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What are External Parasite Bite Reactions?

External parasites are organisms that spend most of their lives feeding or reproducing on the surface of another animal. Some of the external parasites that affect dogs can drain the animal of excessive amounts of blood, causing anemia, or transmit dangerous bacterial or viral infections such as babesiosis. Bites by external parasites are also a frequent cause of allergic reactions, causing itching, crusty or scaly skin, and sensitivity to touch. In rare cases, a severe allergic reaction known as anaphylactic shock may also occur.

Reactions to the bites of most external parasites can include symptoms that may include mild bumps and itching, anemia, or even potentially life-threatening anaphylactic responses.

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Symptoms of External Parasite Bite Reactions in Dogs

Symptoms characteristic of an external parasite infestation can include:

  • Crusting
  • Discoloration
  • Infections
  • Loss of hair
  • Obsessive licking
  • Pawing at the face
  • Pustules
  • Redness
  • Scaly or leathery appearance
  • Sensitive to touch
  • Sores 
  • Swelling of the face 
  • Unpleasant odor
  • Unusual vocalizations
  • Warm to the touch
  • Wrinkling

Occasionally external parasite bites may cause a serious allergic reaction called anaphylactic shock. If your dog shows the following symptoms, it should be treated as an emergency: 

  • Cold limbs
  • Coma
  • Difficulty breathing
  • Elevated heart rate
  • Excessive drooling
  • Low blood pressure
  • Pale gums
  • Seizures
  • Sudden diarrhea
  • Sudden vomiting

External parasites may also carry other illnesses that can be spread from animal to animal such as Lyme disease, Rocky Mountain spotted fever, and West Nile disease.

Types

There are several types of parasites that can affect your dog. These can include:

  • Fleas - These tiny, jumping insects are the most common external parasite found on dogs; flea infestations often result in reddened, itchy, and sometimes ulcerated skin 
  • Flies - Flies are known to cause a disorder known as fly strike in dogs, biting at the ears and leaving wounds; in some cases, the flies then lay their eggs in the wounds they create
  • Lice - There are two types of lice that can affect dogs, chewing lice that feed off of dead skin and debris and sucking lice that suck blood from their hosts 
  • Mites - There are several types of mites that commonly affect canines, several of which can be transmitted to other animals in the house as well as to humans 
  • Mosquitos - Mosquito bites pose as much hazard to dogs as to humans, transmitting dangerous diseases such as West Nile disease and heartworm
  • Ticks - Ticks are blood-sucking parasites that are closely related to mites and to spiders; they are a common transmission vector for many illnesses, including ehrlichiosis and Lyme disease

Causes of External Parasite Bite Reactions in Dogs

The most common way for dogs to pick up these types of parasite is by being outdoors. Dogs are lower to the ground and tend to walk through the bushes and grass the parasites live in, and their fur frequently hides the infestation. Canines who visit kennels or have interaction with other dogs may pick up the infestation from other animals as well.

Diagnosis of External Parasite Bite Reactions in Dogs

When you bring your dog into the veterinary clinic, a physical examination will be completed, and a sample of the skin affected by the parasites will be collected for a process known as cutaneous cytology. Cutaneous cytology is the microscopic examination of the sample to check for any parasites, fungus, and sometimes even bacteria. The examiner may also choose to use either a flea comb or a piece of tape to collect some of the parasites if movement on the skin or fur is detected. Most of these parasites are easy to see either with the naked eye or with a microscope making an initial diagnosis fairly simple. 

However, parasites may also carry other illnesses, so standard diagnostic blood tests such as a biochemical profile and a complete blood count will be used to detect these microorganisms. If an allergic reaction is suspected, an intradermal skin test, also called a patch test, may be recommended. In a patch test, minuscule amounts of the allergens that are suspected will be injected just under the skin. This will induce a localized reaction that will allow for a more accurate identification of the allergen.

Treatment of External Parasite Bite Reactions in Dogs

Treatment of these disorders will be dependent on which type of reaction the patient is experiencing. If a tick is found on your dog, the veterinarian will remove it right away, being careful not to leave any parts left in the patient as any bits or pieces that remain may cause infection. Treatment for symptoms of anaphylactic shock will typically be started even before an official diagnosis has been determined. Epinephrine is typically administered as soon as possible, and other supportive therapies, such as supplemental oxygen or intravenously administered fluids, are also likely to be offered. 

If your dog has experienced a negative reaction to a bug bite and an EpiPen is required to stop the reaction, it is crucial that you still bring the animal to the nearest clinic immediately for supportive therapy as the allergic reaction can recommence once the medication has worn off. This typically involves the clipping of long or thick hair, followed by a medicated bath to remove any parasites that are living on the animal. Additional topical pesticides can be applied using a rinse, a dip, or an ointment or lotion. and the amount and frequency of the treatment will depend on which specific medications and methods are used. 

Frequently utilized medications such as Milbemycin and Ivermectin can be administered orally, and Ivermectin may also be employed by injecting it under the skin. It is crucial to inform your veterinarian if your dog has any herding breeds in its family history as Ivermectin is toxic to these breeds. Breeds that are more susceptible to Ivermectin toxicity may include:

  • Australian Shepherd
  • Collie
  • German Shepherd
  • Old English Sheepdog
  • Shetland Sheepdog

Recovery of External Parasite Bite Reactions in Dogs

The prognosis for animals that are infested with external parasites depends on the type of parasite, the extent of the infestation, and whether or not additional microorganisms are transferred to the host animal. Cases of parasitical infestation caused by fleas, mites, and lice may take several weeks to clear up, and treatments should be employed for all of the animals in the house. Any bedding that has been in contact with infested pets should be laundered, and carpets and upholstery should be vacuumed to prevent further invasions of these pests.