Treating infections may worsen other conditions: parasite study

Using drugs to treat an infection could allow other co-existing conditions to flourish, a study at the Universities of Liverpool and Edinburgh have shown. The study suggests infections co-existing in the body can compete with each other to alter disease

Researchers studying wild mice – which typically carry multiple parasitic infections at once – found that when these animals were treated for one type of bug, other infections that they carried tended to worsen.

Infections compete
The findings suggest that infections that co-exist in our bodies can compete with each other to alter disease. Treating one infection may have unintended consequences by enabling others to gain a stronger foothold – perhaps to the overall detriment of our health.

Scientists at Liverpool and Edinburgh treated wild wood mice for a gut worm infection over several weeks. During treatment, researchers monitored levels not only of the worm, but also tested the animals for dozens of other common parasite infections.

During treatment, levels of the gut worm fell, but levels of other parasites in the gut increased.

Dr Andy Fenton, from the University's Institute of Integrative Biology, says, ''This work shows that treating one disease can have undesirable effects for other diseases, and may help us understand the effects of similar treatments in people and domesticated animals.''

The study is the first of its type to show that multiple infections in wild animals can compete with one another and that treating one infection can directly impact on others that may be present.

Knock-on effect
Dr Amy Pedersen, of the University of Edinburgh's School of Biological Sciences, said: ''In nature, infections rarely occur by themselves, and this study shows for the first time that treating infections in isolation can have knock-on effects for other diseases that may be present.

''More work is needed to understand the effect of drug treatment for disease where individuals are prone to, or likely to be carrying a range of infections.''

The study, published in Proceedings of the Royal Society B, was supported by the Natural Environment Research Council and the Wellcome Trust.