A Health Advisory to Dog Owners
WHAT IS CANINE ANAPHYLAXIS?
Anaphylaxis is a potentially
fatal allergic reaction to a foreign agent such as insect venom, vaccines,
drugs, etc. This allergic response involves the mast cells, a type of
connective tissue cell which secretes heparin and histamines, and thus plays
a role in inflammatory reactions. There are two forms of anaphylaxis:
anaphylactic reaction and anaphylactoid reaction.
Anaphylactic reactions are
immune-mediated, that is, when a dog is exposed to a particular agent,
called an antigen, for the first time, its body will produce antibodies to
that agent which bind to the mast cells. When the dog is exposed to the same
agent at a later time, these antibodies activate the mast cells to produce
an inflammatory response.
Anaphalactoid reactions are
identical to anaphylactic reactions in terms of clinical symptoms, however,
anaphylactoid reactions are the result of non-immunological factors which
directly activate the mast cells. As such, a single exposure to the foreign
agent may result in clinical symptoms.
In both conditions, activation
of mast cells results in a number of physiological changes affecting
respiration and circulation which may present a life-threatening emergency.
WHAT ARE SOME AGENTS WHICH CAUSE
Snake or insect venom, the
leptospirosis component or preservatives in canine vaccines, and antibiotics
and other drugs are some of the common agents which can bring on
WHAT ARE THE SYMPTOMS OF
Symptoms of anaphylaxis
usually occur within one hour following exposure to the agent. Reaction may
be restricted to the site of contact with the agent as seen with local
swelling and redness associated with insect stings or may occur systemically
in which the whole body will swell. Dogs suffering from systemic anaphylaxis
are usually restless and excitable. Vomiting and bloody diarrhea, followed
by collapse, convulsions, coma and eventually death indicate a state of
anaphylactic shock secondary to systemic anaphylaxis.
WHAT IS THE TREATMENT FOR
constitutes a medical emergency. Circulatory collapse associated with
anaphylaxis results in oxygen deprivation to major organs particularly the
liver and gastrointestinal system. Fluid therapy to replace blood volume and
epinephrine, which serves to increase blood flow as well as inactivate mast
cell response, are the first course of treatment for anaphylaxis. Oxygen
therapy may also be necessary.
Follow-up therapy includes
administration of corticosteroids and antihistamines to control persistent
mass cell release. Additionally, antibiotic therapy is indicated to prevent
secondary infection related to gastrointestinal permeability which occurs
during systemic anaphylaxis.
WHAT ARE SOME COMPLICATIONS
ASSOCIATED WITH ANAPHYLAXIS?
Complications associated with
anaphylaxis can be severe and result in long-term or irreparable damage.
Because the liver is considered as the major "shock organ" in canines
experiencing anaphylaxis, liver damage can lead to liver disease. Loss of
blood supply to the gastrointestinal system often results in "gastric
ischemia" which is death of the tissue lining the intestines and presents as
hemorrhagic diarrhea and vomitus. Under these circumstances, permeability of
the intestines can lead to release of bacteria which may cause peritonitis.
In some cases, whole sections of the intestine may die requiring surgical
resection. Yet more severe cases may cause complete collapse of the
gastrointestinal system. Additionally, one occurrence in anaphylaxis is the
pooling and coagulation of blood which leads to a decrease in circulating
platelets. This decrease in platelets has the potential to result in
CAN ANAPHYLAXIS BE PREVENTED?
usually occurs unexpectedly and very rapidly. The key to prevention is to
avoid the agent which produces the reaction. However, in regard to vaccine
and drug reactions there is no reliable prevention for anaphylaxis; rather,
reducing the severity of the reaction has become the next best
recommendation. In regard to reactions to vaccines, it is recommended that
following vaccination the dog be observed in the veterinarianís office for
at least half-an-hour before leaving. In this way, the dog will have
immediate medical attention if a reaction occurs. In those dogs which have a
previous history of anaphylaxis, pretreatment with antihistamines or
corticosteroids are methods currently used to reduce reaction severity.
Cohen, R. D., Systemic
anaphylaxis. In Kirk, R.W. (ed): Current Veterinary Therapy XII. Philadelphia,
WB Saunders Co., 1995, p.150.