Cockroach Allergy

Cockroaches are now recognised as being important indoor allergens, along with housedust mites and domestic pets.  Cockroach allergy is common in South Africa, particularly at the coast.  In the Durban area, cockroach allergy is present in 80% of asthmatic children.  Exposure to cockroaches is a risk factor for hospital admission with asthma in patients living in poor socio-economic circumstances.  In South Africa cockroaches affect homes across the social spectrum.  A recent study demonstrates that 40% of patients in Natal and the Western Cape who are allergic to one or more inhalant allergens are sensitised to cockroach.  The corresponding figure for the inland highveld is 32-35%.

What are the allergens?
The cockroach allergens are associated with proteins found in the body of the cockroach, in it’s saliva, it’s remains and dried faecal matter.  The highest levels of allergen are found in kitchens.  In South Africa, both the German cockroach (Batella germanica, Bla-g;1) and the American cockroach (Periplaneta americanus) are found.

It is possible to measure the antigenic levels of cockroaches in homes using commercially available ELISA laboratory tests.  The highest levels of allergen are found in kitchens.

What are the clinical effects?
Cockroach antigens are believed to play a role in the ongoing airway inflammation in certain asthmatics.  Asthma attacks result in high rates of emergency room visits, hospitalisation, periods of breathing difficulty, missed school days and sleep-deprived nights.  The role of cockroach allergy in perennial rhinitis is, as yet unclear.

How is cockroach sensitivity diagnosed?
A diagnosis of allergy to cockroaches may be confirmed using the CAP RAST test on a small blood sample sent to a laboratory, or by using a skin prick test.

It is recommended that patients allergic to cockroach are also tested with a panel of other indoor allergens (e.g. housedust mites, dogs, cats and moulds).  This is because many patients with cockroach allergy are also allergic to other allergens.  In particular, a recent study in South Africa has shown that if the patient is allergic to cockroach then there is a very high chance of simultaneous sensitisation to House Dust Mite (86%), Bermuda grass (64%), Timothy grass (79%), various weeds (79%), various moulds (93), and dog dander (71%).  In USA, a recent study has shown that 37% of inner-city children were allergic to cockroaches, 35% to House Dust Mites, and 33% to cats.  The study showed that 50% of the rooms had high levels of cockroach allergen, compared with 9.7% with Dust Mite antigen, and 12.6% with cat allergen.

What is to be done?
Patients who have positive allergy tests to cockroach allergens should actively take steps to avoid exposure to cockroaches in their homes and workplace.

Cockroaches are very hardy and resistant creatures.  Crevices and possible portals of entry for cockroaches into the home should be sealed off.  Fumigation should be arranged when numbers of cockroaches are identified in a home.  Regular cleaning of cupboards and surfaces is essential.  The covering of food and the sealing of garbage is also very important, as well as washing plates and dishes promptly.

Copyright: Allergy Society of South Africa.
 Endorsed by ALLSA

This information sheet is obtainable from:
ALLSA
P.O. Box 88
Observatory, 7935
Cape Town,
R.S.A.

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