Vaccines and Adverse Reactions

Vaccine Reactions in Horses

by Robert N. Oglesby DVM

Introduction

Introduction » Diagnosing Vaccine Reactions » How Vaccines Cause Reactions » Treatment of Local Reactions » Treatment of Systemic Reactions » Prevention of Severe Reactions » More Info & Discussions

There is no doubt vaccinations have greatly reduced the incidence of life threatening diseases in horses. Tetanus, eastern viral encephalitis, western viral encephalitis and Venezuelan viral encephalitis are examples of diseases that have been greatly reduced in horses due to vaccination. But vaccinating is not a innocuous procedure. Local reactions that vary from mild soreness to full blown abscesses are possible. Systemic reaction from mild fever to life threatening anaphylactic reactions can occur. This article discusses these reactions, treatment, and prevention. Also discussed are the various vaccines propensity for causing reactions versus their efficacy.

Diagnosing Vaccine Reactions

Introduction » Diagnosing Vaccine Reactions » How Vaccines Cause Reactions » Treatment of Local Reactions » Treatment of Systemic Reactions » Prevention of Severe Reactions » More Info & Discussions

Just about any illness that occurs around a vaccination can be suspect as a vaccine reaction. However atypical events away from the injection site may of may not be related to the vaccine and investigations for other causes should be undertaken. The type of reaction along with its frequency and severity varies by the type vaccine given and the technique used, for information on a specific vaccine efficacy and reaction rate see the article on the disease. Vaccine reactions are usually divided into 2 types: reactions at the site of the injection called local reactions, and those that are due to a systemic response.

Local Reactions

Local reactions can range from local inflammation to infection. Good technique will minimize reactions. Taking the symptoms in approximate order of severity and from symptoms of transient inflammation to abscessation:
  • Symptoms of transient inflammation usually occurring 24 to 72 hours post vaccination. One or all of these symptoms may be present, usually developing in the order given:
    • Mild soreness at the site of injection
    • Stiffness walking. If given in the neck it may appear as a generalized stiffness and inability to lower the head and if given in the hip or leg lameness may result. The stiffness and soreness following vaccination can be remarkable accompanied by a short shuffling gait resembling founder.
    • Fever, depression, inappetence that responds to NSAID's (see treatment below).
    • Mild painful swelling that responds to NSAID's (see treatment below).
  • Symptoms of abscess formation, usually following a week of symptoms of inflammation:
    • persistent and worsening remarkable swelling, soreness, stiffness, depression, fever that does not respond to NSAID's.
Vaccines differ in their ability to cause local irritation. Most of the common vaccines for life threatening diseases (tetanus, the viral encephalitides, and rabies) are efficacious and have a low local reaction rate. It is probable that all horses receiving these vaccines have some reaction: have you ever had a tetanus shot that did not cause some soreness? But when given properly most of these reactions are subclinical and do not cause overt soreness or swelling, the local reaction rate of these is on the order of 5%. On the other hand influenza and herpes vaccines have a higher reaction rate that approach 10 to 20%. Worse of the commonly used injectable vaccines is the Strangles vaccine, with a local reaction rate of around 30 to 60%, with the stiffness worse than for the other vaccines.

The abscess can be either sterile or infected. Sterile abscesses form when the reaction is severe enough to cause local necrosis and white blood cells flood the area in an attempt to clean up the necrosis. Infections maybe introduced by the injection but may also be activated bacteria that were lying dormant in the muscle tissue. Serious clostridial myositis can occur this way.

Systemic Reactions

Systemic reactions can develop within minutes to hours after administration of the vaccine.
  • Hives: may be a precursor to developing anaphylaxis
  • Colic: cause unknown, perhaps a drop in blood pressure?
  • Anaphylaxis: allergic shock, usually first noted as respiratory distress in horses.
  • Purpura: immune mediated vasculitis, bilateral hot swelling in the legs, may take weeks to develop
Whether you get a local reactions or systemic reaction depends on which part of the immune system is over stimulated.

How Vaccines Cause Reactions

Introduction » Diagnosing Vaccine Reactions » How Vaccines Cause Reactions » Treatment of Local Reactions » Treatment of Systemic Reactions » Prevention of Severe Reactions » More Info & Discussions

                       
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