Cockroach, German

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Code: i6
Latin name: Blatella germanica
Source material: Whole insect
Family: Blattellidae
Common names: Cockroach, Roach, German cockroach

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:

Argentinian – Blattaria sudamericana
Asian – Blattella asahinai
Australian – Periplaneta australasiae
Brown-banded – Supella longipalpa/Supella supellectilium
Dusky-brown – Periplaneta fuliginosa
Madeira – Leucophaea madera

Insect

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

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. (1) 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.

The most common of these is the German cockroach. (2) 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.

German cockroach females, unlike most other roaches, carry the egg case (ootheca; a tiny, brown, purse-shaped capsule about 8 mm long and 2 mm wide, containing 30 to 40 eggs) protruding from their abdomen until the eggs are ready to hatch. Then the case is dropped in a secluded location and the eggs hatch within a day; or the eggs hatch while the female is still carrying them. This species produces more eggs and has more generations per year (3 or 4) than other Cockroaches; thus, a troublesome infestation can develop rapidly after the chance introduction of just a few individuals. (3) Moreover, German cockroach appears to survive better than others in cold temperatures. Particularly agile and wily, they often escape predators. This roach is spread by commerce and transportation as well as mass migrations.

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. With their preference for higher temperatures and humidity, American cockroaches are the predominant species in tropical countries, including Taiwan and Brazil. (3, 4)

The Oriental cockroach is black, 3 cm long when full-grown, and has short wings, the wings of the female being only rudimentary. 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. (3)

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.

The German cockroach is particularly omnivorous and widespread. Not only do they adulterate food with their faeces and defensive secretions, but during heavy infestations have been reported to bite humans and feed on food residues on the faces of sleeping humans. These are the most common roaches found in homes, restaurants, hotels, food plants, warehouses, dumps, office buildings, hospitals, retail stores and ships. During the day, these roaches may cluster hidden behind baseboard moulding, in cracks around cabinets, closets or pantries, and in and under stoves, refrigerators and dishwashers. If numbers of roaches are seen during the day, the population is large. German cockroaches usually travel 10 to 12 feet from their harbourage for food and water in kitchens, bathrooms, utility rooms, etc., preferring darkness. Without food or water, adults may die in two weeks, but can live a month with only water. These roaches will move from building to building during the warm summer months. They hitchhike into the home on egg or soft drink cartons, sacks of potatoes or onions, used furniture, beer cases, etc.

Allergen Description

Cockroaches produce potent allergens that are an important cause of asthma. At least 29 allergens have been detected from German cockroach that contribute to asthma, (5, 6) including allergens of molecular weight 92, 80, 67, 48, 36, 27, 25 and 18 kDa. Considerable heterogeneity in the IgE-binding patterns is seen between patients. (7) Although there are common IgE binding components between American and German cockroach, the results of one study showed that there are different IgE-binding components between these insect species. (8) German cockroach was shown to contain novel serine protease activity, which has a direct pro-inflammatory effect on airway epithelial cells. (9)

Allergens characterised to date:

Bla g 1, a 21-56 kDa heat-labile protein. (10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24)

Bla g 2, a 36 kDa heat-stable protein, an inactive aspartic proteinase. (11, 12, 14, 18, 21, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39)

Bla g 4, a 21 kDa protein, a lipocalin (calycin). (11, 18, 24, 40, 41, 42, 43, 44, 45, 46)

Bla g 5, a 22-23 kDa protein, a glutathione-S-transferase. (6, 11, 18, 24, 27, 39, 47, 48, 49, 50, 51)

Bla g 6, Troponin C, a 18-21 kDa protein, a calcium-binding protein. (11, 20, 24, 27, 39, 52, 53)

Bla g 7, a 31-34 kDa protein, a tropomyosin. (11, 20, 24, 39, 40, 54, 55, 56, 57, 58)

Bla g 8, a light chain myosin. (11,)  (59, 60)

Bla g 9, arginine kinase. (24, 61)

Bla g Trypsin, a 35 kDa protein, a serine protease. (62)

Bla g Enolase. (24)

Bla g RACK1, a receptor for Activated Protein Kinase C-like protein.

Bla g Vitellogenin, an apolipophorin. (24, 63, 64)

Bla g TPI, a triosephosphate isomerase. (24)

Bla g GSTD1, a 25 kDa protein, a glutathione-S-transferase. (65, 66, 67)

 

Bla g 1 is an isoallergen as there are several allergenic isoforms. The Bla g 1 isoallergens range in molecular sizes from 21-56 kDa. (25)

Bla g 1 elicits a positive SPT in 30-50% of cockroach allergic subjects. (7, 13)

Molecular cloning of Bla g 1 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). High levels of Bla g 1 were found in Cockroach hindgut and proventriculus. (68) Bla g 1 protein has also been reported to be most prevalent in the midgut. Although Bla g 1 is produced by both sexes and all life stages of the German cockroach, adult females produce and excrete significantly more Bla g 1 in their faeces than males or nymphs, even proportionally to body mass or mass of voided faeces. The concentration of Bla g 1 in faeces of adult females is 6- to 7- and 30-fold higher than in adult males and nymphs, respectively, probably because adult females process more food than do other German cockroaches. (11)

Principal allergens include Bla g 2 and Bla g 4, to which 60-70% of Cockroach-allergic patients make IgE antibodies. Bla g 2 is expressed only by B. germanica, whereas DNA-encoding Bla g 4 is present in P. americana, but is not transcribed into mRNA. (39, 39)

Bla g 2 is one of the most potent Cockroach allergens, causing sensitisation in approximately 50 to 80% of Cockroach-allergic patients. It shows homology to the aspartic proteinase family of enzymes. (25, 28) Bla g 2 appears to be species-specific, having been demonstrated in German cockroach, whereas no similar protein is found in American cockroach, the other principal species in the U.S.A. High concentrations of Bla g 2 were found in Cockroach digestive organs (esophagus, gut, and proventriculus). The allergen appears to function as a digestive enzyme in the Cockroach. (69)

Bla g 4 is a ligand-binding protein (or calycin) that causes IgE antibody responses in 40% to 60% of patients allergic to Cockroaches. (40) Significantly, members of the calycin protein family can cause IgE antibody responses by inhalation or ingestion and are associated with asthma and food hypersensitivity.

Bla g 5 is glutathione-S-transferase (GST). The Bla g 5 has 40-50% amino acid homology to GST of other insects and 28% homology to Der p 8 of Dermatophagoides pteronyssinus. (48) About 70% of sera of German CR allergic subjects contained IgE that bound to the protein.  (25)

Recombinant Bla g 6 (troponin-C) bound IgE in 14-46% of cockroach-allergic subjects. (25)

Among German cockroach-allergic sera, 16.2% have been demonstrated to be sensitive to rBla g 7. (57)

Cockroach-allergic individuals are usually allergic to a combination of Cockroach allergens. For example, in a survey of 106 sera from Cockroach-allergic patients, the prevalence of IgE antibodies to Bla g 1 and Bla g 2 was 30.2% and 57.6%, respectively. (47)

These 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). (70) 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. (71)

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. (72, 73) 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 (27) 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. (74) 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. (75)

Cockroach debris has been found in purchased flour. (76) Wheat flour, Wheat processed mixes, and, to a lesser degree, Corn/Maize meal, have been shown to be contaminated with Bla g 2 allergen. Heating flour at 178 (O)C (350 (O)F) for 30 minutes produced a significant decrease in Bla g 2 allergen levels. (77)

Potential 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 the molecular weight range of 40 to 45 kDa that reacted to most sera from Cockroach-allergic patients with asthma. (78)

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. Analysis of individual serum with each of the Cockroach extracts showed considerable heterogenicity in the IgE-binding pattern. Although the Asian cockroach demonstrated a considerable number of 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. (8)

Bla g 1, a major German cockroach allergen, has been shown to have allergenic cross-reactivity with American cockroach allergen, Per a 1. (15, 79, 80) 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. (46, 81)

Bla g 4, a calycin (lipocalin), belongs to a protein family which contains several important allergens: beta-lactoglobulin, from Cow’s milk, and Rat and Mouse urinary proteins. Although the overall sequence homology between these proteins was low (approximately 20%), members of the calycin protein family can cause IgE antibody responses by inhalation or ingestion and are associated with asthma and food hypersensitivity. (41)

Bla g 5, a glutathione S-transferase (GST), has a sequence identity of 42-51% to the GST-2 subfamily from insects, including Anopheles gambiae and Fruit fly (Drosophila melanogaster). (42) Similarly, GST from Sheep scab (Psoroptes ovis) displays homology to GST allergens isolated from House dust mite (Dermatophagoides pteronyssinus) and German cockroach. (82)

Cloned Bla g 7, a tropomyosin, shares up to 91% amino acid sequence identity with other Cockroach tropomyosins. (48, 83) 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). (84) Vertebrate tropomyosins are considered non-allergenic. (85) 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. (86)

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. (43) 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. (64) 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. (87) 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. (88)

In a study of 46 atopic asthmatic subjects aged 3 to 58 years, skin specific IgE was detected to extracts of cockroach in 70%, to American cockroach whole body and/or German cockroach whole body in 70%, to American cockroach whole body in 63%, to German cockroach whole body in 57%, to American cockroach fecal extracts and/or German cockroach fecal extracts in 63%, to American cockroach fecal extracts in 52%, to German cockroach fecal extracts in 50%, to both American cockroach whole body and German cockroach whole body in 48%, and to both American cockroach fecal extracts and German cockroach fecal extracts in 39%. Subjects with positive skin specific IgE tests to American cockroach whole body and/or German cockroach whole body (70%) were the same individuals who had skin specific IgE to extracts of cockroach (70%), supporting earlier observations of shared interspecies allergens between American and German cockroach whole bodies. (89)

Clinical Experience

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. (25, 90, 91, 92, 93, 94, 95, 96 ) Cockroach allergens (like Mite allergens) have an association with socioeconomic factors and population density. (97)

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. (98) 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. (4)

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. (99,)  (100) Also, recent studies have demonstrated that sensitisation to Cockroach allergens correlates strongly with increased asthma morbidity for adults and children. (101, 102) Yet a sustained decrease in environmental exposure to Cockroach allergen is difficult to accomplish, even after successful extermination of Cockroach populations. (103, 104) 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. (105)

The clinical presentation of asthmatic patients with Cockroach allergy is typically nonspecific. (106) Most commonly, patients have a history of perennial asthma, possibly worse in the winter, (107) 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. (86) Cockroach allergen should therefore be considered in patients with perennial asthma.

Sensitisation to Cockroach may occur early in life, even in utero, (108) 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. (109) 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. (110) 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. (111)

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. (82)

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. (112) 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. (113)

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. (70)

Cockroach allergen has also been implicated in flare-ups of atopic dermatitis. (75)

Importantly, Cockroach allergens may result in allergic reactions as a result of contamination of food, (55) nebulisers, (114) and the workplace. (115) 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. (93)

North America

In the USA, sensitisation and exposure to Cockroach allergens were reported to be associated with increased asthma morbidity, especially among lower socioeconomic groups, including African American and Hispanic populations. The principal domestic Cockroach species are Blattella germanica and Periplaneta americana. (82) The prevalence of Cockroach allergy ranges from 17% to 41% in various studies involving both children and adults. Cockroach-induced asthma occurs whenever substandard housing permits Cockroach infestation. This includes rural and semirural areas, suburbs, and small towns and cities across the United States. (82)

High levels of Bla g 1 or Bla g 2 in house dust have been associated with urban residence, African American race, and low socioeconomic status. (8, 22) A significant association has been reported between housing deterioration and Cockroach allergen levels in kitchens. High bedroom allergen levels were associated with housing instability and ethnicity. (116)

A number of studies from New York reported a high incidence of Cockroach sensitivity in children, and also reported that Cockroach sensitivity was associated with low socioeconomic status. (117,)  (118) Sensitisation and exposure to Cockroach allergen were shown to be associated with increased asthma morbidity in children living in the inner cities of the United States. (82)

Other studies have also indicated that Cockroach allergens are significantly greater in urban populations than in rural groups. (119) In a study of 476 children with asthma from 8 inner-city areas in the United States, utilising skin-specific IgE testing, 36.8% were shown to be allergic to Cockroach allergen, 34.9% to Dust mite allergen, and 22.7% to Cat allergen. Investigation of bedrooms of children found that 50.2% had high levels of Cockroach allergen in dust. Children who were both allergic to Cockroach allergen and exposed to high levels of this allergen had 3 times more hospitalisations a year, compared with the other children, and almost twice as many unscheduled medical visits for asthma per year. They also had significantly more days of wheezing, missed school days, and nights with lost sleep, and their parents or other care-givers were awakened during the night and changed their daytime plans because of the child's asthma significantly more frequently. (120)

Studies have provided the basis to propose threshold levels of Cockroach exposure above which susceptible individuals would be at an increased risk for sensitisation or asthma symptoms. These levels have been defined as 2 U/g and 8 U/g of allergen, respectively. (82)

Studies are reporting a dose-response relationship between exposure to Cockroach allergens and sensitisation. The combination of sensitisation and exposure to Cockroach allergens was reported to be a risk factor for severity of asthma in children from large cities in the United States. (12) In one study, exposure to Bla g 1 levels of greater than 8 U/g in children's bedrooms was strongly associated with increased hospital admission and other parameters of asthma-related morbidity. This study demonstrated a clear relationship between current exposure to Bla g 1 and sensitisation to Cockroach allergen in asthmatic children 4 to 9 years old living in inner-city Baltimore. The best correlation between sensitisation and allergen concentration was found in the bedroom, even though the highest levels of Cockroach allergens were in the kitchen. The proportion of children with a positive skin-test response to Cockroach allergen increased as the level of exposure to Bla g 1 increased, from 32% among children exposed to 1 to 2 U/g to a plateau at 40% to 45% among those exposed to concentrations higher than 4 U/g. (74)

Sensitisation to indoor allergens is associated with increased severity of airway obstruction in elderly subjects with asthma. In a study of an indigent population of subjects aged > or = 60 years in New York City, serum-specific IgE tests demonstrated that 60% of subjects were sensitised to at least 1 allergen, and that Cockroach was the most common allergen to which subjects were sensitised, with 47% displaying an elevated serum-specific IgE level. (121)

In a study of children with asthma, 6 to 17 years of age, recruited from 3 counties surrounding Baltimore city and from 1 practice located within Baltimore city limits, 41% of 339 experienced kitchen Bla g 1 levels of greater than 1 U/g. Among the suburban-rural subgroup, 21% were sensitised to Cockroach, compared with 35% of the city group. Exposure to kitchen Bla g 1 levels of greater than 1 U/g was associated with Cockroach sensitisation. The study concluded that Cockroach allergen exposure might be more common in suburban middle-class homes of asthmatic children than previously thought, and re-affirmed that low-level Cockroach exposure is a risk factor for Cockroach sensitisation. (122) Importantly, environmental data collected from 385 school rooms in 60 elementary schools in southeast Texas showed detectable levels of Cockroach allergen (Bla g 2) in all schools (median 5.5 ng/g), with 10% of rooms over the recommended threshold. (123)

Latin America

In Latin America, a number studies have reported high prevalence of Cockroach sensitisation.

In Brazil, 55% of children and young adults with asthma, rhinitis, or both were reported to have skin-specific IgE to Cockroach allergen.  (5) Similar to the results of studies in the USA, public places, including schools and daycare centres, were identified as sources of exposure to Cockroach allergens. (124) In the metropolitan area of Recife, Brazil, a study of children diagnosed by means of a questionnaire as having asthma found that in the 172 houses studied, 79 children had been exposed to Cockroaches. Asthma was diagnosed by the questionnaire in 31.6% of the exposed group and in 11.8% of the non-exposed group, indicating that exposure to Cockroaches was significantly associated with asthma among the children studied. Blattella germanica and Periplaneta americana were the species found in 96% of the infested houses. (125)

In Caracas, Venezuela, patients attending allergy clinics of 2 medical institutions were skin-tested with 6 Cockroach species extracts for skin-specific IgE, and among the 176 patients, sensitisation to at least 1 Cockroach extract was positive in 83.1% of the atopic patients. The prevalence of sensitisation was higher in patients from lower socioeconomic levels and those attending the public institution. (126)

Similarly in Puerto Rico, the examination of a total of 126 dust samples of mattresses and bedside floors from houses showed that 36.5% of the patient group demonstrated exposures to sensitising levels of Bla g 1. Over 26% of patients were exposed to high levels of Cockroach allergens capable of triggering asthma symptoms. (127)

Europe

Cockroach allergy is less frequent in European than in American children, and also less well characterised. (128) In a French study of predominantly black children (,129) the clinical features of acute asthma attacks differed in children who were sensitive only to Cockroach from those in children with other sensitivities.

Results of a study conducted in Dresden, Germany, suggested that allergic sensitisation to German cockroach was less frequent in asthmatics than in their counterparts in US cities. (107)

In an Italian study in Genoa evaluating the significance of German and American cockroaches in allergic rhinitis, approximately 20% of patients were shown to have skin-specific IgE to Cockroach antigens. (130) In a study of Cockroach allergy in atopic Italian children, 482 children with at least 1 positive skin-specific IgE test to a common allergen, and with personal history of atopic disease, were investigated. Of these children, 61/482 (12.7%) had positive skin-specific IgE to Cockroach extracts, and the prevalence was greater in children living in urban areas. (131) Similarly, sensitisation to Cockroach was tested using a mix of 3 species of Cockroach (Blattella orientatis, Blattella germanica and Periplaneta Americana) on 414 atopic patients in an urban region of Naples; it was found that only 19 (4.58%) were sensitised to Cockroach. The majority of Cockroach-sensitive individuals were males and exhibited perennial respiratory symptoms; 17 of these patients were also sensitised to Dermatophagoides pteronyssinus allergens. (132) In a study in Naples of 317 subjects examined for perennial nasal symptoms that were suspected of being IgE-mediated, researchers used skin-specific IgE tests with commercially available allergenic extracts and an allergenic extract containing the whole bodies of German, Oriental, American cockroaches. Fourteen of 317 subjects were shown to be sensitised to Cockroach allergens. (133)

In a study in Amsterdam, in the Netherlands, Cockroach allergen (Bla g 1) content in the floor dust of 46 homes with recent Cockroach extermination was evaluated; the allergen was found to be present in floor dust from 44% of the homes. Levels up to 3899 ng Bla g 1/g were found. However, only 7 of the 46 adults and only 1 of the 46 children studied had serum-specific IgE antibody to Cockroach. In children without a history of Cockroach infestation of the home, positive specific IgE against Cockroach was found in 16% of those with respiratory symptoms and in 4% of those without. Of the 18 children with serum-specific IgE against Cockroach, only 1 had a history of Cockroach infestation of the home, and 16 also had serum-specific IgE against House dust mite. (134)

In a Portuguese study, the prevalence of Cockroach sensitisation among 155 patients with a mean age of 29 +/- 12 years was studied using skin-specific IgE tests with 4 commercial Cockroach extracts and common inhalant allergens. Skin-specific IgE was found to at least 1 of these 4 extracts in 27 patients: in 26 (96.2%) to Oriental cockroach, in 10 (37%) both Oriental and German cockroach, and in 1 (3.7%) exclusively to German cockroach. Patients sensitised to Cockroach were often 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 better reflect the real prevalence and clinical significance of sensitisation to Cockroach. (135)

Similarly in Norway, in an evaluation of Cockroach’s possible association with IgE-mediated diseases in 100 Norwegian families (426 subjects), only 31 subjects (7.5%) were sensitised (5 monosensitised) to Cockroach. The authors suggested that since Cockroach sensitisation was relatively frequent in Norwegian atopic families, albeit with unclear clinical implications, Cockroach allergy should be considered in atopic subjects with respiratory disease. (136)

Importantly, although cross-reactivity occurs among 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, with ages ranging from 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 homes, mostly Oriental cockroach. (137)

Sensitisation to Cockroach was reported to be high in adolescents and adults aged 17-66 years in the capital of Estonia. In a random sample of 516 subjects, the prevalence of allergic sensitisation was 34.5%; the most prevalent sensitisation (15.5%) was against the German cockroach, particularly among adolescents. (138)

Cockroach sensitisation was reported to be more prevalent and significant in Poland, where in a study of 160 children, Cockroach sensitisation using skin-specific IgE determination was found in 24.3% of the group. Of these, 13% had mild asthma, 26% moderate, and 61% severe. The study concluded that children with Cockroach hypersensitivity have severe asthma more often than children with dust and pollen sensitivity. Class 3 and 4 in specific IgE levels correlated with severity of asthma. The authors concluded that hypersensitivity to Cockroach antigen seemed to influence the course and severity of asthma in children. Bla g 2 antigen was detected in 55.13% of samples with the highest levels found in old houses, without central heating, and in houses with lower income. (139)

A high prevalence of sensitisation to German Cockroach has been reported in Russian studies, including studies of children with allergic diseases. (140) In 124 patients with asthma (50 adults and 74 children), specific IgE to B. germanica were detected in 34% of the examined adults and 63.5% of the children. (14) In a study of patients with atopic asthma, 69.3% of were sensitised to house dust, and in 68.4% of these, IgE antibodies to Cockroach allergens were detected. Patients with atopic asthma who were not sensitised to house dust were found to have sensitisation to B. germanica in 12.2% of cases. (141)

Asia

A number of studies have reflected the importance of Cockroach as an allergen in Turkey. In a study of 216 asthmatic patients from Eskisehir, 29.1% were found to be atopic according to skin-specific IgE determination, of whom only 4.7% were found to be sensitised to Cockroach. (142) However, this low prevalence is contradicted by a number of other studies. In a second study of 206 asthmatic patients, of whom 63% were considered atopic by skin-specific IgE determination, skin-specific IgE to Cockroach was detected in 25.7% of all the asthmatics. The authors concluded that it would be reasonable to include Cockroach allergen in the routine battery of inhalant specific IgE tests, but that the value of this might depend on geographic location. They also suggested that possible cross-reactivity with Mites has to be taken into consideration during the clinical evaluation of subjects with Cockroach sensitivity, especially in a population with high rates of House dust mite allergy. (143)

Cockroach allergen has been reported to be one of the important inhalant allergens in Japan, where 12.6% of adult asthmatics were found to be sensitised, according to serum-specific IgE studies. (144) Periplaneta fuliginosa has been reported to be the predominant Cockroach species in homes in Tokyo. In a study assessing serum-specific IgE antibody in 171 asthmatic children, 16% were positive for P. fuliginosa, 9.9% for B. germanica and 85% for Dermatophagoides farinae. (145)

In Thailand, about 44-61% of atopic patients have been shown by skin-specific IgE determination studies to be sensitised to Cockroach. (146, 147) In a study evaluating Cockroach allergen levels in relation to Cockroach species and their contribution to the high prevalence of sensitisation in the houses of Cockroach-sensitive patients, 6 Cockroach species were identified: Periplaneta americana (American cockroach), Supella longlpalpa, Periplaneta brunnea, Periplaneta australaslae, Neostylopyga rhombifolla, and Blattella germanica (German cockroach). The predominant species was P. Americana, and allergens were detectable in all homes studied, with the highest levels in the kitchen areas. The range of allergen levels in house dust varied from 0.40 to 162.00 microg per g of dust. The median and mean allergen levels in kitchen dust were 59.16 microg and 62.80 microg per g of dust, respectively, while the median allergen level in bedroom dust was only 15.90 microg per g of dust. The German cockroach allergen (Bla g 2) was not detectable in any of the houses. The results were very different from those commonly encountered in Europe and the USA, with American cockroach being the predominant Cockroach and an insignificant prevalence of German Cockcroach. (126)

Cockroach has been reported to be an important allergen in Korea in both urban and rural children, being the 4 (th) most prevalent sensitising allergen, affecting 11.3% of a study group. (148)

American and German cockroach are both common in Taiwan. In a study of 236 asthmatic patients examined for skin-specific IgE using allergen extracts from both American and German cockroaches, 39.4 and 36.4% of asthmatic patients were hypersensitive to American and German cockroaches respectively. Fifteen were allergic only to American cockroach, and 8 to German cockroach. Evaluating 596 asthmatic patients for serum-specific IgE to German cockroach resulted in a finding that 36% of the sera contained specific IgE to German cockroach extract. Eighty-nine sera positive for German cockroach were then further tested for the presence of specific IgE to American cockroach, and 68% were positive. This study demonstrated that there are different IgE-binding components between American and German cockroaches and that although most Cockroach-hypersensitive patients were allergic to both American and German cockroaches, more asthmatic patients were allergic to American cockroaches. (9) A second Taiwanese study suggested that sensitisation to Der f and German cockroach was a critical factor for lower pulmonary function observed in school children with asthma. (149)

Africa

Studies from Africa have also shown a high prevalence of sensitisation to Cockroach. Sensitisation to Cockroach has been reported as an important factor for asthma in Ghanaian children. (150) Similarly in Tunis, according to a prospective study of 105 patients who were investigated for symptoms suggestive of allergy, B. germanica (34%) was the species patients were most frequently sensitised to, followed by B. orientalis (23%) and Periplaneta americana (5%); other Cockroach species affected only 3.8%. (151)

In Lagos, Nigeria, of 202 patients with asthma and 100 non-asthmatic control subjects, 44.6% and 9% had positive skin-specific IgE tests to Cockroach allergen, respectively. Cockroach sensitivity was related to age, duration of asthma, nocturnal asthmatic attacks, frequency of attacks, and the levels of infestation. (152)

In a study in the Ivory Coast of 140 adult and infant subjects with asthma, rhinitis or sinusitis, 30.7% were found to have skin-specific IgE to Cockroach. In asthmatics, it was 16.5%. (153) In Ethiopia, Cockroach (B. germanica) skin sensitisation was more prevalent in rural than in urban children. (154)

Investigation of the prevalence of common allergens involved in bronchial asthma and allergic rhinitis in Qatar, a partly humid and partly desert country, of 1106 adult patients over 12 years of age diagnosed with bronchial asthma and/or allergic rhinitis, 51.4% had a positive skin-specific IgE test. Sensitisation to Cockroach allergen (Bla g 1) was found in 32.2%. (155)

b. Other reactions

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

Compiled by Dr Harris Steinman, harris@allergyadvisor.com

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As in all diagnostic testing, the diagnosis is made by the physican based on both test results and the patient history.