Food Allergies

Canine Food Allergies – A Man-Made Problem

Does your dog itch and scratch? Does she suffer from recurrent ear infections, hot spots or hair loss? If so, she’s not alone.

Food allergies are a growing concern. In fact, it’s the third most common cause of allergies in dogs, after flea bite allergies and atopy.

It’s important to know the difference between a food allergy and intolerance. Food intolerance is the result of poor digestion and the results usually include diarrhea or other intestinal upsets.

Food allergies are the result of the over-response of the immune system to an invading food protein. Nearly all food your dog eats contains protein and these proteins all have the ability to trigger food allergies.

The most common proteins that cause allergy symptoms in dogs are beef, dairy and chicken, although some plant based proteins including corn, wheat and soy, can also be triggers.

While food allergies are an increasingly large problem in dogs, most vets and pet owners are most concerned with treating existing allergies through food elimination diets or immune suppressing drugs. But the cause of food allergies isn’t much understood.

Or it has been forgotten. After all, allergies have been around for over 100 years.

In 1913, French physiologist, Charles Robert Richet won a Nobel Prize for his vaccine experiments. He injected dogs with trace amounts of jellyfish poison, to see if the dogs would develop a tolerance to it. When he injected the dogs the first time, they seemed OK. When he injected them the second time, the dogs reacted violently and quickly died.

This response was opposite to the protection that Richet expected and he named this reaction ana-phylaxis. This is latin for anti-protection.

Curious about these results, Richet experimented further. Over the next few years, he injected trace amounts of milk and meat proteins into cats, rabbits and horses and found the same results. The first injection seemed to create a sensitivity to the injected protein.

These results weren’t a complete surprise to Richet. At the same time he was performing his research, Austrian pediatrician Clemens von Pirquet noticed that up to half of vaccinated children developed a strange illness after the first mass scale use of the diphtheria vaccine. This illness was simply called “serum sickness” until Pirquet began studying it. What he noticed was the symptoms were much like those in people who were hypersensitive to pollens and bee stings. In 1906, he created the word allergy to better describe this reactivity.

Large scale allergies like serum sickness were unknown before vaccines were developed. But by the turn of the century, doctors had clearly identified vaccines as a cause of allergy.

But this created a problem …

Serum disease, as this is called, is a man-made malady. If we had no curative serums and if there were no such thing as a hypodermic syringe with which to introduce the material under the skin, there would be no serum disease. Instead multitudes would still be dying from diphtheria and lockjaw … Thus, we find ourselves in somewhat of a dilemma, faced with the necessity for choosing the lesser of two potential evils.

Allergist Warren Vaughan, 1941 (Malady)

When dogs eat food protein, it’s first digested in the stomach where stomach acids enzymes break complex proteins into smaller pieces. This partially digested food then moves into the intestines, where it is further digested and the proteins are broken down into their smallest parts: amino acids. These amino acids are then absorbed by the body, where they pass through special cells called enterocytes. These cells are capable rejecting any amino acids they see as a threat.

When food proteins are injected directly into the blood stream, a type 1 hypersensitivity reaction against this new allergen causes a response in a type of immune cell called a TH2 lympocyte, which belongs to a subset of T cells that produce a cytokine called interleukin-4 (IL-4).

These TH2 cells interact with other lymphocytes called B cells, whose role is the production of antibodies.

Coupled with signals provided by IL-4, this interaction stimulates the B cell to begin production of a large amount of a type of antibody specific to food proteins, known as IgE.

Secreted IgE circulates in the blood and binds to an IgE-specific receptor on the surface of other kinds of immune cells called mast cells and basophils, which are both involved in the acute inflammatory response. The IgE-coated cells are then sensitized to the allergen (food proteins).

If the vaccinated dog now eats these foods, the food proteins bind to the IgE held on the surface of the mast cells or basophils. Cross-linking of the IgE and Fc receptors occurs when more than one IgE-receptor complex interacts with the same food allergenic molecule, and activates the sensitized cell.

Activated mast cells and basophils undergo a process called degranulation, during which they release histamine and other inflammatory chemical mediators (cytokines, interleukins, leukotrienes, and prostaglandins) from their granules into the surrounding tissue, causing several systemic responses, such as vasodilation, mucous secretion, nerve stimulation and smooth muscle contraction. This results in itchiness and anaphylaxis.

Depending on the individual dog, the allergen, and how it’s introduced, the symptoms can be system-wide (anaphylaxis), or localized to particular body system like the skin.

In other words, an allergic reaction occurs to the foods that contain the food proteins that were present in the vaccine.

For most viruses (like distemper and parvovirus), the pathogen itself needs to be grown and harvested to make the vaccine. This process begins with a small amount of virus, which needs to be grown in cells. Various types of cells can be used, including chicken embryos, calf serum, or other cell lines that reproduce quickly and repeatedly.

Once the antigen is grown, vaccine manufacturers try to isolate it from the cells. But proteins and other food particles can still be present in the vaccine. Then an adjuvant (a material that stimulates an exaggerated immune response) may be added, as well as stabilizers or preservatives.

The Centers for Disease Control (CDC) has a document called “Recommendations of the Advisory Committee on Immunization Practices (ACIP)”. This paper includes research from Nakayama et al (A clinical analysis of gelatin allergy and determination of its causal relationship to the previous administration of gelatin-containing acellular pertussis vaccine combined with diphtheria and tetanus toxoids. J Allergy Clin Immunol 1999). This is what they found:

In the same paper, Sakaguchi et al concluded the following: “We reconfirmed a strong relationship between systemic immediate-type allergic reactions, including anaphylaxis, to vaccines and the presence of specific IgE to gelatin.”

This is the same conclusion Charles Richet arrived at over 100 years ago. Several vaccines contain gelatin (which is derived from collagen, normally from cows or pigs), as well as other food proteins.

Robert S. Mendelsohn MD, professor of pediatrics at the University of Illinois warns,

No one knows the long term consequences of injecting foreign proteins into the body. Even more shocking is the fact that no one is making any structured effort to find out.

Until the day comes when scientist, vets and doctors make an effort to learn more about how these injected foreign proteins cause allergies and many other auto-immune diseases in our dogs (and ourselves), it seems the best approach to food allergies in dogs is prevention.

As allergist Warren Vaughan said, we find ourselves in somewhat of a dilemma, faced with the necessity for choosing the lesser of two potential evils.

As savvy vets and pet owners are starting to delve deeper into the safety and even the necessity of vaccines, the next hundred years of what will hopefully be more objective vaccine research, might make a difference in which evil pet owners will choose.


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