Ragweed is an invasive, highly allergenic weed predicted to expand its habitat with warming global temperatures. Several Ambrosia species have been identified in South Africa for well over a century; however, its presence remained undetected by allergists and aerobiologists until the development of an extensive aerospora monitoring system across South African urban areas since 2019. This paper presents the inventory of preliminary investigation of the Ambrosia airborne pollen and the taxonomic identification of ragweed species. Burkard volumetric spore traps for collecting pollen samples are set up in 9 South African cities (Johannesburg, Cape Town, Pretoria, Kimberley, Durban, Potchefstroom, Ermelo, Bloemfontein, and Gqeberha). Light microscopic identification was combined with environmental DNA metabarcoding analysis to confirm the species level of airborne Ambrosia at selected monitoring stations. Ragweed sensitisation was examined in Cape Town between February 2019 and February 2024, using Allergy Xplorer (ALEX²) multicomponent allergen array. Ambrosia pollen was detected in 5 aerobiological monitoring stations over the sampling period (Durban, Kimberley, Pretoria, Potchefstroom, Johannesburg). Periods of 4 consistent pollination years were observed in Kimberley (min: 1; max: 16 p.g/m³) and Durban (min: 26; max: 66 p.g/m³). In Pretoria, ragweed pollen was detected for 2 years (2020–2021; 2022–2023) with average total annuals (5-17 p.g/m³). A peak flowering period between March and April was observed in Potchefstroom, and several ragweed pollen peaks were present between the end of December and the beginning of May in Durban. The highest number of Ambrosia pollen grains was recorded in Potchefstroom, with 308 grains, and a maximum peak of 47 p.g/m³. eDNA metabarcoding confirmed the presence of Ambrosia artemisiifolia and A.trifida species. The overall prevalence of Ambrosia-sensitisation amongst 673 tests (age range 7–72 years) was 8.2% (55/673), with no significant difference in sensitisation patterns between age groups. Our study confirms the need to monitor the spread of ragweed, and an increasing awareness of Ambrosia as an allergen of concern in Southern Africa. Extension of aerobiological networks and testing for Ambrosia sensitisation across urban and rural sites will be required.

South Africa’s urban population is increasing, and in parallel, urban green infrastructure has shown an increase in alien tree species, e.g., mulberry (Morus sp.), oak (Quercus spp.) and plane trees (Platanus spp.) to name a few. This causes ecological problems since alien trees are often more water-demanding and competitive than indigenous trees, but they also increase the abundance of respiratory diseases often triggered by an allergic reaction towards the pollen of those alien taxa. In the current study, utilizing 7-day volumetric spore traps, we illustrate that the most abundant tree pollen in the two largest cities of South Africa, Cape Town and Johannesburg, is produced by alien trees with a high risk of allergenicity. This adds another aspect related to public health when evaluating plant species composition in urban forestry and urban ecology, which underlines the urgency of more intense monitoring. More importantly, this—for South Africa—newly emphasized risk for public health underlines the applicability of current directives [i.e., Spatial Development Frameworks (SDFs), localized Precinct Plans, Land Use Schemes (LUSs)] and implementation options in urban planning. Here, we present ideas that may be implemented in such a framework. From both a public health and an ecological perspective, it is recommended to plant indigenous trees like Combretum erythrophyllum, Vachellia and Senegalia spp. that have fewer ecosystem disservices, like a lower impact on public health due to lower allergenicity/lower pollen occurrence and providing more ecosystem services such as lower water needs.

Pollen is a major cause of allergic respiratory diseases. In Qatar, data on the presence and prevalence of allergenic airborne types of pollen is quite limited. The study aimed to determine and correlate the most frequently implicated airborne pollen detected by aerobiological monitoring samplers in respiratory allergy symptoms. An aerobiological survey was started on May 8, 2017. Airborne pollen was collected using two Hirst type seven-day recorder volumetric traps. Skin prick test in patients attending allergy clinics in Doha using commercial extracts was conducted. Twenty-five pollen types representing the native, as well as the introduced plants, with a relatively low daily mean concentration were observed from May 2017 to May 2019. The highest pollen concentrations were reached by Amaranthaceae (58.9%), followed by Poaceae (21.7%). SPT revealed a comparatively higher degree of sensitization to pollen. Among 940 patients, 204 were sensitized to pollen (54% female) with 135 (66.2%) and 114 (55.8%) to Amaranthaceae and Poaceae, respectively. Some patients had polysensitization. There was a statistically significant association between Amaranthaceae, and asthma (r = 0.169, P = 0.016) and allergic rhinitis (r = 0.177, P = 0.012). This is the first study to monitor airborne pollen in the state of Qatar. The main pollen detected were Amaranthaceae and Poaceae. Pollen may represent a possible exacerbating factor in adult patients with allergic diseases such as asthma and allergic rhinitis.

Daily monitoring of airborne fungal spores was carried out for the first time in Al Khor city, Qatar, using a Hirst type 7-day recording volumetric spore trap, from May 2017 to May 2019. During the sampling period, the annual and monthly fluctuations, as well as intradiurnal variations of airborne fungal spore concentrations, were evaluated. Cladosporium, followed by Alternaria, were the spore types most abundant in the atmosphere of the city, with a strong interannual variability in the atmospheric concentrations being observed. The Annual Spore Integrals (ASIns) were 3334 and 1172 spore * day/m³ (2017–2018), and 6796 and 1538 spore * day/m³ (2018–2019) for Cladosporium and Alternaria, respectively. Total daily spore concentrations showed significantly positive correlations with mean, minimum, and maximum temperatures but significantly negative correlations with relative humidity. However, due to the scarce rainfalls’ days, we did not find a statistically significant correlations between Cladosporium and Alternaria spore concentrations and this parameter. Despite this, the spore peaks were strongly related to precipitations that occurred during the previous month. In general, no significant correlations were found with wind speed but, regarding wind direction, the higher percentage of spores were collected when wind blows from the 4th quadrant (NW). According to the intradiurnal pattern, Cladosporium fungal spores displayed their maximum daily concentration during 8:00–10:00 h in the morning, with a second peak in the afternoon, while for Alternaria, the maximum peaks were observed between 08:00 and 14:00 h. Because no consistent previous aerobiological studies exist from Qatar, the aim of this study is to define the seasonality and intradiurnal behaviour of these two airborne fungal spore and the role that, in such arid scene, the meteorological parameters play on the spore concentrations.