Register for an account

X

Enter your name and email address below.

Your email address is used to log in and will not be shared or sold. Read our privacy policy.

X

Website access code

Enter your access code into the form field below.

If you are a Zinio, Nook, Kindle, Apple, or Google Play subscriber, you can enter your website access code to gain subscriber access. Your website access code is located in the upper right corner of the Table of Contents page of your digital edition.

Health

Asthma and the Curse of Cleanliness

By Jocelyn SelimJanuary 2, 2004 6:00 AM

Newsletter

Sign up for our email newsletter for the latest science news

Hepatitis A, a liver-infecting virus commonly associated with poor sanitation, may be a guardian angel against asthma and allergies, says immunologist Dale Umetsu of Stanford University. This unexpected result may finally explain the enigmatic rise of these disorders in the United States.

Earlier studies have shown that the cleaner an area is, the more likely it is that children there suffer from asthma. Some researchers have proposed a “hygiene hypothesis” that sterile surroundings deprive infants’ immune systems of proper training. In search of the root cause, Umetsu and his colleagues focused on the possible role of hepatitis A, a nonfatal disease spread by contact with human feces.

Since the 1970s, the hepatitis A infection rate has dropped from nearly 100 percent to less than 30 percent; meanwhile, the incidence of asthma has doubled. After analyzing hundreds of DNA samples, Umetsu found a link. More than half of Americans carry a variant of an immune-response gene, TIM-1, that makes people much less likely to get asthma—but only if they have been exposed to hepatitis A.

“The statistics show that carrying this gene, combined with being infected with hepatitis A, conveys an enormous protection against asthma, allergies, and related diseases,” Umetsu says. He suspects that hepatitis A infection activates the TIM-1 immune receptor, which blocks the allergic and asthmatic response. Although the mechanism remains unknown, this finding begins to expose the biology behind the hygiene hypothesis.

It also seems to debunk theories blaming vaccines or antibiotics for the rise in asthma. “Hepatitis A infection rates are a good indicator of cleanliness, vaccination rates, and antibiotic use,” he says. “It seems we should be looking at hepatitis A, and possibly a few other specific diseases, rather than general indicators or infections as a whole.”

2 Free Articles Left

Want it all? Get unlimited access when you subscribe.

Subscribe

Already a subscriber? Register or Log In

Want unlimited access?

Subscribe today and save 70%

Subscribe

Already a subscriber? Register or Log In