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Allergy

Updated 31 January 2020

Highly allergenic weed has invaded SA – it could spell trouble for everyone, not just allergy sufferers

For now, KwaZulu-Natal residents are most at risk, but the weed has already spread as far as Heidelberg – about 50km from Johannesburg.

Ragweed, a highly allergenic plant native to North America, was detected by scientists in South African pollen spore traps for the very first time this week.  

The discovery was made by Dr Dilys Berman, aerobiologist at the University of Cape Town (UCT) and Professor Jonny Peter, head of the UCT Lung Institute's Allergy and Immunology Unit.

Palynologist, Dr Frank Neumann, based at Wits University whose research focuses on the impact climate change has on vegetation, also confirmed that the pollen grains belong to the invasive Ambrosia species.

Why the sudden invasion?

The threat of allergy causing plants, such as ragweed migrating southward, because of climate change, was always a cause for concern, said Peter, but they had not expected the "incredibly invasive" weed to show up so soon.

“Its potent pollen has been problematic in the US for many decades. In recent years, allergy sufferers in Europe and South America have also come under threat as ragweed started to invade these areas.

“Based on historical data, ragweed thrives in hot, dry environments and produces more pollen when CO2 levels are high,” Peter said. However, Peter also explained that because of the world’s changing climate, ragweed is projected to decline in some areas as it may over time no longer be climatically suited to grow there.

Ragweed pollen was detected at the Durban monitoring site over the last few days, placing KwaZulu-Natal residents most at risk. Peter explained that the counts are relatively low at this stage, but that they are being monitored daily to detect any sudden spikes. 

While the Eastern and Western Cape are still ragweed-free, a small population of ragweed has been found on the banks of the Vaal River near Heidelberg – about 50km from Johannesburg.

Read:SA’s pollen count is rising, and people who don’t normally get hay fever may now be affected

Ragweed’s implication for human health

Berman warns that ragweed has serious implications for human health, and says that it’s one of the most loathed weeds in the US.

She adds that this weed has been making life a misery for 23 million Americans, and that it's estimated that the number of people affected by ragweed allergy in Europe will increase from 33 to 77 million over the next two decades. While sensitisation to the plant hasn’t yet been reported in South Africa, it is a cause for concern, says Berman.

People who don’t suffer from allergies may develop sensitivities

“Increasing amounts of fine-powder ragweed in South Africa could exacerbate hay fever symptoms and asthma for the estimated 17 million South Africans who suffer from allergies.

“Given that it's highly allergenic, people who normally don’t suffer from pollen allergies may develop sensitivity in the future as the weed proliferates," explained Berman.

Once ragweed sprouts, Peter says it can multiply and grow up to two metres in height in a matter of weeks.

According to the Asthma and Allergy Foundation of America, there are 17 types of ragweed that grow in North America. Ragweed pollen can travel far and is commonly found along the roadside, on riverbanks, and in vacant lots and fields. 

Common hay fever symptoms include:

  • Red, itchy and watery eyes
  • Runny, itchy or congested nose
  • Post-nasal drip, which may irritate and restrict the airways making it difficult to breathe

Removing ragweed

The removal of ragweed should be a priority, and weed control boards should add ragweed to their invasive weeds list as soon as possible before it becomes impossible to control, said Peter. 

“Some studies also suggest that ragweed poses a threat to crop health. It drains the soil and oppresses plant growth, so it is definitely a weed that should be kept an eye on and monitored carefully,” he added.

As the pollen problem worsens, precise and expanded monitoring becomes even more essential. And here's how you can help.

Amid the highest recorded pollen counts in history, Health24 will be bringing you exclusive weekly pollen count updates courtesy of the UCT Lung Institute's Allergy and Immunology Unit.

Image: Supplied/Meropa PR

 

Ask the Expert

Allergy expert

Dr Morris is the Principal Allergist at the Cape Town and Johannesburg Allergy Clinics with postgraduate diplomas in Allergology, Dermatology, Paediatrics and Family Medicine dealing with both adult and childhood allergies.

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