Cheyletiellosis: Night of the Walking Dandruff

Sorry to mislead you into thinking this blog was going to be about the ever popular zombie creature. It's actually about a different kind of monster, a microscopic mite commonly referred to as "walking dandruff" that likes to prey on bunnies. What better time to talk about mite monsters than Easter? What if the cute little twitch in Peter Cottontail's nose is because of an itch?

Meet "Lucky," a young rabbit presented to our veterinary clinic during the winter of 2014 because of a recently noticed skin condition. Lucky was missing large clumps of hair between his shoulder blades, and the area was covered in huge flakes of white dandruff. His physical examination was rather unremarkable besides his obvious skin disease. He did not even act that itchy, but his skin was quite red everywhere and the hair fell out easily anywhere you parted it.

The other rabbit in the home, kept separately, showed no symptoms of skin disease. The bunnies had been adopted over a year ago and had spent some time penned outside during the warmer months of 2013, but had no interaction with each other much less other animals.

Examination of the affected rabbit revealed a large amount
of dandruff, hair loss and red, irritated skin.

I suspected the "walking dandruff" mite even though no movement was seen in the flakes of dead skin. The official name for this parasitic insect is Cheyletiella and there are numerous species which can plague various mammals from rabbits to dogs to cats. Cheyletiella ("kai-la-tee-ell-a") are highly contagious and can even bite people, but they can't live on us for long. The mites tend to live on the animal's skin within the keratin level; they less commonly invade the nasal passages. The mites are fairly large as mites go, and their scurrying among the excess amounts of dead skin produced in response to irritation resulted in the nickname "walking dandruff."


Animals acquire Cheyletiellosis by direct contact with an afflicted animal in most cases. However, the mites and their eggs can also survive for a short period (days to weeks) within bedding and the environment, so transmission may occur via indirect contact as well. Some animals carry around Cheyletiella mites but don't show symptoms at all! 

At the center of the field are two Cheyletiella mites as well
as a large mite egg.

Definitive diagnosis of Cheyletiellosis in Lucky was swift and satisfying. I collected some dandruff from his back on the sticky side of transparent tape and applied the entire thing to a glass slide. At relatively low magnification under the microscope, I saw numerous mites and mite eggs amid hair shafts and epithelial skin cells.

In some cases, mite bodies and eggs may be seen during microscopic evaluation of a stool sample instead. This is a good way to diagnose Cheyletiellosis in cats. Because they are such fastidious self-groomers, infected cats often ingest the excess dandruff as well as the mites making diagnosis from physical examination alone more difficult.

Fortunately, treatment of "walking dandruff" is much easier than eliminating an apocalypse of the walking dead. Various treatments are available to kill Cheyletiella mites. Because rabbits are weirdly sensitive to certain topical insecticides--for instance, over-the-counter products containing fipronil, well-tolerated in dogs and cats for the treatment and prevention of fleas, are devastatingly toxic to rabbits--we selected topical prescription-only selamectin which has been used safely and effectively in rabbits for mites of various kinds.

Dr. Kim Everson applies a dose of medicine to Lucky to treat
his bad case of Cheyletiella mites.

In addition to thoroughly cleaning the hutches and surrounding environment as well as replacing the bedding and feed hay, we decided to treat the asymptomatic rabbit as well. Both bunnies will receive a small amount of medicine on the skin between the shoulder blades once a month for several months in a row. Any mite bites on the humans in the household are expected to resolve once the bunnies have completed treatment.

Shortly after the first dose of medicine, Lucky was reportedly showing signs of improvement in his skin. By now, he should be feeling fine -- just in time for delivering the family's Easter baskets!

Ring Around the Ringworm

Ringworm is one of my least favorite parasitic diseases. {Having written that prompts me to ask myself what is my most favorite disease! Ear mites are definitely high on the list of creepy, cool parasites that are fun to treat.}

A cat with ringworm lesions on its face (hairloss)

Anyway, I hate ringworm. It is a common, non-lethal contagious fungus (not a worm at all as the name suggests) that infects the skin, hair and nails. There are many different species of ringworm fungi, or dermatophytes, and they can affect just about any species of mammal imaginable: goat, horse, cow, guinea pig, dog, cat, human. Ringworm is fairly ubiquitous in the environment, hanging around in the soil, animal housing structures, and of course on the skin and fur of the animals it calls home.

In animals, a ringworm infection typically appears as patches of hairloss sometimes with crusty, scaling skin underneath. On people, the fungus usually creates a reddish ring-shaped rash on the skin (hence the name). It is variably itchy. Prognosis for a cure is very good with appropriate treatment.

There are several reasons why I hate ringworm.

1. It is zoonotic. This means infected animals can share the fungus with people. In fact, many times pets are presented to me for inspection because a human family member has classic ringworm symptoms and the pet is the suspected source. It stinks when the cute cuddly new kitten is suddenly a pariah.

2. It is sneaky. Like a Typhoid Mary, a ringworm carrier can quietly infect a legion of other animals and never even appear sick. Therefore, even though it is not a deadly disease, it is a population medicine nightmare. In animal shelters, ringworm is an endemic threat to the health and adoptibility of the animals. A ton of money and time is spent testing, treating and retesting shelter animals, especially cats, for ringworm. In some shelters, cats entering the shelter with known or suspected ringworm might even be euthanized to prevent its spread.

3. There is no one great test. A Wood's lamp can help screen dogs and cats for ringworm because a fair number of cases will fluoresce, or glow. I become quite giddy when a cat or dog ringworm suspect lights up like a city skyline at night under the Wood's lamp. {It's almost as cool as watching ear mites swim through mineral oil under microscope magnification.} Definitive diagnosis of ringworm, however, is made by culturing the organism from the fur. This test can take days to weeks and occasionally fails due to the persnickety nature of certain ringworm types who may refuse to grow well in the lab.

Lime dipping a cat with ringworm

4. There is no one great treatment. A diagnosis of ringworm comes with a laundry list of different topical and oral treatment options. Some are antiquated and dangerous. Some are stinky, messy and flat out obnoxious. Others are terribly expensive. Current veterinary protocols for treating ringworm usually involve a combination of multiple obnoxious lime dip baths and costly oral antifungal medication.

5. A ringworm household can turn into veritable Superfund Site. Ringworm is spread through "hairborne" fungal spores, which easily become airborne on shed fur and dust. Careful, thorough vacuuming and dusting (including heating/cooling ducts if the ducts culture positive) and laundering is necessary to prevent re-infection of the affected animal. A bleach solution can be applied to bleach-safe surfaces.

Most of us who spend time around animals--either in our home, in the workplace or on the farm--will have  a ringworm infection at some point in our lives. Fortunately in people the infection is usually fairly easy to treat with topical medications. For affected animals, my recommendation is, be aggressive and be vigilant because this particular parasite really bites.

Cuterebra are not cute (and maggots are just plain gross)

Parasites create a buzz of excitement in a veterinary clinic. Creepy, crawly, stinky? Bring it on!

This week was especially interesting with the appearance of two different species of parasitic larvae arriving inside the skin of two of my mammal patients. The technical term for parasitic fly larvae is "myiasis."

Rabbit afflicted with Cuterebra larva

First, a father called worried that his daughter's pet bunny had been shot with a B-B gun while it was in its outside enclosure because it had a hole on either side of its neck. When the bunny arrived she was bright and alert. Although she had two large wounds on her neck that were leaking fluid and pus, I learned she was not acting sick at home. As I prodded one of Flopsy's wounds a little maggot head peeked out at me! "Cuterebra!" I exclaimed happily.

While disgusting, cuterebriasis is a common and treatable condition in rabbits. Sometimes these larvae show up in the skin of kittens, cats and dogs as well. In the spring and early summer the female Cuterebra fly lays her eggs on blades of grass. When a rabbit or other mammal brushes against the infected grass, the egg or a recently hatched maggot attaches to its fur and then eventually burrows under the skin where it sets up shop. Occasionally these maggots migrate to the wrong place (like the lungs or brain) and cause all sorts of problems, but usually they mature into grubs inside their "warble" under the skin. Eventually they drop off the animal back into the soil where they finish developing. The B-B sized holes seen on Flopsy are the grubs' tell-tale breathing holes.

Removing Cuterebra larva from its warble under the skin

I very carefully removed a pair of fat Cuterebra grubs from Flopsy's neck, cleaned the wounds and started her on an antibiotic for the secondary bacterial infection in her skin. While removing Cuterebra larvae, care must be taken not to break or rupture the grub inside the skin because the pieces will cause festering wounds.*

I know it may be a matter of personal preference, but I find that while Cuterebra are not cute, they are definitely not as disgusting as regular old maggots. Our second myiasis patient, Trina, was an obese outdoor kitty who came in crawling with maggots. Trina had a terrible skin infection around her vulva (she couldn't clean herself because she was so obese) and a ruptured anal gland abscess. Flies had been attracted to her stinky, moist, dying flesh and had laid eggs there. We pulled dozens of wriggling white maggots from Trina's skin, inside her vulva and surrounding fur. (Yes, it was gross even for us veteran parasite handlers.) Then we shaved off the nasty matted fur on her back end, cleaned her wounds and administered pain medication and antibiotics. By the time we finished Trina looked, smelled and felt a million times better. Once we get her through this rough patch, Trina's family and I will be working together to get the extra Lbs off her.

*One theory behind the medical and veterinary symbols of a "snake" wrapped around a staff may stem from a skin parasite in people called Guinea Worm (dracunculus medinensis).  A traditional method of treatment is to wrap the end of worm around a small stick, gradually and carefully twisting the stick until the worm is completely extracted from the person's skin. Breaking the worm inside the skin can create a life-threatening bacterial infection such as tetanus.

Witchy Over Itchy

As a new mom at Little League, I was relieved to bump into an acquaintance mother in the stands. She had brought her adult Boxer and my American Bulldog puppy was enamored of her.

As the two dogs rough-house in the grass near us, the woman suddenly announces how angry she is at her current veterinarian (always dangerous territory)! Turns out her veterinarian said not to breed her female dog because she has allergies. Before I can respond another mom interjects dismissively, "Pfht! All dogs have allergies." Feeling ambushed, my veterinarian instincts overcome my social delicacy instincts and I blurt out "No! Allergies-are-an-expensive-and-difficult-problem-for-many-owners-and-terrible-for-dogs. I-even-know-of-one-dog-who-was-put-down-because-of-her-suffering!"

You could hear a pin drop.

While the Boxer's owner stares at me with mouth slightly agape, I try to salvage the conversation by asking calmly about her dog's symptoms and severity. To no avail. The conversation has died and cannot be resuscitated. At least for this baseball game, I have become a pariah among Little League moms.

Having had some time to reflect on the scene, I find myself agreeing with Second Mom's statement that "all dogs have allergies." It certainly seems that way some days as dog after dog visits my veterinary clinic with complaints of painful ear infections, inflamed paws and uncontrolled itching.

Yes, many dogs like people have mild seasonal allergies. We don't discourage people who suffer from hay fever from procreating. We don't even stop people with life-threatening peanut or shellfish allergies from marrying and having kids. The thought is just plain ludicrous. But dogs are not people, obviously. It is our responsibility in this age of pet-overpopulation to be cautious and judicious about which dogs we allow to reproduce and why. Many allergies in pets have a hereditary component. If not breeding a known allergy sufferer might prevent similar suffering in future canine generations, all the veterinarians I know would be in favor of that.

Canine allergies vary in cause and severity. Like bee sting reactivity in people, canine allergies may worsen with time. A mild seasonal allergy causing red, itchy eyes for a few weeks in a puppy can worsen with successive allergy seasons. The season itself may lengthen to all year round as the pet accrues additional allergy triggers including house dust mites and other unavoidable airborne particles. Symptoms too may worsen with some dogs living their entire lives with expensive, difficult-to-manage chronic ear infections, anal gland problems, and skin disease. Gastrointestinal upset ranging from picky eating, frequent vomiting and soft stools may indicate food allergy, which are historically difficult to diagnose and very expensive to manage.

Yes, Second Mom, so many dogs suffer from some degree of allergies I think most pet owners do consider it normal. The constant foot licking some dogs do, for example, may not be merely boredom. Butt scooting, reported with hilarity as if the dog performs the act for comic relief, may actually signal a food allergy. And let us not forget cats whose allergies are perhaps more challenging to manage than dogs': the puke piles you step in several times a week are not strategically placed to annoy. And not all bald cat bellies and legs are due to obsessive-compulsive disorder. Just because these things are common does not make them normal and acceptable in our pets!

Faced day-after-day with disgruntled, frustrated pet owners and miserable pets who hate taking the medicine that will provide merely temporary relief from their allergy symptoms, I forgive myself the "faux paw" of erupting at my fellow Little League moms. I hope they will forgive me knowing my rudeness is just exuberance on behalf of my afflicted patients.

P.S. Some breeds of dogs are more commonly affected by allergies than others (remember, that hereditary component of allergies?) so do your research befor acquiring a new pet. Ask the breeder or former owner if the dog or its parents have a history of allergies or allergy symptoms (itchy skin, excessive licking, ear or anal gland problems, chronic upset stomach) so you can go into the adoption with eyes wide open.

The "Cone of Shame": A Necessary Evil

The figure of speech "going off to lick your wounds" is okay in the metaphorical sense, but not when we're talking about dogs and cats after surgery.

Veterinarians cringe when well-meaning owners proudly announce that Fido has been licking a surgical wound in order to heal it.  Dog saliva may indeed contain compounds that numb the wound and neutralize some microorganisms. However, doggie drool and kitty spit also has potentially harmful bacteria in it, and the act of licking itself can ruin a good surgical closure.

Dogs and cats routinely create serious infection in their skin from over-licking an area due to allergies, injury or post-surgical discomfort. That's why veterinarians regularly dispense an Elizabethan collar (e.g., e-collar) following spays, neuters and other surgeries. The "cone of shame" prevents the dog or cat from licking the incision, allowing the wound to heal faster and without complication.

Sometimes, however, the e-collar is an inadequate deterrent.  I have met Houdini-like dogs who escape from their e-collars no matter how they are fastened. Some dogs figure out a way to chew through the plastic rendering the cone useless, while others ram it into things until it cracks, bends or (especially in Wisconsin winters) shatters. Many dogs act so demoralized initially that sympathetic owners can't bear to keep the cone on them at all. Most recently, I had a canine patient whose long nose poked over the edge of her cone just far enough that she managed to lick her spay wound to the point of infection and dehiscence.

Dehiscence is a fancy medical word for the splitting open of a wound. A dehiscence may be minor, involving a tiny part of the skin incision and requiring no special treatment. Or maybe a few skin staples will be placed to hold the wound edges closer together for faster healing. The worst kind of dehiscence, the kind that keeps veterinary students up all night and biting their nails following their first spay, is an opening completely down through the abdominal wall so that the animal's abdominal fat or even intestines protrude through the wound. Dogs have been known to chew on their own insides when this happens! Yikes! Thankfully, this is exceedingly uncommon.

Maddie's abdominal skin dehiscence looked a lot like this

Even Maddie, the long-snouted Springer Spaniel who managed to ferociously lick outside the cone, presented with just a partial dehiscence. While I could peer down through her subcutaneous tissue and fat to the sutures holding her abdominal wall together, thankfully the abdominal closure remained intact and her guts stayed in. Maddie's dehiscence was so severe, however, that she required general anesthesia so the dead, infected wound edges could be trimmed away, or debrided. I resutured the wound, placed Maddie on a course of oral antibiotics and gave her a larger e-collar. I expect the wound to heal normally after this, but I won't be surprised if she develops a seroma, or pocket of fluid under the skin, from bouncing around too much before the area completely heals.

Don't assume if your pet isn't licking their incision immediately after surgery that they won't. Some animals leave their surgery site alone during the early phase of healing, but attack it just as the skin finally starts to mend. If you have ever experienced insanely itchy skin as a surgical incision or even a minor cut begins healing you'll understand why dogs and cats suddenly notice their surgical wound a week after the fact!

The "cone of shame" is obnoxious, humiliating and completely necessary in most cases. Even with the cone on, however, pets can develop complications in their surgical wounds that require follow-up care by their veterinarian. Please follow your veterinarian's post-op instructions closely regarding exercise restrictions, wound care and medications. And most of all, don't let Fido lick!