FromMedScape

Childhood asthma is reduced by half when the first dose of diphtheria, pertussis, and tetanus (DPT) is delayed by more than 2 months vs given during the recommended period, according to the results of a retrospective longitudinal study reported in the March issue of the Journal of Allergy & Clinical Immunology.

“Early childhood immunizations have been viewed as promoters of asthma development by stimulating a TH2-type immune response or decreasing microbial pressure, which shifts the balance between TH1 and TH2 immunity,” write Kara L. McDonald, MSc, from the University of Manitoba in Winnipeg, Manitoba, Canada, and colleagues. “Differing time schedules for childhood immunizations may explain the discrepant findings of an association with asthma reported in observational studies. This research was undertaken to determine whether timing of diphtheria, pertussis, tetanus (DPT) immunization has an effect on the development of childhood asthma by age 7 years.”

The investigators analyzed data from the complete immunization and healthcare records of a cohort of children born in Manitoba in 1995, from birth until age 7 years. Using multivariable logistic regression, they computed the adjusted odds ratio for asthma at age 7 years according to the timing of DPT immunization.

Among 11,531 children who received at least 4 doses of DPT, the risk for asthma was halved in children in whom administration of the first dose of DPT was delayed by more than 2 months. For children with delays in administration of all 3 doses, the likelihood of asthma was 0.39 (95% confidence interval [CI], 0.18 - 0.86).

“We found a negative association between delay in administration of the first dose of whole-cell DPT immunization in childhood and the development of asthma; the association was greater with delays in all of the first 3 doses,” the study authors write. “The mechanism for this phenomenon requires further research.”

Limitations of this study include possible ascertainment bias; findings not yet confirmed with the diphtheria, acellular pertussis, tetanus (DaPT) vaccine; and inability to refute the issue of early-life infections as an explanation for the association between delayed immunization and protection against the development of asthma.

“Further study is vital to gain a detailed understanding of the relationship between vaccination and allergic disease, because a perception that vaccination is harmful may have an adverse effect on the effectiveness of immunization programs,” the study authors conclude.

But researchers admit study doesn’t prove cause and effect

From HealthDay

Farm women who come in contact with some widely used pesticides may have an increased risk of developing allergic asthma, a new study suggests.

However, the risk of developing non-allergic asthma does not increase for women exposed to pesticides, according to the study authors.

“Women who apply pesticides on farms were 50 percent more likely to have allergic asthma, although this was not true for non-allergic asthma,” said study author Jane Hoppin, a staff scientist with the National Institute of Environmental Health Sciences in Research Triangle Park, N.C. “Also, women who grew up on farms were protected against allergic asthma and that protection was evident whether or not you applied pesticides.”

The findings are published in the January issue of the American Journal of Respiratory and Critical Care Medicine.

According to the Asthma and Allergy Foundation of America, non-allergic asthma is caused by factors not related to allergies. But allergic asthma — the most common form of asthma, affecting more than 50 percent of the 20 million asthma sufferers in the United States — is characterized by symptoms that are triggered by an allergic reaction. Some typical triggers for allergic asthma include dust mites, pet dander, pollen and mold.

Experts already knew that growing up on a farm minimizes the risk of allergic disease, that pesticides have been associated with respiratory symptoms in farmers, and that farmers are at increased risk for respiratory diseases — including asthma — due to exposure to grains, animals, dust and other factors.

Little research, however, has delved into respiratory risk factors for farm women.

Hoppin and her colleagues examined data on 25,814 such women in North Carolina and in Iowa who are participating in the Agricultural Health Study, a large government-funded look at the effects of environmental, occupational and other factors on the health of the agricultural population.

“This is the largest study of farmers and their families in the world, so it gives us an opportunity to look at diseases that haven’t been well characterized,” Hoppin said.

The women reported whether or not they had been diagnosed with asthma and were then divided into two groups: those with atopic (allergic) asthma and those with nonatopic (non-allergic) asthma.

More than half the women in the study had used or been exposed to pesticides. Sixty-one percent of the women were raised on a farm, which protected against allergic asthma and, to a lesser extent, non-allergic asthma. Using pesticides was associated almost solely with allergic asthma, increasing the risk almost 50 percent, the study found.

The association between pesticide use and allergic asthma was strongest among women who had grown up on a farm. But because of the protective effect of having grown up in an agricultural setting, these women still had a lower overall risk of allergic asthma than women who did not grow up on a farm.

Women who were raised on farms but did not use pesticides had the lowest overall risk of allergic asthma, compared with women who neither grew up on farms nor applied pesticides.

Some less commonly used pesticides such as parathion were associated with triple the risk of allergic asthma. Some more commonly used pesticides such as malathion were also associated with a higher risk, the researchers said.

Other experts said the study findings were far from clear-cut.

“It’s a little bit confusing,” said Dr. Len Horovitz, a pulmonary specialist at Lenox Hill Hospital in New York City. “I would expect that there would be more allergic asthma in anybody who grew up on a farm, but that’s not exactly what they’re saying. Also, it’s difficult to separate farm work from pesticide use. I would need to see more data before coming to the same conclusions as the authors of the article did.”

Because Hoppin’s analysis was “cross-sectional,” it can’t show a cause and effect. “But given what we see in animals, it suggests that we should do a prospective analysis where we can then say pesticide use preceded asthma or asthmatic symptoms. That’s really the next step,” she said.

Hoppin said she and her colleagues are in the process of planning that next study.

From News - Revolution Health

Breast-feeding seems to protect children from asthma later in life, but only when the mother does not have the respiratory disorder herself, U.S. researchers said on Thursday.

They found that breast-feeding for more than four months helped improve lung function in children whose mothers did not have asthma.

But breast-fed children whose mothers had asthma did not benefit and actually showed a significant drop in lung function later in life.

That does not mean women with asthma should stop breast-feeding.

The researchers cautioned that the study, published in the American Journal of Respiratory and Critical Care Medicine, was preliminary and the findings needed more study.

Breast milk is almost always considered best for infants. It can be digested easily and supplies antibodies that can protect babies from bacterial and viral infections, including many of the respiratory tract.

Dr. Theresa Guilbert of the University of Wisconsin-Madison wanted to see if longer breast-feeding — lasting four months or more — improved lung function in children.

She and colleagues at the Arizona Respiratory Center analyzed data from the Children’s Respiratory Study in Tucson, which followed 1,246 healthy infants through adolescence.

Of those, 697 had lung function tests from the ages of 11 to 16 that evaluated air flow and lung volume.

For the most part, breast-fed children with non-asthmatic mothers had better lung volume and no decrease in air flow.

But children of mothers with asthma who were breast-fed four months or more did not show any improvement. In fact, these children had a significant reduction in airflow.

The reason, Guilbert suggested, may be altered lung growth.

Guilbert believes breast milk may contain certain factors that promote lung development, factors that may be impaired in mothers with asthma.

“These findings suggest that growth factors in milk have the potential to modify lung development, which might account for some of the protective effect of breast-feeding,” she wrote.

Researchers found a similar effect in mice born to non-asthmatic mothers who were breast-fed by mothers with asthma. These mice developed airway inflammation.

“It is important to emphasize that the clinical significance of these findings is unknown,” Guilbert wrote.

“Further study is needed to confirm our findings and to determine a biological basis for the relationships observed.”