Visiting Veterinarian : Mite-y Lion
Lion is an athletic young German shepherd who loves to play Frisbee, so when crusty sores appeared along his lips, Lion's owner naturally assumed they were caused by repeated Frisbee catching. "But what about these areas on his back?" his dad asked when Lion arrived for his annual physical. I ran my fingers over the coat - definite thinning in patches on the shoulders. Moving up to his head, I noticed another small bald spot on the muzzle. "And he's been limping on his right front foot," his owner continued.
I picked up the paw, bending it to examine the underside. Whoa. The skin between his toes was bumpy, raw, and infected. I picked up the other front foot. That one too. And the third. And the fourth. Uh oh, I thought. Multiple bald patches. Badly infected feet (called pododermatitis). Could be allergies. Could be a straight bacterial infection. But there was another more worrisome possibility. "I need to take skin scrapings," I sighed, unwrapping a scalpel blade and lining up a row of microscope slides. "To check for demodectic mange."
Demodex mites are microscopic critters, shaped like tiny cigars with legs, which are normal inhabitants of a dog's skin in small numbers. In certain circumstances these mites proliferate and cause problems. The most common presentation is localized demodecosis. Occurring primarily in dogs under six months of age, pups develop bald patches on the face, head, and/or front legs. Ninety percent resolve spontaneously without treatment as the pup's immune system matures. Ten percent, however, go on to develop generalized demodecosis. This is defined as a case in which there are more than six lesions, or one very large lesion affecting a major body region, or evidence of pododermatitis caused by mites.
Lion's feet looked too raw to scrape. "I'll start with his face," I said. My assistant held Lion still. I gently scraped above his lip with my blade, squeezed the lip hard, then scraped again. Demodex mites burrow down into hair follicles so sometimes you have to squish them out. I rubbed the debris into a drop of oil on a slide, and after sampling multiple areas, I examined the slides under the microscope. Sure enough, lots of wiggly little cigar mites.
Generalized demodecosis often indicates that an animal has underlying issues compromising its immune system. In young dogs it may be as simple as poor nutrition or intestinal parasites. In adults, it may be serious illness such as Cushings disease or cancer. At 16 months old, Lion didn't quite fit into the puppy category, but other than his skin, he looked as healthy as the proverbial horse. We decided to try a conservative approach, treating the secondary bacterial infection with antibiotics and shampoos, and waiting to see if Lion's immune system kicked in and helped him self-cure.
Two months later, Lion wasn't improving. His feet were not quite as raw but scrapings still found a significant population of mites. It was time for serious mite-killing medications.
The standard FDA-approved treatment is the dip Mitaban, which contains the chemical amitraz. First you shave the dog's coat down short. (I'm sure Lion's owner would love that.) Shampoo, rinse, then soak the dog head to toe in smelly dip. Air dry while observing for side effects including depression, lethargy, hypothermia, diarrhea, abnormally slow heart rate, vomiting, and very rarely, sudden death. Because the chemical affects the patient's ability to maintain homeostasis, avoid stress for 24 hours. Repeat every two weeks for six treatments, sometimes more. Reported cure rates range from 60 to 96 percent.
Other treatment options include a relatively new pour-on flea and tick product called Promeris, or off-label use of milbemycin or ivermectin (the stuff in heartworm preventatives like Interceptor and Heartgard, respectively). From what anecdotal information I have read, Promeris apparently smells awful, and there have been a worrisome number of bad reactions to it. I prefer the treatment recommended by many dermatologists - oral ivermectin. Can you just give Lion a whole bunch of Heartgard (or Interceptor)? Yes, but it would cost a fortune, as either choice needs to be given daily for months, and, in the case of ivermectin, the dose for demodecosis is about 40 times higher than the dose for heartworm prevention. To make ivermectin treatment affordable, with an owner's understanding that this is "off label" usage, we give small doses of cow or horse dewormers, which are far more concentrated.
I broke the news to Lion's owner on Friday afternoon. "I'll order the medication and we'll get started next week." Details could wait until Monday. We would start with a low dose and watch for side effects - disorientation, tremors, drooling, incoordination, or in very rare cases, even blindness and coma. Luckily, with ivermectin, side effects are often reversible by simply discontinuing treatment. (Some collies, shelties, Old English Sheepdogs, and other white-footed herding dogs can't take ivermectin. A simple genetic test must be done first to determine if an individual can tolerate it.) If no problems, we would gradually increase the dose, continuing daily until we got two negative skin scrapings two weeks apart, plus one month more. Generally this takes two to eight months.
"There's one hitch," I reported on Monday. "There's a backorder on all oral ivermectin products." We couldn't get the (relatively) yummy horse wormer. Instead we had the bitter-tasting bovine stuff, intended for injection, not breakfast. "Hide it in ice cream," I advised. "Or in something else delicious."
I have been lucky with past cases of generalized demodecosis. They have responded well to treatment and few have relapsed. I have high hopes for Lion's recovery, and as soon as his paws and lips heal, he can play as much Frisbee as his big puppy heart desires.