A Lousy Reason for Asthma and Allergies

Parasites may reduce their hosts' risk of developing immune dysfunctions

The incidence of asthma and allergies are on the rise. In the United States alone, asthma rates have doubled since the 1980s. And, according to a recent article by the BBC, doctors once estimated 15 percent of the population had some type of allergy, but now believe the figure is closer to 40. More patients are also suffering from multiple allergies than ever before. The reason for this trend has been widely disputed, but a new study points the finger at a surprising culprit: lice.

According to research conducted at the University of Nottingham (PDF link), some parasites may reduce their hosts’ risk of developing immune dysfunctions like asthma, allergies, and some forms of arthritis. The study analyzed the effects of various parasites on the immune activity of wild wood mice and discovered that the louse Polyplax serrata triggered an immunosuppressive effect in mice. While this sounds like a negative effect, the finding supports the idea that modern, parasite-free populations have heightened immune responsiveness, and it is this heightened immune response that might increase the risk for allergic diseases.

Theories like the “Hygiene Hypothesis” point to our sanitary modern lifestyle as the cause for the prevalence of allergies and asthma. Because humans are no longer exposed to many types of bacteria, viruses and parasites, we may be loosing our ability to fight certain diseases. Basically, we are too clean for our own good.

“Much like laboratory mice, people in developed countries are currently exposed to a very different profile of infections than encountered by their ancestors,” explains lead researcher Janette Bradley in a press release. “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.”

Since parasites like Polyplax serrata dampen innate immune responses, they help protect against immune dysfunctions like asthma or allergies. According to the study, populations without immunosuppressive parasites may have “unnaturally” elevated levels of innate immune activations, and therefore increased risk of immunopathology.

This is why the study used wild mice, who have “normal” levels of parasite infestations. Laboratory mice are raised under unnatural pathogen conditions and stress-free circumstances, but studying wild mice allowed scientists to better analyze how immune systems function in a natural environment. Immunological analyses of wild populations may provide a breakthrough for immunology and give scientists a better understanding of how immune systems respond to natural levels of diverse microorganism exposure.