Various tablets and capsules

Evolving resistance

Evolution of pathogens can be bad news

Pathogens like influenza viruses and tuberculosis (TB) bacteria are constantly evolving resistance to drugs, which means that it is becoming harder and harder to treat some diseases. But how do they do it?

Think about how evolution works: within species there are individuals that display different traits. Those with the most beneficial traits win out because they survive to pass on their genes. The variations between individuals are the result of mutations that occur randomly in their DNA.

The same thing happens in pathogens, including certain bacteria and viruses. Mutations may be harmful to the pathogen or, on the contrary, offer some benefit that means they can actually survive the drugs designed to kill them. Those that survive are said to have evolved resistance.

In HIV, for instance, resistance occurs routinely because the virus copies itself very rapidly, and doesn’t have a means for repairing copying mistakes, unlike humans. These ‘mistakes’ are the mutations that may turn out to be beneficial.

HIV-positive people are advised to stick carefully to their treatment regimens, to keep the level of virus in their body, known as the viral load, low, thus minimising viral replication and the potential for HIV to gain beneficial mutations. Treating drug-resistant HIV requires more expensive ‘second-line’ drugs.

Lead image:

Gatis Gribusts/Flickr CC BY NC

About this resource

This resource was first published in ‘Epidemics’ in September 2007 and reviewed and updated in January 2015.

Microbiology, Health, infection and disease, Medicine
Education levels:
16–19, Continuing professional development