Ringworm in dogs

Written by Dr Andrew Miller MRCVSDr Andrew Miller MRCVS is an expert veterinary working in the field for over 10 years after graduating from Bristol University. Andy fact checks and writes for Pure Pet Food while also working as a full time veterinarian. Pure Pet FoodPure Pet Food are the experts in healthy dog food and healthy dogs featured in media outlets such as BBC, Good Housekeeping and The Telegraph. Working with high profile veterinary professionals and nutritionists, Pure Pet Food are changing dog food for the better. - Our editorial process

If you’ve noticed that your dog’s fur is shedding way more than normal, their hair seems dull and dry, and they have a few round, red patches of dry skin, it’s possible they’ve caught ringworm.

Ringworm probably has you imagining creepy crawlies under your dog’s skin and causing havoc. Except ringworm is actually a misnomer and a bit less yucky, because it’s actually a skin infection. It’s still uncomfortable and unsightly for your dog though and it will require veterinary treatment to prevent it from getting worse or spreading.

So let’s take a look at what ringworm actually is, how to identify it, and what ringworm treatment for dogs will help get your pup bright-eyed and bushy-tailed again.

What is ringworm in dogs?

Despite what the name might imply, ringworm is not a worm or any form of parasite at all. (Unlike hookworms, tapeworms, or roundworms which are all pesky parasites.) Instead, ringworm is actually a kind of fungal infection. It doesn’t always grow in rings, either.

You might hear your vet call it “dermatophytosis”, which is the medical term for the infection. It’s so named because the species of fungi that cause the infection are called dermatophytes.

There are several different kinds of dermatophytes that can infect your dog and cause ringworm. These fungi will live in the superficial layers of their skin and inside their hair follicles. Sometimes, it can even grow in their nails and nail bed. The fungus then feeds off the keratin in your dog’s hair, nails, and skin.

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Like most infections, ringworm can vary in severity. Healthy adult dogs might develop a very mild case that goes away on its own. More severe cases will require veterinary treatment to clear up the infection and make your dog more comfortable.

What causes ringworm in dogs?

Around 65% of all ringworm infections in dogs are caused by the fungus Microsporum Canis. Although “canis” means dog, this particular fungus is also responsible for 94% of all ringworm infections in cats.

Microsporum Canis is not the only fungus that causes ringworm though, and your dog may be infected by other species such as Trichophyton Mentagrophytes or Microsporum Gypseum. These three species of fungi are the most common causes of ringworm in dogs and cats. However, they are also zoonotic, which means humans can be infected by them too.

There are many other species of fungi that can cause ringworm, but they are much rarer and sometimes species-specific, so they only seem to affect one species of animal.

Is ringworm in dogs contagious?

Yes, ringworm is highly contagious! If you have any other pets in your household, they can catch ringworm from your dog. Dogs, cats, rodents, horses, even birds can all become infected with ringworm. It’s said that any domestic animal can catch ringworm, and many wild species can be infected with ringworm too and whilst these other animals are infected, they can also spread it.

Once your dog has ringworm, they will be contagious for a few weeks. Even if your dog has a mild infection that goes away on its own, they can still spread infectious spores for some time after their ringworm has cleared up. Any other animals in your home or that come into contact with your pooch can easily catch the infection themselves.

Having a case of ringworm that then clears up does not mean that your pup will become immune from infection, and they can become reinfected. Because ringworm spores can survive in the environment for over a year, they might be affected with repeat infections if proper treatment isn’t provided and if there isn’t sufficient cleaning around the home.

As you can see, once you’ve got a ringworm infection in your home, it can cause havoc for some time!

Can humans catch ringworm?

Yes, humans can catch ringworm. In fact, “athlete’s foot” is caused by the exact same fungus that causes ringworm. The three most common species of fungus which cause ringworm are all zoonotic, meaning they can infect humans as well as our pets.

If your dog has been infected with the fungus, then you can catch ringworm by stroking or touching your dog, or coming into contact with anything they have touched such as your sofa, the carpet, or their toys.

When your dog has contracted ringworm, you must remember to wash your hands after handling your dog or anything they have touched. You should also thoroughly clean surfaces your dog has laid on, their grooming equipment, as well as any toys and other objects they regularly handle.

However, healthy adults are quite good at resisting infection and unless your immune system is compromised, or there is a break in your skin for the fungus to enter into your body, you might avoid infection.

Just like with dogs, any human with a compromised or underdeveloped immune system is more at risk of infection, including children and the elderly. If you or anyone in your family develops a round, red, itchy rash or any strange lesions on your skin you should contact your GP as soon as you can.

How is ringworm spread?

There are two ways in which ringworm can be spread. Most of the time, your dog will catch ringworm after coming into direct contact with another infected dog or animal.

Your dog could also catch ringworm by sharing an environment with an infected dog and coming into contact with the fungus spores.

Animals infected with ringworm will shed spores from the fungus, which are essentially like seeds. These spores will continue to live on surfaces and in the environment for up to 18 months and can infect other people or animals in this time.

Anything your dog uses or touches could potentially become covered in spores, whether it’s a rug, your sofa, the dog bed, blankets, their toys, or the brushes you use on their fur.

Any other animal, or human, could then come into contact with these spores and become infected themselves. If there’s a break in their skin’s barrier, such as a scratch or a cut, the spores will enter their skin and cause infection. If your pup’s skin is healthy, they can sometimes go without infection even if they come into contact with a dog that has ringworm or the spores from the ringworm fungus.

These spores are usually spread when your pooch sheds the fur from the hair follicles infected with the fungus. As the strand of fur falls out, it releases the spores from inside the follicle. The same can also happen if the strand of fur breaks.

Once infected, it takes a little while before symptoms begin to show. Your dog might develop lesions on their skin between 1 or 2 weeks of being infected, however, it can take up to 3 weeks for any signs of illness or infection to appear.

Are some dogs more at risk of ringworm infection?

All dogs of any age or breed can catch ringworm. However, fungal infections like ringworm are typically more common in dogs with weaker or under-developed immune systems.

That means puppies, senior dogs, and immunocompromised pooches are more at risk of ringworm infection and when they are infected, it tends to be more severe and affect a wider area of their body.

How to prevent ringworm in dogs

There’s not a lot you can do to prevent ringworm except to keep your pup clean and dry. You should bathe your dog every few weeks, and regularly wash their toys, bedding, and blankets to get rid of any spores that might have found their way into your home. You should also routinely vacuum your house and wash surfaces your dog will come into contact with, like the floors or the sofa.

It’s very difficult to prevent ringworm, but once your dog has been infected, you need to take every precaution to try and clean your home and prevent reinfection and to stop it from spreading to anyone else in your home.

This will include putting your pup in quarantine to prevent the spread of spores, as well as all the routine cleaning listed above. Treating ringworm is one of the most important aspects of preventing the spread of infection because the medication can stop the fungus from reproducing. Plus, until your dog is treated and cleared of ringworm, other people and pets can catch it from them, and they will continue to shed the spores around your home.

The signs and symptoms of ringworm in dogs

The main symptoms of ringworm in dogs are:

  • Round, raised patches of red skin

  • Patches of red, crusty skin

  • Patches of grey, scaly skin

  • Red rings on the skin (more common in humans)

  • Small, circular areas of alopecia (hair loss)

  • Larger, irregular patches of alopecia

  • Dry, brittle fur

  • Rough, brittle claws that are easy to break

It is possible for dogs to be asymptomatic carriers of the fungi responsible for ringworm. In other words, they are infected and the fungus is living inside their body but the dog shows no symptoms of illness and seems completely normal.

Although these dogs have no symptoms, the fungus they are carrying is still infectious and can spread to other animals and people. Anyone infected by asymptomatic carriers are not necessarily asymptomatic themselves, and they could develop lesions on their skin or other symptoms that are typical of ringworm.

There are many other skin problems your dog might have that share similar symptoms with ringworm. If you notice any changes to your dog’s fur or skin, you should take them to the vet for an examination to find out what’s wrong so you can treat it appropriately.

Diagnosing ringworm

If you suspect your dog might have ringworm, it’s important they visit the vet to be diagnosed as soon as possible. Because if they are infected, they’ll need to be treated to prevent ringworm from spreading to other human and furry family members.

Your vet will first examine your dog’s skin to see if their physical symptoms like hair loss and dry, red sores are due to ringworm or another skin condition.

They might also use a blacklight (also known as UV light, or a Wood’s Lamp), to examine your dog. Your dog might be in a darkened room under a blue lamp like some sort of crime scene investigation, but there’s a good reason. Some strains of Microsporum Canis, the most common cause of ringworm, will fluoresce under blacklight, creating a green glow in the infected hairs. However, not all Microsporum Canis glows, and other fungi that cause ringworm don’t always glow, so it’s not a completely foolproof way to diagnose ringworm in dogs.

Your vet might also take a sample of your dog’s skin to examine under a microscope to see if they can see the fungus. Otherwise, they might place another sample in a petri dish to see if the fungus will grow inside. Growing the culture in a lab like this is the most reliable way of diagnosing an infection, but the problem is, it can take anywhere from ten days up to a month for the fungus to grow. Usually, your vet will be able to tell if your dog has ringworm within ten days.

Ringworm treatment for dogs

Ringworm treatment for dogs can typically be done orally or topically. Although most cases of ringworm will go away on their own, treatment will allow your dog to heal faster and help to prevent the spread of the infection to other people or pets.

Although it won’t treat the infection, many vets will advise clipping a dog’s fur at least around any lesions they have, if not all over. This is because the shorter fur is less likely to break and spread spores. It can also make applying topical treatments a little easier.

Washing away the problem

Your vet will probably prescribe some medicated shampoo for your dog to use which will have special anti-fungal properties to kill off the ringworm fungus. You can also buy anti-fungal shampoo from most pet stores. Usually, you’ll need to bathe your pooch twice a week for six weeks using this special shampoo for it to be effective and clear up their infection. But remember to check the instructions on the bottle or from your vet’s prescription and follow the advice you are given.

Just washing your dog a few times a week with normal doggy shampoo won’t cut it, and will probably dry out your dog’s skin and fur even more. The shampoo you use must have some sort of antifungal ingredient to kill off the fungus causing your dog’s ringworm.

Many people also choose to use a lime sulfur dip as an effective ringworm treatment for dogs. This dip is a powerful antimicrobial agent and kills off parasites, bacteria, and fungus that live in the surface layers of the skin. It does smell quite strong when you use it, but the odour will fade as your dog’s fur dries off. It will also give their fur a yellow tinge, and will also stain any clothing or jewellery that comes into contact with the dip.

Lime sulfur dip is usually safe for use in pregnant dogs and puppies, but it’s always best to check with your vet. Your vet will also advise you on how many times to wash your dog in lime sulfur, but it’s usually once a week for about six weeks.

Medicines to make them better

There are also topical ringworm treatments for dogs in the form of lotions and creams that can be applied directly onto their skin. Again, these will have some antifungal agents that will help to kill the fungus that is causing their infection. These lotions might be rubbed on all over your dog’s body, or just applied to any lesions they have.

Finally, there is an oral medication that your vet might prescribe to your pooch. It’ll be a tablet that contains anti-fungal medicine that will enter your dog’s bloodstream and help to clean out the infection from the inside out.

Oral medication can give some dog’s a few gastrointestinal side effects, such as loss of appetite and diarrhoea. These will usually clear up within a few days after they finish their treatment.

This medication does stop the fungus from being able to reproduce, which means your dog won’t be shedding infectious spores, which is very helpful if you need to prevent infection among other pets or vulnerable family members.

Both antifungal baths and oral medication are very safe and effective forms of treatment for ringworm in dogs. Your vet might only advise you to take one or the other, but in severe cases of ringworm, they might suggest that you try both at the same time.

How long will treatment last?

Consistency is key when it comes to treating ringworm in dogs or cats. Most pooches will need to be treated for at least six weeks, regardless of whether it’s with shampoos, lotions, or medicine. Your dog will also need to be isolated while they are being treated to prevent the ringworm infection from spreading around your home and infecting other people or pets.

As well as treating your dog, you will need to thoroughly clean your home and anything your dog might have been in contact with to get rid of any remaining spores and prevent further infections.

Your dog will need to have two negative culture samples before the vet will say they are clear of ringworm and can stop treatment. Your dog will need to be treated until they get the all-clear.

If you stop treating your dog because their skin looks better, you run the risk of stopping the treatment before the fungus is actually killed off, and your dog can become infected again. Continuing treatment until you have confirmation from your vet is the best thing to do to prevent your dog from having to face an uncomfortable ringworm infection again, and to avoid even more medication and extra bath times.

Home remedies for ringworm treatment for dogs

Technically, most of the ringworm treatments for dogs count as home remedies because you can buy them over the counter at most pet shops and apply them at home (such as shampoos, lime sulfur dip, and lotions). As far as treatment goes, these are always your best option and usually aren’t very expensive either.

Some people advise rubbing diluted apple cider vinegar onto ringworm to help treat it. Although there are studies that suggest that apple cider vinegar might have antimicrobial properties, it’s best not to try this at home because the acidic nature of the vinegar can upset your dog’s skin pH and cause further skin problems like blistering, open sores, and scarring.

Tea tree oil has also shown some promise as a treatment for ringworm because it has proven antifungal properties. Anecdotally, some people use it to treat athlete’s foot, which is essentially ringworm.

Plus, a study on horses has shown that diluted tea tree oil did seem to work in treating ringworm infections. More research is needed though, especially when it comes to the effect on dogs. However, tea tree oil is toxic if ingested by humans or hounds, so unless you can guarantee your dog isn’t going to lick it off their skin, it’s safest not to use it.

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  2. In Vitro Activity of Tea Tree Oil Against Candida albicans Mycelial Conversion and Other Pathogenic Fungi Journal of Chemotherapy, 12, (4), July 2013, 377-383, doi.org/10.1179/joc.2001.13.4.377
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