Summary

Hamsters are small rodent species that belong to the family Cricetidae. Several different species of hamsters are distributed globally, with the popular ones being Mesocricetus auratus (Golden/Syrian hamster), and the two varieties of Phodopus species i.e. Phodopus sungorus (Djungarian Siberian hamster), and Phodopus roborovskii (Roborovski hamster). Hamsters are commonly used as laboratory animals; however, they have recently gained popularity as domestic pets. The hamster urine is identified as the most potent allergen source, followed by epithelium, saliva, fur, dander, and hair. Airway inhalation is the main route of exposure to hamster allergens, and since the size of airborne particles is minute, it can easily penetrate through the lower respiratory tract, causing allergic symptoms. Besides, direct skin contact (through hamster bite) may be considered as the secondary route of exposure to these allergens. In sensitized individuals, allergic symptoms to hamster allergens may occur either via contact in the laboratory or through its ownership. Allergic symptoms may include asthma, allergic rhinitis, rhino-conjunctivitis, skin reactions (urticaria and angioedema), and even anaphylaxis. Mes a 1 (Golden/Syrian Hamster) and Phod s 1 (Djungarian Siberian dwarf hamster) are major allergens of hamsters that belong to lipocalin protein family. Substantial immunoglobulin E-cross-reactivity has been reported between Phod s 1 and Roborovski hamster. Furthermore, cross-reactivity has also been identified between Phod s 1 and Dermatophagoides pteronyssinus (Der p) allergen as well as hamster serum albumin and horse meat allergen.

Epidemiology

Worldwide distribution

Laboratory animal allergies (LAA) and bronchial asthma pose a considerable occupational disorder among large number of laboratory technicians, researchers, physicians and animal handlers, whose job demands exposure to these animals. In occupational settings, the association between LAA or occupational asthma and rodent exposure is well documented. It is estimated that between 11% and 44% of people working with laboratory animals will develop allergies related to their occupation.

In a cross-sectional survey conducted in Japan among 169 laboratory workers (handling animals), the prevalence of LAA was reported to be 17.6%.

A Spanish study was conducted among 75 animal workers (aged 20-60 years) that were exposed to laboratory animals, such as a hamster, rat, rabbit, mouse, and guinea pig. It was found that ~12.5% of the workers handled hamsters. The study findings showed that the skin prick test (SPT) with extracts of hamster epithelia was reported to be positive in 3% of laboratory animal handlers.

In a study conducted in Iran that compared 100 laboratory animal handlers (21-60 years) with 50 controls, the SPT result for hamster extract was found to be positive in 10% of animal handlers, while no sensitization was reported among the controls (p<0.05).

In a cross-sectional study conducted in Brazil among 455 laboratory animal handlers (age: 32±10 years) and 387 non-animal handlers (age: 33±11years), the prevalence rate of respiratory allergies was assessed among animal handlers. Out of 455 animal workers, 4.0% (n=18) were exposed to hamsters. Further, sensitization to work-related allergies was reported to be greater among animal handlers in comparison to the non-animal handlers (16% vs. 3%, p<0.01).

Of interest, a cross-sectional study compared 100 children (age: 1.5-15 years) and 100 adults (19-65 years), suffering from asthma with the other 100 healthy subjects (3-54 years), without any asthma or atopic disease (acted as controls). The study findings reported sensitization rate to hamsters being significantly greater in adult asthmatics when compared to controls (p=0.02). Furthermore, with respect to the age group, sensitization to hamster was observed to be higher in asthmatic children (8%), when compared to adult asthmatics (6%).

Risk factors

Exposure or contact with rodents has long been identified as a risk factor for the development of allergic symptoms in sensitized individuals. The primary risk factor responsible for causing LAA is anticipated to be exposed to animal allergens. Individuals involved in animal research and its care are more likely to develop allergic reactions towards these allergens.

Large quantities of airborne particles (<5µm), containing animal allergens are found in air, that remain suspended for a prolonged period and hence are responsible for causing allergic reactions in sensitized individuals. Besides, the level of allergen exposure depends on the number of animals and the type of work conducted by the workers.

Additionally, it has been observed that animal care workers pose a greater risk of developing sensitization towards animal allergens if they (i) had a history of allergic symptoms during pollination season, ii) had airway hyperresponsiveness, (iii) had sensitization towards dog/cat allergens, and (iv) were exposed to laboratory rodents for an extended period of time. It has been reported that up to one-third of animal care workers will have symptomatic asthma. An atopic background and the intensity of exposure are further risk factors.

Route Of Exposure

Main

Airway inhalation is the main route of exposure to hamster allergens. These airborne allergens are most prevalent in hamster’s urine, dander, hair and saliva. The characteristic feature of these allergens is that it can easily penetrate through the lower respiratory tract and cause allergic symptoms since the size of the airborne particles are very small

It has been reported that inhalation of these allergens may lead to inflammation of airways as well as occupational asthma in individuals working in the laboratories, which may even be life-threatening in certain individuals.

Secondary

Direct skin and eye contact may be considered as the secondary route of exposure to these allergens. The percutaneous exposures may happen from the bite of the animal, infected needles with the animal allergens, injury on person’s hand, or contamination of lesions with the antigen.

Clinical Relevance

According to the literature, a correlation exists between LAA/occupational asthma and exposure to rodents. Sensitization associated with occupation may result in respiratory symptoms, such as asthma, allergic rhinitis (AR), rhino-conjunctivitis, and increased bronchial responsiveness, as well as skin reactions. Anaphylaxis (from immediate-type I allergy) associated with hamster bite has also been reported.

Allergic rhinitis, rhino-conjunctivitis, and Asthma

A cross-sectional study conducted in Brazil investigated the prevalence of respiratory allergies in 455 lab animal handlers. The results reported that 58.1%, 29.6%, 9.6% and 2.8% of animal handlers suffered from AR, rhino-conjunctivitis, asthma and work-related asthma, respectively.

In a study conducted among 100 lab animal handlers and 50 controls (to assess the sensitization to animal allergens), occupational allergic reactions were observed in 52 animal handlers, among them 71.1% (n=37), 65.3% (n=34), and 63.4% (n=33) showed AR, asthma and rhino-conjunctivitis, respectively.

In a study conducted on 90 children with parents exposed (n=50) and not exposed (n=40) to laboratory animals, the frequency of respiratory allergic diseases (AR and asthma) was found to be significantly greater in children with exposed parents compared to children with non-exposed parents (8% vs 2%; p<0.05) respectively.

Interestingly, in a study involving 6 patients, Siberian hamster was found to induce rhino-conjunctivitis and allergic asthma, based on the result of SPT, serum-specific IgE, and clinical symptoms.

Besides occupational exposure, development of asthma, while coming in contact with hamster at home has also been reported in a few studies:

A study was conducted in Japan among 30 adults, who developed asthma while being exposed to pet hamster. Symptoms of asthma followed by hamster bite were mild-to-severe. Most asthma attacks initiated with repetitive cough, followed by dyspnea and wheezing. Among 3 patients, common cold led to asthma attack requiring hospitalization, whereas aggravation of asthma was reported in 2 patients who needed intensive care. Of interest, among all the hamster species, dwarf hamster (Phodopus variety) was found to be the most common species inducing allergic reactions in 18 patients (out of 30), with 77.7% (14 out of 18) being exposed to Phodopus sungorus (Djungarian hamster) and 16.6% (3 out of 18) exposed to Phodopus roborovskii (Roborovski hamster).

Another study conducted in Japan among 9 asthmatic patients, rapid onset of asthma was reported in patients within 6 to 36 months of keeping hamsters as pet. Furthermore, 100% (9 out of 9) of patients showed positive-IgE radioallergosorbent (RAST) score for hamster epithelium.

Likewise, a case study reported asthma associated with pet hamster exposure in a 39-year-old woman with positive SPT result for hamster epithelium.

Anaphylaxis

Anaphylactic reaction caused by bite of hamster has been reported in a few case studies. These are as mentioned below.

Two case studies (Case 1: Chinese girl - 13-years and Case 2: Japanese boy - 11-years) were identified where the bite of a hamster led to anaphylactic reactions in children, who kept it as pet in their house. Both of them showed history of AR, bronchial asthma as well as allergy to Dermatophagoides pteronyssinus (Der p). The reports revealed generalized urticaria and angioedema in fingers, immediately after the bite of their pet. Interestingly, both the children did not develop any allergic symptoms previously, when bitten by their pet.

Two other cases of hamster-bite-related anaphylaxis were reported in 36-year-old women who had history of asthma as well as atopic dermatitis (although both had tolerated the bites of their pet hamsters on several occasions previously without manifestations of allergic symptoms). In one woman, following hamster bite, a sudden warm flush that progressively led to generalized urticaria and pruritis of eyes along with sneezing and breathing difficulty was reported. The SPT result showed positive reaction towards saliva of hamster. In another woman, within 20 minutes of hamster bite, angioedema and dyspnea developed. Further bites led to urticaria and swelling in hand. The SPT result was found positive for hamster saliva, whereas serum-specific IgE for epithelia of hamster was also detected.

Prevention And Therapy

Prevention strategies

Avoidance

The initial step in the management of allergic reactions to hamster is to prevent exposure towards the allergen. Accelerated improvement in the allergic symptoms was observed in a study, where a hamster was no longer kept as a pet.

In laboratory settings, the use of personal protective equipment can diminish the exposure of allergens in animal handlers, alongside offering protection to animals from irresistible infectious particles that might be transferred via clothes, shoes or through skin. Respirators likewise give an elevated level of security against LAA. Furthermore, laboratory animal handlers who used gloves, masks, laboratory coats, shoe covers, and respirators showed reduction in allergic symptoms by 58%.

Changing of animal cage may lead to intense allergen exposure and thus considered as a potential risk factor. However, it has been observed in a study that use of ventilated air-exhausted cabinets may decrease the exposure to these allergen, further enhancing the ergonomic posture during tasks.

Cross-Reactivity

Cross-reactivity has been reported among certain species of hamster, and this may be because they belong to the same family, Cricetidae. Extensive degree of cross-reactivity has been reported between Roborovski hamster and major allergen (Phod s 1) of Siberian hamster. It has been found that both the allergens exhibit substantial IgE-cross-reactivity (fur allergens), due to high sequence homology between them. However, no cross-reactivity has been identified between Phod s 1 and Golden (Mes a 1)/European hamster, in spite of them belonging to the same family.

Furthermore a 21-kDa allergen identified from saliva of Siberian hamster have reported to cross-react with Der p allergen.

Of interest, cross-reactivity has been reported between hamster serum albumin (SA) and allergy to horse meat. This evidence is supported by a case identified in a 39-year-old woman who developed asthma as a result of exposure to hamster (used as pet), and it was found that she was also allergic to horse meat. On ingestion of horse meat, the women experienced lip angioedema. The RAST showed partial IgE-cross-reactivity (30%) between the horse meat and hamster SA. Other cases have also been identified, where interaction between dander of hamster species and horse meat was reported.