| Lice may suppress asthma, allergies|
|Having lice may not be such a bad thing, with a UK study finding infested mice have calmer immune systems.|
The study, published in the BioMed Central journal BMC Biology, adds to evidence supporting the so-called hygiene hypothesis, which suggests the rise in asthma and allergies can be linked to hyper-clean living.
The idea is that if the immune system is not properly primed in childhood, immune cells can improperly react to harmless triggers such as pollen. Bacterial and viral infections do not seem to be the priming factor, but researchers have been focusing lately on parasites.
Dr Joseph Jackson of the University of Nottingham and colleagues wanted to test real, wild mice, not hygienic lab mice that had been raised for generations in ultra-clean conditions.
"Our understanding of mammalian immunology is largely based on rodents reared under highly unnatural pathogen- and stress-free conditions," says Nottingham's Janette Bradley, who helped lead the study.
They trapped mice using peanut butter-laden traps and studied their immune systems.
Mice not infested with the louse Polyplax serrata had much more excitable immune systems than the mice carrying a heavy load of the parasites, they found.
They speculate lice might be suppressing the immune system in mice by transmitting bacteria or other pathogens or secreting a substance from their saliva while they feed.
The hygiene hypothesis holds that the immune system evolved when people were constantly infected by a host of worms and other parasites - from the mosquito-transmitted malaria parasite to various lice and ticks.
"Much like laboratory mice, people in developed countries are currently exposed to a very different profile of infections to that encountered by their ancestors," the researchers write.
"It is possible that the immune dysfunctions we see today are the result of immune systems calibrated for a set of challenges completely different to those they now routinely face."
Humans can also be infested with lice (Pediculus humanus), although the species does not affect other animals.