By Henry Ehrlich
There’s a saying that gets repeated frequently these days: “If you want a friend in Washington get a dog.” But if the lonely legislator (or whoever) is allergic to them that’s a problem. The Obama children were advised to get Portuguese water dogs, which have a non-allergenic reputation, but that’s all it is. I knew that shots for dog allergy have a so-so record of effectiveness, but I had no idea how complicated mere diagnosis is until I ran across a new article by Roy Gerth van Wijk MD, PhD to be published in JACI, about these doggy difficulties.
For a start, many self-reported dog allergies are wrong, as we might expect. But the professionals often don’t do any better. Structured allergy history results in false-positive rates of 27% compared with a formal allergy workup. Accuracy of skin-prick tests (SPT), one of the pillars of allergy testing, is hampered by the fact that extracts don’t always contain the relevant allergens. In one study, van Wijk writes, “five extracts from European manufacturers were examined. SPT extracts showed a 20-fold variation in protein content, whereas the dog allergens Can f 1 and Can f 2 varied widely between extracts with undetectable levels in one of five extracts.”
Some allergens are distinctively doggish, but are only reactive in 50-90% of patients. Others are cross-reactive for other furry animals from cats to horses similar to the way birch pollen Bet v 1 allergen that appears under various names in other plants, such as the Ara h 8 component of peanut. Some allergens are only found in male dogs, so if the testing extract is only drawn from females, you’re out of luck. Component testing is useful for diagnosing peanut-allergy; Ara h 2 and Ara h 6 track pretty closely with susceptibility to serious reactions during food challenges. But while many components can be associated with dog allergy, in the test tube it’s hard to line them up with the results of a nasal challenge, which is the nearest equivalent of the gold-standard oral challenge for food allergies. You can’t stick a whole dog in the patient’s nose the way you can eat some version of the whole peanut during a food challenge. For nasal challenges, doctors have to rely on the same widely variable extracts used for skin testing. This turns out to be more of a fool’s gold standard.
Our contributor Brian Schroer MD upon reading the Van Wijk article, elaborated on certain points “Studies have shown that dog allergen comes from the skin, saliva and in male dogs the prostate. So, the only way to have a truly hypoallergenic dog is to find a skinless or spitless dog. However, I do not know if I would want one!” Unless of course as many others have pointed out, it’s the kind of dog you put on a bun and eat with mustard.
“That being said,” Brian continues, “many dogs produce different levels of allergen. Some dogs may be ‘more’ allergenic than others, but this is not a breed-to-breed thing, it is an individual dog vs individual dog thing.
“The other thing to consider is that dog dander is ubiquitous. It is in schools, offices, and medical buildings. But the allergen levels are much higher in the homes where the dog lives. In the case of patients with dog allergies it can be hard to know if your dog is contributing to your symptoms. This is because if you live with a dog the allergen is always around and you are therefore constantly exposed. That constant exposure leads to constant lower level symptoms than you would have if you are not regularly exposed to other people’s dogs. This means you may have constant low level nose congestion and dripping with some mild sneezing from your own dog whereas someone else with dog allergies but no dog at home will have more fast onset and more severe symptoms when they do go around the dog. This often includes more sneezing, worse dripping and nose congestion and even eye symptoms. Asthma is another disease where dog can be one of many triggers and when you live with a dog it can contribute to more frequent or severe symptoms than if you do not live with a dog.”
“While history or testing alone are not perfect it is helpful to see an allergist to see if your dog maybe contributing to symptoms. Despite the potential for allergen extracts being falsely negative, a positive test and a good history is the best available way to know if your dog or other dogs are contributing to nose allergies or asthma.”
Thank you, Dr. Schroer.
Dog image from “The Fatal Glass of Beer” by WC Fields, 1933