The common name, "ringworm", is somewhat confusing since the disease is NOT caused by a worm, but rather by one of several species of fungi. The medical term for infection is "dermatophytosis". Causative fungi are sometimes found as normal inhabitants of soil. However, more often than not, contaminated households, kennels and catteries readily serve as sources of infection, as decontamination of these areas can be extremely difficult. Some infections can be spread from a single animal to another animal or rarely, to a human. The disease itself has a very low mortality but in ill-thrifty animals, invasion of the compromised outer skin layers (see below) by other organisms is possible and severe illness may ensue. Ringworm is the most common infectious skin disease of cats.

Clinical signs result from penetration and digestion of the non-viable outer skin layer and of hair shafts by infective fungal elements. Often, there is some trauma to the skin, including bites from fleas, clipping wounds, etc. Arthrospores (the infective element) are present on the broken hairs, collars, and brushes from infected or carrier animals and contamination of the environment from these sources is common Arthrospores invade hair shafts and stratum corneum (the outer-most layer of the epidermis...see "SkinBasics" page).Some strains can also invade "living" tissue as well. Immune and inflammatory responses to organisms and their metabolic by-products contribute, in part, to the appearance of gross lesions (see below). In rare instances, an infected hair follicle may rupture and spread organisms to tissue beneath the skin (subcutaneous tissue) producing a firm, sometimes painful nodule known as a "pseudomycetoma". The disease is highly contagious, and Microsporum canis, the most common species in cats, is zoonotic, meaning that infections are transmissible to other species, including humans. (Not all dermatophyte species are transmitted between animals)

Risk factors for dermatophytosis ...at least in cats, which have been extensively studied... include very young and older animals and animals that are immunocompromised. Grooming inhibits development of infection, so animals which are not grooming are at increased risk, as well. Additionally, and quite significantly, long-haired cats are at considerably greater risk for infection and/or maintaining a reservoir of infectious elements (arthrospores). These "carrier" animals may actually show no clinical signs of disease! Finally, there may be genetic factors that predispose some cats to increased suseptibility.

Environmental factors also present risks. High humidity, favors arthorspore survival. Bathing of cats may remove naturally protective skin secretions (sebum and serum) which increases the probability of invasion and infection by fungal elements.

More details about risk factors and other circumstances favoring infection is described in the downloadable pdf file. (If you have a pdf browser plugin installed, you will see the document open in a separate browser window ; you can then save the document to your hard drive.)

• Typical: Some animals show no clinical signs of infection but may carry infective spores on the fur and skin. For the most part, manifestation of infection result from penetration and digestion of the non-viable, outer ("stratum corneum") layer of skin, and hair by fungal elements, although some strains can infect living tissue as well.

• There are many different expressions of clinical infection producing a host of skin and fur changes, none of which is truly "typical".
  The most common signs are:

• Broken and brittle hair
• Partial or patchy hair loss
• Scales or crusts: primarily on the head and feet but lesions can appear anywhere, or everywhere (generalized dermatophytosis)
• Multiple scales, swollen or ruptured follicles on the chin and back:
  • that resemble lesions caused by flea and other allergies.
• Areas of self-mutilation:
  • one or more areas where inflammation or itching are prevalent

· In cats, Infection may present with any combination of the following

• Pruritis (itching): it may me non-pruritic or severely pruritic (resulting in self-mutilation)
  • unilateral or bilateral pinnal (outer ear) pruritis with scaling is another un(der) recognized presentation of Microsporum canis infection
  • miliary dermatitis
• Hair-Loss:
  • may be subtle or dramatic, symmetric or asymmetric, inflammatory or non-inflammatory
  • symmetrical alopecia may be seen in cats predisposed to dermatophytosis due to prior glucocorticoid administration or because the dermatophyte, itself, produced a symmetrical pattern of alopecia
• Crusting and Scaling:
  • lesions are usually exfoliative
  • in some cats scaling is severe…it could resemble Pemphigus foleaceus
  • mounds of thick, adherent crust may accumulate on the face, ears, nail beds especially on long-haired cats
  • erythema and scaling of inner and/or outer ear (with pruritis)
• Comedo-like ("blackhead-like") lesions:
  • chin acne in young cats
• Hyperpigmentation (darkening of skin):
  • this is an uncommon clinical finding in cats in general; however when it is present, it is most likely due to dermatophytosis
• Paronychia:
  • crusted or exudative paronychia (inflammation of nails) may be the only sign of dermatophytosis in some cats
• Erythema (reddening): is a common finding is early lesion…and is often accompanied by hair loss
• Eosinophilic plaque: usually due to allergy, but can occur secondary …to pruritic Microsporum canis lesions
• Military dermatitis (multiple scales, crusts, scabs, papules):
  • these lesions may be seen after clipping (due to trauma of clipping?).
  • is a form of folliculitis
• Indolent ulcer:
  • these are red, raised, glistening lesions around mouth usually
  • there is evidence that M. canis is an unrecognized …cause of this
• Granulomatous lesion:
  • may present ad non-healing wounds or nodules (especially in long-haired cats)
• Miscellaneous:
  • facial folds and periocular (around eyes) hair
    • most common when treated with lyme-sulfur dips, because owners are reluctant to apply this obnoxious dip to face
    • animals also have facial-fold pyoderma (superficial skin layers are infected), conjunctivitis and blepharitis
      
• Varied lesion distribution:
  • may be focal (in one place) or multifocal (in more than one location)
  • even if focal, spores will be present throughout the coat, due to grooming
  • in young kittens:
    • Scaling and alopecia on the face, ears, muzzle and forelimbs
  • in older kittens and young cats:
    • Irregular patches of alopecial with or without crusting
• Other signs:
  • "excessive shedding" (is a common complaint)
    
  • constipation, vomiting (from hairballs)

• Atypical: Rarely, infection extends to the deeper (subcutaneous) tissues and a painful, inflammatory lesion follows.

• Dermatophyte Culture: This is the most reliable method for the definitive diagnosis for the presence of ringworm organisms. Results typically take seven to ten days. Microscopic examination of cultured organisms taken from culture media is frequently a helpful adjunct tool.
• U-V Fluorescence: A few species will cause a distinct apple-green fluorescence in infected hair shafts when these are illuminated by an ultraviolet light source. Many infections are due to non-fluorescing species and false positives (fluorescence) are also possible.
• Microscopic Examination: The presence of infective spores on hair shafts may occasionally be visualized microscopically. The possibility of false negative results is, however, great.

Considerably more details, including pictures of diagnotic methods, findings and interpretations can be seen in a downloadable pdf file. (If you have a pdf browser plugin installed, you will see the document open in a separate browser window; you can then save the document to your hard drive).

• PCR Tests: There appears to be a relatively new development in the molecular technique known as PCR (polymerase chain reaction) for identifying certain dermatophyte antigens in submitted samples. For example, in J Clin Microbiol. 2005 May, the DiversiLab system for identification of the dermatophytes is described and compared to standard culture and morphological identification techniques. As more information becomes available about the reliability, availability and cost of this technique, I will update details about that option here.

• Treatment Approach:
  • a combination of topical and systemic treatment of infected inviduals as well as painstaking hygiene and decontamination of the environment are required to eradicate this often stubborn pathogen.
• Clipping:
  • is absolutely a key component of effective treatment and management of dermatophytosis, especially in cats
  • all long-haired cats and short-haired cats with generalized infection (or generalized carrier status) must be completely clipped; this eliminates a major source of infective spores...broken hairs...and provides for greater efficacy of topical antifungal agents (below)
  • since clipping itself can cause microtrauma to the sking it can, then temporarily increase the risk of infection! A number 10 blade is recommended...as this blade is less likely to nick skin than blades (e.g. #40) which clips closer to skin surface
• Topical Treatment:
  • in conjunction with systemic therapy, topical treatments generally shorten the total duration of therapy...and hence the cost of therapy, in comparison to systemic therapy alone
  • there are several choices for topical therapy:
    • Lime-sulfur (LymDyp® -DVM Pharmaceuticals, use 8 oz per gallon of water)
      • This is therapy of choice (if enilconazole is not available)…is consistently effective!
      • Is administered twice weekly…can be sponged on
      • Is irritating to mucus membranes…cat’s should be prevented from grooming the wet solution afterwards
      • It stinks…but odor rapidly diminishes when it dries (DO NOT RINSE OFF!)
        
      • It stains white cats yellow or green!
      • Owners should wear protective gloves and a mask and should apply the dip in a well-ventilated room
    • Enilconazole (Imaverol^® Janssen Pharmaceuticals; a 10% concentrated solution) is NOT licensed in the USA
      • Apply twice weekly as dip for 5-10 weeks
      • Well tolerated, but associated with hypersalivation, anorexia, vomiting, idiopathic muscle weakness, elevated ALT (a liver enzyme)
      • Do not rinse after applying
    • Enilconazole ( Clinafarm EC^® a 0.2% emulsion, Janssen Pharmaceuticals)…is licensed in the USA
      
      • Mix 55.6ml with gallon of water and apply as topical dip (sponge)
      • Is technically illegal to use, since it is EPA approved (not FDA approved)
      • Do not rinse after applying
      • Is applied twice weekly
    • Miconazole Shampoo (Malaseb^® -DVM Pharmaceuticals)
      • Used alone or in combination with chlorhexidine (however, chlorhexidine has essentially no efficacy against dermatophytes!)
      • Miconazole shampoo needs a contact time of 10 minutes, before rinsing
      • Bathe twice weekly
    • NOTE: The following products have NO efficacy against dermatophytes:
      • Capstan
      • Povidone Iodine
      • Chlorhexidine
• Drugs: There are a number of drugs topical and systemic which are useful for treating clinical ringworm infection in individual animals (usually cats). Aside from topical and systemic antifungal class of drugs, such as itraconazole, there is more recent information which suggests that lufenuron (Program^®) is inconsistently efficacious (and is NOT recommended in problematic cases), but it is very safe! The vaccine (see below) can alleviate the clinical signs BUT does not eliminate infection!
  • Itraconazole (Spronox®)
    • MOA: alters fungal wall permeability by inhibiting ergosterol synthesis. Is fungistatic at low doses, fungicidal at high doses
      
    • Vomiting and diarrhea are most common side effects…but drug is well tolerated by most cats (side effects are dose-dependent)
    • Several dosing regimens have been proposed:
      • Dose(1): 10 mg/kg once daily...until complete resolution of clinical signs and a negative fungal culture is obtained
      • Dose(2): 10 mg/kg once daily for 28 days then on alternate week therapy at this dose
        
        • A 2001 study in the Veterinary Dermatology 12: 347-350 supports this dosing protocol
      • Dose(3): (Short term cycle therapy): 10 mg/kg once daily for 15 days followed by fungal cultures 10-15 days after terminating treatment. If the culture is positive, the cycle is repeated. These 15 day treatment cycles are especially cost-effective in multi-cat situations
        
  • Terbinafine ((Lamisil^® Tablets, Novartis)
    • MOA: suppresses the biosynthesis of ergosterol by inhibiting the fungal enzyme squalene epoxide. Is fungicidal vs dermatophytes
    • Is well tolerated by cats; vomiting is the most common side effect
    • Dosing options, using 30-40 mg/kg per day are otherwise identical as for itraconazole (see Dose(1), Dose(2) and Dose(3) for itraconazole, above).
    • Lamisil^® is useful in cats that are unable to tolerate side effects of itraconazole
  • Griseofulvin
    • MOA: inhibits nucleic acid synthesis and cell mitosis by interfering with spindle microtubules
      
    • Absorption is enhanced with fatty meal
      
    • Is a teratogen…do NOT use in pregnant animals and in breeding male animals because it also interferes with spermatogenesis
      
    • Do NOT use in cats with FIV infection because of propensity to cause severe neutopenia (low white blood cell count) in these animals
      
    • Side effects are fairly common, and include vomiting, diarrhea and anorexia (which can be managed with dividing to twice-daily dosing)
    • Dose depends on size of suspended drug particles:
      • Dose: (using microsize): 25-50 mg/kg PO once daily or the same total dose but divided, twice daily
      • Dose (using ultrasize): 5-10 mg/kg once daily or the same total dose but divided, twice daily
  • Lufenuron (Program^®, Novartis)
    • MOA: benzoylphenylurea---disrupts chitin synthesis (chitin is a critical component in the outer cell wall of fungi)
      
    • While initial studies were promising for this drug, more recent research indicates that this drug is NOT efficacious using a variety of protocols. It is not recommended!

• There is a commercial vaccine for ringworm in cats (as of 2003, the availability of the FeloVax MC-K vaccine (Fort Dodge) is limited, if at all) .
• Animals must be at least four months old to receive the initial and subsequent booster immunizations. This vaccine has been shown to:
  • Reduce clinical signs of infection BUT does NOT eliminate organisms from the animal.
  • result in improvement after vaccination that may last eight weeks (i.e. up to two week following the last booster) at most.
  • cause, in approximately 8% of cases, a mild adverse reactions, ranging from local soreness to discrete nodules at the injection site. These usually resolve over a period of a few weeks
  • be sometimes useful anyway. When combined with appropriate topical and systemic therapy, vaccination may be a beneficial adjuvant therapy
    • Fungal vaccination may be a practical alternative to topical therapy when topical therapy can not be used
    • This assumes that the coat is clipped and that appropriate systemic antifungal therapy and environmental decontamination procedures are used

• General: Herein lies a major problem, since environmental contamination with infectious spores can be widespread, especially in multiple-cat households. Spores, unfortunately, are extremely resistant to most disinfectant protocols, including dilute (1:100) bleach, chlorhexidine, phenolic and quarternary ammonium solutions. Bleach (e.g. Clorox) at 1:10 dilution or diluted lime-sulfur dip (1:33) have some ability to inactivate spores in the environment. Bleach is about 20% efficacious. Enilconazole, if available, can be used as disinfectant area fogger (Clinafarm SG—American Scientific Labs, Janssen Pharmaceuticals ) but is not approved for this purpose in the US.
• Recommendations:

• Thoroughly clean all hard surfaces, including floors, baseboards, heating registers and auto interiors to mechanically reduce the amount of infected material. If feasible, swab surfaces with 1:10 dilute bleach and/or dilute lime-sulfur (1:33). There are also newer medical grade antifungal and virucidal chemicals which may be useful (but information regarding the efficacy of these in controlling Ringworm is not evident to this author).
• Bedding, rugs, cages, litter pans, carriers and similar products are vacuumed, scrubbed, washed in hot water with detergent and 1:10 dilute bleach (if this is too strong for some fabrics, then repeated washings at 1:30 dilution can be tried).
• Vigorously and frequently vacuum or steam clean all carpets, upholstery and drapes (dry cleaning of drapes, if necessary)
• Replace forced air furnace filters weekly....
• Frequently groom or clip cat(s) to mechanically remove spores and to prevent the establishment of infection (or reinfection).
• More specific recommendations regarding monitoring of infected cats and households will be described here in more detail but are already summarized in the downloadable pdf file.