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Pigweed invasion threatens people with hay fever

Doctors warned people with hay fever to be cautious as the pigweed season is at its peak.

Pigweed can cause serious health threats to people with hay fever, or pollinosis, because it sheds large amounts of pollen when it blooms in July and August, said Hsu Ling-ming (徐玲明), an assistant research fellow with the Council of Agriculture (COA).

A single pigweed plant can release a million pollen grains per day and pigweed pollen can be carried up to several hundred kilometers by the wind, Hsu said.

People with hay fever have allergic reactions when the density of pollen reaches 20 to 40 grains per square meter.

Some common allergic reactions caused by pigweed include irritated eyes, sneezing, a runny nose and sometimes allergic rhinitis — an inflammation of the mucous membrane that lines the nose — or asthma, said Tsai Chao-chi (蔡肇基), an allergy specialist at Taichung Veterans General Hospital.

While pigweed is a common allergen in Western countries, in Taiwan it originally only grew on the northwest coast. It can now be found in Taichung County and is also spreading to the northeastern part of the country, COA studies showed.

In the past, pigweed has caused health problems in Kinmen, as it covers large areas of the island. Pigweed has been listed as one of the 20 most threatening invasive vegetation species since it was first found on Taiwan proper more than 10 years ago, said Huang Shih-yuan (黃士元), another COA assistant research fellow.

Huang suggested that pigweed may have arrived in Taiwan with imports of grains.

Nowadays, pigweed can be easily spotted in abandoned lots or along roads in rural areas in Taipei, Taoyuan, Hsinchu and Miaoli counties.

According to Tsai’s own study, 80 percent of allergy cases in Kinmen are caused by pigweed, and as it continues to spread in Taiwan proper, it may soon become a top threat for allergy patients, he said.
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