Case study shows cat bites may lead to allergy, should be included in medical history

Key takeaways:

• A girl had no history of cat allergy, atopic dermatitis or food allergy when she was bit on the back of her hand and immediately developed two erythematosus spots.
• Two months later, the girl developed conjunctival redness, sneezing and breathing difficulties upon visiting the house with the cat again.
• Subsequent skin prick testing was positive for cat dander, and specific IgE assays were positive for cat extract and rFel d 1.

A girl who was bitten by a cat and then developed a cat allergy may be the first reported case of allergic sensitization through cat bite, according to a letter published in Pediatric Allery and Immunology.

Because the bite disrupted the skin barrier, this case indicates that a pre-existing barrier defect might not be a prerequisite for sensitization, Gualtiero Leo, MD, of the pediatric allergy and asthma unit, department of childhood and developmental medicine at ASST Fatebenefratelli Sacco Hospital in Milan, Italy, and colleagues wrote.

The girl, aged 7 years, was visiting the house of a friend in November 2021. The friend had a cat that bit the girl on the back of her hand. Although the girl had visited this house before, this was the first time that the cat had ever bitten her.

Immediately, the girl developed a pair of erythematosus spots without any bleeding. Two months later, when the girl visited this house again, she developed conjunctival redness, sneezing and breathing difficulties within 30 to 60 minutes after arriving. A month after that, she experienced another asthma episode in another house with a cat.

An allergy checkup in March 2022 included a positive skin prick test for cat dander (8 mm) and positive specific IgE assays for cat extract (9.76 kU/L) and rFel d 1 (10.9 kU/L). Specific IgE assays for Fel d 2 and rFel d 4 were negative. Total IgE was 129.8 IU/mL.

Previously, at age 18 months, the girl began experiencing frequent respiratory tract infections with rhinitis, nasal mucous secretions and cough. She had no clinical history of atopic dermatitis or food allergy. A previous SPT for inhalant allergens including cats, conducted at age 2 years, 10 months, was negative. She had no pets at home.

In September 2019, the girl began taking 50 µg of fluticasone once a day as long-term treatment for asthma and to prevent exacerbations in her upper respiratory tract infections. SPT in September 2021 were positive for grasses (5 mm), olive tree (5 mm), Dermatophagoides farinae (6 mm) and Dermatophagoides pteronissinus (6 mm), but negative for cat extract.

Fel d 1, which the authors of the case study called the primary cat allergen, mainly is produced by the cat’s saliva and sebaceous glands. A cat bite can trigger anaphylaxis, according to the researchers, which suggests that a bite could include enough allergen to trigger symptoms and sensitization.

Finding a new route for allergic sensitization to cats seems unlikely after decades of studies, the authors wrote, although patient histories typically do not include information about cat bites. The authors suggested, then, that providers include specific questions about cat bites in medical histories.

Further, the authors recommended future studies on the effects of tissue disruption caused by cat bites, which could provide data on possible higher risks for sensitization to cat dander due to skin barrier defects.