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Treat and Prevent Ringworm in Dogs and Cats

Mycosis in dogs: tips for recognising it and the most effective treatment.

Mycosis or ringworm in dogs and cats: here is the definitive guide.

Mycosis or ringworm in dogs and cats. Mycoses are relatively frequent diseases in our pets. They can be associated with reduced immune defences and are infectious for humans, incredibly unhealthy ones. They are, therefore, a zoonosis. That is why knowing about them and trying to prevent their occurrence is necessary.

Mycosis in dogs and cats: what is ringworm?

Mycetes, i.e. fungi, are tiny microorganisms that live on the skin of our animals (including our own) as commensals, together with other populations: bacteria, yeasts, viruses and others.

They are widespread on all surfaces, in the soil and the environment.
Some species of fungi can create lesions of a different nature if the organism that hosts or encounters them is in a predisposed state of health.

The disease they cause is called mycosis, vulgarly known as ringworm.

Depending on the species they belong to, fungi can feed on

  • Organic material of plant and animal origin (saprophytes).
  • Use that of other living organisms (parasites).
  • Please share it in symbiosis with them (symbionts).

Knowing their metabolic characteristics is essential for their typing in culture (when you have to make a diagnosis in practice), a fundamental step, especially in relapse or resistance to treatment.

Dermatophytes: Skin fungi

Dermatophytes, i.e. fungi that are carriers of skin disease, use keratin as their primary food source’. They are, therefore, defined as keratinocytes, i.e. able to degrade keratin. They are particularly resistant, especially if they remain attached to the animal’s fur to stay viable for up to 12-25 months in the environment.

Depending on the natural habitat they prefer, they are divided into three groups:

  • Geophiles: they replicate efficiently in the soil where they decompose (feed on) organic material from hair, skin scales, animals or humans;
  • Anthropophilic: adapted to humans, they can survive in the environment but generally do not replicate there, living as parasites on human skin. They are unlikely to cause disease in our pets;
  • Zoophiles are adapted to the animal world and are all agents of zoonoses. They are not species-specific but have a ‘reservoir host’ represented either by a single species (e.g. Microsporum canis for cats) or by a taxonomic group (e.g. Trichophyton mentagrophytes for lagomorphs and rodents).

The species that most frequently cause disease on the skin of our animals are three:

  • Microsporum canis
  • Trichophyton mentagrophytes
  • Microsporum gypseum

What mycoses for our pets?

M. canis is the most isolated zoophilic dermatophyte in cats. You can also find it in dogs (70-80% of dermatophytosis cases), horses, rabbits, rodents and wild animals.

Other fungi, such as M. gypseum and T. mentagrophytes, are more common in rural areas: hunting dogs and all those who frequent woods and country areas may be more susceptible. Mentagrophytes are more common in rodents but have also been isolated from other animals, such as dogs, horses and rabbits.

Incidence of the disease in which areas is it present?

It is interesting to note that, especially in recent years, we have seen an increase in cases of mycosis in dogs and cats.

By the way, the latter could be a healthy carrier of infection as they often show no signs. In addition, warm, humid areas are favoured by fungus.

However, there is no greater disease incidence in one geographical area than in another. What has, however, been observed in cats (in Switzerland) is that those which have access to the outdoors and can prey on small rodents are more exposed to T. mentagrophytes, which is, therefore, the fungus most isolated in the case of manifest disease, compared with M. canis, which is typical of those confined indoors.

This fact is all the more relevant if one considers the former a source of infection for owners with severe skin inflammation.

Mycosis: how does contagion occur?

Mycosis or ringworm in dogs and cats: here is the definitive guide.
Mycosis. The spore can remain alive even on objects.

Cutaneous mycoses can be contracted through direct contact, either animal-to-animal or animal-to-human.

Moreover, the infecting part, the spore, can also remain viable on


Thus, the infection can also occur indirectly through contact with spores carried by other materials. Moreover, some individuals can be considered healthy carriers because they are not symptomatic but infectious.

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Why does everyone who comes into contact with fungi not get sick?

The leading cause of fungal infection is a reduction in the subject’s defences and an imbalance in their skin bacterial flora. Indeed, fungi are often commensals of the skin. That is, they live in equilibrium with other living microorganisms.

These do not allow them to replicate excessively, thus providing good competition on the skin’s surface. But there are two other fundamental defence mechanisms:

  • First is a chemical defence mechanism: the sebaceous glands, by producing the right amount of sebum, consisting mainly of fatty acids, provide an unsuitable substrate for fungal growth. In reality, this function is still performed by the bacteria on the skin, which degrades and transforms (through hydrolysis) the triglycerides into fatty acids, potent antifungals.
  • A mechanical mechanism: if the skin has the correct turnover of stratum corneum cells, it does not give the fungus the suitable substrate to implant itself. In short, healthy, dry, undamaged skin may harbour the fungus but will not be infected.

To create lesions, the fungi must overcome the stratum corneum and penetrate the hair follicle or epidermis.

Fungi in dogs and cats: how does injury occur?

Mycetes can produce many enzymes that digest keratin, which makes up hair and skin. However, the largest colonies of spores are established at the hair follicle level.
These enzymes produce an inflammatory response from the host (the animal that has become infected), which then summons the immune system.

The inflammation that sets in causes the fungus to move centripetally, creating typical circular lesions. If the immune response is correct, the fungal lesion is self-limiting because the animal is healthy and does not require intervention.
The organism can fight the disease on its own, and within a few weeks, it can recover.

Other animals, however, may have an exaggerated response to the infection. This allergic-type reaction is subjective and can determine the severity or otherwise and the difference in lesions present from one animal to another.

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Causes of fungal infections in dogs and cats

Some conditions are strongly predisposed to the onset of full-blown disease.

General physical conditions:

  • Very young subjects appear to have a lower concentration of fatty acids in the sebum. Therefore, they are more predisposed, as are older issues with a less efficient immune system.
  • Debilitating diseases: diseases such as feline immunodeficiency triple the incidence of dermatophytosis in cats.
  • Malnutrition.
  • Intestinal parasitosis.
  • Stress and debilitation from overcrowding are also aggravated by subjects’ closer contact with each other (catteries, kennels, colonies).
  • Drug-induced immunodepression: chemotherapy (also in humans).

On the subject of immune-depleting drugs, I would like to point out that cortisone therapies are immune system depressants.
Their administration causes a lowering of the defences to such an extent that it can trigger the disease.

Skin conditions:

  • Skin lesions from animal bites.
  • Scratching lesions.
  • Ectoparasites and bite-induced lesions.

The hygienic condition of the dog can be an inciting factor. Contrary to what one might think, excessive hygiene is a predisposing factor:

  • Too frequent washing with unsuitable products.
  • Use of products that alter the skin’s pH, etc.
  • Too regular use of disinfectant wipes.

Environmental conditions:

  • The warm, humid season helps spore germination, which occurs most favourably in temperatures between 24 and 30°C;
  • The highest incidence is found in the autumn season.

There also appears to be a predisposition for long-haired subjects (Yorkshire Terriers, Persian cats).

Symptoms of mycosis in dogs and cats: how to recognise ringworm?

Mycosis or ringworm in dogs and cats: here is the definitive guide.
Mycosis can present itself in a somewhat inconsistent manner.

Depending on the subject’s response, the disease can be somewhat inconsistent. The most characteristic signs in dogs are

  • Loss of hair
  • Production of scales and crusts
  • Itching (not always present).

The typical lesion is a round alopecic area with small lesions around it represented by pustules or inflammatory papules. Still, it does not always manifest itself in this way.

Moreover, if the lesion is not very recent, the hair in the centre may grow back, and a characteristic hairless ring may remain all around.

Mycosis in dogs may occur in all areas of the body, with prevalent localisation on the head, nose, lips, area around the eyes, ears (especially the rim) and front part of the body in general, with varying numbers of concomitant lesions.
They usually increase in number (if the body does not react) depending on the part that comes into contact with the lesion (from the head to the paws if one scratches them, for example).

Another typical lesion of mycosis is the one in which it appears as an area of acute, oedematous and moist inflammation, oozing purulent material, in which a fungal and bacterial infection has taken place. It is always somewhat regular in its roundish shape.

Cats can be healthy carriers of the disease even when they have been infected and then cured. One becomes aware of the presence of the fungus if the owner manifests skin symptoms despite the cat being healthy.

Subjects with even significant infestation of M. canis that are asymptomatic are not uncommon.
If, on the other hand, the disease does manifest itself, it may present with extensive hairless areas, up to even deep dermatitis.

The areas mainly affected by cats are

  • The area around the eyes
  • Back of the nose
  • Tail
  • The outer surface of the ears
  • Edge of the ears
  • The lower part of the limbs

Mycosis in dogs and cats: contagion to humans

I am writing a specific paragraph on this subject to explain this better.

Fungi in animals, like humans, can only take root, grow and create damage if a predisposing situation allows them to develop.
Contagion occurs in the same way as in animals:

  • By direct contact with the animal,
  • By indirect contact with contaminated tissue or objects.

The disease can manifest itself in humans under conditions of:

  • Immunodepression
  • Very young subjects who are not yet immunocompetent
  • Ancient immunocompromised subjects
  • In the case of immunodepressive disease (viral infections such as HIV)
  • Immunosuppressive treatments (chemotherapies, cortisone and immunosuppressants) and similar conditions.

Dermatophytoses in humans manifest themselves as eczema and dermatitis, which are round and can be treated with antifungal drugs for topical or systemic use, depending on the medical indication.

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Diagnosis of dermatophytosis

When you go to your doctor, getting a diagnosis will be relatively easy, even at the mere sight of the lesions. Nevertheless, the moral practitioner will undoubtedly need to confirm the diagnostic suspicion of mycosis through relatively simple and not-at-all-invasive examinations:

Diagnosis with WOOD lamp: what is it?

It is a UV lamp that, by illuminating the hair, can highlight 50% of the M. Canis species (not the other species) that infest dogs and cats, thanks to their luminescence capacity.
However, one must be careful what one looks at; only the luminescences attached to the hair indicate mycosis; everything else is not part of the disease.

How to interpret the examination?

If the luminescence is all over the hair, it is a recent lesion, whereas it is healing there if the colour is only visible in the lower part of the hair.

Beware of false negatives or false positives.
The absence or presence of fluorescence could be related to the administration of drugs that interact by inducing or suppressing the reaction to light.
Furthermore, the absence of response could be attributable to fungi other than M. canis.
Therefore, there is a need for further testing in the presence of a lesion and the absence of a reaction to the light.

Other diagnostic examinations for mycosis

When in doubt or for diagnostic confirmation, it is always helpful to carry out other examinations, which may highlight the fungus microscopically and macroscopically.

Observation of material under the microscope.

Hairs can be taken from the most peripheral part of the lesions, where the fungi are most likely present, and then suitably treated and observed under the microscope.

Also, utilising the scotch test, hairs can be taken and observed under the microscope.
A small portion of hair adheres to simple, transparent scotch tape and then, after placing reagents, placed on a slide and observed under the microscope.

Test Culturing material.

The safest test is to take a hair sample and place it in culture.
Depending on the species, the fungus will take between 7 and 45 days to grow and can then be typed according to its shape and characteristics and observed microscopically.

Mycosis of dogs and cats: what remedies?

About treatment, it is helpful to remember that remission of symptoms often occurs spontaneously within about three months if the subject is healthy and the lesions are not generalised.
Short-haired dogs and cats are facilitated in this. In long-haired dogs and cats, and in the case of infections in several areas of the coat, treatment is necessary and not always easy to arrange.

Topical or systemic treatment?

In the case of ringworm, systemic (oral) drugs are only effective up to the hair follicle, as they cannot reach the fungi on the hair.
This medicine is why they are helpful, but only in combination with a local treatment that can be carried out through ointments or shampoos and total sponging to be carried out twice a week.

The necessity of shearing the hair (entirely or only locally) is debated. However, not everyone agrees with its application, mainly because the skin may be traumatised during the operation, aggravating the situation.

Mouth medicines for mycosis in dogs and cats

As far as active ingredients are concerned, there are many molecules with systemic antifungal action:

  • Itraconazole is the first choice drug, having good efficacy and persisting for 2-4 weeks after discontinuing therapy. It has few side effects (anorexia). The medicine should be administered during meals to allow for better absorption. It is the only one registered for veterinary use.
  • Terbinafine is a remarkably effective fungicidal agent not registered for veterinary use. The drug accumulates in high concentrations in sebum, stratum corneum and hair follicles, where it persists in therapeutically effective concentrations even 2-3 weeks after discontinuation of administration (Noli and Scarampella, 2002).
  • Ketoconazole should be avoided due to its essential side effects on metabolism.
  • Griseofulvin: may have side effects such as vomiting and diarrhoea, especially in cats. It has fungistatic action and, therefore, serves to inhibit the growth of the fungus without being able to eradicate it. It can be administered in cases of an efficient immune system.
  • Griseofulvin is strongly teratogenic (i.e. causes malformations in the foetus), so it should never be administered during the first two-thirds of pregnancy; it should also not be used during the first 6-7 weeks of life because it can cause severe aplastic anaemia in cats.

Topical medicines for mycosis in dogs and cats

The active ingredients that have proved most effective are:

  • Enilconazole: from studies carried out in vivo, it was evaluated as the only drug for M.canis infection.

As early as five weeks after the start of therapy, the culture test for fungi remained negative until the end of the 10-week control period. After that, however, it has side effects such as hypersalivation, anorexia, weight loss, and vomiting. Chlorhexidine alone as a topical treatment in mycosis has been evaluated as ineffective.

Therefore, its use is always recommended in formulations with other active ingredients. It must be remembered, however, that topical treatment in dogs and cats is always intended to be general.

Because fungal forms can quickly move, especially in long-haired dogs, treatment only at the site of the lesion (as in humans) would be completely ineffective. In addition, using Betadine locally, with small touches, can help slow down the development of the fungus.

Treatment of mycosis (ringworm) in dogs and cats: how long does the therapy take?

Mycosis or ringworm in dogs and cats: here is the definitive guide.
Treatment is crucial and should always be evaluated according to the outcome of examinations.

The duration of the treatment is a crucial point. Therefore, it should always be evaluated based on the results of the control examinations that must be carried out during the therapy.
It is well known that, even if there is a remission of symptoms, if the fungus is still present in the patient, as soon as the treatment ends, it resumes its growth, thus being able to remain infectious for the other subjects in the home.

Unfortunately, it is impossible to predict the recovery time, as many variables determine the success and success of treatment.
It takes at least three weeks / 1 month of treatment, which should not be interrupted without having done the correct assessment, but the time could be much longer.

Confirmation must come from the culture, which must be carried out in several steps.

An initial culture two to three weeks after the start of therapy (growth time about ten days, which may not be sufficient), if negative, is repeated about two to three weeks later.
A further negative confirmation could then be confirmed with a final culture.
It is essential to suspend treatment a few days before taking the culture in order not to inhibit growth.

Protocols must be evaluated according to the type of fungus and the subject treated.

M. gypseum, for example, will be less infectious for other subjects and often manages to be self-limiting, whereas for M. Canis, the treatment, especially in dogs and cats with long hair and predisposition, may be very lengthy.

Environmental treatment against mycosis

should also remember that the treatment of the environment is also crucial.

Poor environmental decontamination could reduce the effectiveness of the treatment because it would allow recontamination.

What to do, therefore?

  • Use vacuum cleaners with disposable bags to be destroyed after use and vacuum, especially in the areas where the animal is most at rest.
  • Wash surfaces with active antifungal products (bleach). You should note that chlorhexidine has also proved ineffective in this case.
  • I am washing carpets, rugs, sofas, etc., at high temperatures (with steam tools at 100°).

Well, that’s all for today—many thanks to Doctor Dimitris Tachos for his cooperation in writing this article.

Thank you for reading the article to the end. Your reading contribution was significant to us.

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The "Frenchie Breed" website is a blog aimed at dog owners. We regularly publish articles about our four-legged furry friends. Among the contents of our blog, you will find ample space on the latest news in the sector, with information and in-depth analysis dedicated to the world of dogs in all its forms, the latest trends and news of the moment, curious facts, events devoted to dogs, product reviews, as well as an intense activity of information regarding the health and well-being of pets.

Please Note: The articles in the 'Frenchie Breed Blog' are for information purposes only; nothing published can or should be construed as an attempt to offer professional advice or consultation with a physician, veterinary surgeon or another health professional.

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Written by Frenchie Breed

The "Frenchie Breed" website is a blog aimed at dog owners. We regularly publish articles about our four-legged furry friends. Among the contents of our blog, you will find ample space on the latest news in the sector, with information and in-depth analysis dedicated to the world of dogs in all its forms, the latest trends and news of the moment, curious facts, events devoted to dogs, product reviews, as well as an intense activity of information regarding the health and well-being of pets.

Please Note: The articles in the 'Frenchie Breed Blog' are for information purposes only; nothing published can or should be construed as an attempt to offer professional advice or consultation with a physician, veterinary surgeon or another health professional.

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