Nasal Mites and the MDR1 Gene

Could your dog have nasal mites? Mine did. It all started when one of my Shelties had what appeared to be an upper respiratory infection. Only it didn’t
clear up after a few days. The poor little guy was sneezing and “reverse sneezing.” He would also rub his muzzle on the furniture and scratch his
muzzle with both his front and hind paws.

Then a second Sheltie started the same symptoms, then the third, so it was obviously contagious. Because the first one had been having symptoms for
about a month I took him to see my vet. His exam in the office didn’t turn up anything so my vet suggested the possibility of nasal mites. What???
I had never heard of nasal mites, and I was not alone. No one I talked to after that had ever heard of nasal mites.


Nasal mites (Pneumonyssoides caninum) can infect any canine species including coyotes, foxes, and wolves in addition to domestic dogs. They are found
worldwide, including the USA and Canada, Europe, the Scandinavian countries, Japan, South Africa, Australia, and Iran. These countries that are
singled out have documented cases and are also the areas where the mites are quite common.


The mites set up shop in the sinuses and nasal cavity. Most symptoms are not real serious, but some dogs can develop a chronic, watery nasal discharge
and nosebleeds. Sneezing and “reverse sneezing” can sometimes be chronic and severe.


The mites are transmitted by direct contact between dogs, although they can also be picked up from plants, especially those in the Agave and Ginger
families. Fortunately nasal mites cannot be transmitted to people.


A positive diagnosis requires seeing the mites, which are extremely tiny, perhaps a millimeter or less. Sometimes they can be seen through rhinoscopy,
but they are more commonly detected by flushing the sinuses and nasal cavity while the dog is under anesthesia, collecting the retrieved fluid,
and looking at it under a microscope.


Because treatment is relatively inexpensive and safe, it is more common (and economical) to treat a dog for nasal mites without detection, in order
to avoid anesthesia. If the symptoms disappear after treatment, you can assume the dog had mites.

Nasal mites are killed with heartworm medications, mainly Ivermectin or Milbemycin, at higher doses than the standard heartworm treatment. Because
heartworm is not common in our area, most dogs are not routinely on heartworm medication, or they are only on it during summer when traveling to
other areas. For that reason, our area is particularly open to nasal mite infestations.

Of these two drugs, Ivermectin is the most commonly used to treat nasal mites (although it is an off-label use, it is widely accepted). My Shelties
were treated with Interceptor (Milbemycin) at double the usual dose, three times, ten days apart. So far, no symptoms have returned.

However Ivermectin may not be safe for all dogs… namely those with something called the mutant MDR1 gene (a group of dogs that includes my Shelties
[but not Kerry Blues]).

The MDR1 Gene

The MDR1 (Multi-Drug Resistant) gene encodes a protein that is responsible for ridding the brain of drugs. If a dog has the mutant form of this gene,
it can’t get rid of some drugs in its brain, which can cause neurological problems. It’s a serious genetic condition: affected dogs may need hospitalization
or can die.

The most commonly affected breeds are Collies, Australian Shepherds (both normal sized and minis), Long-haired Whippets, Silken Windhounds, Shelties,
English Shepherds, and German Shepherds. This is not a complete list by far, and any breed in the herding group is suspect.

Washington State University can test your dog’s blood to determine whether or not it possesses the mutant variety of the MDR1 gene. Most responsible
breeders of the severely affected breeds now test their breeding stock for this gene.

Ivermectin is not the only drug that can cause problems. Here are a few of the drugs that can cause serious problems in dogs with the mutant MDR1 gene:

  • Acepromazine (WSU vets recommend reducing the dose by 25% in dogs that are heterozygous for the MDR1 gene, meaning they have one mutant and one
    normal gene, and 30-50% in dogs with both genes mutant)
  • Butorphanol (a pain killer and pre-anethesia drug)
  • Erythromycin
  • Ivermectin
  • Immodium (avoid with all dogs with any MDR1 mutation)
  • Milbemycin (at 10-20 times higher doses)
  • Moxidectin (at 10-20 times higher doses)
  • Selamectin (at 10-20 times higher doses)
  • Chemotherapy drugs

For a more complete list of problem drugs please visit the WSU website at:

In conclusion, if your dog is sneezing and snorting, has a runny nose, even nosebleeds, and an itchy face and muzzle, consider the possibility of nasal
mites. Some heartworm medication at a higher dose and more frequent use as directed by your veterinarian can cure the problem. If your dog is a
member of the AKC Herding group or is a mixed breed with a parent from the Herding Group, avoid using any of the drugs mentioned above.

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