Resistant Virus Grows Less Fit If Therapy Is Maintained

Continued use of protease-inhibitor'based antiretroviral therapy in patients who develop resistance to the medications results in HIV becoming even more resistant to the drugs, but it also leads to prevalence of virus that is less able to effectively replicate, report University of California, San Francisco, researchers in a November issue of the Journal of Virology. 'Indeed, it appears that the virus is often constrained in its ability to become both highly resistant and highly fit,' researcher Steven Deeks told Reuters Health. The scientists studied 20 HIV-positive adults who remained on the same drug regimens even when viral loads persisted above 500 copies per microliter of blood. After an early rise in viral levels, most patients exhibited stable viral loads or showed only gradual increases that remained well below pretreatment levels. The researchers concluded that 'drug-resistant viruses appear to be 'painted into a corner' of a viral fitness landscape from which they cannot readily escape without sacrificing the ability to replicate in the presence of the drug.'