Cat dander

Further Reading

rFel d 1 (recombinant, Cat)

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Code: e1
Latin name: Felis domesticus
Source material: Dander
Family: Felidae
Common names: Cat, Domestic cat

Allergen Exposure

Sensitization to cat is strongly associated with asthma, especially in environments free of mite and cockroach (1). The presence of domestic pets increases the prevalence of respiratory symptoms in asthmatic children (2), and children sensitized to cat allergen are more likely to develop a more severe asthma than children with negative tests to cat (3).

Potential Cross-Reactivity

Cat-allergic patients with IgE antibodies to Fel d 1 have been shown also to react to the corresponding protein of ocelot, puma, serval, siberian tiger, lion, jaguar, and snow leopard (24).
 
A subgroup of cat-allergic patients also react to dogs and sometimes to other animals. Serum albumin is the main common component (25, 26). Extensive cross-reactivity even occurs between albumins of distantly related species (27) and subjects with IgE antibodies to cat albumin may also react to horse, cattle, pig, rodents (28), and fur animals like mink and fox (29). However, great variability exists between patients and selective sensitivity to limited numbers of species occurs, (28) indicating shared and specific epitopes.
 
Common and species-restricted epitopes have also been observed on the major cat and dog allergens Fel d 1 and Can f 1 (30).
 
Allergy to cat dander and pork meat, also referred to as the pork/cat syndrome (31), was shown to be mediated by IgE antibodies recognizing cat and pig serum albumin (32). In addition, other kinds of meat may be a risk for patients with this type of sensitivity, as indicated by a case with cat-specific IgE antibodies and exercise-induced anaphylaxis after eating pork or beef (33).

Clinical Experience

IgE-mediated reactions
IgE-mediated sensitization to cat is a risk factor for asthma attacks. Allergen exposure plays a causal role in the development of bronchial hyperreactivity and of the chronic inflammatory responses seen in patients with asthma (40). Infants exposed to cats developed skin prick test sensitivity about three times more often than those without such exposure (41).
 
Review
Tobacco smoke, prenatal and postnatal, has been shown to have an adjuvant effect on cat sensitization in exposed children (4).
 
Allergic reactivity to pollens may be aggravated by environmental priming with ubiquitous animal dander (5).  Allergy to cats or dogs also seems to be an important risk factor for the development of laboratory animal allergy (6).

Data strongly suggest that those with a predisposition for allergy should avoid having pets in the home (2).
 
Cat allergens
Several cat-derived proteins are involved in allergy. An acidic glycoprotein and cat serum albumin are common sensitizers (7-9).
 
The glycoprotein, now called Fel d 1, is a major allergen, and more than 80% of cat-allergic patients have been reported to have IgE antibodies against this molecule (10).
 
Fel d 1 has an apparent molecular weight of about 36 kD and is a dimer of a polypeptide comprised of two covalently bound chains called 1 and 2, or a and b (11). Chains 1 and 2 contain 70 and 92 amino acid recidues respectively (12). The IgE binding epitopes appear to be primarily conformational and do not involve carbohydrate residues, although chain 2 carries an oligosaccharide (13-16).
 
Studies on recombinant chain 1 and chain 2 showed that both chains contain IgE-binding epitopes and contribute to the allergenicity of the protein (17).
 
Allergen localization
Fel d 1 is present on the skin surface and in the fur of the cat. The protein has been demonstrated in, and may be produced by, salivary glands and lacrimal glands (18), skin sebaceous glands (19, 20) and anal glands (21). The allergen production appears to be hormonally regulated and male cats produce more Fel d 1 than females and castrated males (22, 23)
 
Cat parasites
It is also worth mentioning that cats may carry exoparasites that could contribute allergens and possibly add confusion in the investigation of allergy related to animals.
 
The cat flea is an example. Carried by the cat and occasionally biting humans, it is also an allergenic insect among many, and may add to the allergen content of indoor dust (34-36).
 
Prevalence of cat allergy
Exposure to cat allergens is one of the most common causes of respiratory allergic disease and is of worldwide importance. The prevalence varies because of cultural differences and environmental factors. Keeping cats as pets in homes is an obvious risk leading to prevalences up to 80% or above in atopics (1, 37-39).
 
Cold climates may contribute to the risk in the sense that the cats spend more time indoors (38). Cat is the major cause of indoor asthma in dry, high altitude areas like Los Alamos, NM, USA, where mites and cockroaches are virtually absent (1) and it adds severely to the burden in more humid climates with high level mite exposure (39).
 
Fel d 1 exposure
IgE-mediated sensitization to cat is a risk factor for asthma attacks. Allergen exposure plays a causal role in the development of bronchial hyperreactivity and of the chronic inflammatory responses seen in patients with asthma (40). Infants exposed to cats developed skin prick test sensitivity about three times more often than those without such exposure (41).
 
The concentration of cat allergen Fel d 1 is highest in homes with a cat, but is usually also measurable in houses where cats were not kept (42- 45). In many cases, the Fel d 1 level exceeds proposed threshold levels for cat sensitization (46). Furthermore, the low level cat exposure that occurs in many homes without cats is capable of inducing symptoms in some patients who are sensitive to cats (47).
 
In dry climates, Fel d 1 is a major cause of indoor allergy, e.g. in northern Sweden, where mite and cockroach allergens are undetectable in homes (48). Even in Japanese homes, the airborne Fel d 1 concentration is much higher (160 times) than those of the major mite allergens (49).
 
Carpets, matresses and upholstered chairs are reservoirs of cat allergens (50-52).
 
Cat allergen is carried on human clothing into environments never visited by cats (53-55). Transport of Fel d 1 on clothing from the domestic to the school environment is in fact a major source of classroom cat allergen (56). The cat allergen concentration in classes with many cat owners may be higher than that found in the homes of non-cat owners (57).
 
Avoidance
Avoidance of cat allergens is an important measure to take in the treatment of sensitized asthmatics, decreasing symptoms and decreasing the need for drugs (58). The Fel d 1 concentration in dust is significantly lower in homes from which the cat has been removed than in homes keeping the pet (51, 59).
 
Encasing covers and hot washing of linen reduce cat allergens in matresses in the absence of cats (60). Washing the clothes of cat owners is an effective method for prevention of cat allergen dispersal (61).
 
Dry heat up to 140°C has little effect on the Fel d 1 content of house dust (62) and tannic acid treatment is not a reliable method for reduction of indoor cat allergen (63). The effect of air cleaners in homes with cat seems uncertain in terms of reducting symptoms (64-66). In addition, washing or spraying cats does not lead to significant reduction of Fel d 1 shedding.
 
Only removal of the cat leads to a lasting decrease of the allergen exposure (67-69).
 
Diagnostic efficiency of IgE antibody measurements
The aggreement between IgE antibody and in vivo tests is generally high. A study of optimization of skin testing showed 94% concordance between Phadebas RAST and SPT (70). Pharmacia CAP System showed 91% efficiency relative to SPT in one study (71) and was considered superior to skin testing in another (72).
 
A contributing factor to the variability of the degree of agreement may be the variability of the skin test extracts (73). Also, it has been shown that even low levels of naturally induced Fel d 1-specific IgG antibodies affect the skin reactivity (74).
 
Table 1
 
Region

 

Preval.
%

Study group n Procedure Ref
America            
USA Chicago, Ill 29 Child asthma 138 SPT 75
40 Asthma 592 SPT 76
New York, NY 38 Adult asthma 73 SPT 77
Morgantown, WV 14 Infantile asthma 196 SPT 78
Los Alamos, NM 62 Child asthma 21 IgE Ab(PCS) 1

San Diego, Cal

10

Child asthma

41

SPT

79

California

39

Asthma and/or rhinitis

141

SPT

80

Canada

Vancouver, BC

13

Asthma/asthma-like/bronchitis

504

SPT

81

Sainte-Foy, Quebec

77

Atopic

2698

SPT

82

Montreal, Quebec

84

Atopic

155

SPT

37

Mexico

Mexico Valley

13

Atopic children

247

SPT

83

Puerto Rico

Ponce

17

Asthma

576

SPT

84

Brasil

São Paulo

11

Child asthma

80

SPT

85

Europe

 

 

 

 

 

 

Sweden

Uppsala

14

Random adults (34% atopic)

527

SPT

86

15

 

472

IgE Ab(PCS)

 

Umeå (north)

73

Child asthma

41

IgE Ab(PCS)

38

Linköping (center)

62

 

37

 

 

Helsingborg (south)

39

 

46

 

 

United Kingdom

Birmingham

59

Asthma

54

SPT

87

Germany

Hamburg

12

Random adults

739

IgE Ab(PCS)

88

Erfurt

8

 

718

 

 

Freiburg

18

Child, general population

583

SPT

89

Austria

Vienna

20

Random adults

191

SPT

90

40

Adult asthma

70

 

 

44

Adult rhinitis

117

  

 

Spain

 

21

Adult asthma

136

IgE Ab(PCS)

91

Barcelona

16

Random adults

342

IgE Ab(PCS)

92

Albacete

4

 

170

 

 

East Mediterran.

 

 

 

 

 

 

Turkey

 

16

Asthma and/or rhinitis

614

SPT

93

Saudi Arabia

Dhahran

17

Atopic, Saudi Arabs

806

SPT

94

32

Atopic, Expatriates

241

 

 

South Atlantic

 

 

 

 

 

 

Tristan da Cunha

 

20

General population

282

SPT

95

13

Born >1y after cat extermination

51

 

 

South East Asia

 

 

 

 

 

 

Thailand

Bangkok

10

Child asthma

100

SPT

96

Bangkok

29

Adult rhinitis

100

SPT

97

Malaysia

Kuala Lumpur

73

Rhinitis

314

SPT

98

Japan

 

 

 

 

 

 

 

Sagamihara

78

Adult asthma

90

IgE Ab

99

Sagamihara

31

Asthma and/or rhinitis

458

SPT

100

Tokyo

70

Child asthma, cat at home

44

IgE Ab (PCS)

39

34

Child asthma, no cat at home

394

 

 

Australia

 

 

 

 

 

 

 

Sydney

4

Child, general population

1217

SPT

101


PCS = Pharmacia CAP System™

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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.