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Some Grass Species Worse for Seasonal Allergies Than Others, DNA Analysis Shows

NEW YORK — Particular grass species are associated with an increase in hay fever and more severe asthma, an environmental DNA analysis has found.

More than 400 million people around the world have allergic rhinitis, or hay fever, and more than 300 million people have asthma, with overlap between the groups. Grass pollen is a key player in outdoor allergies, but which grasses — there are more than 11,000 species — contribute the most to allergies has been unclear.

Researchers led by the University of Exeter's Benedict Wheeler used environmental DNA (eDNA) sampling and quantitative PCR to measure the relative abundance of grass species during two pollen seasons in the UK. As they reported Thursday in Current Biology, they further examined patterns between these pollen levels and prescription rates for allergy medication as well as hospitalization rates for severe asthma to find that certain grasses have an outsized effect.

"These findings represent a first step towards changing and improving our understanding of the complex relationships between pollen and population health," Wheeler said in a statement. "If confirmed and refined, this research could help to improve pollen forecasts and warnings in the future, supporting individual and community-level prevention strategies and management of healthcare system responses."

The researchers collected airborne pollen samples from six sites across the UK in 2016 and a further seven sites in 2017. Samples were taken daily during the grass pollen season of late spring to late summer. The researchers pooled samples collected over consecutive days, generating 605 samples for further analysis.

For their qPCR analysis, they used species-specific primers designed to target the ITS2 region of the grass genome, as it has multiple copies and all UK native species have DNA reference barcodes for it. Common grass species in the UK include Anthoxanthum odoratum or sweet vernal grass, Lolium perenne or perennial ryegrass, and Poa pratensis or smooth meadow-grass, among others.

They found that the timing of sample collection was a good predictor of which grass species would be present. The grasses' pollen abundance peaked at different times and locations, and latitude and longitude were also good predictors of pollen abundance for each species.

The researchers also correlated data on emergency asthma-related hospital admissions with the presence of grass pollen from different species. High levels of pollen from Cynosurus cristatus (crested dog's-tail) and Phleum pratense (Timothy) were linked to an increased probability of being admitted for asthma. At the same time, high levels of P. pratensis were linked to lower hospital admissions.

They additionally examined prescribing rates for respiratory antihistamines and drugs used in treating nasal allergies over the course of the grass pollen season. High levels of grass pollen belonging to Alopecurus or Agrostis and high levels of C. cristatus pollen were associated with higher allergy drug prescribing rates, whereas high levels of L. perenne and P. pratensis were associated with lower prescription rates.

The findings underscore the importance of species-specific pollen monitoring, especially of Alopecurus/Agrostis, C. cristatus, and P. pratensis, according to the researchers.

"We've known for a long time that grass pollen has important implications for health at population scales, but we didn't really know very much about different types of grass pollen," co-author Georgina Brennan from Bangor University added in a statement. "This research suggests that there may be important differences in the public health impacts of pollen from different grasses."

He and his colleagues hope to obtain broader geographic pollen monitoring coverage for more seasons to further investigate the effect of different grasses on health.