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What is Rabies Vaccine Allergy?

If your horse is bitten by an infected animal, symptoms will usually present within 2-9 weeks but can take longer than 6 months. Horses are naturally curious and will investigate other animals, including wildlife. This makes them more susceptible to getting nipped or bitten by a potentially rabid animal. Therefore, vaccinating your horse against rabies is essential. 

The equine rabies vaccine contains mercury and this can cause your horse to have an allergic reaction to the vaccine. Mercury is a very potent neurotoxin. Some horses are very sensitive to mercury and will begin exhibiting symptoms that can be alarming.

Rabies is a viral, zoonotic disease. This means it can pass between species. Rabies is transmitted through the saliva or the tissues of the nervous system from an infected mammal to another mammal, including humans. Rabies attacks the central nervous system and will cause severe neurological symptoms before causing the infected mammal to die. It is the deadliest disease in the world and has a fatality rate of 99.9%.

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Symptoms of Rabies Vaccine Allergy in Horses

It is necessary that your horse receive a rabies vaccine, for equines it is recommended that they have a rabies vaccine yearly. For horse owners who have horses that experience an allergy to the rabies vaccine, it can be scary when it is time to vaccinate. Always have your veterinarian present when the rabies vaccine is administered. Symptoms of rabies vaccine allergy include:

  • Soreness at the injection site
  • Swelling at or near the injection site
  • Abscess develops at or near the injection site
  • Limb or muscle swelling 
  • Fever
  • Stiffness 
  • Lethargy
  • Refusal to eat
  • Difficulty breathing
  • Anaphylaxis

Causes of Rabies Vaccine Allergy in Horses

Equine rabies vaccines contain mercury. Mercury is a known neurotoxin and horses that are sensitive to neurotoxins will show symptoms of an allergic reaction. Many of these reactions will not present immediately following the injection of the vaccine; instead, it could take up to 30 days for symptoms to appear. Anaphylaxis will generally appear within 12-24 hours of the vaccine being given. 

It is best for your horse to only receive one vaccination at a time and not receive all needed vaccines in the same day. Your veterinarian can set up a vaccination schedule for your horse that will limit the number of vaccinations administered at one time.

Diagnosis of Rabies Vaccine Allergy in Horses

Depending on the severity of the symptoms and how quickly they present, diagnosing an allergic reaction to the rabies vaccine can be easy. If your horse experiences anaphylaxis following the administration of the rabies vaccine, obviously they have an intolerance to the vaccine. When symptoms occur several days to weeks later it can become more difficult to determine the exact cause.

Your veterinarian will review your horse’s medical history as well as current medications and supplements. They will perform a full physical examination of your horse including a complete blood count, biochemistry panel and urinalysis. These tests will rule out other causes and help narrow your veterinarian’s search. 

Be sure to tell your veterinarian about any vaccines that your horse recently received and where on your horse’s body the injection was given. Swelling, pain or abscesses near an injection site will alert your veterinarian as to what is causing your horse problems.

Treatment of Rabies Vaccine Allergy in Horses

When your veterinarian has diagnosed your horse with a rabies vaccine allergy, they will discuss what treatments can be done. Treatments will depend on the severity of the reaction. Pain, mild fever and mild swelling will generally go away without medical treatment. Close observation will be necessary to ensure that the problem does not get worse and does not persist longer than a few days.

Horses that have developed abscesses near the injection site may need to have the abscess drained. This is done by cutting open the abscess and draining the pus that has formed. Antibiotic medication will be prescribed, either orally or injectable, to prevent further infection from occurring. 

Anti-inflammation medications may also be given if your horse is experiencing extreme swelling in their limbs. Pain medications can also be prescribed if your horse is in severe pain from the rabies vaccine.

Severe reactions include difficulty breathing and anaphylactic shock. When your horse is experiencing anaphylaxis their blood pressure will drop suddenly and their airways will narrow potentially blocking normal breathing. This can be fatal if not treated immediately. Generally, anaphylaxis will occur within 30 minutes of receiving the vaccine but it can occur up to 24 hours after receiving the vaccine. It is important that your veterinarian be close by in the event that your horse suffers from anaphylaxis after receiving the rabies vaccine. 

If your horse suffers from anaphylactic shock, your veterinarian may recommend your horse be hospitalized for a day to closely monitor their vitals and ensure that they are recovering from the allergic reaction. Your veterinarian will need to make a note in your horse’s file about their allergy to the rabies vaccine.

Recovery of Rabies Vaccine Allergy in Horses

There are some measures that can be taken to try and prevent your horse from having another reaction to the rabies vaccine. This can include changing brands and changing injection sites. If your veterinarian has other brands of rabies vaccines available, ask them to not give the same brand that they gave before to see if your horse can tolerate the vaccine.  Give the injection in a different location, such as the other side of the rump or the neck. 

There has been some success with horses suffering from vaccine allergies that are exercised after the vaccination. In other words, once your horse receives their vaccine, get them out and moving. Exercise gets your horse’s blood pumping and the blood then circulates more quickly through the muscle and the vaccine moves through the entire body faster.

Rabies Vaccine Allergy Questions and Advice from Veterinary Professionals

Arab Mare
8 Years
Serious condition
0 found helpful
Serious condition

Has Symptoms

lack of appetite

Just found this site and sharing my experience in case anyone else has a vet dismiss the possibility of a delayed vaccine reaction.
My Arabian mare had a delayed reaction to the rabies vaccine, not once but twice. The first year it happened, the rabies vaccine was given during the same vet visit that she received her combo vaccines. At about 21 days, I thought I noticed her being a bit lethargic when stalled, didn't greet me with the typical whinny when I arrived in the morning, etc., but seemed to move around and act pretty much normal when turned out. A couple more days passed, I noticed she wasn't eating as enthusiastically and was still hanging back a bit in her stall. Then, I'd say at about day 27, I came to the barn in the morning to find she was sweaty across her back. Called the vet. Horse had a temp of 103 or 104. At first the vet suspected Potomac Fever and began treatment (don't recall all she was given, but I remember an IV was hooked up, may have drawn a blood specimen). Vet said she would be out the next morning to do the next treatment. When vet arrived the next morning, it was like a different horse was standing before her. Totally back to normal. Vet remarked, "I guess we can rule out Potomac Fever since she responded so quickly." I remarked that I suspected a vaccine reaction, but vet doubted it since she said they usually happen within 24 hours.
Fast forward to the next year. Time for vaccines. I decided we would only do one vaccine this time. Vet administered the rabies vaccine. I kept a close watch on the mare the following weeks. Same timeline post vaccine, at about 21 days, I noticed the mare being more stand offish (and this is an in your pocket type mare) and not eating as enthusiastically, and called the vet out. This time a different vet from the same clinic came and and he agreed with me, since the time line was the same, and the only vaccine that was administered was the rabies vaccine, he agreed it was a vaccine reaction. At least this time I caught things before they got as bad as the previous year.

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16 Years
Serious condition
0 found helpful
Serious condition

Has Symptoms

Rapid Heartbeat

Our gelding was given a rabies shot and a flu/rhino shot in the late morning. The next morning he ate breakfast and was turned out in his
own paddock. I saw him, he whinied to me, and then dropped and rolled and kept getting up and rolling, he would walk with me and then
roll, he did not sweat, he did not paw. His legs got wobbly and he had trouble breathing.
The vet. that gave the shot was local and refused to take our call and it was an Emergency. Another vet, came to give him iv's and tube him.
This went on all day and he Stood the Entire time by then. She gave him Rompun. He wanted to eat grass but could not swallow it.
What does this sound like? Someone said he had an anaphlyactic reaction and was Abandoned by his regular vet who administered the
shot. He never even called to see how he was feeling. They sent a cow doctor. What does this sound like to you? Thank you.

Dr. Callum Turner, DVM
Dr. Callum Turner, DVM
3320 Recommendations

Adverse reactions to rabies vaccination may occur and are more common than other vaccines; but in high risk areas or horses (or other animals at risk) the risk of the vaccine will be less than the severity of clinical disease with rabies. Future vaccinations should be done with caution and if not 100% necessary for the rabies vaccine to be administered you should not vaccinate; if you live in an at risk area then consult your (or a new) Veterinarian. I don’t know why your local Veterinarian didn’t respond to the emergency call or why they didn’t at least call back to check on Leo.  Regards Dr Callum Turner DVM

Hi Dr. Turner,
What are the signs of an anaphylactic reaction to spring shots - rabies and flu/rhino....Leo was fine that evening, he had his breakfast the next
morning and later that morning when he was turned out he seemed fine - when he saw me drive up he Whinied loudly, dropped and rolled,
as I explained in my first comment he got stressed, he did not sweat, he had a b.m., he did not paw. He did Not want the nice carrot I put to him
- that Never happened in 5.6 years we owned him! That is when I knew - something is Wrong...then he started to roll! He did not seem to be able to
swallow and I think his throat was swollen if he had a bad reaction. The 2nd. vet. ultrasounded him and did a belly tap, the tap was Clear, that was
good but then they said we Think He might have a problem inside. We had a second opinion on the ultasound at a later time, and they said there
was Nothing there! Leo Stood in the Wash stall and then walked to his Stall with me and STOOD FOR HOURS like this! That does not sound like
a Horse that had a strangulation in his abdomen - we think he was misdiagnosed and his Vet. for years was not even Decent enough to call us back.
And - never did - What do you think the situation was here?

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