Allergic Reactions, Shock, Vaccine Reactions And Anaphylaxis

In Your Dog, Cat Or Ferret

Ron Hines DVM PhD

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What Is Anaphylaxis?

Anaphylaxis is a sudden and violent allergic reaction to a normally harmless substance (an allergen) that has been introduced into your pet’s body. It is a more severe form of the milder and slower phenomenon, common allergies. Common allergies in your dog or other pet are much more common than severe anaphylactic reactions. Allergies in dogs usually take the form of itchy skin, itchy ears, and itchy, reddened eyes. A few cats suffer allergy or anaphylactic problems too, but in cats, it is their respiratory tract is often the primary allergy target. When it is your pet’s digestive system that is the primary target, vomiting and diarrhea are common. In between the two, allergy and anaphylaxis, are hives  – more rapid and intense than allergies, but less severe than anaphylaxis. All three share common immune system pathways, and the milder forms are sometimes only a prelude to eventually developing the more severe ones. 

Most allergens are large, complex protein molecules. They are substances that your pet’s immune system has mistakenly identified as “foreign and dangerous”. As such, your pet’s immune system will attempt to destroy them. A potential anaphylactic allergen can be a drug, an insect sting, a vaccine component, a food ingredient – any product containing large complex organic molecules that manage to enter its body. The immune system cells that have made this mistaken decision are your pet’s CD4+ T cells. When these T cells make that mistake, they cause your pet’s body to produce antibodies (immunoglobulins of the E class IgE). These antibodies reside on the surface of cells in your pet’s blood called basophils and on tissue cells called mast cells. When the IgE coated receptors on these cells encounter the specific antigen they were designed to recognize, they release powerful inflammatory chemicals (= degranulation). Depending on the amount of these inflammatory chemicals released, where in your pet’s body they are release, and the speed with which they are released, these compounds can cause anything from a mild itch to destructive changes in your pet’s heart function, blood pressure, blood vessel permeability (leakage) as well as injury to the surrounding tissue. These are the visible and invisible components of anaphylaxis. 

What Are The Symptoms of Anaphylaxis?

The symptoms of a typical anaphylactic reaction occur within one hour of exposure to the allergen product, whatever it was. The most common form veterinarians like myself see are attacks brought on by a booster vaccination. But I also encounter them in pets after bee or fire ant stings. As I mentioned, these reactions occur very rapidly – often within thirty seconds. When they do not meet the one-hour time factor or the symptomatology of true anaphylaxis, I suspect that many of these reactions are at least partially psychological in nature because they usually occur in fearful, anxious or high-strung pets. That doesn’t mean they are not real. Fear and anxiety causes the release of many physiological mediator chemicals that make drug reactions more likely and sometimes worse. 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 same allergen. In addition to these signs, moderate cases often develop urticaria, which is also called “goose bumps” hives or wheals. These raised patches develop primarily over the pet’s 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.

When your pet experiences a severe cases of anaphylaxis, the first sign will often be a rapid drop in its blood pressure. This causes its gums to become pale, and it’s breathing to become rapid and difficult. These pets often urinate, defecate and vomit in response to the histamines released. Their heartbeat is often rapid, weak, or irregular, and pets experiencing these reactions often appear uncoordinated, restless and frightened. Bloody diarrhea or dark stools may follow. When swelling of their larynx occurs they 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 run fevers.

Allergic And Anaphylactic Reactions To Vaccines

Veterinarians tend to think of dog, cat and ferret vaccinations and anaphylaxis together – although, as I mentioned, many things, from bee stings to food can trigger an anaphylactic event. (read here) Please remember that the vast majority of pets that receive vaccinations will not experience anaphylaxis. But the event is so dramatic and destructive when it does occur that no one having viewed one will ever forget it. One critically important factor in anaphylaxis is the genetic susceptibility of your pet. (read here) But other factors come into play. The production of the virus and bacteria that vaccines contain require a complicated “brewing” processes. In that process, many potentially allergenic proteins are added: living cell from various species other than dogs and cats, bovine serum albumin, embryonating chicken eggs or fibroblasts all to allow tissue culture cells and the pathogenic organisms they contain to grow and multiply. Attempts are always made to remove as much of these ingredients from the final vaccine products as possible. But those attempts are never 100% successful and the immune system of a dog, cat or ferret can recognize exquisitely small amounts of those residues. Most veterinarians believe that when anaphylactic reactions do occur subsequent to a vaccination, they are probably due to ingredients other than the bacterial or viral components the vaccine contains. Keep in mind that the more often you ask your pet’s immune system to deal with the ingredients in vaccines, the more opportunities you give your pet’s CD4+ T cells to make judgement errors – another reason to not over vaccinate. Antibiotics, are also added to many vaccines to minimize the possibility that bacteria will be carried into your pet’s body with the hypodermic needle. The most common antibiotic added to veterinary vaccines is gentamycin

When a vaccine contains killed bacteria, some of the proteins in those bacteria have the potential to cause anaphylactic reactions themselves. I believe that is particularly true for dog vaccines that contain killed leptospirosis organism or their protein-containing fragments. Those type of vaccine is called a bacterin. They contain every protein that was present in the living disease organism. (read here) In one study, scientists identified 3,654 distinct leptospirosis proteins. (read here) That is probably why canine vaccines that contain leptospirosis are the most prone to unwanted side effects. 

I Read That Anaphylactic Reactions Never Occur During A Pet’s First Exposure To A Vaccine. But This Was My Pet’s First Time!

In pets (and people), anaphylactic reactions are not thought to be able to occur until the second or more time that the immune system encounters a specific antigen (a foreign protein). Until recently, veterinarians just called those mysterious first-encounter vaccine reactions “anaphylactoid” reactions for lack of a better word. But there are several ways a first-time-exposure vaccine reaction might occur: It might be that your pet had already become allergic to one of the many ingredients in the vaccine – one of the many added vaccine ingredients I previously mentioned.  Or, it might have been that the vaccine contained a protein very similar to some other protein your pet was already allergic too. Some antibodies are promiscuous. That is, the antibody alerts the immune system to more than one distinct antigen protein. (read here)   IgE antibodies, the basis of all allergic and anaphylactic reactions, are known to occasionally be promiscuous. (read here)  Veterinarians in Brazil learned that when they discovered that cattle, recently vaccinated against leptospirosis, then gave false-positive antibody tests for exposure to brucellosis. The cow’s antibodies were cross-reacting. (read here)   

What Should I Do When An Anaphylactic Event Occurs?

Get your pet to your veterinarian as quickly as possible. If possible, have someone else 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. Remove its collar. If it feels chilled, cover it. Do not give it anything by mouth. That includes water. If it stops breathing, begin CPR. Always remember that agitated and frightened pets will sometimes bite the ones they love. 

What Your Veterinarian Will Do:

A severe anaphylactic reaction is always a veterinary emergency. Severe means any time the reaction is affecting your pet’s breathing. Call ahead to alert your veterinarian if you can. Don’t take a seat in the waiting room – ask the receptionist to have your pet examined immediately. If your pet is having difficulty breathing because of a swollen larynx, your veterinarian might insert an endotracheal tube down its windpipe. A drop in blood pressure and circulatory collapse starve the body of oxygen. In less severe situations, that can be usually corrected if the pet is placed in an oxygen-rich environment. When the situation is more critical, pure oxygen can be supplied through the plastic tracheal tube using rhythmic hand pressure (“bagging”) or mechanically.  The liver, intestines and kidneys of pets in anaphylaxis are also affected. There, and throughout its body, capillary blood vesicles become more permeable and leak blood serum into tissues, dangerously decreasing its blood volume. To counteract this, veterinarians usually placed your pet on an intravenous “drip” of sterile fluids. These pets need to be closely monitored so as not to over-flood their lungs with fluid (pulmonary edema). Balanced crystalloid salt solutions and such as Ringer’s solution are often given to counteract circulatory collapse. (read here) Urination and return to a more normal respiratory pattern are both a very positive signs that these fluids are helping. Intravenous fluids containing blood volume expanders such as dextran are preferred by some veterinarians over simple saline solutions because they do not leave the circulation (leak out) as rapidly as Ringer’s and similar products. Some advanced veterinary centers use them when they believe that they are more appropriate. Most of these struggling pets also receive injections of epinephrine. Epinephrine is normally produced by your pet’s adrenal glands. It increases heart rate and blood pressure and slows mast cell disintegration – the underlying cause of anaphylaxis. In severe cases, besides oxygen, epinephrine, intravenous administration of rapidly-acting steroids such as prednisolone sodium succinate (SoluDeltaCortef®) are often given. It is unclear how effective they are. At the same time your pet might receive an injection of an H1 antihistamine (e.g. chlorpheniramine maleate/Chlor-Trimeton® or diphenhydramine/Benadryl®). Pets that have abnormally low body temperature (hypothermic) need supplemental warmth. Pets with a body temperature above 104.5 F (40.3 C) need to be wrapped in chilled soaked towels. Pets in anaphylaxis are often also given an injection of a penicillin-class antibiotic to prevent secondary infections related to their increased intestinal and pulmonary susceptibility to infection (increased permeability to bacteria).

What Complications Might Occur?

Sometimes, nothing I can do will halt the cascade of events that make up an anaphylactic episode. Your pet’s situation can become critical so quickly. If this cascade cannot be stopped, the pet will die or be left irreparably damaged. I mentioned that your pet’s liver might suffers greatly during an anaphylactic shock episode. Many believe that it is the primary “shock-affected organ” in the body. That is because liver cells are very sensitive to oxygen deprivation. After initial recovery, your veterinarian might detect that injury through specific blood tests.  When your pet’s stomach and intestines do not receive enough oxygen during an anaphylactic crisis, their cells may die leading to fatal ulcers. Pets so affected often vomit bloody mucous and/or pass blood in their stools. In some cases bacteria gain access to the animal’s abdominal cavity (peritonitis) through these ulcerated areas – another good reason for antibiotic injections. In some severe 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.

Are There Ways I Can Prevent An Anaphylactic Reaction?

Be sure to let your veterinarian know if your pet experienced any abnormalities subsequent to any injection in the past. Do not be afraid to request that your pet be premedicated with antihistamines. Antihistamines do not affect the effectiveness of veterinary vaccines.  Unfortunately, most cases of anaphylaxis occur unexpectedly. Pets can receive identical vaccinations for a number of years with no problems, only to subsequently develop symptoms after the current one. Once a dog, cat or ferret has developed a reaction to a vaccination of any kind, I no longer suggest periodic booster shots. The only vaccine I will administer to these pets is a periodic rabies booster as the law requires. Request a 3-year duration rabies vaccine be given. An offending brand of vaccine that caused anaphylactic or other undesirable effects in your pet should never be used again. If you have premonitions that an anaphylactic reaction might occur, or if one did in the past, have your veterinarian phone in a prescription for an Epipen® or Epipen Jr. or competing brand. Many physicians have decided that although the directions suggest that the minimum body weight for an Epipen Jr is 33 lbs/15 kg, it can be administered safely to human infants weighing as little as 22 pounds (10 kg). For pets that weigh less than that, your veterinarian will have to dispense a hypodermic syringe and needle with the appropriate dose. The pediatric Epipen Jr. contains 0.15 mg of epinephrine. 

Occasionally, I have vague premonitions that a vaccination reaction might occur in a pet. Perhaps the pet has symptoms of autoimmune disease or evidence of some other corticosteroid-responsive disease such as atopic dermatitis or IBD & here. Perhaps it came to my hospital with urticaria in the past after a supposed bee or ant sting, spider bite, food allergy, etc. Perhaps the breeder sold prior litters that experienced anaphylactic issues. Your pet’s genetics can play an important role in its susceptibility to anaphylaxis too. (read here) In all those situations, I pre-medicate the pet with an injection of antihistamine, 30 minutes prior to vaccination. Then I administer the smallest possible amount of the vaccine with a low dose syringe and observe the pet for a half hour. If no reaction has occurred I give the remainder of the vaccine with epinephrine and oxygen close at hand.  

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