Ideally, the cause of urticaria and anaphylaxis is established to reduce the risk of recurrence secondary to re‐exposure [3]. Known causes of both in companion animal patients include the following [3, 5, 21, 33, 46–55]:
● Vaccines ● Transfusions ● Envenomation ● Drugs, including anesthetic agents and radiocontrast media Anecdotal case reports appear in the veterinary litera-ture that suggest food may also trigger anaphylaxis in dogs [3]. Peanut ingestion by a nine‐year‐old Schnauzer dog and walnut ingestion by a five‐year‐old Vizsla dog resulted in erythematous wheals and gastrointestinal signs [56, 57].
Reports of additional triggers, such as stress, appear in the human literature [3]. Whether or not stress is a trig-ger for veterinary patients remains to be determined.
Because so many factors may contribute to an anaphy-lactic reaction, thorough history taking is essential [3].
Careful review of past pertinent medical records by the attending clinician is also critical to pinpoint any poten-tial triggers, such as prescription drug therapy.
Additionally, when planning medical management that is known to trigger anaphylaxis, it is critical that the veterinary team anticipate potential problems and com-municate these to the client before problems arise.
Troubleshooting problems early is more likely to result in favorable patient outcomes.
When no overt cause of anaphylaxis has been identi-fied through history taking or review of the patient’s medical record, a diagnostic investigation is launched.
This may involve intradermal testing, IgE serology, or the submission of surgical biopsies for histopathologic anal-ysis (see Figure 11.5).
11.2.1 Vaccines as a Trigger for Urticaria and Anaphylaxis The goal of administering immunizations is to prevent disease, both in the individual and within the population [42, 58]. Although we do not tend to think of companion animal medicine from the perspective of “herd health,” that is precisely what vaccinations aim to do.
No vaccine is without risk. Despite being vetted by the United States Department of Agriculture (USDA) for effi-cacy, potency, purity, and safety, vaccines may still cause unexpected responses or so‐called adverse events [58].
The majority of these responses do not require medical management [58]. For example, vaccines often induce one to two days of general malaise, with or without fever [59]. These symptoms tend to be self‐limiting [58].
However, type 1 hypersensitivity reactions may result [42, 58, 60]. When these do, they typically occur shortly after vaccination, on the order of minutes to hours [58].
Pruritus and urticaria are anticipated sequelae of type 1 hypersensitivity reactions. Gastrointestinal signs, angi-oedema, respiratory, and circulatory collapse are possi-ble [58, 59]. Anaphylaxis represents a serious reaction to vaccination.
Few studies explore the frequency with which vaccine reactions, severe or otherwise, occur.
The most comprehensive study to date was conducted by Moore et al. in 2005 [61]. Electronic records from 1,226,159 dogs at 360 veterinary hospitals were exam-ined between January 1, 2002 and December 31, 2003 for evidence of nonspecific vaccine reactions, allergic reactions, urticaria, shock, or anaphylaxis [61]. During that two‐year period, there were 4,678 adverse events associated with administering 3,439,576 vaccine doses [61]. There were, in other words, 38.2 adverse events for every 10,000 dogs [61].
Additional analysis was performed on a random sam-ple of 400 affected dogs [61]. Of these dogs, 30.8% pre-sented with facial swelling and 20.8% presented with urticaria [61]. Fifteen percent exhibited generalized pru-ritus [61]. One in ten affected dogs presented with vom-iting, and 8% of dogs developed vaccinated site swelling or soreness [61].
Figure 11.5 Feline intradermal skin testing. Source: Courtesy of Stephanie Horwitz.
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