and claim any Petri dish as her own.
And since she was invaluable to research, institutions all around the world sustained colonies of her, and with generations she evolved and changed in new and unexpected ways,
ways which allowed her to expand even further.
*She contaminated the rivers.*
By the time someone noticed the translucent pink foam covering a lake near a site where used medical instruments were illegally dumped, she found her way into the bloodstreams of fish and birds.
Her hosts carried her through the waters and the skies for as long as they could before the tumours made them too sick to swim and fly.
And when the scientists analyzed the bloated animal corpses which littered the shores, they realized their tumours were made of *human* cells,
and announced the most horrifying discovery of the twenty-first century:
“Cancer can become contagious.”
The situation wasn't unprecedented. In the 90's, a mutation of one Tasmanian devil's facial tumour had caused it to become transmittable and wipe out three quarters of the species within ten years.
*Her* cells were much stronger than that and they knew no boundaries. Short-term contact was enough to spread tumours from one host to another, growing the number of the infected exponentially.
First reports of parasitic cancer in humans inevitably spawned thousands of “zombie virus” comparisons.
The parallels stopped being so funny when people making the jokes learned that they themselves suffered from the contagion. It didn't come as a surprise. Everybody suffered from the contagion.
*She contaminated food.*
Wildlife and livestock all suffered from different stages of malignant tumours and she survived in their meat and their milk, absorbing nutrients, waiting for better carriers.
*She contaminated the water supply.*
Strains of her clogged the pipework and made their way into the bodies of whoever drank the water.
*She contaminated developing embryos.*
A few of cells of her body passing through the umbilical cord were enough to turn an embryo into the hub of a new tumour colony,
a uterine brood parasite swallowing up the last generation of humans to ever be conceived before it could be born.
Perhaps there were still secluded islands where the last remnants of humanity can survive, people thought, looking out into the seas. Uncontacted tribes untouched by the infection.
At the same time, Andamanese bow-hunters who've never heard of *helacytosis* wondered why the fish they caught for supper were all covered in strange tumours.