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Skin Problems

by Debbie “The Rat Lady” Ducommun

updated 11/14/13

Male rats tend to produce more skin oil on their backs than females, and some males produce enough skin oil that it can look like a problem to the uninitiated. This oil can appear as orange deposits on the skin of the back, and this is perfectly normal. The oil can even result in blobs of dandruff that can look suspiciously like parasites. However, this dandruff never moves, the way lice and visible mites would do. Some males produce so much “buck grease” that the fur on their back looks unkempt, and it can even cause clumps of fur to fall out. None of this is actually a health problem, although it can be unsightly. Excess oil can be washed off with a little Dawn dishwashing liquid dissolved in water. (Be sure to rinse it off well.) However, the skin will just produce more oil. The only way to eliminate the oil permanently is to have the rat neutered.

The most common skin problem in rats is caused by itching. The rat scratches herself which creates scabs, most often on the neck and shoulders, but sometimes also on the face, chin, or forehead. These scabs are sometimes mistaken for injuries caused by other rats. The most common cause of itching is fur mites. Much less commonly, itching can be caused by an allergy, eczema, a fungus infection, and possibly excessive dietary protein (such as fish or cat food). Skin problems in rats is almost never caused by a bacterial infection.

Itching also seems to be related to stress, common for eczema. Rats can have mites without any symptoms for a long period of time and then suddenly start itching.  Maybe they don’t itch until their immune system is suppressed by stress. It’s also possible that some rats with mites eventually develop an allergy to them. If you have more than one rat with scabs, it’s probable that mites are the cause.

Regardless of the cause of the itching, when the rat scratches, her back toenails break the skin which can allow bacteria to enter. As the scratches heal, scabs form and can themselves itch which causes more scratching, resulting in a vicious cycle. The first step to breaking the itching cycle is to clip the rat’s back toenails. Trimming off the sharp tips reduces the amount of damage the nails do to the skin. You might need to clip the nails as often as once or twice a week. You can also put a concrete block in your rats’ cage in a location where they would be likely to jump up onto it to help her wear down their toenails.

You might also apply a vitamin E cream or an antibiotic ointment to the scabs once or twice a day. Neosporin Plus contains a topical anesthetic which can be especially helpful. This treatment may be sufficient to clear up the scabs. If they recur, you need to look for another cause.

External Parasites

There are three kinds of external parasites that can be a problem for rats: mites, lice, and fleas.  Lice and fleas are wingless insects, and mites are relatives of ticks and spiders.  Any of the three can carry internal parasites or diseases they can pass onto the rat, so it’s important to prevent these pests or get rid of them quickly.

 

The simplest to identify, although the least common cause of problem in rats, are fleas, which are about 2 mm long.  The most common types of fleas are dog and cat fleas (several species) which are dark brown and easiest to see in light colored fur.  Rats are not the primary host for these fleas, but if your home is infested with dog or cat fleas, some will be happy to feed on your rat.  Even if you don’t see the fleas themselves on your rat, you might see their droppings, which look like black dirt.  To tell if they are flea droppings, put some on a damp sheet of white paper. Flea droppings are really digested blood, so they’ll dissolve and turn red, and dirt won’t.  You might also see some scabs on your rat where the fleas have been biting.

 

Rat lice (Polyplax spinulosa) are most common on the back, neck and shoulders where the rat has trouble reaching.  They are only ½ to 1 ½ mm long, and narrow so they’re hard to see. They are cigar-shaped, and are usually yellow or tan, but they can have a brown or red spot in the middle. Using a magnifying glass can make them easier to spot.  Often it’s easier to see the nits (eggs) which appear as a silvery coating on the hair.

 

Lice can cause rats to itch and scratch out hair, but don’t usually cause damage to the skin.  If there are scabs, your rat might also have mites or fleas.  Like fleas, lice suck blood, and both can cause anemia and debilitation. All lice are species-specific and live on only one type of animal (so humans can’t get rat lice and vice versa). They live their whole life on their host, laying their nits on the hair.  For this reason, lice can’t survive on hairless rats!  The life cycle of the rat louse is 26 days, and adults can live 28-35 days.

 

Mites

Rat mites come in three types.  The rat fur mite (Radfordia ensifera) sucks blood and is very common.  This mite can cause intense itching, leading to self-inflicted scabs most commonly seen on the shoulders, neck and face.  But some rats can have these mites for long periods of time without any symptoms.  These mites are too small to be easily seen, but when a rat dies, if you leave the body for several hours, the mites will crawl to the tips of the rat’s fur where you can see them like tiny white specks of dust.  Rat fur mites only live on rats and cannot bite humans or other animals.

 

Fur mites mostly live in the fur, although they can also live under the skin. The mites can sometimes be seen under a microscope on plucked fur and transparent tape pressed against the fur.  However, it can be difficult to actually find the mites. Finding the mites with a skin scraping is also equally difficult. The simplest thing to do is just treat for the mites, since the treatment is harmless to the rat.

 

The tropical rat mite (Liponyssus bacoti) is more like a tick and is basically round in shape.  The larva are microscopic but the adults range from about the size of a pinprick to 1 mm long when engorged with blood.  They usually appear dark red to brown or black.  They live in cracks around the rat’s cage and only crawl on the rat to suck blood.  This parasite can also bite humans and other animals causing a very itchy welt.  Fortunately they are uncommon. 

 

The rat mange mite (Notoedres muris) is rare. It burrows into the skin and causes crusty bumps on the ears and sometimes nose and rarely red bumps or blisters on the tail, feet and genitals.  This mite  It is microscopic—only 0.04 mm long—so can only be seen under a microscope.  It only lives on rats. Nothing else causes the same symptoms.

 

The picture of Valentine below shows scabs caused by rat fur mites, which made her itch and scratch and damage her skin. 

These two pictures below show rat fur mites on a dead rat.  As the dead body cools, the mites crawl to the tips of the fur to try to catch a ride on a living rat.  It is almost impossible to see the mites on a live rat.  Observe that the mites are only slightly wider than the rat’s whiskers.

 

 

The picture below shows a rat with lice.  On the right you can see the little brown lice themselves, and on the left, you can see the eggs, called nits, which are silvery blobs stuck to the fur.

The picture below shows a rat with such a bad case of lice, her skin formed a crust.  See where I pulled off two pieces of the crust to reveal red moist irritated skin.  The poor rat!  She also had thinning fur on her belly and sides.  Even with such a bad case of lice, this rat did not develop scabs like rats with the fur mites can.

 

On the left is Monty, who has a very early case of mange mites on his ears.  On the right is a rat with a moderate case of mange mites.

 

 

Below is Alfie on May 23, 2010 (left) and on June 1, 2010.

 

 

Below is Prancer, with a severe case of mange mites with lesions on his ears, nose and tail.  One treatment with moxidectin cleared it up completely.

 

 

Below is Blitzen, Prancer’s brother, before and after treatment with moxidectin. His ears are just a little bit ragged now.

 

 

Clipping Toenails

Trimming your rat’s toenails is really quite easy to do once both you and the rat are used to it. The best tools to use are human fingernail clippers. Hold your rat on your lap facing left if you’re right-handed (reverse these directions if you’re left-handed). Press him against your stomach with your left forearm to hold him still and hold his foot in your left hand. Pull his foot backward and clip the nails with your right hand. You only need to clip off the sharp tip on the end of the nail. If you cut too much off, the nail will bleed. It’s a good idea to have some styptic powder or silver nitrate sticks on hand to stop any bleeding, but if you’re careful, bleeding rarely occurs. You can eliminate the chance of accidentally cutting a toe by holding the foot so only the nails stick out. Your fingers protect the toes.

If your rat really struggles, only do a few nails at a time. Reward him with a treat afterward. You can also distract him during the procedure by giving him a treat in the beginning.

Mite Treatment

The next thing to try is to treat for fur mites. You must treat all of your rats, since if one rat has fur mites they probably all do, even if they don’t all have scabs.  Rats can have the mites without any symptoms.

 

Mite spray doesn’t work, plus rats hate the spray, and it is quite toxic and causes some rats to have a bad reaction!  I also don’t recommend powders because they can’t kill all the mites that live in the skin, and you don’t want rats inhaling the powder.  Shampoos don’t work either.

 

Ivermectin used to work against the rat fur mites, but now they are resistant.  Treatment with ivermectin will kill most of the mites and help relieve the rat’s itching, but it probably won’t kill all the mites and the itching will return.

 

So far, Revolution (selamectin) is a treatment which reliable works to eliminate mites.  Unfortunately, in the U.S. Revolution is only available from your vet (with a prescription in the U.S.)  You can also get Revolution at www.joespetmeds.com and www.petshed.com.   In the UK or Australia you can order it from www.pets-megastore.com.au or 1-866-270-2303.

 

Your vet might want to do a skin scraping to look for the mites first, but often this will still not show the mites, and can be a waste of money. Your vet can also press a piece of tape to the rat’s parted fur and look for any mites stuck to the tape under a microscope. But this method of looking for mites can also be hit or miss. Even if there are no mites on the tape, the rat can still have mites.

 

Revolution is a spot-on product, a liquid that is applied to the skin on the shoulders.  After application, you need to distract your rats so they don’t scratch off and eat the liquid, or lick it off of each other.  The liquid will dry in about 5 minutes.  Only one dose is needed.

 

Revolution comes in tiny tubes of different sizes for different size cats or dogs.  Packages of Revolution come with either 3 or 6 tubes of liquid.  (If your vet treats a lot of small animals, he or she might be willing to split a package and sell individual tubes.)

 

Each tube costs about the same amount no matter how much Revolution it contains, so you want to figure out which tube will treat all your rats.  To figure out what package to buy you will need to weigh each of your rats, total the number of pounds and multiply that by the dose (6 mg/lb).  That will tell you the total number of milligrams of Revolution needed to dose all your rats.  (Please note that this dose is higher than the dose for dogs and cats. This is because rats have a higher metabolism.)

 

Here’s a summary of all the packages of Revolution:

color         size of pet                   total mg           concentration

mauve       up to 5 lbs                    15                    60 mg/ml

blue           5.1-15 lb (cat)              45                    60 mg/ml

purple       5.1 10 lb                      30                    120 mg/ml

brown       10.1-20 lb                    60                    120 mg/ml

red            20.1-40 lb                    120                  120 mg/ml

teal (green) 40.1-85 lb                   240                  120 mg/ml

plum          85.1-130 lb                  120 + 240        120 mg/ml

 

The dose for the tubes that contain 60 mg/lb is 0.1 ml/lb (10 units/lb).  The dose for the tubes that contain 120 mg/ml is 0.05 ml/lb (5 units/lb.)

 

The amount of liquid needed per dose is quite small, and is best measured using an insulin syringe with the needle (or the whole top) broken off.  Insert the syringe into the tube slowly as it will easily overflow.  Once a tube is opened, it must be used within a few hours. 

 

Here is a peer-reviewed article on the Internet about using Revolution in rats in case your vet has objections: http://www.jarvm.com/articles/Vol5Iss3/Beck%2087-96.pdf

 

Another treatment you can try for fur mites is ivermectin.  However, I’m finding that most fur mites are now resistant to it.  It might help for a while, but the problem usually comes back. It needs to be repeated once a week for at least 6-12 weeks.  Most veterinarians will use ivermectin injections instead of giving it orally and will charge much more for a series of injections than you would pay to buy the ivermectin yourself from a feed store.  Since the ivermectin may not work for the mites, I do not recommend paying a lot of money for treatment.

 

Another treatment that has worked in some cases is moxidectin (another relative of ivermectin) which is available from feed stores as Quest brand horse wormer.  I used this product successfully on several rats with mange mites.  The dose is 1 mg/lb13. The amount to give a 1-lb rat is 0.05 ml (5 units). The Quest product is a clear oral gel that is easy to suck into an insulin syringe (with the whole top broken off) for accurate measurement. If you can’t get an insulin syringe (say from a friend with diabetes) then you can try to judge the right amount by size. For a 1-lb rat, the dose is a dab about half the size of a split pea, or maybe a little smaller than a BB.  It tastes nasty so needs to be well mixed with yummy food.  Moxidectin stays in the rat’s body for a long time, so one dose should be enough to kill lice, and hopefully mites.  If you try this product, please let me know your success.

 

I have a report that the product Frontline (fipronil) did not work for fur mites in one case. It must be used with extreme care as it is very toxic to rats if ingested.  If you use it, you must be absolutely sure the rat does not eat any of it.  After applying it, make sure the rat does not scratch or lick it off until the liquid dries.

 

Revolution also works for tropical rat mites.  Ivermectin does not.  I have had tropical rat mites in my house twice.  Just treating my rats with Revolution eliminated them, but I do not have carpet in my house. If you need to treat for tropical rat mites and have carpet, you may need to also spray or bomb the carpets, but try just the Revolution and cleaning around the cages first.

 

Flea & Lice Treatment

If your rat has fleas, it is more important to treat your other pets and possibly also your house and yard instead of the rats.

 

The best treatment for lice in rats is oral ivermectin.  When given at the proper dose ivermectin is very safe, but it should be given orally because in some rats when it is given by injection, it can interact with a genetic bleeding tendency and be fatal. 

 

Ivermectin is also available in a horse paste wormer from feed stores and catalogs.  A tube of horse paste costs about $12-15.  The dose for the paste is 0.01 ml/lb (1 unit on an insulin syringe) which is about the size of an uncooked grain of rice.  Put the dose on a tiny piece of bread or graham cracker for your rat to eat.  You can add butter or jam on top if your rat is reluctant to eat it plain.  Dose your rats with the ivermectin once a week for 3-4 weeks to get rid of all the lice.

 

You can also get injectable ivermectin, which can be given orally, from a feed store or a mail order catalog.  The injectable form can be accurately measured with an insulin syringe, but only comes in 50 ml bottles which is fairly expensive.  The dose is generally 1-2 units/lb.

 

Ivermection should not be used in pregnant rats, and only in nursing rats if the babies are over 2 weeks of age.

 

Other treatments that might work are Advantage, Program and Revolution.  Lice eggs normally hatch in 5-6 days, so any eggs that haven’t hatched after that time are dead and harmless but will remain stuck to the hair until the hair is shed.

 

Bumblefoot

 

Bumblefoot (the medical term is ulcerative/granulomatous pododermatitis) is a bacterial infection in the bottom of the heel that usually appears as a round reddish swelling (the bumble) or an ulcer that can form a yellowish crusty scab.  It sometimes breaks open and bleeds.  It often affects both back feet, although one foot is usually worse than the other.  If pus or a bad smell is present, it means that a secondary abscess has formed under the bumble and surgery may be necessary.

 

Below are some photos of severe bumblefoot lesions.

 

 

 

 

Bumblefoot is most common in older, overweight rats who live in wire cages.  The infection occurs through continuous pressure and irritation on the foot and is a chronic problem.  It may also be associated with the use of pine or cedar shavings.  It also seems that some rats may have a genetic predisposition to the problem, as it seems to run in families.  Once the infection occurs, it can be very difficult to eliminate.  Neither oral nor topical antibiotic treatment is very effective.

 

Bumblefoot Treatment

For years, the best treatment I could recommend for bumblefoot was Blu-Kote, a wound medication for horses.  However, it doesn’t help in all cases, it can sting, and it’s very messy. To use it, dab it on the bumble with a cotton swab once a day.  Blow on the foot to help the Blu-Kote dry. Once it is dry, your rat won't be able to lick it off.

 

Blu-Kote does not work for all lesions, so an alternative to try is grapefruit seed extract (GSE). Mix 4 drops of GSE with 1 teaspoon of olive oil and store in a small container.  Mix well and apply this mixture to the bumble with a cotton swab twice a day.

 

Another treatment that has worked in some other cases is a calendula ointment.  Check at your health food store.  Someone else reported good results with Altabox, an ointment containing 1% retapamulin (a new antimicrobial from mushrooms).  And someone else recommeded Betagen Topical Spray, a combination of gentamicin and a steroid, from Med-Pharmex.

 

Preventative Treatment       

Treating bumblefoot involves not only treating the sores, but also changing the conditions that led to the problem.  Often, changing the rat’s environment will cause mild sores to heal on their own.  Most important is to change the type of litter or flooring in the cage.  If the rat is in a cage with wire floors, the floors should be removed or covered, or the rat moved to another cage without wire floors. Even if the rat seems to spend little time on the wire floor, it’s still important to eliminate it.  Wire floors can be covered with vinyl flooring, Contact paper, carpet, plastic needlepoint canvas or vinyl sink mats.

 

If there is no wire floor, and the bottom of the cage is covered with litter or bedding, try switching to another type.  Eliminate pine or cedar shavings and avoid corn cob litter, which is rough.  You might need to experiment with different floor coverings to find what works best.  Confining the litter to a litter box instead of covering the whole floor might help.  Or, covering the floor with pieces of carpet or rags also might help.

 

If the rat is overweight, she should be put on a diet to reduce the amount of pressure on her feet.  First weigh her so you’ll be able to keep track of her progress.  You can buy an inexpensive kitchen scale for this.  If your rat won’t stay still on the scale, put her inside a small paper or cloth bag first.  Be sure to subtract the weight of the bag.  First reduce the amount of food you give your rat by one third, and in particular eliminate any extra high fat foods such as peanuts.  Often the rat will lose a certain amount of weight and then reach a plateau.  If further weight loss is needed, you’ll again have to reduce her rations by one third until the desired weight is reached.  

 

Fortunately, bumblefoot usually seems to cause rats little pain or discomfort.  However, if the sores haven’t healed after treatment and your rat does experience discomfort—usually indicated by the rat limping on the affected foot or showing a reluctance to move—or if the sores bleed profusely, then surgical treatment is indicated.  Surgery will be able to completely remove the infection and rats usually tolerate the procedure well.  At the time of the surgery, a culture and sensitivity test should be done on the infection to determine the best antibiotic therapy following the surgery.

 

 

Allergies

The most common foods for a rat to be allergic to are peanuts and dairy products, including yogurt drops. Eliminate these items for at least two weeks to see if this solves the problem. If the problem is another allergy, or eczema, treatment with a steroid will stop the itching. You can try a hydrocortisone cream (be sure to rub it into the skin well), or ask your vet for oral predisone an antibiotic should be given with it because steroids depress the immune system). Sometimes the steroid treatment alone will clear up the problem, but if the itching returns after the treatment, you must try to identify what the rat is allergic to.

It is rare for a rat to be allergic or sensitive to most litters, other than pine or cedar shavings, but you might want to try changing your rat's litter or bedding. Because I think a rat can develop an allergy to fur mites, I recommend treating for mites if you can’t identify another allergen.

If you know your rat’s problem is an allergy, the next step is to test for further food allergies. A good testing diet is a mixture of cooked brown rice and raw millet, plus 1 teaspoon of Nutri-Cal per day. You can buy Nutri-Cal at any vet hospital. If you see an improvement in 7-10 days you then add foods one at a time to see if they cause itching. If you identify the food your rat is allergic to, then you can put her back on a normal diet, minus the offending food.

It is also possible for a rat to have eczema, which causes itching with no known cause. The treatment in this case is a topical steroid cream or shampoo, and you often have to continue the treatment for the rest of the rat’s life.

Dermatitis/Eczema

 

In one case two siblings developed dermatitis with ulcerating blisters that didn’t seem to hurt or itch.  A shampoo containing benzoyl peroxide was used 3 times a week until the ulcers started to heal, and then once a week as a preventative. 

 

Fungus

If your rat hasn’t responded to the ivermectin or the prednisone, the only thing left is to treat your rat for a fungal infection. Like the skin scraping for mites, biopsies or skin scrapings for fungus often yield a false negative. Therefore, you must try the treatment.

The fungus infections that can grow on the skin are commonly called ringworm, because of the red ring they can cause on human skin.  Ringworm is very contagious and can be passed from humans to other animals and back again.  Rats who have a fungal infection of the skin don’t always show symptoms.  If your rat does have a skin lesion, you can try an over-the-counter cream such as Lotrimin. Antifungal shampoos don’t seem to work.

 

For a rat who has widespread lesions, or for a rat who shows no skin lesions at all, you should use an oral fungicide.   For griseofulvin  the dose is 12-25 mg/lb twice a day for at least 4-6 weeks.  Give griseofulvin with a meal that includes fat.  For ketoconazole (Nizoral) the dose is 4 mg/lb three times a day for at least 3-4 weeks.  With either treatment you should see improvement in 1-2 weeks.  In some cases treatment may be needed for up to 3 months. Program may also be an effective treatment for fungus (veterinarians are still not sure of this.) Because fungus thrives on sugar, a rat with a fungal infection should receive only limited amount of sugar (including fruit) in his diet.

 

There is a type of fungus called Trichophyton mentagraphytes that can be passed from animal to humans.  It doesn’t usually cause any symptoms in the animals. In people it usually starts out as a small red pimple-like bump that develops over several days into a blister. I have had this fungus several times and in my case, there was no itching, but the lesions are very tender and painful if bumped.  They may cause itching in some people.  This fungus should be treated with a topical anti-fungal cream twice a day. The sooner you recognize it and treat it, the sooner it will go away.  Below is a picture of one of my fungus blisters.

 

 

Dry Skin

Dry skin and dandruff can be symptom of a poor diet, or it might be that rat has a higher than normal need for essential fatty acids. You can buy a supplement of essential fatty acids to add to the diet at either a health food store, or a pet store. (Look for ferret supplements.) Dry dandruff can also occur in rats with hindquarter paralysis since they can't groom themselves normally. If the humidity in the air is too low, it usually affects the tail rather than the skin. This can prevent the dead skin cells on the tail from shedding properly resulting in patches of scaly skin and discoloration. The solution is to run a humidifier in the room.

Ringtail is a skin problem caused by dehydration that is occasionally seen in baby or hairless rats, and rarely in haired adults. Dehydration can occur if baby or hairless rats are kept on litter that is too absorbent (commonly corn cob litter) or in any rat if the water bottle malfunctions. In babies ringtail causes a constriction at the base of the tail. In adults it can cause a moist oozing sore at the base of the tail. The problem usually goes away when the rats are rehydrated, although if the problem is bad enough a baby may lose part of her tail.

The picture on the left shows a tail with excessive unshed scales which should be picked or scrubbed off.  Letting scales stay like this can result in the formation of scabs, as you can see in the second picture.  The picture on the right shows Ruckus, a rat with an infection in the end of his tail.

        

Hair Loss

There are two main causes of bald spots in rats. The most common is barbering, a behavior where a rat obsessively grooms itself or another rat to the point of nibbling off the hair. The result is bald patches or areas where the hair looks like its had a bad haircut. Usually there is no damage to the skin, but sometimes there can be scabs. The most common areas for self-barbering are the front legs and stomach. The most common areas for barbering another rat are on the head, face, neck, and shoulders. These bald spots are not usually symmetrical. Because this behavior doesn't usually cause any health problems, there is no reason to separate a barber from her roommates, unless you are showing your rats. Another cause of bald spots is fungus (see above.)

Another type of hair loss is a general thinning of the hair. This can occur in a rat infested with lice or tropical rat mites. Although in these cases the rat usually doesn't self-inflict scabs, constant scratching can cause general hair loss, most commonly on the back. Rex rats may tend to have thinning hair as they grow older or if they are stressed due to disease.

In some other animals, such as dogs and cats, a hormone problem can cause hair thinning, although I haven’t seen this in rats. This type of hair loss is usually seen on the flanks, hindquarters and sometimes the stomach and is usually symmetrical.


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