Summary

Although disagreement exists, most schemata place Cockroaches in class Insecta, order Blattaria, suborder Blattoidea, and families Blattidae, Blattellidae, Polyphagidae, Blaberidae, and Cryptocercidae. In addition to German, Oriental and American Cockroaches, the following are important species to consider in connection to allergy:

Insect

An insect, which may result in allergy symptoms in sensitised individuals.

Allergen

Allergen Description

Cockroaches produce potent allergens that are an important cause of asthma. Although there are common IgE binding components between American and German cockroach, the results of studies show that there are different IgE-binding components between these insect species, and this may well apply to Oriental cockroach.

Allergens characterised to date:

Molecular cloning of Bla g 1 of German cockroach has demonstrated a high homology with the major American cockroach allergen Per a 1, as well as with a mosquito protein involved in digestion (ANG12 precursor), and future studies may find this applicable to Bla o 1.

According to studies on German cockroach, Cockroach allergens have been found not only in living Cockroaches, but also in cast skins, egg shells and faeces. The allergens bind to the gastrointestinal epithelium and the contents of the intestinal tract, as well as to the Malpighian vessels (equivalent in function to the kidneys). A study reported that there are major differences between the allergenic components of German cockroach whole body extracts and German cockroach faecal extracts, and that based on the amounts of major allergens (Bla g 1, Bla g 2), German cockroach faeces are a more important source of allergen than the whole body for respiratory allergic diseases. This is likely to apply to Oriental cockroach as well.

Allergic individuals can be affected by Cockroach antigens by various means: inhalation of Cockroach antigens from living quarters – Cockroach allergens have been identified as a potent allergen source in house dust – and by ingestion of allergens due to contamination of foodstuffs, including cereals.

Cockroach aeroallergen particles have similar properties to Mite allergens in that they are relatively large (>10 mm in diameter) and detectable only after disturbance. Although Cockroach allergens are found throughout the house, including in beds, furniture, and carpets, the highest levels are typically in the kitchen, and these levels are perhaps the best indicator of Cockroach infestation in a house. However, the lower levels of allergen found in bedding, on the bedroom floor, and in sofa dust may be more relevant in causing sensitisation. Cockroach allergen may also be found in childcare centres and schools. In a study of 20 day-care centres surveyed for Mite, Cat, and Cockroach (Per a 1) allergens in Tampa, Florida, USA, Per a 1 was detected in all centres in quantities ranging from 8 to 1,806 ng/g of dust. However, other factors may contribute. In a study evaluating the presence of Bla g 1 and Bla g 2 in school environments where asthma prevalence was high, common allergens known to trigger asthma were detected in all. However, the overall allergen levels were low, indicating that other factors, including exposures in the homes of asthmatic patients, may have more relevance to sensitisation and symptoms than school exposures.

Route Of Exposure

Allergen Exposure

Cockroaches are probably the oldest insect in the world and have been found in fossil records. Over 3,500 Cockroach species exist worldwide. Although they are cosmopolitan, they are found mainly in warmer, rich forest environments. In the United States, there are approximately 31 genera and 74 species of Cockroach, the majority having been introduced. Around 50 species of Cockroaches across the world have adapted to live in or around buildings. Most Cockroaches have a flattened, oval shape, spiny legs, wings, and long, filamentous antennae. Immature stages are smaller and have undeveloped wings but resemble the adults in most other respects.

Most household Cockroaches are in the families Blattellidae (German, Brown-banded) and Blattidae (American, Oriental, Smokey-brown). The most important Cockroach species in industrialised countries are the German and the American.

Oriental cockroach is thought to be from Africa or south Russia but has colonised much of the world and become a major household pest in parts of America. It is also sometimes referred to as the "Black beetle" or "Water bug" because of its dark-black appearance and tendency to harbour in damp locations.

It is dark-brown to black, up to 3 cm long when full-grown, and has short, non-functional wings, the wings of the female being only rudimentary. The inner wing folds like a fan and is membranous. The females are more numerous than males and carry the egg cases and deposit them in a sheltered location near or within a food supply at a warm, sheltered spot. It is a relatively sluggish insect, living on filth and travelling along sewage systems into homes, or entering buildings through ventilators, broken foundations, and under poorly fitted doors. It thrives in damp, cool areas such as basements and crawl spaces, mulch, garbage piles and the environs of leaky pipes.

The American Cockroach, P americana is a large Cockroach, up to 5 cm in length, that infests houses, schools, hospitals, and other large buildings. It prefers damp areas such as basements, and may be found around pipes, sewage systems, and drainage systems. It is reddish-brown or mahogany with light markings on top of the thorax. The nymphs are greyish-brown and wingless. The adults may live for up to 18 months. With their preference for higher temperatures and humidity, American cockroaches are the predominant species in tropical countries, including Taiwan and Brazil. It prefers damp areas such as basements, and may be found around pipes, sewage systems, and drainage systems in homes, commercial buildings and greenhouses. Domiciliary Cockroach species tend to spend most of the time hidden from sight and aggregate around dark and humid places, and therefore Cockroach infestation may not be apparent to the patient.

The German cockroach, B germanica is a small Cockroach, growing up to approximately 2 cm in length that is found throughout the world in association with humans. It is unable to survive in locations away from humans or human activity. Often confused with the Asian cockroach, it is long and brownish-tan in colour and has two black parallel lines just behind the head. Adults have wings, but rarely fly. The nymphs are darker and wingless, with a single light stripe, separating two black bands, running about halfway down the middle of the back.

Cockroaches eat almost everything, from glue in furniture to drainpipe waste to other insects. Breeding takes place in kitchens, bathrooms, and walls. Radio and television sets may become infested, as well as the insulation of refrigerators and sometimes ovens. Domiciliary Cockroach species tend to spend most of the time hidden from sight and aggregate around dark and humid places, and therefore Cockroach infestation may not be apparent to the allergy patient (although an unpleasant odour may be a sign of an infestation). For every Cockroach that is seen, twenty may be waiting for darkness in order to become active.

Oriental cockroaches are more sluggish than the other common Cockroaches, travelling mainly through plumbing and foraging mostly at or below ground-level structures. The most common areas in which to find these Cockroaches are basements, crawl spaces, other areas between the soil and foundation, underneath sidewalks, in sewer pipes, in floor drains, under sinks or in any other damp, cool area in the house. They are usually not found in cupboards, on walls or on upper levels of buildings. They occur outside during warm weather, especially around garbage or mulch, and during cool periods may migrate in masses indoors. They can be found outdoors and in unheated buildings during the winter as well, because of their tolerance of cooler temperatures. These insects seem to prefer decaying organic matter and are considered the filthiest of the house-infesting roaches.

Early medical studies on Cockroach did not pay much attention to Oriental cockroach or its distribution. In an early study evaluating the prevalence of Cockroach species in Rostock, East Germany, the German cockroach was found to be the prevalent species. But Oriental cockroach also occurred and, in one case, Periplaneta australasiae. American cockroach was said to be “occasionally introduced from warmer regions of the globe via containers.” A low prevalence of Oriental cockroach was reported in Potsdam, Germany, where German cockroach was found in 2,644 properties; Oriental cockroach in 20 properties, and both were found in 70 properties. The authors particularly noted that infestation with Cockroaches increases with urbanisation. In contrast, the species most common in Poland were found to be German cockroach and Oriental cockroach. Recent studies have indicated an increase of Oriental cockroach in human habitats. The frequency at which Oriental cockroach was observed in outdoor habitats may indicate that this species sometimes spreads to new areas without human assistance.

Clinical Relevance

a. IgE-mediated reactions

Cockroach may commonly induce symptoms of asthma, allergic rhinitis, allergic conjunctivitis and allergic dermatitis in sensitised individuals. These are the most common ailments attributable to Cockroach infestation of housing and are important public health problems. Cockroach allergens (like Mite allergens) have an association with socioeconomic factors and population density.

Cockroach allergy was first reported in 1964 in a study demonstrating that positive skin-specific IgE responses to Cockroach allergen were found in 44% of 755 allergy clinic patients living in New York, where German and American cockroach are the prevailing species. Significantly, 13% of patients who would have been considered nonatopic were sensitised to Cockroach allergen alone. Subsequently, Cockroach allergy has been reported to be associated with asthma in many regions of the world, including Taiwan, Japan, Thailand, Singapore, Costa Rica, Puerto Rico, India, South Africa, and parts of Europe.

Of 150 atopic asthmatics studied in Madrid, Spain, for combined Oriental and German cockroach-specific IgE antibodies, approximately 15% were sensitised to Cockroach. Twenty-two of 61 patients who had a positive history of Cockroach exposure had positive skin-specific IgE tests, and only 3 of 89 patients who had no history of exposure were shown to have skin-specific IgE to Cockroach. Of 25 patients with Cockroach-specific IgE, 23 were shown to have specific IgE antibodies against Oriental and German cockroach.

In a study in Naples of 317 subjects examined for suspected IgE-mediated perennial nasal symptoms, researchers used skin-specific IgE tests with commercially available allergenic extracts and an allergenic extract containing the whole bodies of German, Oriental, and American cockroaches. Fourteen of 317 subjects were shown to be sensitised to Cockroach allergens.

In a Portuguese study of the prevalence of Cockroach sensitisation among 155 patients, researchers used skin-specific IgE tests with 4 commercial Cockroach extracts and common inhalant allergens. Skin-specific IgE to at least 1 of these 4 extracts was found in 27 patients: in 26 (96.2%) to Oriental cockroach, in 10 (37%) both to German cockroach and Oriental cockroach, and in 1 (3.7%) exclusively to German cockroach, with no significant concordance between these results. Patients sensitised to Cockroach often were sensitised to other indoor allergens, namely House dust mites, animal dander and fungi. Notably, the study reported on the heterogeneity of the positive skin responses, which suggested the incomplete standardisation of Cockroach extracts. Complete standardisation would help reflect the real prevalence and clinical significance of sensitisation to Cockroach.

In a study in Caracas, Venezuela, of 176 patients evaluated by skin-specific IgE tests with 2 mite and 6 Cockroach extracts (Periplaneta americana, Periplaneta fuliginosa, Periplaneta australasiae, Blattella germanica, Blattella orientalis, and Supella longipalpis), sensitisation to at least 1 Cockroach extract was shown in 83.1% of the atopic patients. An increased sensitisation rate to Cockroach allergens was observed in patients from lower socioeconomic levels and those attending the public clinic as opposed to the private one.

In Tunis, Africa, a prospective study of 105 patients investigated for symptoms suggestive of allergy showed that German cockroach (34%) was the species patients were most frequently sensitised to, followed by Oriental cockroach (23%) and American cockroach (5%); other Cockroach species affected only 3.8%.

In a Dominican Republic study of 51 atopic children with asthma and/or allergic rhinitis, skin-specific IgE tests were used, with an extract mix of 3 Cockroach species (German, American and Oriental). Among the subjects, 16% were found to be sensitised to the Cockroach mix. Sensitisation to Cockroaches was associated with housing quality.

Importantly, although cross-reactivity occurs between Cockroach species, studies have demonstrated that individuals may be sensitised to a combination of species of Cockroach. A study was conducted on 171 urban patients with rhinitis and asthma, aged 7 to 68 years, in Madrid, Spain, to assess skin test reactivity and specific IgE antibody reactivity to pollen and Cockroach extracts. It was found that 90.5% were atopic, that 66.5% were pollen-allergic, and that 25.7% were sensitised to Cockroach. Skin-specific IgE was demonstrated to Oriental cockroach in 37 (21.6%), to American cockroach in 20 (11.6%), to German cockroach in 19 (11.1%) and to German cockroach faecal extract in 5 (2.9%). Three (1.7%) patients were sensitised to Cockroach alone. All had perennial rhinitis and/or asthma. Eighteen (10.5%) patients had serum-specific IgE to Oriental cockroach, 13 (7.6%) to American cockroach, and 6 (3.5%) to German cockroach. Eighty (46.7%) patients had visual evidence of Cockroach infestation in their home, mostly Oriental cockroach.

Most research has focussed on German and American cockroach, but as these 3 species are closely related, many parts of these studies are applicable to Oriental cockroach. But clinicians will need to consider the prevalence of Oriental cockroach as compared to German and American cockroach to fully appreciate the Oriental cockroach’s role. This may be difficult, however. Compared to those on German cockroach, very few prevalence studies have been done on Oriental cockroach specifically. But in many studies it appears that the 2 are commonly present together, although the ratio may vary considerably. See also German cockroach for more information.

A causal relationship between Cockroach allergy and asthma has been demonstrated by bronchial challenge studies, and early, late-phase, and dual bronchoconstriction after inhalation have been shown. (50) Also, recent studies have demonstrated that sensitisation to Cockroach allergens correlates strongly with increased asthma morbidity for adults and children. Yet a sustained decrease in environmental exposure to Cockroach allergen is difficult to accomplish, even after successful extermination of Cockroach populations. Cockroach allergen levels could be reduced by 80% to 90%, but in many homes allergen levels remain above the proposed threshold of 8 U/g of dust.

The clinical presentation of asthmatic patients with Cockroach allergy is typically nonspecific. Most commonly, patients have a history of perennial asthma, possibly worse in the winter, without a clear history of onset of symptoms on exposure to Cockroaches. Although some patients may be exclusively allergic to Cockroaches, sensitisation is usually to multiple indoor and/or outdoor allergens. Asthmatic subjects with Cockroach allergy have been reported to have longer durations of asthma, and a higher proportion are steroid-dependent, suggesting a more severe disease, compared with patients allergic to Ragweed. Cockroach allergen should therefore be considered in patients with perennial asthma.

Sensitisation to Cockroach may occur early in life, even in utero, and exposure to Bla g 1 or 2 Cockroach allergen at 3 months of age was reported to predict allergen-specific lymphocyte proliferative responses at a median of 2 years of age. In 196 (50 female/146 male) children less than 3 years of age with infantile asthma (infantile asthma was defined as 3 or more episodes of wheezing in a child less than 3 years of age), 45% of the infants and children tested had at least 1 positive skin test. Twenty six percent (51/196) were skin test-positive to Cockroach. Among 49 children less than 1 year of age, 28.5% were positive to Cockroach. Allergy to Cockroach and other indoor allergens may be a significant contributor to infantile asthma in a rural setting. A study stated that Cockroach allergen exposure was a significant predictor for recurrent asthmatic wheezing, and that therefore exposure to Cockroach allergen early in life might contribute to the development of asthma in susceptible children.

Cockroach may be the only sensitising allergen in many young inner-city children. Exposure to Cockroach allergens in the first 3 months of life has been associated with repeated wheezing and asthma.

In a study evaluating recurrent wheezing in 63 children younger than 4 years of age, 15 (23.8%) had Cockroach allergen sensitivity, compared with only eight patients (12.7%) who had specific IgE to Dust mite allergen. The youngest patient with a positive reaction to Cockroach allergen was 6 months old. Nine children younger than 4 years of age (14.3%) were monosensitised to Cockroach allergen, in contrast to 3 children (4.8%) who were monosensitised to House dust mites.

In a study of inner-city children not previously identified as atopic, more than a third showed sensitivity to at least one allergen, and although dust mite was the most common allergen to which the children were sensitised, Cockroach sensitivity was the only allergen that correlated significantly with previous episodes of wheezing.

Early sensitisation is supported by a study which demonstrated that exposure to Cockroach allergens in the first 3 months of life correlated with the development of repeated wheezing in the first year. The correlation between levels of Bla g 1 or Bla g 2 greater than 0.05 U/g of dust in the family room and repeated wheezing continued to be significant after adjustments for socioeconomic factors, such as income and race.

Cockroach allergen has been documented to be significant in causing allergic conjunctivitis. In a Thai study, 445 patients with a history of itching, foreign body sensation, lacrimation and red eyes, the majority of the patients had perennial allergic conjunctivitis. Common allergens causing sensitisation were House dust mites, house dust, Cockroaches, and grass pollen.

Cockroach allergen has also been implicated in flare-ups of atopic dermatitis.

Importantly, Cockroach allergens may result in allergic reactions as a result of contamination of food, nebulisers, and the workplace. Affected parties would include laboratory researchers, farmers, bakers, dockers, maintenance people and cleaners, mill workers, and others in any area where Cockroaches are allowed to breed, or exposed to any Cockroach-contaminated object. For example, 2 asthmatic children experienced life-threatening exacerbation of their symptoms after the use of a nebuliser, which was found to be contaminated with both Bla g 1 and Bla g 2. The nebuliser provided an opportunity for allergen exposure directly into the lung’s small airways.

Workers occupationally exposed to grain dust have a high prevalence of respiratory symptoms, and although sensitisation to cereal flour is common, Storage mites, tenebroids, and Cockroaches as stored-grain pests may be responsible. In a study, 50 grain workers were selected for in vivo diagnostic tests with 9 genera of mites, Tenebrio molitor and Blatta orientalis. Of the study group, 36% were sensitisated to Oriental cockroach.

b. Other reactions

Cockroaches can contaminate food with certain microorganisms that result in food poisoning, dysentery, or diarrhoea.

Cross-Reactivity

An extensive cross-reactivity among the different individual species of the genus could be expected.

For example, in an American study, allergens of 3 common Cockroach extracts, crude whole body extract of the American cockroach (CA), crude whole body extract of the German cockroach (CG), and crude whole body extract of the Oriental cockroach (CO), were studied using sera of Cockroach-allergic asthmatics (10 from Chicago [C group], and 6 from Lexington, Kentucky [L group]). Results were then compared with sera of control subjects with asthma. Qualitative differences in protein bands were noted among CA, CG, and CO in laboratory studies. Two to 12 allergenic bands of variable molecular weights from 14 kDa to greater than 116 kDa were identified by 13 of 16 individual sera from cockroach-allergic patients in the case of all 3 extracts. In total, CA demonstrated 55 bands; CG, 58 bands; and CO, 51 bands. Allergenic bands of CA were identified by 6 sera of the C group and 1 serum of the L group, whereas bands of both CG and CO were noted by 9 sera of the C group and 4 sera of the L group. All 3 species had an allergen band in molecular weight range of 40 to 45 kDa that reacted to most sera from Cockroach-allergic patients with asthma.

Similarly, whole-body extracts of the Asian cockroach (Blattella asahinai) and the 3 main domestic Cockroach species, German, American, and Oriental, were compared using an IgE serum pool from 4 German cockroach-sensitive individuals. The Asian cockroach shared allergenic activity primarily with the German cockroach and to a lesser extent with either the American or Oriental cockroach. Analysis of the whole-body German cockroach extract and IgE serum from individuals sensitive to German cockroach revealed 8 allergenic components with apparent molecular weights of 92, 80, 67, 48, 36, 27, 25 and 18 kDa. Five components could be identified in the whole-body extract of the Asian cockroach, corresponding to apparent molecular weights of 92, 67, 48, 40, and 32 kDa. Analysis of individual serum with each of the Cockroach extracts showed considerable heterogenicity in the IgE-binding pattern. Although the Asian cockroach demonstrated considerable cross-reacting allergenic components to German and relatively fewer cross-reacting allergenic components to either the Oriental or American, it is too early to establish genus- or species-specific Cockroach allergens.

Per a 1, a major American cockroach allergen, has been shown to have allergenic cross-reactivity with German cockroach allergen, Bla g 1. Molecular cloning of Bla g 1 demonstrated a 66-70% amino acid sequence identity with Per a 1, as well as homology to a mosquito protein involved in digestion (ANG12) and to mitochondrial energy transfer proteins. To date, studies have not examined the relationship between Bla o 1 and these 2 allergens.

Cloned Bla g 7 from German cockroach, a tropomyosin, shares up to 91% amino acid sequence identity with other Cockroach tropomyosins. Similarly, American cockroach tropomyosin has been reported to have high homology (80% identity) with other arthropod tropomyosins but less homology with vertebrate ones (50% identity).

Vertebrate tropomyosins are considered non-allergenic. In a study evaluating 4 species of Cockroaches that reside in Korean homes, cross-reactive allergenic components of the Dusky-brown cockroach (Periplaneta fuliginosa) were demonstrated with German cockroach and House dust mite, and found to be identical with that of American cockroach tropomyosin (a 98.5% sequence identity). Native tropomyosin inhibited the binding of IgE to P. fuliginosa, B. germanica, and D. farinae extracts by 65, 52, and 39%. The study concluded that tropomyosin was a major allergenic component accounting for the cross-reactivity between Cockroaches and Dust mites.

Extensive cross-reactivity has also been demonstrated between tropomyosin found in Shrimp (Pen a 1) and that in other crustacean species, House dust mite and German cockroach. At least 80% of Shrimp-allergic subjects are sensitised to the major allergen identified in Shrimp, the muscle protein tropomyosin, which is also an important allergen in other crustaceans such as Lobsters, Crabs and mollusks, as well as other arthropods such as House dust mites and Cockroaches. Based on amino acid sequence similarity and epitope reactivity, it has been reported that Lobster tropomyosin has the strongest and Cockroach the weakest cross-reactivity with Shrimp but that the clinical relevance of this needs to be determined. Positive skin-specific IgE responses to Cockroach may be related to positive skin IgE responses to Mites or Storage mites, probably due to cross-reactivity.