Asthma, Hayfever and Allergy – Cockcroach Allergy in Durban

Brief Communication

AI Manjra MB ChB (Natal) FC Paed (S.A.), Ruth Prescott BSc (Allergology Unit, UCT), PC Potter MB ChB (UCT) FC Paed (S.A.) MD (UCT)

Cockroaches have become increasingly recognised as important components of house dust allergens causing allergic sensitization. Cockroach allergy was reported to cause allergic reactions by Bernton and Brown in 1964 in a study that demonstrated that 40% of their asthmatic patients reacted on skin prick testing to cockroach extract. Many subsequent studies have identified the cockroach as an important indoor allergen, responsible for causing asthma in urban inner city dwellers.

In a study by Kang in Chicago, USA, on a group of 592 asthmatics it was demonstrated that more than 60% were allergic to cockroaches. Bronchial provocation testing in patients with cockroach allergen demonstrated reactively in 80% of patients. When compared with asthmatics in general they found that cockroach sensitive asthmatics had a more severe type of asthma, required higher corticosteroid usage and that more than 90% of these patients had multiple hospital admissions for acute asthmatic attacks. Kang et al have demonstrated in many other studies the aetiologic role of cockroaches in asthma. Pllart and Gelber in two separate studies in Charlottesville, Virginia, Atlanta studied the epidemiological trends in these patients. They showed that both sensitization and exposure to cockroaches are major risk factors for hospital admission with asthma, especially in patients living in poor social circumstances.

Cockroaches have also been reported to cause asthma in other parts of the world e.g. Central America, Asia and South Africa. In a study performed in Durban in the 1970s Fraser demonstrated that 30% of asthmatics presenting at Addington Hospital reacted to cockroach allergen on skin prick testing.

Cockroach Allergens

There are many different species of cockroaches but only three have been implicated in the pathogenesis of asthma. These are the American, German and Oriental cockroaches, Periplaneta Mericana, Blatella germanica and Blatella orientalis respectively. The important cockroach allergens have been identified using immunochemical techniques. They are designated Bla g I, Bla g II and Per a I. Bla g I is a Be. Germinica allergen and 30-40% of cockroach allergic patients have serum IgE to Bla g I. Bla g II is a specific blatella allergen and 60-80% of CR allergic patients have specific IgE to Bla g I. Per a I cross reacts with Bla g I. Its quantification using monoclonal antibodies may indicate total allergen load in our area since it is a common allergen shared by important cockroaches associated with asthma.

Aims of the study

Durban is a coastal city with a warm humid climate conducive to mite and cockroach infestation. It is well known that Durban has a heavy cockroach infestation. The only published data to date on cockroach allergy in Durban was a study conducted by Fraser in 1979. We therefore studied the prevalence of cockroach allergy and environmental contamination in a prospective trial in Durban. Our aims were:-

1. To assess the level of cockroach sensitisation in Durban asthmatics.
2. To determine the presence of cockroach allergen in the homes of cockroach sensitive asthmatics using immunochemical methods.
3. To assess which assay is most suitable for local environmental surveys.

Methods

Skin prick tests were performed on 70 asthmatic children randomly selected from our practice. The skin test extract used was the Dome Hollister Stier extract. The mixed cockroach extract consisted of extracts from B germanica, orientalis and p. Americana. Skin prick testing was performed in a standardised manner with the following extracts: mite, grass, pollen, zea mays, cat, dog, bermuda grass pollen, moulds, tree pollen, weed pollen, and mixed cockroach extract. A wheal diameter of greater than 5 mm was regarded as positive.

Dust was collected from the homes of mite and cockroach sensitive asthmatics using a vacuum cleaner over 1 m squared in the patients’ bedroom. The dust was collected from the bedroom floors of twenty two patients’ homes and dust samples was sent to the Allergology unit, U.C.T. Medical School for immunochemical assays. The allergens Bla g I, II and per a I were measured using monoclonal antibodies. The assays were performed using the method described by Schou et al and the Bla-g-I antibodies were purchased from Dr Martic Chapman (USA).

Results

The skin prick tests were positive to the mixed cockroach allergen extract in 29 of the patients tested (table I). This constituted 41% of patients. Skin test reactively to house dust mites was demonstrated in 95% of patients. Cockroach sensitivity is thus the second most common reactive allergen on skin prick testing in Durban area.

Allergen Assay

Bla g I levels were undetectable in 6 (27%) homes and found to be moderately high in 15 (68%) homes. It was very high in one home. Bla g II levels were undetectable in the majority of homes studied, i.e. 18 (81%) and detectable only in 4 (18%) homes studied (Figure 1). These were six homes in which Bla g I levels were undetectable but had measurable levels of Per a I whereas 16 homes had detectable levels of Per a I and Bla g I. Per a I levels (ng/ml) on fig. 1 are shown in ng/ml, and can be converted to ug/g dust by multiplying by a factor of 0.30.

TABLE I : Skin Prick Test on a Atopic Asthmatic Children in Durban

Allergen		% Positive

House dust mite		 95%
Cockroach		 41%
Cat			 22%
Bermuda grass		 14%
Dog			  7%
Moulds			  4%




TABLE II:  CR Allergen Levels     n = 22

Levels						Number		%

Bla I    <0.02 (undetectable)		       6		27.3
0.2  - 5				      15		68.2
>5					       1		 4.5

Bla II    <0.02			  	      18		81.8
0.2  - 5				       4		18.2
>5					       0		 ---

Discussion

Our study has shown that cockroach allergy is the second most common allergy in asthmatic children following house dust mite allergy in Durban.

There are significant levels of Per a I allergen in the homes of our cockroach sensitive asthmatic patients. Our data shows that Per a I is detectable in all the homes that we studied. The low and undetectable lows of Bla g I suggests that blatella germanica is a less important allergen of indoor house dust. The very high levels of Per a I in some homes suggests that other species of cockroaches such as Blatella orientalis or other species may also be contributing to the total allergen load. Measuring Per a I level is a useful measurement since it quantifies the total allergen load and is not a species specific allergen.

Considering the studies of Kang et al and our studies it is apparent that exposure to cockroach allergens it contributes to the pathogenesis of asthma in our patients. Their observation that cockroach sensitive asthmatics are usually steroid dependent and experience severe symptoms must be kept in mind when treating cockroach sensitive asthmatics. These patients often require frequent hospitalisation for acute asthma. Thus prophylactic asthma therapy and environmental control needs to be aggressively instituted in these patients.

Our study also has other important therapeutic implications. When considering immunotherapy for patients with mite sensitive allergic rhinitis it is important that cockroach allergy be excluded in the Durban area. Immunotherapy may fail if measures are not introduced to reduce exposure to cockroach allergen.

In practice therefore, it may not be appropriate to desensitise against house dust mites for nasal allergy if the patient has a concomitant cockroach allergy. Avoidance measures that are used for house dust mite reduction also help with reducing cockroach exposure. However the use of fumigation techniques and insect killer sprays must be combined with house dust mite avoidance protocols, in patients with cockroach allergy.

One major drawback of our study was that we measured cockroach allergen levels in the patients bedrooms. Levels have been found to be highest in kitchens in other studies. This needs to be taken into account in future studies.

Our results also differs from Pollart et al study in that cockroach infestation and sensitivity in their study affected mainly poor communities. In our study, cockroach allergy was shown to affect homes across the spectrum.

We therefore suggest that doctors practising in areas with a heavy cockroach infestation carefully look for cockroach allergy in their asthmatic patients since this has important therapeutic implications. We also suggest that skin test kits in the Durban area should have the cockroach mix extract as part of the standard kit. If patients are unsuitable for skin testing, RAST (Pharmacia) can be performed and is available from all commercial laboratories.

In conclusion, cockroach allergy is a problem in the Durban area and more detailed studies need to be performed to quantify the extent and significance of the problem.

References