Thanksgiving effect: UVA studies cat allergies

When Dan Robinson headed home for his first break from college two years ago, he was greeted by a nasty surprise. Instead of rest and relaxation, he spent the Thanksgiving weekend barely able to breathe and found sleeping impossible.

He could not know then– but sure knows now– that coming home is hazardous to his health. Suddenly, mysteriously, the cats back home are triggering severe asthma attacks.

Robinson had lived with a cat practically all his life with no problem. But then he leaves for several weeks and returns with a violent, new allergy to felines.

"I always make sure I have a good stock of puffers when I go home," says Robinson, 20, now in his third year as a political science major at Mount Allison University in Canada. He is accustomed to the new reality back home in Prince Edward Island– where there are now two cats.

His is no isolated case. As freshmen at universities and colleges across North America leave their dorms and head home for the first time for Thanksgiving break, more than a few will come away with a newly discovered allergy.

Specialists are still trying to discover exactly why this is happening and how many people it touches. The phenomenon– dubbed the Thanksgiving effect– turns topsy-turvy some commonly held beliefs on allergies and could some day lead to an inoculation against them.

"Traditionally, we have taught if you decrease exposure to an allergen you will not only get better, but in the long run, your allergy will get better," says Thomas Platts-Mills, a professor of medicine at UVA and director of its Asthma & Allergic Diseases Center. "The idea that exposure to an allergen makes you become sensitized and gives you symptoms that's the traditional view."

But with the Thanksgiving effect, increased and prolonged exposure may be actually suppressing a reaction. When exposure disappears, the body's immune system may finally be free to react.

And it seems to happen often when cats are around.

Dr. John Costa, an allergist at Brigham & Women's Hospital in Boston, likes to joke that selling college students pillows stuffed with cat hair could be a lucrative business.

"What we don't know is what it is about having cats in the house that is important," says Dr. Costa, who teaches at Harvard Medical School. "Is it the cats, per se? Is it the allergen that they release? Or is it the fact that with five cats in the house, you are going to have more– not to be gross, but this is what we talk about– fecal contamination."

A European study published last year in the New England Journal of Medicine found that children exposed to endotoxins by living on farms are less likely to develop allergies and asthma later in life.

Animal feces and saliva contain endotoxins that stimulate the immune system. So it could be the stuff in the cat's litterbox behind the protection against allergies at home or perhaps even a friendly lick or two from Fido.

It fits with the emerging "hygiene hypothesis"– the idea that too much cleanliness can actually make children susceptible to problems like allergies or asthma because the immune system has not been built up properly.

And, to the surprise of researchers, a study published in the Journal of the American Medical Association last summer revealed that children who grow up around pets are half as likely to develop allergies or irritable airways than those who do not.

The study followed nearly 500 healthy babies in Detroit– roughly one third of whom had two or more dogs or cats at home. By age seven, children with animals had a 50 percent lower risk of these health problems than those without. Again, endotoxins were thought to help build the children's defenses.

Researchers are now trying to pinpoint what lies behind the Thanksgiving effect. At UVA, 40 students are enrolled in a study that tests their allergic reactions throughout the year to see if they change after trips home.

All have cats back home and live in dorms where pets are not allowed. It may not just happen with cats, but there is no question that cats can provoke strong reactions in the body.

(Contrary to perception, it isn't cat hair triggering fits of sneezing and wheezing, but cat dander– dead flakes of skin– and a protein in cat saliva.)

"The cat is a very good allergen. Exposure is very high. There is no question– a child living in a house with a cat gets 10 times more exposure to cat than to dust mite," says UVA's Platts-Mills.

"Does the same thing happen with a dog? That is confusing. Some of us would like to say that dog is actually a second-rate allergen that simply doesn't sensitize many children and does not induce much immune response," he says.

If researchers discover what is evoking the Thanksgiving effect, it could lead to a vaccine or other preventive treatment against allergies. But that is years away.

For people like Robinson, the only solution is to cope as best they can with today's medicines– or stay home for more than a couple of days. Spring break, for instance, is easier for him. At least he can breathe by the end of the week.

"When I'm home for a good length of time, I start to get better again," says Robinson, who suspects it's just not the cats at home that make him ill, but the neighboring farm fields and pesticides in the air. "When I go in for a checkup, you would still be able to hear a little bit of rattling and stuff like that. You would still be able to hear it through a stethoscope. Not so much that I would notice it, though."