Hives
Your hor is telling you there's something wrong; the problem is, it's in Braille.
By Nancy S. Loving, DVM
At all times a hor’s body is under siege from the abundance of microorganisms prent everywhere. A healthy immune system keeps the minute organisms at bay as inflammatory cells wage invisible battles to repel foreign proteins (antigens) attempting to invade the body. Normally, the immune system holds its line of defen without the hor even knowing that its immune system is at work.
When microbes invade and colonize, a hor shows clinical signs of dia. But occasionally, an immune respon overreacts to a noninfectious cau. Such a hypernsitivity respon is referred to as an allergy; it can range from a rious, life‐threatening systemic reaction (anaphylaxis) to a mild, but disagreeable, skin reaction such as hives or itching.
Hives are a clinical sign rather than a specific dia. Also referred to as urticaria, hives tend to develop about the neck and shoulders, along the thorax, and on the buttocks. Urtica is Latin for “stin
ging nettle” and if you’ve ever walked through a cop of stinging nettles, besides immediate discomfort you’ll appreciate just how quickly bumps form on your skin. Hor owners often refer to the bumps as feed bumps, protein bumps, or heat bumps, since the terms describe some caus of hives. Usually, an allergic reaction remains localized to the skin, but if clinical signs persist or are not arrested early on, there might be a systemic respon as the internal workings of a hor’s body wage war on the offending allergen.
What is an Allergy?
Constant surveillance by a hor’s immune system helps it recognize foreign proteins as a threat. In respon, the immune system manufactures antibody proteins directed toward specific antigenic targets. Patrick Henl, DrMedVet, Dipl. ACVD, is a board‐certified specialist in dermatology at the University of Georgia College of Veterinary Medicine. He explains, “An allergic reaction usually is not prent with first exposure to an allergenic protein. Clinical signs start to appear once the skin becomes nsitized and re‐expod to an offending allergen.”
Becau hypernsitivity reactions take weeks to months or even years to develop, a sudden ont of hives is not necessarily a result of a recent change; this makes it difficult to pin down the actual source of the problem.
“An allergic reaction usually is not prent with first exposure to an allergenic protein. Clinical signs start to appear once the skin becomes nsitized and re‐expod to an offending allergen.” ‐‐Patrick Henl, DrMedVet, Dipl. ACVD
Henl notes, “Many caus of urticaria have been identified, including medications such as antibiotics, antiparasitic drugs, hormones, vaccines, foods like plants, hay, and supplements, or are due to hypernsitivities like an adver food reaction, contact allergy, or genetically linked atopy (an allergic reaction with strong family tendencies). Occasionally urticaria develops from bacterial, fungal, or parasitic infections, or from stinging incts.”
Allergen‐specific antibodies (immunoglobulin E, or IgE), preprogrammed on first exposure, trigger a Type I hypernsitivity reaction the next time they encounter that antigen. The unique structure of IgE antibodies
allows them to bind to the surface of mast cells (resident cells of connective tissue) and basophils (specialized white blood cells) and nsitize them. When nsitized mast cells again contact the allergen, they relea biochemical substances such as prostaglandins and histamines, which elicit a cascade of inflammatory events. Once this chain reaction is under way, localized inflammation begins within minutes of the chemical summons.
Hives can develop on the skin in as few as 15 minutes or up to 24 hours following exposure to a foreign protein; luckily, they resolve as quickly.
What are Hives?
Urticaria is en as localized, raid bumps on the skin. The can vary in number, verity, and frequency of occurrence.
Inflammation induced by allergens caus small veins to dilate and increa capillary permeability in the skin. “Fluid” leaks into surrounding tissues to form wheals or plaques of edema (fluid swelling). The first appear as small, firm lumps, which might coalesce into a large plaque or line of bumps. In a ca of noncomplicated hives, overlying skin appears normal with no hair loss and usually no itching.
William Miller, VMD, Dipl. ACVD, chief of dermatology at Cornell University College of Veterinary Medicine and board‐certified in dermatology, says other types of hor bumps are compod of cells rather than “fluid” so you can usually tell the difference by their feel. Hives are easily compresd, leaving behind a fingertip imprint of pitting edema, whereas other nodular lesions have cellular infiltration, such as scar tissue or a tumor, and they are firm and noncompressible.
Miller notes that the size of a wheal (hive) is influenced by various things, but, he stress, “In the broadest n, the bigger the hive, the more reactive the hor. A typical hive takes between 15 and 30 minutes to reach its maximum size. Once the trigger event is gone, the hive usually only lasts for an hour or so.”
In certain situations, though, the hive process can persist. Miller clarifies, “If a hor eats something he is allergic to, hives can last for days. However, an individual hive bump does not last that long. As one hive disappears, a new one appears, making an owner believe that the hives are persisting. The only way to follow a specific hive bump is to circle an individual lesion, then check it hourly.”
Henl notes, “Pollens, foods, and drugs are the most likely ‘systemic’ caus of hives, which is a common clinical sign in hors with allergies. However, nonallergic factors such as pressure, sunlight, heat, cold, exerci, psychological stress, genetic abnormalities, and adver reactions to drugs or chemicals need to be kept in mind as potential caus of urticaria.”
Any of the factors can intensify an allergic respon.
Both practitioners report that incts are not usually a direct cau of hives, unless a hor is allergic to that particular inct. Henl elaborates: “Papular urticaria are small‐diameter (3–6 mm) reddened
bumps with the appearance of hives. More typically, inct bite hypernsitivities cau other clinical signs such as asonal itch. Associated inten itching caus the hors to continually traumatize themlves with scratching, rubbing, and biting. This creates hair loss, crusting lesions, and skin trauma, particularly along the mane, ba of the tail, lower thorax, and abdomen.”
An allergic respon of hives is not usually associated with itching or pain, but in some cas itching is obrved.
One other type of allergic manifestation is a dia called atopy, which tends to be a multifactorial problem that includes a genetic predisposition. Anecdotally, Arabians or Thoroughbreds have been reported to be at higher risk. Typically, the problem shows up by age 4, or it can appear in a mature hor when he is moved to a nsitizing environment.
Atopy describes a skin or respiratory allergic respon to nsitizing antibodies in the environment. The are often asonal allergens like pollens, molds, grass, weeds, trees, incts, or dust mites, and they have been attributable to materials such as blankets or saddle pads. Miller and Henl stress that atopic hors can be itchy, have hives, or both, making it difficult to identify the underlying cau.
What to Do for Acute Hives?
Call your veterinarian right away in the ca of an acute allergic respon. Miller says that most hors with hives could care less, but “some hors itch, and for tho individuals, cool water soaks might help relieve your hor’s discomfort,” he says. “But in general, I wouldn’t recommend doing anything. You want your veterinarian to e your hor as is and not as modified by drugs or topical medications.”
Henl reports, “Hives rarely affect the general health of the hor and usually disappear within one to two days. In such cas, treatment is not necessary. In more vere cas, treatment may be indicated with epinephrine and corticosteroids.” Although antihistamines don’t em to work very well for acute hives, an antihistamine like hydroxyzine might limit the allergic respon.
Before implementing any treatment during an attack, your vet will attempt to differentiate an allergic respon from infections such as skin parasites or bacterial/fungal (ringworm) infections. Even a few days of corticosteroids can turn a mild infection of the latter into a vere ca that is difficult to resolve. In most cas of ringworm, the hair falls out within a few days, whereas there is no hair loss with hives.
"Hives rarely affect the general health of the hor and usually disappear within one to two days. In such cas, treatment is not necessary. In more vere cas, treatment may be indicated with epinephrine and corticosteroids." ‐‐Patrick Henl, DrMedVet, Dipl. ACVD
If your hor develops hives, immediately eliminate any new medications or food supplements. In this ca, less is more. Rather than trying to fix the problem by adding more supplements or herbs to your hor’s diet, it is often more productive to eliminate everything but hay.
Besides conventional Western medical treatment, other methods are often tried and sometimes uful. Holistic therapy us acupuncture to address an allergic problem head‐on. Regardless of whether the approach to medical management relies on Western or Eastern philosophy, refrain from exercising your hor under saddle when he has hives. Sweat amplifies the physical discomfort around the bumps, and tack further irritates inflamed tissue. Wait a day or two for full resolution before putting your hor back to work.
Identifying the Source
For the one‐time occurrence of hives, you might never discover the incriminating source. However, if hives recur, you might be motivated to track the allergen. Start by mentally reconstructing any chang
es in diet, environment, medications, vaccinations, or stress factors that occurred in recent months. Provide your veterinarian with a list of suspicious items. Time‐honored strategies for managing hives eliminate ingestion, contact, or inhalation of as many things as possible.
With a little sleuthing, you might be able to identify the cau and successfully eliminate the problem from
your hor’s future. Read more about finding the source and how to reintroduce feedstuffs after determining the cau of food allergies in article /ViewArticle.aspx?ID=1773.
Another diagnostic technique, albeit expensive and time‐consuming, us intradermal allergy testing to try and isolate an allergic source from pollens (plants, bushes, and trees), molds, grass, weeds, dust mites, incts, and farm plants. The hor should be pulled off medications (steroids or antihistamines) at least 10‐30 days prior to testing.
Once a particular antigen has been identified, immunotherapy (historically referred to as hyponsitization) injections might target that allergen. The process is slow and should be continued for at least a year. Henl describes the process: “By injecting small amounts of allergy vaccine, a h
or’s immune system should become tolerant to the allergen over time, resulting in mild to no reaction during re‐exposure.”
Learn more about intradermal and rum testing and immunotherapy
/ViewArticle.aspx?ID=5262.
Progressive Allergic Reactions
Hives can turn into something much more rious, called angioedema. Miller describes what happens: “Angioedema is basically a ‘deep’ hive. In the classical hive, fluid leaks out of the superficial blood vesls in the skin; the amount of fluid that leaks out is limited in its amount becau of tissue resistance. With angioedema, the fluid leaks out of deeper vesls where tissue pressures are less, so more fluid can escape, potentially pressing on surrounding tissues. If this develops around a hor’s larynx, the airway will narrow and could clo entirely, making this a life‐threatening situation.” Henl remarks that angioedema most commonly involves the muzzle, eyelids, belly, and legs.
With any allergic condition, there is always concern that the next attack could turn into a vere anap
hylactic one. Miller and Henl agree that anaphylaxis is rare in the hor, but it can occur, with the hor exhibiting immediate restlessness and sweating.
Miller advis what to watch for: “If, at each episode of hives, the bumps em taller or deeper, the hor might be tending towards anaphylaxis.”
Take‐Home Message
When purchasing a hor, question the ller about any known allergic respons. Inform your veterinarian, trainer, and barn manager about the dangers of certain drugs or feeds/forages that affect your hor’s health. Just as people who are allergic to bee stings or penicillin might wear a necklace or wristband describing this condition, you can prevent an anaphylactic reaction to known substances by advertising this fact about your hor. Place warning sign describing known allergic reactions outside the hor’s stall.
