Animals and Asthma- to have or to have not?

  Photo by Bethany King

Recent research has challenged our previous recommendations regarding the role of a pet in the development of asthma and in the development of allergy. The hot topic today is a review of a publication by M. Kerkhof and colleagues titled ‘ Effects of pets on asthma development up to 8 years of age: the PIAMA study’ (Allergy 2009; 64: 1202-1208).

Background: four papers written between 1999-2003 found that a pet in the home during the early years of a child’s life prevented the development of allergy. Six reports between 1999-2004 gave mixed results as to whether or not a pet prevented the development of asthma. A meta-analysis (where the findings of a number of studies are combined) found a small (20%) increase in asthma with early pet exposure up to age 6 years. There have been no studies published regarding the relationship of pet exposure after the first few years of life and the development of asthma. This study fills that void.

Purpose: the study looked at the effect of the presence of cats and dogs in the home at any age during childhood and the incidence of asthma up to age 8 years.

Methods (how they studied this): This was a major survey performed in the Netherlands. There were 2951 children involved. Questionnaires were completed every year for 8 years.

Results (what they found): at age 3 months, 34 % of the children had a cat and 16% had a dog in the home.

1. When a dog was in the home, there was less allergy to house dust mites and to pollen at age 8 years.

2. The presence of a dog or cat in the home at 3 months of age was not associated with the presence of asthma or asthma symptoms when the child was 8 years old.

3. The occurrence of wheeze and a dry cough at night after age 2 years was higher in the children who had a dog in the home at the beginning of the study. The wheeze was more in boys and the dry nighttime cough favored the girls.

4. Removing a dog from the home was associated a higher incidence of wheezing (Odds Ratio = 2.59) and having a prescription for an inhaled steroid (Odds Ratio = 3.03). This was observed in the year after the removal of the animal. Note: a simple way of interpreting the Odds Ratio is that wheezing occurred 159% more and prescriptions for inhaled corticosteroids were 203% more in children where the dog was removed.

  Kita one of our Siberian Huskys- a real snow dog

Conclusions:

1. Pet exposure early in life may prevent the development of allergic sensitization to pollen and house dust mites at age 8 years.

2. Exposure to pets at any age in childhood did not affect the development of asthma up to age 8 years.

3. Exposure to dogs after the first two years of life increased the transient symptoms of wheeze and dry cough.

4. Dog removal increases the risk of wheeze and the need for an inhaled steroid.

Comments: the authors point out weaknesses in their study. One weakness is the problem with having a clear definition of asthma. This is a problem for many studies like this. The authors were able to examine 1132 of the 2951 children and validated the presence of asthma with specialized tests. This becomes an issue when trying to understand the transient wheeze and dry cough. Was this truly asthma or symptoms due to a viral illness? In the discussion it was thought that this was a response to the endotoxin in the environment from the dog that stimulates immune processes away from allergy.

Another potential weakness identified by the authors is that the measurement for allergy was done in only 1248 of the children.

Studies like this start us thinking about what advice to give to families on this subject. It is important to note that this work was done in the Netherlands and not done  in this country. This concept needs to be proven in the United States.  The differences in the populations  may limit our ability to extend the findings to current clinical practices here.

When evaluating a child for asthma, I think we have to be sure of the relationship of the symptoms to the skin test findings. All too often a family is told to get rid of the pets based on the results of an initial set of allergy tests. I am not sure this is an immediate way to proceed and we need to think of other family dynamics that are involved. I have frequently taken advantage of a more sophisticated measure used in asthma care/diagnosis to help figure out the relationship between triggering events and the clinical relevance of an allergy test result. At Riley we can measure exhaled nitric oxide. eNO is a by-product of allergic airway inflammation. When it is elevated there is most probably an allergic trigger causing the symptoms. I may not consider that a positive allergy test to dog relevant when there is significant exposure and the eNO is normal during an event. The asthma episode may be triggered by something else that requires investigation.

No, I am not ready to tell all my families to obtain an array of pets in anticipation of having children. I wonder what to do for those families who do not want the expense of feeding/picking up after pets. Ccould they purchase a ‘Bag o Pet’. This would contain all those things that are responsible for preventing sensitization and the development of asthma and not the live creature. Just a quick thought.

  Loki- (Brandon and Amanda’s cat- name for the Norse god of mischief)

Fred Leickly