Allergic Reactions Shock And Anaphylaxis In Your Dog Cat Or Ferret

Vaccine Reactions

Ron Hines DVM PhD

You can read a more complete article that pertains to these reactions in dogs and why they often occur  here

Another Entrée With The Same Flavor here

Allergic reactions to vaccinations are not uncommon in dogs and cats. We tend to think of vaccines/anaphylaxis first because cause and effect are so obvious and dramatic and because a known chain of decisions led to their occurrence. But vaccines are not the only things that can cause this type of reaction in genetically-susceptible pets. Dogs and cats that have become allergic to specific antibiotics or antibiotic families can suffer similar reactions (mast cell degranulation). (ref) In fact, any drug, food, or other material that contains proteins and gains entrance to the body can, on occasion, cause anaphylaxis. (ref)

Most veterinarians believe that when anaphylactic reactions occur subsequent to a vaccination, they are due to added chemicals of three kinds. When There are three ingredients in vaccines that have the potential to cause anaphylaxis:

The first, called adjuvants , have traditionally been added to vaccines to increase their potency. Some commonly used adjuvants are aluminum hydroxide, aluminum phosphate, calcium phosphate, mineral and peanut oil. But many others are used as well.

The second, antiseptics, are added to insure the products remain sterile. The most common one is thiomersol (thiomersol).

The third, antibiotics, are added for the same reason – to minimize the possibility that bacteria will be carried into your pet’s body with the hypodermic needle. In many cases, the addition of antibiotics and antiseptic ingredients were mandated by the Federal Government (USDA/FDA,EMA).

When a vaccine contains killed bacteria, the proteins in those bacteria probably also have the potential to cause anaphylactic reactions as well. I believe that such is the case when vaccines contain the killed leptospirosis organism or protein-containing fragments of it. The mass production of virus and bacteria to be used in the manufacture of vaccines requires a complicated “brewing” process. In that process, other proteins are added: cell tissue cultured to grow the virus, bovine serum albumin to allow these cells and pathogenic organisms to grow and multiply. Attempts are made to remove as much of these ingredients from the final products. But those attempts are not always successful.

I no longer use adjuvanted vaccines in pets because I have seen too many side effects. 

What Are My Pet’s Options?

1) If you do decide to continue periodic vaccination, do so as seldom as the law allows. Do not patronize establishments that use cheap, generic vaccines. If you see the same vaccine in feed stores, that is not a brand to use.

2) Adult dogs do not need yearly vaccinations against common pet diseases- despite reminders you may receive from your veterinarian. Does you physician send you yearly reminders to receive polio, hepatitis and tetanus boosters?

3) When a vaccine is given, be sure that equipment and medications to manage an anaphylactic crisis are readily available to the veterinarian. They are often not available at vaccination clinics that move from place to place. Ask before frequenting these sites – better yet, avoid them.

4) If your pet has had a prior reaction or if it acted as if it may have had a reaction on a previous vaccination, discuss having your pet premedicated with an antihistamine injection. This is not a guarantee that a serious reaction will not occur. But it might lessen it’s severity. Remember, the severity of reactions to vaccinations and other foreign protein exposures tend to get worse with repeated exposure. Consider that first mild reaction, a warning ticket from your friendly traffic policeman. The next time he stops you he will probably not be that friendly.

5) Be particularly vigilant if you know that siblings or parents of your pet have had vaccine reactions.

6) Inquire if your State or City Health Department exempts reaction-prone pets from rabies vaccination. If your pet has a mellow temperament and only leaves the house on a leash, it is highly unlikely to bite. If you do not live in an endemic rabies-prone area – do a risk-benefit assessment of the situation before making a decision. In some cases, a ten day rabies quarantine after a bite incident might be preferable to the likelihood of a fatal anaphylactic reaction. Although I would question why one would harbor an untrustworthy pet. (In those situations one needs to know the limitations of your home or office liability insurance policy and your local laws as well).

6) Many pharmaceutical companies, now offers non-adjuvanted “3-year” vaccines for dogs, cats and ferrets. These are the vaccines that I use frequently. They are only called “3 year” because that was as long as the manufacturers tracked their effectiveness in preventing the diseases they were designed to prevent. Their effectiveness lasts much much longer. They contain none of the adjuvants that might cause cancer or auto-immune diseases later in your pet’s life; although I cannot guarantee that they do not contain other elements that might trigger anaphylactic responses. Another good choice, when available, are intranasal vaccines which require no injection at all – they are placed in your pet’s nose instead.

What Is Anaphylaxis?

Anaphylaxis is a sudden and violent allergic reaction to a foreign compound that has been introduced into your pet’s body. It is a more severe form of a slower but similar phenomenon, common allergy. Common allergies in your pet appear much slower and take the form of a rash and itching, respiratory congestion or vomiting and diarrhea.

An allergen, is any substance that causes either reaction. Most allergens are complex proteins. They are substances that the immune systems of a few pets and people recognize as “foreign” or “dangerous” but which cause no response in the majority of pets and people. An anaphylactic allergen can be a drug, an insect sting, a food ingredient, a vaccine component, any injected product containing large molecules or an ingredient in cosmetics.

Allergens cause the body to produce antibodies (immunoglobulins of the E class (IgE)). These IgE antibodies are bound or joined to cells in your pet’s blood called basophils and to tissue cells called mast cells. They cause both these cells to release powerful chemicals when they come in contact with an allergen they have “met” before. The chemicals these cells produce, cause negative changes in your pet’s heart function, blood pressure, blood vessel permeability as well as injury to surrounding tissue. These are the visible signs of anaphylaxis. There are two forms of anaphylaxis: true anaphylactic reaction and anaphylactoid (anaphylactic-like) reactions. Clinically, it is difficult to distinguish between the two.

How Anaphylaxis Works:

When mast cells living in the connective tissue are damaged, they secrete heparin and histamines. Histamine is an important chemical in causing the changes associated with anaphylaxis and inflammation. When your pet’s body is exposed to an allergen the first time, it’s body produces IgE antibodies that stick to these mast cells. When your pet is exposed to the allergen a second time, at some later date (even years later), the mast cells disintegrate, liberating heparin and histamines. Anaphylactoid reactions are identical to anaphylactic reactions in terms of clinical symptoms. However, anaphylactoid reactions are the result of non-immunological factors, which directly stimulate the mast cells. Unlike anaphylaxis, anaphylactoid reactions do not require a multiple exposures. A single exposure to the foreign agent can result in anaphylactoid symptoms. In both conditions, activation of mast cell histamine results in a number of physiological changes affecting respiration and circulation, which often cause life-threatening emergencies.

Symptoms of Anaphylaxis In Your Pet:

The symptoms of anaphylaxis will occur in your pet within one hour of exposure to the allergen. The most common form I see in my practice is anaphylaxis brought on by a booster vaccination. These reactions occur very rapidly – usually within thirty seconds. Many of the vaccine reactions that owners report to me do not meet the time factor or symptomatology of true anaphylaxis. I suspect that many of these reactions are at least partially psychological in nature because they usually occur in fearful or high-strung pets. This doesn’t mean they are not real. Fear causes the release of many physiological mediator chemicals that make drug reactions more likely. In mild cases, the only signs are low fevers, sluggishness and loss of appetite. Pets that develop a mild first case often go on to develop more severe cases during subsequent exposure to the allergen. In addition to these signs, moderate cases often develop urticaria, which is also called “goose bumps” hives or wheals. These raised patches develop over the head and trunk. Urticaria is a more common sign in dogs than in cats or ferrets. In anaphylaxis, the lips of dogs and cats may also become reddened and puffy. With time, areas of urticaria usually become intensely itchy and later peel like a sunburn.

If your pet is experiencing a severe cases of anaphylaxis, the first sign will be a rapid drop in blood pressure. This causes its gums to become pale and it’s breathing to become rapid and difficult. (ref) The pet often urinates, defecates and vomits in response to the histamine release. The pet’s heartbeat is often rapid, weak, or irregular and they often appear uncoordinated, restless and frightened. Bloody diarrhea or dark stools may follow. When swelling of the larynx occurs these pets can die due to their inability to breathe. In the most severe cases, shock, collapse, convulsions and coma, can occur. Sometimes the pet’s temperature falls to subnormal while others they run fevers.

Vaccination Reactions In Ferrets:

Throughout the 1950’s to 70’s the Fromm Corporation produced a chick embryo origin distemper vaccine for use in fox which also worked well in ferrets. When this Company merged with Solvay Corp., it ceased production of the vaccine. A similar product, Fervac-D was then introduced by United Vaccines. Although this Company denied it, this vaccine caused an unacceptably high incidence of anaphylactic episodes in ferrets. Signs of anaphylactic reaction in ferrets are hyperemia (bright red gums), salivation, swelling of the face and feet, dyspnea (difficulty breathing), and vomiting. Because of these reactions, I stopped using this product many years ago. Fortunately, an acceptable vaccine with low incidence of anaphylactic reactions is available, Purevax®, produced by Merial Pharmaceuticals (in 2017 acquired by Boehringer Ingelheim).

What You Can Do when Anaphylaxis Occurs:

Get your pet to a veterinarian as quickly as possible. Get someone else to drive you. On the way, stroke and reassure your pet and try to keep it calm. Place it on a blanket on its side with its rear legs slightly elevated. Loosen its collar. If it feels chilled, cover it. Do not give it anything by mouth – including water. If it stops breathing, begin CPR.

What Your Veterinarian Will Do:

Severe anaphylaxis is a veterinary emergency. Do not take a seat in the waiting room – ask that the veterinarian see your pet immediately. Call ahead to alert them if you can. If the pet is having difficulty breathing through its swollen larynx, the veterinarian will insert a tube into its windpipe. A drop in blood pressure and circulatory collapse starve the body of oxygen. This can be usually be corrected by putting the pet in an oxygen-rich environment. The liver and intestines are particularly affected in anaphylaxis. Capillary blood vesicles throughout the body become more permeable and leak blood serum into the tissues. To counteract this, intravenous fluids are usually given rapidly and in large quantities. These pets will be closely monitored so as not to over-flood their lungs with fluid (pulmonary edema). Salt solutions and fluids such as Ringer’s solution are often given to counteract circulatory collapse. Urination is a good sign that fluids are working. Colloidal fluids such as polysaccharide, dextran or hetastarch, are preferable to saline solutions because they do not leave the circulation (leak out) as rapidly as Ringer’s solutions and some advanced centers will use them. Many of these pets receive injections of epinephrine . This compound, normally produced by the adrenal gland, increases heart rate and blood pressure and slows mast cell disintegration. Oxygen therapy can also be very helpful, as can the intravenous administration of rapid-acting steroids such as prednisolone sodium succinate (SoluDeltaCortef®) or dexamethasone sodium phosphate (Decadron®). At the same time the pet may receive an injection of antihistamine (chlorpheniramine maleate, Chlor-Trimeton®) or diphenhydramine (Benadryl®). Pets that are hypothermic (low body temperature) are given warmth. Pets with a body temperature above 105F (40.5C) are rubbed down with iced water or chilled towels. Often, the pet is given an injection of a penicillin-like antibiotics to prevent secondary infections related to increased intestinal and pulmonary leakage.

Complications Of Anaphylaxis:

Sometimes nothing a veterinarian can do will stop the cascade of events that make up an anaphylactic episode. If this cascade can not be stopped, the pet will die or be left irreparably damaged. The liver suffers greatly during anaphylactic shock. It is the primary“shock-affected organ” in the body. This is because liver cells are very sensitive to oxygen deprivation (see the tests ). When the pet’s stomach and intestines do not receive enough oxygen during an anaphylactic crisis, their cells may die leading to fatal ulcers. These pets may vomit bloody mucous and/or pass blood in their stools. In some cases bacteria gain access to the abdominal cavity (peritonitis) through these ulcerated areas. In some cases entire segments of the intestine die. Another result of anaphylaxis can be a condition called disseminated intravascular coagulation (DIC). In this condition, pooled blood coagulates within the vessels of the circulatory system leading to a deficiency in platelets. Without sufficient platelets, hemorrhages occur throughout the body. This can also be fatal.

Preventing Anaphylactic Reactions In Your Pet:

Be sure to let your veterinarian know if your pet experienced any abnormalities subsequent to an injection. Do not be afraid to request that your pet be premedicated with antihistamines. In the case of vaccines, it is often the antibiotic added to the vaccine as a preservative which is the offending allergen.

Unfortunately, most cases of anaphylaxis are not expected. Pets can receive identical vaccinations for a number of years with no problems only to subsequently develop symptoms.

Once a pet has developed an anaphylactic reaction to vaccinations, I no longer suggest periodic booster shots. The only vaccine I will administer to these pets is a yearly rabies booster if required by law. The offending brand of vaccine should never again be used on the pet. If the reaction to rabies vaccine was life-threatening and the pet is at low risk of developing rabies I discuss the option of non-vaccination with the owners.

When I am only suspicious or have a vague premonition that a vaccination reaction might occur, I premedicate the pet with antihistamines 15 minutes prior to vaccination. Then I administer the smallest possible amount of the vaccine with a low dose syringe and observe the pet for an hour. If no reaction has occurred I give the remainder of the vaccine.

When a pet has developed an anaphylactic reaction to an insect sting or bite, I phone a prescription in to the owner’s pharmacy for an EpiPen®. This pen-shaped device is an auto-injector that administers epinephrine when tapped against the skin. I prescribe the junior size for cats and small dogs and the adult size for larger animals.


Many veterinarians still recommend that pets receive vaccinations much too frequently. The protection most vaccines afford lasts for years and some for a lifetime. In Western World, veterinarians have traditionally over-vaccinated pets to generate the revenue that helps supports under-charging for more complex procedures. A brave Texas veterinarians brought this uncomfortable fact into the limelight some years ago (ref). Before you revaccinate your pet, consider if the risks outweigh the needs and the benefits.

But do remember, certain properly-timed kitten-hood and puppy-hood vaccinations are absolutely essential – you wouldn’t go without a polio shot as a child. But you wouldn’t get a booster every year either!

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