A paper published recently on fungal triggers of asthma in PLOS Pathogens says that asthma is a complex disease without a single cause, defined by its symptoms. Wheezing, chest tightness, and breathlessness are triggered by airway inflammation. The natural histories of asthma are diverse and involve both genetic and environmental parameters.

For example, children with variants of the ADAM33 gene are at risk for asthma, while attendance at day care in the first six months of life and the presence of older siblings appear to protect against asthma. Allergies are intimately associated with asthma. Asthma can result from direct inhalation of allergens, but atopic asthmas are caused by the body’s interaction with allergens outside of the lungs. It is a public health burden, and the prevalence of asthma is increasing.

WHO defines asthma as a chronic disease characterised by recurrent attacks of breathlessness and wheezing, which vary in severity and frequency from person to person. During an asthma attack, the lining of the bronchial tubes swells, causing the airways to narrow and reducing the flow of air into and out of the lungs. The causes of asthma are not completely understood. However, risk factors for developing asthma include inhaling asthma “triggers”, such as allergens, tobacco smoke and chemical irritants. Asthma cannot be cured, but appropriate management can control the disorder and enable people to enjoy a good quality of life.

Asthma is also caused by the presence of fungal spores of Alternaria (fungi) and Cladosporium (fungi), tiny particles that allow fungi to multiply. They are like seeds in plants.

“The diversity of fungal spores in air is vast, but research on asthma focuses on a handful of easily identified, culturable species. Ecologists are developing new tools to probe communities and identify the full complement of fungi in habitats. These tools may enable identification of novel asthma triggers, but scientists involved in public health or medicine rarely interact with mycologists focused on ecology,” said Anne Pringle, mycologist at Howard University, Cambridge, Massachusetts, in the above paper.

As disease prevalence continues to rise, enabling research on the roles of fungi in asthma makes sense. Pringle said, “Humans appear to be reshaping the ecology of the kingdom: elevated CO2 concentrations appear to stimulate sporulation and climate change appears to influence the timing of sporulation. A current hypothesis suggests a connection between the global change and the rise of asthma and allergies.”

Different species or spore types may have different surface properties or internal metabolisms, and different potentials as causes of asthma. While logic would dictate a systematic search for triggers grounded in what’s most abundant in the environment, instead research has focused on easily cultured fungi with distinct spore shapes. “Treatment involves giving inhalers with a mixture of steroid and bronchodilators,” said Dr Mehta. “These cause minimal toxicity, local action and can be used long term. Children respond easily to inhalers,” he said.

A hospital-based study on 20,000 children under the age of 18 years from 1979, 1984, 1989, 1994 and 1999 in Bangalore by Dr Paramesh, showed a prevalence of 9 per cent, 10.5 per cent, 18.5 per cent, 24.5 per cent and 29.5 per cent respectively, in 2002.