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Background: The identification of ‘unknown’ allergic sensitizations may determine the prognosis and treatment of patients with respiratory airway disease. Currently, the presence in homes of ‘exotic’ animals as pets is increasing. In this article the Siberian hamster or dwarf hamster (Phodopus sungorus) was identified as a new indoor source of aeroallergens and respiratory disease.
Methods: The subjects were six outpatients who were treated for asthma and rhinitis. Siberian hamster hair extract was prepared with a standard wt/vol method, and patients were skin-prick tested with the extract. Serum-specific immunoglobulin (Ig)E against the Siberian hamster, common hamster (Cricetus cricetus) and golden hamster (Mesocricetus auratus) was determined. IgE-immunoblotting was also performed for all six sera. Specific bronchial challenge was carried out with the Siberian hamster extract.
Results: Skin prick tests (SPT) with the Siberian hamster extract, and specific IgE-antibodies against Siberian hamster, were strongly positive in all six patients. Determinations of specific IgE-antibodies against C. cricetus and M. auratus were negative in all patients. IgE-immunoblotting of the sera revealed two IgE-binding fractions (MW 18 and 32 kDa) in five of the six sera. Specific bronchial provocation tests resulted in early asthmatic responses in the two patients who were challenged.
Conclusions: The present study reveals the Siberian hamster to be able to induce both sensitization and disease, and this species of hamster should be taken into consideration as a cause of respiratory disease in exposed subjects. A noteworthy finding was the lack of sensitization in our patients to common hamster allergens (M. auratus and C. cricetus) that are usually tested when hamster allergy is suspected.
In patients with respiratory airway disease, the recognition of the factors that cause allergy may determine the prognosis and treatment of asthma and rhinitis. Some patients may be sensitized to unknown allergens not included in skin test batteries of common aeroallergens. The detection of new removable allergenic sources such as ‘uncommon’ domesticated animals and pets is of particular significance.
Domestic animals currently represent the second most frequent source of indoor aeroallergens after house dust mites (1). Cats and dogs are the pets found most frequently in dwellings, and allergic sensitization to these animals is the most prevalent (2), but other domestic animals can also induce allergic sensitization and respiratory disease. Respiratory allergic diseases owing to rodents are well recognized (3). Both domestic and occupational exposure to these mammals play a significant role in the development of immunologic sensitization to animal-derived antigens. The rodents involved in this type of reaction are rats, mice, guinea-pigs (4), common hamsters (5) and gerbils (6).
Currently, ‘exotic’ animals are being acquired with increasing frequency as pets. The Siberian hamster (SH) or dwarf hamster, Phodopus sungorus, is one of the latest rodents to have become a popular household pet. We report evidence that identifies SH as the cause of allergic asthma and rhinitis. We are not aware of other reports of this sensitization.
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The results of SPTS with the SH extract were strongly positive, with the allergen wheal areas being larger than the wheal areas seen with 10 mg/ml histamine in most patients (Table 2). Prick tests with SH extract in 10 atopic and nonatopic control subjects were all negative. SPTs with commercially available hamster extract were negative in all six patients.
Table 2. Results of skin-prick tests, specific IgE determinations and specific bronchial challenge tests
| ||Prick tests||BPT fall in FEV1||Total IgE||Other||RAST (Class) (kU/l) sensitizations**||CAP (Class)|| || |
|Patient No.||Siberian hamster* (P. sungorus)||Golden hamster (M. Auratus)||Common hamster (C. cricetus)||Histamine*||Siberian hamster* (P. sungorus)||Golden hamster (M. Auratus)|| ||Common hamster (C. cricetus)||Histamine*|
|4||14||0||8||3||0||0||Dust mites, Cat dander, Alternaria||186||35%|
|6||8||1||8||3||0||0||Dust mites, Cat dander , Olive||211||ND|
Three patients were sensitized exclusively to SH. The three other patients were also sensitized to common aeroallergens such as dust mites, cat dander and olive pollen. The latent interval from first contact with the SH to the development of symptoms in the three patients sensitized exclusively to this species (patients number 1, 2, and 5) was 1 month, 3 months and 1 month, respectively.
Specific IgE antibodies against SH hair extract were also strongly positive in all six patients (Table 2). RAST class 3 or 4 was found in five sera. Determinations of specific IgE antibodies against C. cricetus were negative in all patients, as were tests for M. auratus.
The results of IgE immunoblotting of sera from all six patients are reported in Fig. 1. Two IgE-binding fractions (estimated MW of 18 and 32 kDa) were detected in five of the six sera. Serum from patient 5 showed a different pattern of IgE-binding proteins: IgE from this serum reacted to only one band at 20 kDa.
Specific bronchial challenge with SH extract was done in only two patients. The test resulted in early asthmatic responses in both patients. No late asthmatic responses were detected. The concentration of the extract that caused a decrease in FEV1 of 20% or greater was 1 : 10 wt/vol in patient 4, and 1 : 1000 wt/vol in patient 5. The results of the bronchial provocation tests are shown in Table 2.
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An exhaustive search for causative allergic factors in patients with respiratory airway disease is imperative. The recognition of allergic sensitizations may determine the prognosis and treatment of asthma and rhinitis. As described previously (13), some patients diagnosed as having ‘Nonallergic asthma or rhinitis’ may, in fact, be sensitized to unknown allergens not included in skin test batteries of common aeroallergens. Of particular significance is the detection of removable allergenic sources such as pets. In this report, SH were established as the cause of allergic asthma and rhinoconjunctivitis in six patients, on the basis or the clinical course, skin tests, serum-specific IgE, IgE-binding fractions in immunoblotting, and bronchial challenge (in two of them).
The SH, dwarf hamster or Djungarian hamster, Phodopus sungorus, is a member of the Cricetinea subfamily of rodents which has recently become a popular household pet. This hamster can also be present in laboratories as an experimental animal (14). The Cricetinea subfamily also comprises the Cricetus and Mesocricetus genera, including the species C. cricetus (common hamster) and M. auratus (golden hamster). The lack of sensitization to these hamsters in our patients is noteworthy, as these are currently the most prevalent species of hamster as pets or laboratory animals. Thus, M. auratus and C. cricetus dander-derived antigens are the allergens usually tested in skin tests, and specific IgE determines when hamster allergy is suspected. Therefore, it is clinically relevant to determine exactly which species each patient is exposed to at home or at the workplace, in order to test the appropriate allergens and avoid false negative diagnoses.
When the six patients in this report were asked about the presence of pets in their homes, only two specified the type of hamster as the dwarf or SH. Therefore, careful clinical questioning should aim to determine the actual hamster species the patient is exposed to.
The short duration of SH exposure before symptoms appeared in the three patients sensitized exclusively to this species suggests that the allergenic power of these antigens is high.
The other three patients also presented sensitizations to common aeroallergens, including cats in two patients. In these patients, cat sensitization seems to be compatible with multiple sensitizations in atopic patients. However, crossreactivity between SH and cat allergens is a possibility worth investigating, as several studies have demonstrated crossreactivity between a variety of rodents and other mammals (15, 16).
The pattern of IgE-binding proteins indicates the presence of two main groups of allergenic proteins: one band at 18 kDa and the other at 32 kDa. These components, which react with five of the six individual sera included in this study, can be considered clinically relevant allergens of SH. The molecular weight of the 18-kDa component coincides with that of lipocalin proteins. The components of the lipocalin family are low-molecular-weight (typically 17–20 kDa) proteins which are generally accepted as an important cause of crossreactivity between furred animals (17). It would be worthwhile to conduct further studies with this SH fraction (MW 18 kDa) to establish the possible lipocalin nature of this protein.
Atopic status seems to be a risk factor for sensitization to SH, as is assumed for other domestic or laboratory animals (18). Thus, although there is some controversy about the development of allergy in children (19), early preventive measures to avoid SH sensitization are advisable for atopic subjects, including children known to have atopic characteristics.
With respect to the clinical course, all six of our patients presented moderate to severe asthma requiring continuous anti-inflammatory therapy. Clinical improvement was observed in all the patients a few weeks after the animals were removed from the homes. Two of the three patients sensitized exclusively to SH remained asymptomatic, and the other patient presented intermittent mild asthma requiring short acting beta-agonist as needed, 14 months after the animals were removed.
The maintenance of ‘hidden’ allergenic exposure could explain why the removal of pets from the home sometimes does not lead to the anticipated decrease in respiratory symptoms in subjects sensitized to common pets (20). Cat and dog allergens can be detected in public places and homes with no pets (21, 22), although it is unlikely that SH allergens are present in public places. However, Fel d 1 is known to persist for several months after the removal of cats from apartments (23). SH allergens can probably also persist in homes for several months after the animal is removed.
No patient was occupationally exposed to SH, but the increasing use of this species as a laboratory animal should be taken into consideration. Sensitization to laboratory animals has a high prevalence among laboratory workers (24, 25), and home transportation of laboratory animal allergens on clothing has been demonstrated (26). Thus, sensitization to SH is a possibility in laboratory workers exposed to SH and in people living with such employees.
The present study show that SH is able to induce IgE-mediated asthma, rhinitis and conjunctivitis (27); we therefore conclude that this species of hamster should be taken into consideration as a cause of respiratory disease in exposed subjects. A progressive increase in SH sensitizations should be expected because of the increase in domestic and occupational exposure to this rodent. Crossreactivity between SH and other hamsters seems unlikely in view of the lack of sensitization to other hamster species in our patients. Further immunological studies are needed to identify and characterize the allergens of P. sungorus, and to determine the degree of crossreactivity between SH, other rodents, and other mammals.