The Scabies Mite

Scabies or Sarcoptic mange, is not the mite infection you want in your home! This is a contagious skin disease, unlike demodectic mange caused by the Sarcoptes scabei mite. Contrary to popular belief, mites are actually arachnids, not insects; yes they actually have 8 legs. However, these mites are extremely small, microscopic in fact, and cannot be seen with the human eye.

The lifecycle of the scabies mite is only around 30-40 days from egg to death. Typically, an adult mite will survive around 4 weeks in a viable host’s skin. Once mated, the female burrows into the skin laying a small cluster of 3-5 eggs in the tunnel she created. The eggs will usually hatch in 5-10 days producing larvae which then travel on the skin surface. Then molting occurs into a nymphal stage, subsequently into an adult mite.

Appearance of the sarcoptic mange

Mites tend to stay in hair follicles and as such will migrate to areas where there is less hair. Initial onset of infection can often be seen on the abdomen, elbows, and ear flaps. The itchy, red, scaly skin is often the first warning sign of a sarcoptic mange infection. The incessant scratching from the infected dog occurs because of the mite movement and burrowing, but also because of an inflammatory response to the laid eggs.

If the infection is left unchecked then most of the dog’s torso and body will be involved as these mites proliferate and travel throughout its skin. It is important to note that these Sarcoptes scabei mites have a lot of close cousins that are the cause of human scabies.

The sarcoptic mites will infect humans, and create an itchy condition, but will not persist as humans are not a viable host – hence the full life cycle cannot be completed. Cats can also get infected but do so with the Notoedres cati mite. Much like humans, sarcoptes scabei mites have limited lifecycle on cats too.

How the infection is spread

Unfortunately, Sarcoptic scabies mites are spread by direct contact between hosts. Unlike human lice, the mites can live off of a host for weeks depending on their lifecycle stage but actually stay infective for only 36 hours, reducing the need for general decontamination in the home.

Human infections, while definitely uncomfortable, are limited because of the incompatible host noted previously. The most likely places to human infection to occur is where the skin is warm (close-fitting clothing and beds!) Yet another reason to not let your dog sleep in your bed! As such the best course of action, post sarcoptic mange diagnosis is to wash bedding, clothing and dog collars/harnesses.

If you have other dogs in the house, it is very important to isolate Fido until the mites have been dealt with if you don’t wish to have multiple cases on your hands.

Diagnosis

The most common method for diagnosis is a simple skin scraping. A small scalpel scrape of the skin will examination of the skin debris to see if the mites are present. Skin scraping is a good positive test that can allow a confident diagnosis quickly. However, in maybe half of the cases, mites are not present because of dog scratching killing and removing the mites, making it a much harder diagnosis. Even with no mites present, the dog may scratch a lot because the egg-laying also releases irritating toxins in the skin.

If skin scraping is not successful, but the location of sores and general conditions support a sarcoptic mange diagnosis, a vet might suggest pursuing a mange medication path to see if it helps clear up the condition. While this could lead to an ‘over prescribed’ perspective, it does serve to cure the potential cause, but also potentially prevents further spread of the contagious mite. About 2-4 weeks in results will be very clear.

Once treatment has been started, it is possible to get skin biopsy confirmation if no obvious improvement is seen. A skilled dermapathologist or histopathologist can tell from the skin inflammation type if sarcoptic mange is present in the dog.

Treatment

Rule number 1 with sarcoptic mange: ALL DOGS IN THE HOUSE, OR DIRECT CONTACT, MUST BE TREATED!

Rule number 2: Do not use Ivermectin or related derivatives with dogs that have an MDR1-gene mutation. This mutation is typically found in collies and related herding dogs. If you are not sure of your pet’s lineage and need to check on the MDR1 mutation, it can be done through the University of Washington.

Ivermectin derivatives Not safe for MDR1 positive dogs

Ivermectin – Ivermectin is arguably the most effective and most prescribed treatment for sarcoptic mange. While ivermectin is used as a general parasiticide, its use here (with an arachnid) is ‘off-label’.  Specific protocols will be determined by your vet but typically expect a weekly or biweekly injection of a larger than normal ivermectin dose.

A second caution for pet owners is an interaction of ivermectin with Comfortis® (active ingredient is spinosad). To treat the sarcoptic mange requires fairly high doses of ivermectin and if Comfortis® is used then ivermectin side effects are more likely to occur.

Selamectin (REVOLUTION®) – Selamectin is an ivermectin derivative, but, importantly, doesn’t come with the same MDR1 gene mutation caveats. Revolution (TM) is marketed for control of fleas, ticks, heartworm, ear mites, and sarcoptic mange mites. Sarcoptic mange can be prevented with a typical monthly dose, but to remove an actual infection typically requires an extra dose about 2 weeks after the initial one.

Moxidectin (ADVANTAGE MULTI®) – As you can tell from the name, this another ivermectin derivative. In this case, it is combined with imidacloprid, a topical used for killing fleas. The final product is designed and cleared to protect against heartworm, hookworm, roundworm, whipworm, and fleas. As a secondary use, the FDA allows labeled use for sarcoptic mange, once again being a good choice MDR1 gene mutation dogs.

Other Mite Killing Treatments

Milbemycin oxime Safer for MDR1 positive dogs

(SENTINEL®, TRIFEXIS®) – This pharmaceutical is approved for monthly heartworm prevention. It is effective against sarcoptic mange, albeit an off-label use.

Amitraz or Lime-Sulfur dips Safe for MDR1 positive dogs

Dipping is a commonly used for both sarcoptic and demodectic mange. The dog is typically shampooed and then a mite-killing dip applied. The two most commons dips are based on Mitaban (Amitraz), or Lime-Sulfur. The dips are given weekly and the disease is typically gone in 4-6 weeks. Dips tend to be a secondary choice in sarcoptic mange treatment because of the smell and the extra work it entails. However, dips can be helpful for the herding dogs who don’t tolerate ivermectin well.

Infection and Sores Treatment

While the primary treatments are dealing with the mites, the pets will be scratching away, leading to potential secondary infections from open sores and wounds. Keeping close control of potential secondary bacterial infections is extremely important for fast recovery and lower bills! Treatments might include cortisone shots/pills to alleviate itchiness and hypersensitivity. In addition, an antibiotic medicine is used as a systemic protection against infection. Additionally, anti-itch shampoos, rinses, and other topicals can be used to improve the quality of life for your dog.

Sarcoptes scabei most certainly can be transmitted from dog to human, though most human scabies does not involve pet transfer and is completely different from the canis version outlined in this article. The Center for Disease Control has more information on human scabies.