9 things you may not know about the highly allergenic weed invading SA

Ragweed has been detected in South African pollen spore traps for the first time.
Ragweed has been detected in South African pollen spore traps for the first time.

Earlier last week Health24 reported on ragweed, a highly allergenic plant native to North America, that was detected by scientists in South African pollen spore traps for the very first time.

Professor Jonny Peter, head of the UCT Lung Institute's Allergy and Immunology Unit shed light on the health implications for South Africans. Here is a roundup of everything we know so far.   

We don’t know how long it’s been in SA

Although ragweed pollen was detected in KwaZulu-Natal (KZN), and on the banks of the Vaal River near Heidelberg, we don’t know exactly how long it’s been there.

Peter explains that there are different species of ambrosia – the genus of which ragweeds are the flowering plants. Two of the most common species of ragweed are artemisiifolia (common ragweed) and trifida (giant ragweed). 

“What’s interesting is that we haven’t monitored pollen in Durban, so it is possible that ambrosia has been there for some time. Giant ragweed has been listed on the eThekwini Municipality's invasive species list in South Africa. But artemisiifolia, the very allergenic one, has not.

“This is highly relevant in the sense that we did not, as an allergy and medical community, even know it’s there. We haven’t been looking for ragweed sensitisation. There are plenty of tests for it, but we haven’t been doing them.”

What is the way forward?

Peter explains that two approaches are now being taken to identify what species exactly are being seen in the pollen trap, but that it’s unfortunately not as easy as it sounds.

“At the level of light microscopy (LM), which is what we use for pollen identification, we can only get to the genus level. So we can only identify this as ragweed, but can’t determine what species it is without taking one of two approaches.”

One of these two approaches involves electron microscopy – and Peter adds that’s what the team has been doing in KZN this week. “That’s probably going to take two to three weeks. In the interim, the environmental teams, both of the eThekwini Municipality and those at government level, are going to start to investigate locally,” says Peter.

How did it get to KZN?

It’s not completely clear how ragweed came to KZN and Heidelberg, although Peter suggests that it could be because Durban is a very big port. 

“Weed seeds are often contaminants in crop seeds, and it could be that they came with groups of crops, or even via people walking on ships – that’s often how seed contamination occurs.” 

KZN also presents the right climate for ragweed to thrive, says Peter. Ragweed doesn’t like a hot, dry climate, and thrives in a more sub-tropical climate, with the right temperature, humidity and dry soil levels.

“And the immediate implications for us, as an allergy community, is that ragweed is now established in KZN and has suddenly become a very important allergy to look for people living in that area, and we need to see how that is contributing to the existing disease burden in that area,” he explains. 

Uncertainty on the rate of invasion in SA

The data counts that we have on the rates of ragweed invasion comes from Northern Europe, and they’ve been tracking it over the course of years, says Peter, so it’s unlikely we can say that it’s now in KZN and will be in Cape Town by next year, for example.

“We base it more on the time frame that we have seen with climate change, and the predictions of climate change indicate that temperatures are going to rise exponentially in the coming years.

“Should the scientific evidence around climate change and temperature levels be correct, then modelling data would suggest that the process of invasion and an increase in sensitisation within the North or South will be occurring within one to two decades.”

If ragweed is not controlled or removed, how quickly can it spread to other provinces?

Once ragweed becomes well-established across a country, it’s much more difficult to control, says Peter.

“You can’t just go around and pull out any plant. But the amount of pollen we’re getting from the traps is still at very low levels, so it’s possible that it’s here only in small amounts.

“I think the main concern is that it could have been here for several years, and if it is established and restricted to KZN, with the impact of climate change, the same effect would be seen as we see in Northern Europe. As the change in climate occurs, the habitat will basically move slightly south, and it will start to move into newer areas.”

I haven't suffered from allergies before. What are the chances of developing it now?

It depends on how long ragweed has been in the area and how well it’s established, says Peter. What makes ragweed unique is that a very low level of pollen (6g per cubic metre) can trigger symptoms. More than this, ragweed pollen is incredibly light and can travel long distances – records in Eastern Europe indicate as far as 600km.

According to Peter, it’s likely that there are a significant number of people that have been sensitised to ragweed if it’s been in the vicinity for a long time, and as it reaches new areas, particularly those who already have allergic rhinitis will become sensitised to it really quickly. 

Monitoring traps is particularly important

One of the reasons ragweed should now be monitored quite closely is because pollen-related allergies all look the same, says Peter.

“They all cause the typical symptoms of hay fever, and if it’s triggering your asthma, it’ll cause symptoms of asthma, so it’s one of the reasons why we do diagnostic testing,” he says.

Treatment options for ragweed allergies

General allergy treatment can be used to manage ragweed allergies, such as antihistamines, nasal sprays etc., but Peter says that if symptoms are severe and cannot be controlled by typical methods, then you may want to consider more advanced therapy such as targeted immunotherapy. 

Tips to reduce your exposure to ragweed pollen

A previous Health24 article mentions a few general tips to protect yourself on days with high pollen counts:

  • Pay attention to how long you leave laundry on the line: pollen settles on your clothing while drying.
  • Stay indoors on windy days.
  • Keep windows closed on high pollen count days.
  • Try to set activities in areas where pollen counts are lower.

Peter stresses the importance of setting pollen monitoring traps in other parts of KZN and other provinces that are not currently being monitored, so that we can know what plants and allergens are out there and inform people of the health implications. 

As the pollen problem worsens, precise and expanded monitoring becomes even more essential. 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: Getty/Vincenzo Lombardo

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