Cockroach, German
Summary
The German cockroach is found in countries with temperate climates and can be present in a wide range of indoor urban locations including food establishments, hospitals, nursing homes, households and hotels, feeding on discarded human food. Exposure to cockroach allergens and sensitization has been described across several continents. The main sources of cockroach allergens are cockroach saliva, feces, eggs and shed skins which can form components of dust. Inhalation of cockroach allergens in dust is the main route of exposure and can lead to the development of asthma and allergic rhinitis. Studies have shown that children who are skin-test positive to cockroach allergens are likely to have more hospital visits, suffer more wheezing and miss more school days. If children’s bedrooms have high levels of cockroach allergens, they are approximately three times more likely to be hospitalized due to their asthma symptoms compared children who were skin-test negative. Cross-reactivity is possible in individuals who are sensitized to German cockroach allergens. Cross-reactivity could be seen with the American cockroach allergens, proteins present in cow milk and the urine of rats and mice, ectoparasites (e.g. sheep scab mite and house dust mite), and shellfish. In terms of treatment, the use of immunotherapy for cockroach allergy is promising based on the results published from a small number of clinical trials, but additional research is needed to identify the key allergenic components in cockroaches. Preventative measures focus on thorough and effective cockroach eradication strategies.
Epidemiology
Worldwide distribution
Exposure to cockroach allergens and sensitization has been described across several continents. A range of prevalence rates have been reported for cockroach allergy in the USA from 17% to 41%. In Poland, it is estimated that a quarter of children who suffer from asthma are sensitized to cockroaches and the majority of their homes had measurable quantities of cockroach allergens. An association was also noted between children with more severe asthma and cockroach allergy.
Cockroach allergens have been found in households in France. In China, cockroach allergens have been found in 11% to 98% of dust samples collected from nine cities.
Risk factors
Exposure to cockroaches is associated with cockroach allergy and related respiratory clinical signs. A major risk factor for developing asthma in people living in low-income urban areas is sensitization to cockroach allergens.
Pediatric issues
Despite adhering to guidelines for managing asthma, it has been shown that children who live in cities can continue to have severe symptoms of asthma which can be attributed to exposure to cockroach allergens. Cockroach allergens have been identified as having a key role in the increased risk of developing asthma within urban populations. In addition, exposure and sensitization to cockroach allergens are responsible for increasing the morbidity and severity of asthma compared to other household allergens such as dust mites and pets. However, mouse allergens have also been linked to poor clinical outcomes for patients with asthma, and exposure to both cockroach and mouse allergens is common.
Air pollution is another contributing factor with studies highlighting that exposure can lead to an increased risk of allergy sensitization, wheezing in children and asthma. Furthermore, prenatal exposure to cockroach allergens is linked to an increased risk of cockroach sensitization and this can be exacerbated by exposure to non-volatile polycyclic aromatic hydrocarbons. In summary, air pollution contributes to cockroach allergen sensitization and associated clinical signs. The molecular understanding for this is currently unknown.
Route Of Exposure
Main
The main route of exposure to cockroach allergens is inhalation. Inhalation of cockroach allergens from house dust can be found on floors and carpets in cockroach-infested households.
Secondary
With an increasing trend in consumption of edible insects such as cockroaches, it has been proposed that the prevalence of insect food allergy may increase but current literature on cockroach allergy is focused on inhalation of allergens.
Clinical Relevance
Allergic rhinitis
Cockroaches are one of the most significant sources of allergens in indoor environments which can cause IgE sensitization and result in allergic rhinitis.
Asthma
Exposure to cockroach allergens can lead to the development of asthma. Cockroach sensitization has been shown to be associated with environmental exposure to cockroaches. There is a strong link between asthma in children and young adults who live in urban environments and sensitization to cockroach allergens.
The National Cooperative Inner-City Asthma Study (NCICAS) reported a relationship between exposure to cockroach allergens and sensitization in children with asthma. Furthermore, a meta-analysis using data from studies published from 2000 to 2013 highlighted the association between exposure to cockroach allergens and more severe asthma symptoms, particularly in those who are sensitized to cockroach allergens. Studies have shown that children who are skin-test positive to cockroach allergens are likely to have more hospital visits, suffer more wheezing and miss more school days, and if their bedrooms have high levels of cockroach allergens, are approximately three times more likely to be hospitalized due to their asthma symptoms compared children who were skin test negative.
Other diseases
Cockroaches are capable of transmitting a range of food-borne microorganisms when they come into contact with food via their cuticle or by ingestion and excretion or regurgitation. This can lead to gastrointestinal symptoms such as vomiting, abdominal cramps, diarrhea, dysentery and if untreated can lead to complications (e.g. intestinal perforations and septicemia).
Diagnostics
Environmental source
The main sources of cockroach allergens are cockroach saliva, feces, eggs and shed skins.
Main methods
Previously, exposure to cockroach allergens was centered on assessing settled dust in low-income urban households. However, other indoor environments such as schools, hospitals and suburban households, nursing homes and hotels have shown to detectable levels of cockroach allergens. The presence of cockroach allergens in the bedroom (bed or from the floor) is associated with allergen sensitization and asthma. It is thought that the cockroach allergens found in bedding is due to passive transfer of allergens from floor dust to the bed by the persons occupying the bedroom.
Measures
The method used to measure the level of cockroach allergens in an environment involves collecting dust from air filters. The polytetrafluoroethlyene (PTFE) filters with pumps can be placed in various locations in the building. Researchers in one study aimed to collect 5 mg of dust which required sampling to take place over seven days using pumps with a flow rate of 10-15 liters per minute.
Prevention And Therapy
Allergen immunotherapy
Currently, the use of immunotherapy for cockroach allergy is promising based on the results published from a small number of clinical trials. However, one of the limiting factors researchers are faced with is the absence of standardized cockroach extracts. The future use of immunotherapy requires additional work to identify the key allergenic components in cockroaches to provide effective therapies.
Prevention strategies
Prevention is centered on pest management strategies to stop and remove cockroaches from indoor environments which will subsequently minimize exposure to cockroach allergens found in dust. This is a strong recommendation to reduce exposure and reduce asthma morbidity. The level of allergen reduction is dependent on the thoroughness and effectiveness of cockroach eradication methods. Cockroach allergy testing when investigation allergic respiratory disease is important to be able to educate patients (and/or caregivers) and incorporate cockroach elimination management strategies in their homes to potentially alleviate asthma symptoms in light of positive results.
Cross-Reactivity
Bla g 1
A key German cockroach allergen, Bla g 1 has demonstrated allergenic cross-reactivity with Per a 1, an American cockroach allergen. Bla g 1 and Per a 1 share approximately 70% of their amino acid identity. In addition, Bla g 1 has a primary structure homologous to the ANG12 protein which is produced post blood meal by female mosquitos and microvilli-like proteins common to other insects.
Bla g 4
Bla g 4 is a calycin which belongs to the family of proteins known as lipocalins and this group of proteins includes some major allergens for example, beta-lactoglobulin found in cow milk, and proteins found in urine excreted by rats and mice. The homology of the amino acid sequence for these proteins is relatively low of around 20%. However, calycin proteins are known to cause IgE antibody responses when inhaled or ingested and for this reason are linked to asthma and food allergies.
Bla g 5
Bla g 5 is a glutathione S-transferase (GST) sharing an amino acid sequence identity of approximately 42-51% to the GST-2 subfamily from insects. Likewise, the sheep scab mite, Psoroptes ovis and house dust mite, Dermatophagoides pteronyssinus share homology with the GST allergen found in the German cockroach.
Bla g 7
Bla g 7 is an allergen belonging to the tropomyosin protein family. Tropomyosin is an allergen found in muscle of numerous animal species. It was first identified as a key allergen found in shrimp however, it is also found in mollusks, arthropods and parasites. There is a high level of homology (approximately 80%) between invertebrate tropomyosins resulting in antigenic cross-reactivity. There is reduced cross-reactivity among vertebrate and invertebrate tropomyosins because they have a lower homology (approximately 55%). In fact, despite tropomyosins being highly conserved proteins within the animal kingdom, only invertebrate tropomyosins are allergenic and vertebrate are considered to be non-allergenic.
A study published by Jeong et al. (2004) concluded that tropomyosin was a key allergenic component responsible for the cross-reactivity between cockroaches and dust mites.
With shellfish allergy affecting approximately 2% of the world population, obtaining a diagnosis can be challenging due to the IgE cross-reactivity of tropomyosin found in a wide range of invertebrate including mites and cockroaches. Approximately 56% of shrimp IgE epitopes were conserved in cockroach species. An Immune Epitope Database and Analysis Resource, an epitope conservation model has been developed which could be useful in the future for identifying cross-reactivity in patients.
References
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