Cat and Dog Allergies

Learning objectives

After this chapter, participants will be able to:

• explain the common cross-reactivities of cat and dog allergens
• describe the applications of component-resolved diagnosis in supporting a diagnosis of pet allergy.

Cat and dog allergies

• Mammalian furry animals, such as cats and dogs, are a significant source of indoor allergens.¹
• In Europe, the mean prevalence of cat and dog sensitisation is 26.3% and 27.2%, respectively.^2,3 However, sensitisation varies greatly between countries.³
  • In the UK, the prevalence of cat sensitisation is 31.7% and the prevalence of dog sensitisation is 21.4%.³
• Sensitisation to pets can be a risk factor for the development of allergic rhinitis and asthma.^4,5
• Allergic reactions can occur through inhalation or ingestion of allergens present in cat or dog urine, serum, dander and saliva.^5–7
• However, exposure to cat and dog allergens are not restricted to individuals with pets. Aerodynamic properties and easy attachment to clothing and hair cause pet allergens to be spread into public environments, placing individuals in the general population at risk of sensitisation.^8–11

Allergens in cats and dogs (I)⁵

• The following allergens have been identified in cats and dogs

Allergens in cats and dogs (II)^5,12–14

Cross-reactivities of cat and dog allergens (I)

• Cat, dog and horse contain cross-reactive allergens, making it difficult to identify the primary source.⁵
• The majority of cat and dog allergens belong to the lipocalin and serum albumin families:
  • Lipocalins are characterized by a common three-dimensional structure and low amino acid sequence identity. They are often synthesised in the salivary glands and are dispersed into the environment via saliva and dander.⁵
  • Serum albumin are highly cross-reactive molecules that are often abundant in dander and saliva.⁵
• Cross-reactivities can occur with allergens belonging to the same protein family:

Cross-reactivities of cat and dog allergens (II)²³

Component-resolved diagnostics (CRD)⁴

Standard diagnostic tests, including specific IgE and skin-prick testing, are available for allergen sensitisation testing against cat and dog extracts.
CRD is also available and may:

• improve specificity of diagnosis to individual species
  • for example, testing for species-specific allergens like Can f 1 for dogs
• identify allergen-specific sensitivity related to different allergic syndromes
  • for example, using Fel d 2 or Sus s (swine albumins) to identify patients with cat-pork syndrome or Fel d 5 (or Alpha-GAL), which is associated with delayed anaphylaxis to red meat but not associated with asthma or allergic rhinitis
• identify allergens that cause sensitisation in patients but are found in low abundance in normal extracts
• identify cross-reactive molecules that are clinically significant
  • for example, Can f 6, Fel d 4.

Using CRD in the diagnosis of cat and dog allergies

• Skin prick tests with extracts are used in patients with relevant clinical symptoms and an indicative medical history and examination.¹² However, high-quality and standardised extracts are often not available for pet allergy diagnosis, especially in dog allergies.^24,25
  • It is therefore advisable to perform specific IgE against the complete extract and use CRD to test a number of available dog allergens.^12,26
  • In patients where cat allergies are suspected, specific IgE against the complete extract or Fel d 1 can be used interchangeably.¹²
• Use of CRD is also advisable in polysensitised patients.
  • It is common for patients to be simultaneously sensitised to both cats and dogs. For example, 75% of individuals sensitised to a pet are fourteen times more likely to be sensitised to other animals.^12,27
• In patients with severe asthma, CRD may be useful in attempting to predict clinical symptoms and severity.¹²
  • Studies have shown sensitisation towards Can f 2, Can f 5, polysensitisation to both animals (and horse) and polysensitisation to lipocalins to be common in patients with severe asthma.²⁸
• In women with human seminal plasma allergy, CRD may be beneficial to determine cross-reactivity.¹²
  • Cross-reactivity among Can f 5 and human prostate-specific antigen can occur.^29,30 Sensitisation to Can f 5 is specific to male dogs, so the family may be able to keep/get a dog.⁵

Can component-resolved testing be advantageous over other methods when supporting the diagnosis of cat and dog allergies?

Summary

• Cat, dog and horse contain many cross-reactive allergens, making it difficult to identify the primary source.
• CRD is specific to the allergen of interest and can be a useful tool in patients polysensitised to several furry animals.
• Identifying sensitisations to specific allergens may provide insight into possible allergic syndromes a patient may be experiencing.

References

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