Received: 6 September 2008

Accepted: 1^st referee: 11 October 2008

2^nd referee: 15 November

Diagnosis of Allergy to Some Arthropods Among Patients with Papular
Urticaria Using Skin Prick Test

Mohamed A Sallam*, Samar A Salem*, Hayat A Raafat^**

Department of Dermatology and Venereology*, Ain Shams University and Holding Company for Biological Products and Vaccine**                                                                                                                                                                                                 

Abstract

Background: Insect bites and stings may induce allergic reactions, ranging from annoying to life threatening. The diagnosis of insect bite reactions may be difficult due to mimicry of other clinical conditions and lack of history of recent contact with an appropriate arthropod.

Objective: To detect the causative arthropods linked to papular urticaria among Egyptian patients suffering from this disease by performing skin prick test (SPT) using allergens of house dust mites, fleas, mosquitoes and flies.

Methods: Fifty patients clinically diagnosed as papular urticaria presenting to the out-patient clinic of Dermatology Department, Faculty of Medicine, Ain Shams University and satisfied the inclusion criteria were enrolled into the study. Clinical history taking and thorough general and local examination were carried out. SPT was performed to all cases using standardized allergens of the following: house dust mites, mosquitoes, fleas, and flies. Histamine was used as the positive control solution and glycerosaline was used as the negative control solution.

Results: The patients included 29 females (58%) and 21 males (42%) with a mean age of 15.6 ± 13.4 years. Thirty-five patients (70%) had positive skin prick test results to allergens of insects either to single (28%) or multiple allergens (42%). Fifty six percent of them were allergic to house dust mite allergens, 42% were allergic to mosquito allergens while 20% and 18% of them were allergic to allergens of flies and fleas, respectively.

Conclusion: The most common arthropod linked to papular urticaria in this study was house dust mite followed by mosquitoes. SPT is an easy and practical test that can be a step forward in the recognition of the role of arthropods in popular urticaria for better prevention and specific immunotherapy.

Introduction

Since time immemorial, insects and related arthropods have been a source of nuisance, economic loss, and illness. Although arthropods are invaluable members of the animal kingdom, they are important in medicine for a multitude of reasons⁽¹⁾. Their bites and stings may induce allergic reactions, ranging from annoying to life threatening. Many arthropod products are also capable of inciting allergic responses in sensitized persons. A common hypersensitivity response to arthropod bites, stings, and products is papular urticaria⁽²⁾.

Papular urticaria is a term used to describe a chronic or recurrent eruption of pruritic papules, often grouped in irregular clusters, frequently seasonal in incidence, and affecting predominantly children between the ages of two and seven years. Adult cases are seen but are less common than childhood cases⁽³⁾. Papular urticaria is a very common hypersensitivity reaction to the bites, stings and contact with insects such as mites, ticks, spiders, fleas, mosquitoes, midges and flies^(2,4).

The diagnosis of insect bite reactions may be difficult, partly because of mimicry of other clinical conditions and partly because of the lack of history of recent contact with an appropriate arthropod(2). Because of the large number of people affected by allergic reactions to many species of arthropods, we tried in this work to study the contribution of some common arthropods to the induction of papular urticaria using SPT.

Subjects and Methods

This study was performed on fifty subjects recruited from the out-patient clinic of Dermatology Department, Faculty of Medicine, Ain Shams University. Their age ranged from 1 to 54 years.

The main inclusion criteria were patients clinically diagnosed as papular urticaria; of any age group, of both sex and accepting to share in this study. Exclusion criteria were patients who cannot stop antihistaminic therapy, patients with extensive skin lesions, scars, dermographism and dark skin.

Patients were subjected to full clinical history taking includingpast and family history of other atopic diseases (Bronchial asthma, Allergic rhinitis, Allergic conjunctivitis and Urticaria). Patients were also subjected to skin prick testing using the following allergens from OMEGA LABORATORIES LTD, Montreal, Canada:

·      House dust mites (Dermatophagoides pteronyssinus and Dermatophagoides farinae): 10,000 AU/ml (Allergy unit/ml) in 5% glycerine (5,000 AU/ml for each species).

·      Mosquitoes (Culex pipiens): 1/40 w/v (weight /volume) in 5 % glycerine.

·      Fleas (Ctenocephalides felis): 1/20 w/v in 5% glycerine.

·      Flies (Muscidae): 1/20 w/v in 5% glycerine.

·      Histamine: 1mg/ml (used as the positive control solution).

·      50% Glycerosaline (used as the negative control solution).

The lancets used in the procedure werestandardized lancets in allergy skin testing, 1mm point length to optimize skin test response, sterile and individually wrapped and disposable. They were purchased fromOMEGA LABORATORIES LTD, Montreal, Canada.

Procedure was done as follows⁽⁵⁾: the skin area to be tested was cleaned with alcohol and allowed to dry. The test sites on the volar aspect of forearm were marked and labeled at least 3 cm apart to avoid the overlapping of positive skin reactions. The marked sites were dropped by the allergen and gently pricked by sterile skin test lancet. Positive and negative control solutions were similarly applied and the patient waited for at least twenty minutes before interpretation.

The longest and orthogonal diameters of any resultant wheal were measured and the average of the two was recorded. The resultant erythema was measured by the same way and the mean diameter (X) was calculatedas follows⁽⁶⁾:

X= (D+d)/2;

where D=largest diameter, and d=perpendicular diameter at midpoint of D.

The following precautions were taken⁽⁷⁾: First generation antihistamines (sedating antihistamines) were avoided at least 72 hours before testing, second generation antihistamines were avoided for at least 5 days before the test and potent topical steroids were avoided on the skin at the site of the test for 2 weeks before skin testing. Digital photos were taken for the patients before and after interpretation of results.

For statistical analysis, data was collected, coded, entered to an IBM compatible personal computer and analyzed with the Statistical Package for Social Science (SPSS) under Windows version 11.0.1. Student t test was used to know whether the mean of the variable of two given samples from two independent groups of individuals and one numeral value of interest is the same in the two groups.Chi-square testwas used to determine the extent that a single observed series of proportions differs from a theoretical or expected distribution of proportions or the extent that two or more series, proportions or frequencies differ from one another based on the chi-square distribution (p value > 0.05 = insignificant, p<0.05 = significant, p<0.01 = highly significant).

Results

A total of 50 patients participated in this study. They were 21 males (42%) and 29 females (58%). Their age ranged from 1 to 54 years with a mean age of 15.6 years. Thirty patients (60%) had a positive family history of atopic disease, 18 patients (36%) had history of other allergies and five patients (10%) had positive parents’ consanguinity. Table (1) shows the distribution of cases according to the associated allergic disorder. Bronchial asthma was the main allergic disorder associated with papular urticaria in our studied cases.

Table (2) shows the distribution of positive allergy to anthropods among the study group. As shown, 35 patients (70%) showed positive allergy to anthropods. The most common arthropod linked to papular urticaria was house dust mite (56%) followed by mosquitoes (42%).

Seasonal distribution and history of pet contact are shown in Table (3). It was found that 46% of the patients were affected in summer, 36% in spring and 18% were affected all over the year. The majority of patients (76%) were exposed to pets either inside or outside the house. This table also shows that legs, arms and trunks were the most frequent sites affected by the lesions (98% and 84% respectively).

A comparison was held between positive and negative allergy to both mites and mosquitoes using Chi Square test (Tables 4 & 5). Table (4) shows a lower percentage of discrete lesions among cases with positive allergy to mites compared to negative cases and the difference is statistically significant. This table also shows a higher percentage of combined (discrete and grouped) lesions among cases with positive allergy to mites compared to cases with negative allergy to mites and the difference is statistically highly significant.

As regards allergy to mosquitoes, Table (5) shows a lower percentage of discrete lesions among cases with positive allergy to mosquitoes compared to negative cases and the difference is statistically significant.

Fig. (1) shows an example of positive skin prick test results to house dust mite allergen, Fig. (2) shows an example of positive SPT results to flies, house dust mites and mosquitoes.

Table 1.    Distribution of the studied cases according to the type of associated allergic disorder

AR: Allergic rhinitis                  BA: Bronchial asthma

 

 

Table 2.    Distribution of positive allergy to arthropods among studied patients

           

Table 3.    Distribution of the studied cases according to season of affection, exposure to pets and location of the lesions

 

Table 4.    Comparison between cases with negative and positive SPT results to mites as regards gender, family history, history of other allergies, exposure to pets, season, site and pattern of lesions

*P<0.05 =Significant, ** P<0.01= Highly significant, BA=Bronchial asthma, AR=Allergic Rhinitis

Table 5.    Comparison between cases with negative and positive allergy to mosquitoes by SPT as regards gender, family history, history of other allergies, exposure to pets, season, site and Pattern of the lesions

*P<0.05 Significant

 

 

 

Fig. 1. Skin prick test result showing positive reactions to histamine and mite

Histamine: Wheal = 8 mm, Flare = 5 cm (Class: +4), Mite: Wheal = 5 mm, Flare = 3 cm (Class: +3)

 

Fig. 2. Skin prick test result showing a positive reactions to histamine, flies, mite and mosquito
(reaction to multiple allergens)

Histamine: Wheal = 5 mm, Flare = 4 cm (Class: +4)

Flies: Wheal = 3 mm, Flare = 3.5 cm (Class: +3)

Mite: Wheal = 2 mm, Flare = 2 cm (Class: +2)

Mosquito: Wheal =3 mm, Flare = 3 cm (Class: +2)

 

Bites and stings from insects are a very common event and may lead to a variety of cutaneous reactions. Most are only local, and their morphology and evolution depend mainly on the immunity of the host. Although local reactions are rarely life threatening, they may be severe or may have at least a considerable impact on life⁽⁸⁾.

Papular urticaria is a common, chronic or recurrent eruption of pruritic papules, often grouped in irregular clusters which may persist for up to 2 weeks⁽³⁾. They occur most frequently on the legs and other uncovered areas such as forearms and face, but can be scattered in small groups all over the body. Papular urticaria is believed to be the result of a sensitivity reaction to the bites, stings and contact with critters such as mites, ticks, spiders, fleas, mosquitoes, midges and flies but virtually any arthropod is capable of inducing such reaction^(2,4).

In the present study, there was no observable significant age or sex predilection. Age ranged from 1 year to 54 years old, with a mean age of 15.6 years. Both genders were involved, 58% were females and 42% were males with no significant sex predilection which agrees with Rook and Frain-Bell⁽⁹⁾ who also found that the two sexes were equally affected. This is in contrast to Raza et al.⁽¹⁰⁾ who found in their study that children and adult males may be more vulnerable to papular urticaria.

This study showed that 36% of patients had a positive present history of atopic diseases including bronchial asthma, allergic rhinitis, urticaria and conjunctivitis and 60% of them had a positive family history of these disorders. These findings agree with the common belief that the allergic disorders are almost always atopic, especially in children⁽¹⁸⁾. In contrast, Settipane and Boyd⁽¹⁹⁾ and Gracia et al.⁽²⁰⁾ believed that the frequency of insect induced papular urticaria is similar in atopic and non-atopic populations.

We found that the most common associated atopic disorder in both present and past histories of our patients was bronchial asthma (20%). This finding is supported by Stewart⁽²¹⁾who reported that allergy to arthropod antigens is the major cause of respiratory allergy such as bronchial asthma and allergic rhinitis. Allergic rhinitis and bronchial asthma can be induced by some mite species such as Dermatophagoides pteronyssinus and Dermatophagoides farinae and Blattella species, respectively. Also respiratory symptoms to Hexapoda allergens (mosquitoes and flies) often occur in occupational situations with extensive exposure to insects or insect parts⁽²²⁾. It is thus possible that arthropods which induce papular urticaria such as mites, mosquitoes and flies can also induce bronchial asthma and allergic rhinitis. Avoidance of such allergens might, therefore, prevent or lessen the occurrence of these forms of allergy. 

Seasonal variation of papular urticaria was apparent; 46% were affected in summer, 36% were affected in spring and the remaining 18% were affected throughout the year. These results agree with Demain⁽⁴⁾ who reported a common seasonal predilection during spring and summer. The results also agree with Rook and Frain–Bell⁽⁹⁾ who found that 62.3% of their patients were affected in summer, 9.2% in the winter, and the remaining 29.5% were equally affected throughout the year. This variation may be due to the difference in the climate which may reflect on the life cycles of insects.

The distribution pattern of papular urticaria in our study was mainly presented by papules grouped in clusters together with discrete papules which agrees with Naimer et al.⁽¹¹⁾ who found that the lesions were normally multiple often with a tendency to clustering and sometimes dispersed in a linear form. Raza et al.⁽¹⁰⁾ in their study found that the most common first appearance was of papules and urticarial plaques grouped in clusters over exposed and covered parts of the body.

We found that the legs and arms were the most commonly involved areas (98% of cases), followed by legs and trunk (84% of cases). Location of lesions is dependent on the arthropod involved^(3,12). Flying insects (flies and mosquitoes) tend to attack primarily the exposed parts of the body⁽¹³⁾. Cats and dogs flea bites occur predominantly on the legs below the knee⁽¹⁴⁾, while scattered lesions all over the body are the usual sites identifying bites of bird fleas, bird mites, or bird bugs^(14,15).

Papular urticaria was seen with greater frequency among households with pets⁽³⁾. In this work, 76% of cases were exposed to pets. However, negative parent reports of pets are not sufficient evidence of low pets’ allergens exposure^(16,17).

To the best of our knowledge, this is the first report in the literature on the use of skin prick test in determining the causative agents or arthropods in papular urticaria using this combination of arthropods. In this work, we found that fifty six percent of patients in this study were allergic to mite mix (Dermatophagoides pteronyssinus, Dermatophagoides farinae)which is the highest percentage among our patients. A study carried out on house dust mites in Egypt, by Koraiem and Fahmy⁽²³⁾in which house dust mites were collected from eight different areas in Cairo found that Dermatophagoides pteronyssinus and Dermatophagoides farinae were the most abundant species and were found to be responsible for most cases of allergy.

In our study, there was a higher percentage of summer affection among cases with positive allergy to mites (46.4%). This can be explained by the seasonal fluctuation of prevalenceof live mites, with highest levels occurring during humid summer months, which are more favorable for breeding and survival^(24,25).

This work showed that 42% of patients were allergic to mosquitoes. Only 20% and 18% of our cases were allergic to flies and fleas respectively. In some cases of allergy to mosquito bites, systemic symptoms and severe anaphylactic reactions can occur⁽²⁶⁾,and thus desensitization with whole-body extracts of mosquito can be successfully applied^(27,28).None of our patients reported history of severe local or systemic reactions and so there was no indication for immunotherapy as desensitization should be considered only in patients who experience anaphylaxis or major and extended local reactions^(29-32).

In conclusion, it is of major importance for the treatment and prevention of papular urticaria that the exact cause is identified. Skin prick test can be a step forward in the recognition of the major role of arthropods in inducing papular urticaria. House dust mite is the most common arthropod in our Egyptian papular urticaria patients with bronchial asthma as the most commonly associated allergic disorder. Only if the eliciting insect is known can effective preventive measures be established, since habitat, behavior and exposure modes vary considerably among the arthropod classes. Further studies on wider scales using a wide range of anthropod allergens are needed to confirm the results of this work. Evaluation of specific immunotherapy in reducing the incidence of papular urticaria and associated allergies is an important issue.

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