Anaphylaxis is a life-threatening condition that involves multiple organ systems as a result of an allergic reaction. Shock results from massive dilation of the blood vessels, histamine release, and low blood pressure. This leads to a high heart rate, which can cause cardiovascular collapse and, potentially, death. Clinical signs will usually occur within the first 30 minutes after exposure to the allergen and will worsen rapidly. The faster the signs appear, the more severe the anaphylaxis will be.
Common Causes of Anaphylaxis
Often, a definitive cause for anaphylactic shock is not found and a diagnosis is made on clinical signs alone. However, some common causes can be identified based on history and physical examination.
- Insect bites. The venom of different insects is a common trigger for an allergic reaction in dogs. The venom of each insect species can result in a cascade of different effects.
- Bee sting: The venom of a bee contains multiple enzymes and peptides that cause pain, and massive histamine release. A bee can only sting once and often you will find the stinger in your pet’s fur. If you see one, remove it immediately.
- Hornets and wasps: Hornets and wasps are much more aggressive than bees, and their sting is more painful. They are also able to sting multiple times. If you suspect your pet has gotten into a hornet or wasp nest, seek immediate veterinary care, as their health can decline rapidly
- Vaccinations. A common cause of an allergic reaction in pets can be the antigen that is found in a vaccine. Signs will start to appear within 30 minutes to an hour after the vaccine has been given. If your pet has had a vaccine reaction before, pre-medication may be necessary. Please speak with your veterinarian before administering vaccines in the future.
- Contrast agents. If your dog is having a diagnostic test involving a contrast agent, an anaphylactic reaction is possible.
- Blood transfusions. Blood transfusions are largely safe in patients, but anaphylactic reactions can occur. These signs are usually limited to urticaria (hives), vomiting, increased body temperature, and facial swelling. If severe, an anaphylactic reaction can be life threatening and it can affect your pet’s blood pressure and breathing.
- Food protein i.e. chicken, beef, lamb. Although uncommon, if a dog is known to be allergic to a food protein, this substance can trigger an allergic reaction.
- Environmental chemicals. i.e. pesticides, solvents, and air pollutants.
Clinical Signs of Anaphylactic Shock
Dogs and cats have different physiologic reactions to anaphylaxis. Dogs primarily have histamine release from the gastrointestinal tract, which results in vomiting, bloody diarrhea, and collapse. Cats primarily have respiratory signs with anaphylaxis including bronchoconstriction (airway constriction).
Common Clinical Signs in Dogs:
- Urticaria (hives)
- Facial swelling (angioedema of the face and muzzle)
- Excessive salivation
- Diarrhea (often bloody)
- Pale gums
- Increased breathing rate and effort
Common Clinical Signs in Cats:
- Respiratory distress
- Excessive salivation
- Facial swelling
- Pale Gums
Treatment of Anaphylaxis
Anaphylaxis is a life-threatening emergency and immediate treatment is required. Due to the quick decline, time to start treatment is extremely important. Once you start to notice an allergic reaction starting, begin by removing the cause if identifiable (i.e. removing a bee stinger). Once your pet is at the veterinary clinic, they will be stabilized by administering of intravenous fluids, oxygen support, and additional medications (i.e. an antihistamine, epinephrine, bronchodilators). Severe cases may require plasma transfusions, blood transfusions, or ventilation. Your pet will likely be hospitalized for close monitoring for at least 24-48 hours.
Preventing Anaphylaxis in the Future
Treatment of anaphylactic shock is entirely based on the progression and signs as they develop. Prevention of anaphylaxis is comprised of avoiding an inciting substance or food, pre-medication for pets that have had a previous reaction (i.e. vaccine reaction), and having medications at home, including diphenhydramine (Benadryl).
Shmuel, Daniella L., and Yonaira Cortes. Anaphylaxis in dogs and cats. Journal of Veterinary Emergency and Critical Care 23.4. 2013: 377-394.