Parasite
Genetically engineered tapeworms that protect most of the human populace from illness, boost everyone's immune system, and even secrete designer drugs begin to change and want out of human bodies they occupy.
Fiction, Genetic engineering, Parasites, Fiction, science fiction, general, Roman
Seanan McGuire
See http://seananmcguire.com/bio.php

Seanan McGuire won the John W. Campbell award for the best new writer at the 2010 Hugo Awards.  She uses the pseudonym Mira Grant to write science fiction/horror and the pseudonym A. Deborah Baker to write the "Up-and-Under" children's portal fantasy series.