Every year spring brings the promise of new life. Flowers display a myriad of colours and make us feel that all is right with the world. For many of us however, the new season unfortunately also marks the start of non-stop sneezing, runny noses and itchy eyes, all of which are of course far less pleasant.

Allergies, also known as allergic diseases, are among the most common chronic conditions worldwide and are caused by a hypersensitivity of the immune system to something in the environment that usually has no harmful effects. The most common allergies found today include hay fever (also known as allergic rhinitis), food allergies, atopic dermatitis, allergic asthma and anaphylaxis (an acute allergic reaction to an antigen – such as a bee sting – to which the body has become hypersensitive). Common allergic symptoms include red eyes, an itchy rash, runny nose, shortness of breath, and swelling.

Alarmingly, according to Prof Robin Green, one of the country's foremost experts on allergies and Head of the Department of Paediatrics and Child Health at the University of Pretoria (UP), the incidence of allergic diseases, especially among children, is increasing worldwide. Statistics show that the prevalence of allergic rhinitis and asthma in South African children, is as high as 38,5% and 15% respectively.

Aeroallergens, which are airborne substances that can cause an allergic response, have been implicated in the pathophysiology of both these disease processes. Typical aeroallergens include house dust mites (HDMs), grass, mould and cockroaches. HDMs have however been identified as the most important indoor aeroallergen affecting allergic patients with asthma and allergic rhinitis in South Africa. One study in the Durban region of KwaZulu-Natal (KZN) found the incidence of HDM allergy among asthmatics to be as high as 95%.

It is known that a number of HDM species are responsible for these allergies, including Dermatophagoides pteronyssinus, D. farinae, Euroglyphus maynei and Blomia tropicalis. One of the most common strategies for treating allergic disease is avoidance of the known allergen. This is however not an option in the case of HDMs because they are found so abundantly in most indoor environments. Immunotherapy specifically aimed at countering a particular species of HDM currently offers the only potential cure for allergies caused by HDM and can comprise either sublingual or subcutaneous therapy. Both options have been found to be effective. In sublingual therapy the patient is given small doses of an allergen under the tongue to boost tolerance to the substance and reduce symptoms, while subcutaneous therapy – or allergy injections - involves the injection of allergens under the skin in order to stimulate the building of immunity.

Identifying the species of HDM responsible for the allergic reaction and then treating the patient accordingly sounds like a straightforward solution, but unfortunately it is not quite so simple. This is largely because conventional skin-prick testing (SPT) panels used in South Africa currently test for Dermatophagoides only, and although B. tropicalis has been described in the tropical and subtropical regions of the country, it is not routinely tested for in any area apart from the Western Cape. Consequently current routine testing methods will not identify patients who suffer from B. tropicalis allergy and the correct immunotherapy will therefore not be ordered for them. This is not an ideal situation as these patients can potentially be cured if a diagnosis of B. tropicalis allergy is made, thus improving their quality of life.

In a recent study, staff in the Division of Paediatric Pulmonology at UP (especially Dr Ashley Jeevarathnum and Prof Andre van Niekerk) set out to determine the significance of B. tropicalis as an aeroallergen in the northern coastal areas of KZN (a tropical environment) and in Johannesburg, where the climate is milder and less humid. The team decided to focus their research on these two areas since B. tropicalis is most abundant in tropical and subtropical regions and they wanted to compare the two settings in respect of the proportion of positive B. tropicalis tests versus positive D. pteronyssinus/D. farinae tests. At that stage no formal study had been done to determine the exact incidence of allergy to this mite in different regions of South Africa. The team’s findings were recently published in the South African Medical Journal (SAMJ) in an article titled ‘Prevalence of Blomia tropicalis allergy in two regions of South Africa’.  

The study was undertaken at two private paediatric practices, one situated at the Clinton Clinic in Johannesburg and the other at Alberlito Hospital in northern KZN. A total of 85 patients between the ages of one and eighteen (50 from northern KZN and 35 from the Johannesburg area), who presented with features of allergic rhinitis and/or asthma were included in the study. All 85 patients had had SPTs for aeroallergens between September 2013 and February 2014.

The team found that there was sensitisation to Dermatophagoides in 40% of children in the Alberlito group as opposed to 22,9% in the Clinton Clinic group – which is not really a significant difference. For B.  tropicalis however, there was sensitisation in 52% of the children in the Alberlito group, as opposed to only 2,9% in the Clinton Clinic group. On further analysis of the patients in the Alberlito group who had tested positive for any HDM, 26% tested positive for B. tropicalis only, 14% for Dermatophagoides only and 26% tested positive for both allergens. In contrast, on analysis of the patients in the Clinton Clinic group sensitised to any HDM, 20% tested positive for Dermatophagoides only and a mere 2,9% tested positive for B. tropicalis. Only one patient in this group tested positive for both B. tropicalis and Dermatophagoides.

Although the study is limited by the relatively small sample size and the relatively short period of time during which it was conducted, the results clearly show that northern KZN has a high incidence of HDM sensitisation. Prof Green and his colleagues strongly feel that if routine testing for B. tropicalis were done in northern KZN, patients who are allergic to it could be given appropriate immunotherapy to improve their quality of life.

Further studies to determine the importance of B. tropicalis in other regions of South Africa, for example in the Western Cape, are already underway and experts are of the opinion that an estimated 40% of allergic patients in the Western Cape could potentially be allergic to B. tropicalis. Prof Green and his colleagues have recommended that more studies be undertaken to ascertain the significance of B. tropicalis as an aeroallergen in other coastal and tropical regions of South Africa, as this would offer a countrywide assessment of the prevalence of B. tropicalis and give an indication of areas in which routine testing should be implemented.