dog and cat on green grass

When a human or pet comes in contact with a substance that their immune system thinks is harmful, the immune system labels that substance an allergen and produces antibodies to fight it. The resulting response is an allergic reaction.

Depending on the allergen and your pet’s immune system, the respiratory tract, gastrointestinal tract, or skin may be affected. If severe enough, the response can create an anaphylactic reaction (also called anaphylaxis or anaphylactic shock), which involves significant damage to multiple organ systems at once.

Anaphylactic reactions can also occur as non-immune-mediated reactions (reactions that are not triggered by the immune system), but veterinary scientists don’t fully understand why this happens.

As with humans, not all animals react the same to all substances, and it can't be predicted if or why an animal will react. Different species of animals may react differently, too. For instance, a substance triggering anaphylactic shock in a dog may not bother a cat or a horse at all.

What Triggers Anaphylactic Shock?

Any substance can cause anaphylaxis. Most commonly, foods, insect/arachnid stings or bites, snake bites, certain medications, and vaccines can trigger anaphylaxis. Non-immune-mediated anaphylactic reactions can occur with heavy exercise, extreme temperatures, and certain medications.

In many cases, the first time an animal is exposed to an allergen that will cause anaphylaxis, they won’t have an obvious reaction. The second time they are exposed, and pretty much every time after that, they can develop life-threatening signs of anaphylaxis. Pets don’t tend to outgrow allergens like people do, so once a pet experiences anaphylaxis toward a substance, it will happen every time they get re-exposed, even many years later.

Signs of Anaphylaxis

An anaphylactic reaction is a sudden, severe, potentially life-threatening reaction and must be addressed immediately. It usually occurs within a few minutes of exposure. Some pets collapse after exposure and can’t be roused. Others may show signs of restlessness, with progression to skin redness, hives, itching, and facial swelling. Vomiting or throwing up and loose stools can also occur. Severely affected animals may have difficulty breathing, show evidence of internal or external bleeding (bruising, nose bleeds, swelling of the belly), or they may develop seizures.

Signs of anaphylaxis can happen very fast, and some pets die before they make it to a veterinarian for treatment. If a substance causes an allergic reaction that compromises your pet’s ability to breathe, this is an emergency, and it is not time to wait and see how serious the reaction becomes. Breathing difficulties can worsen rapidly, and time is not a friend.

Can You Tell if Anaphylaxis Is Happening?

Sometimes, the cause of an anaphylactic reaction is obvious, such as an encounter with a snake. The area around the injury may swell, and bite marks may be seen. Venomous spider or insect bites or stings might swell with no visible signs of an injury. However, anaphylaxis isn’t always triggered by something obvious like envenomation. Let the veterinarian know of any recent changes in diet, medications, vaccines administered, or illnesses (e.g., heartworm or parasite infection).  

In some cases, you may never know what caused the reaction. If your pet struggles to breathe, you see an obvious swelling, and/or your pet is showing other signs of anaphylaxis, don’t waste time trying to figure out what happened. Take your pet to the veterinarian.

Treatment

Your veterinarian will treat this as the emergency it is.

Try to stay calm if the clinic staff rushes your pet to “the back” without a lot of explanation. They will assess your pet’s condition and respond appropriately. Treatment may include IV fluids, oxygen therapy, and administration of epinephrine. Other drugs may be given depending on your pet’s condition, such as antihistamines, steroids, bronchodilators to help open the airways, and pain or anti-nausea medications. In extreme cases, cardiopulmonary resuscitation (CPR), intubation, and/or blood transfusions may be needed. If there is a wound from a sting or bite, the staff will address it and administer pain medication or antibiotics if appropriate.

Blood work, blood pressure, vital signs, and other monitoring tests will be performed regularly until your veterinarian feels your pet is out of danger. It is likely your pet will stay in the hospital for observation at least overnight. When released, your veterinarian will give you instructions on what to watch for at home, if anything, and advise you about continued monitoring.

Prognosis and Prevention

In otherwise healthy pets and with prompt medical attention, recovery potential is fair to good. Long-term effects of anaphylaxis are uncommon, although sometimes kidney disease can occur. If the cause of anaphylaxis is identified, be sure to avoid it for the remainder of the pet’s life. If re-exposed, seek veterinary medical care immediately, even if your pet is not showing signs yet.