SA pollen patterns raise allergy fears

South Africa is experiencing a rise in asthma and allergic diseases, reflecting a similar increase globally, as highlighted by the International Study of Asthma and Allergies in Childhood (ISAAC) study and more recent research.

Medical Academic Quarterly Insights 05

Given that pollen is a major trigger for seasonal allergic rhinitis, monitoring its levels is essential, especially as climate change continues to disrupt regional patterns. South Africa’s diverse climate and nine distinct biomes create a complex pollen environment.  

With historical pollen monitoring largely confined to the 1980s and 1990s, many areas lack current data. This gap is concerning as climate change affects pollen distribution worldwide. Continuous monitoring of the local biomes has been sparse, mainly covering the Fynbos biome in Cape Town. 

To fill this gap, the South African Pollen Monitoring Network (SAPNET) was launched in August 2019. SAPNET aims to provide ongoing pollen and fungal spore data across major South African cities, including Cape Town, Johannesburg, Pretoria, Bloemfontein, Kimberley, Durban, Gqeberha, and Calvinia. The network’s daily pollen counts are publicly accessible, offering critical information for managing allergy risks. 

The first comprehensive analysis of SAPNET’s data, spanning August 2019 to August 2021, sheds light on regional pollen patterns and seasonal trends. Key findings reveal the dominance of exotic northern hemisphere trees over indigenous species and highlight significant variations in pollen types and seasonal patterns across different cities. 

REGIONAL POLLEN PATTERNS 

  • Cape Town: Situated in the Fynbos biome, Cape Town's pollen calendar shows high levels of cypress, grass, pine, myrtle, and plane tree pollen. The cypress and pine seasons peak from late winter to early summer, while grass pollen peaks in early summer. Weeds, mainly from the daisy family, contribute less to the overall pollen index. 
  • Johannesburg: Here, plane tree, grass, mulberry, and cypress pollen are prominent. Grass pollen peaks in late summer, with tree pollen prevalent from early to late spring. The daisy family contributes significantly to the weed pollen index, peaking in autumn and winter. 
  • Pretoria: The city's pollen landscape features high levels of grass, mulberry, and birch pollen. The grass season peaks in early summer, with tree pollen, including birch and plane, peaking in spring. Weed pollen is less significant but includes sedges and minor weeds. 
  • Bloemfontein: This city experiences high grass pollen levels, peaking in spring and summer. Other significant pollen types include false olive, ash, and olive. The tree pollen season starts in early spring and declines toward summer, with some peaks in late summer for specific species. 
  • Kimberley: Grass pollen is the dominant type, with significant levels throughout the year. Olive family pollen and allergenic types like mulberry and cypress also feature prominently. The grass season peaks from January to April, with smaller peaks for olive pollen in summer. 
  • Durban: In this humid subtropical city, grass, mulberry, and ferns are major pollen contributors. Grass pollen peaks in early summer, with tree pollen detected year-round. Weed pollen is also present, peaking in summer and late autumn. 
  • Gqeberha: The pollen index here is lower compared to other cities, with grass, sedges, and myrtle family pollen being most prominent. Seasonal variations are less pronounced, and significant weed pollen is minimal. 

EMERGING TRENDS 

SAPNET’s data reveal a shift towards exotic northern hemisphere trees dominating the pollen landscape, overshadowing indigenous species. This is particularly evident in urban areas, where wind-pollinated plants, including many neophytes, are more common due to favourable climatic conditions. 

The study indicates that indigenous trees, which are often pollinated by insects, birds, or small mammals, are underrepresented. Dominant exotic trees include Platanus, Quercus, Morus, Fraxinus, and Betula—species known for their allergenic properties. These trees, often ornamental, are also found in natural spaces like roadsides and riverbanks, exacerbating allergic conditions. 

Despite the dominance of exotic trees, overall tree pollen levels in South Africa remain lower than in northern hemisphere cities. For example, daily Betula pollen counts in Kraków, Poland, surpassed 4000 in 2016, while peak daily counts in Johannesburg and Bloemfontein were below 1500. Allergic reactions are anticipated to peak during the spring season in Johannesburg, Bloemfontein, Cape Town, and Pretoria, with significant Oleaceae pollen in Kimberley during late summer. 

The study also notes that anthropogenic climate change is shifting pollen seasons and plant growth patterns. Increased temperatures and CO2 levels are altering flowering times for allergenic species, potentially increasing their prevalence. 

Weed pollen concentrations are generally low, though exotic species like Plantago lanceolata, P. major, Urtica dioica, and U. urens were detected. The most common weed pollen came from the daisy family (Asteraceae), with other notable families including Caryophyllaceae, Chenopodiaceae, Cyperaceae, Ericaceae, and Polypodiaceae. The allergenic weed Ambrosia was found in small quantities in Durban, with monitoring planned for future increases. 

LOOKING AHEAD 

SAPNET’s data provide an essential update on pollen patterns, revealing both regional differences and seasonal trends. As climate change continues to influence pollen distribution, ongoing monitoring will be crucial for managing allergic diseases and improving public health outcomes. The dominance of exotic northern hemisphere trees in South Africa mirrors patterns observed in other southern hemisphere regions, highlighting the need for better urban vegetation management to mitigate allergenic pollen. 

Images: Shutterstock.com

REFERENCES

Esterhuizen, N, et al, 2023. The South African Pollen Monitoring Network: Insights from 2 years of national aerospora sampling (2019-2021). Clin Transl Allergy. Nov;13(11):e12304. 

  

 

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