To thrive, they latch onto a healthy host cell and hijack its reproductive machinery, cranking out copies of themselves and spinning off mutant versions that resist any one drug.

FORBES: The Golden Age of Antiviral Drugs

The Vatican has over recent decades issued blanket condemnations of artificial methods of birth control, in-vitro fertilization, therapeutic and reproductive cloning, and human embryonic stem cell research.

FORBES: Venter and the Vatican

But Josephine Quintavalle, director of Comment on Reproductive Ethics (Core), which opposes embryonic stem cell therapies, dismissed the research as "highly speculative".

BBC: Green light for US stem cell work

So the controversy over government funding of embryonic stem cell research quickly reaches into the unregulated domain of reproductive medicine.

CNN: graphic

Reproductive cloning, which created Dolly the sheep in 1997, involves transferring the nucleus of an adult cell into an egg, giving the resulting embryo a full set of genes without the normal sperm-meets-egg fertilisation step.

ECONOMIST: Endangered species