....this is a primer on the fundamental knowledge we have about Ringworm, pertaining to cause, mode of infection, risk factors, clinical signs, diagnosis, treatment, monitoring therapy, vaccination and control. Much more detail can be found in veterinary textbooks and journals. For more depth, the reader is referred to issues of the The Compendium of Continuing Education, published in November and December, 1995.1 Also, Veterinary Medicine, March 2003, pp216 and Veterinary Medicine October 2003, pp845. This author has created a fairly large (~30 page) downloadable Adobe Acrobat-formatted (.pdf) outline of four articles focused on the problem of Ringworm in cats. The original article was designed for veterinarians but is relevant and important to clients and their pets. The salient features are outlined in the pdf file for you. (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.). PLEASE NOTE: the final version of the downloadable pdf file is still in preparation...only a preliminary draft is available now...
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
- 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
- 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)
- 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.
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).
Beginning four weeks, after the onset of treatment, repeat fungal cultures should be performed. These should be repeated at two to four week intervals until negative cultures are obtained. Then culture weekly and treat for additional period until two to three negative cultures in a row are obtained.
Do not allow cats to go outside, and culture any new cats prior to allowing entry into the environment.
Discard any potentially contaminated items in contact with affected cats, vacuum thoroughly and often and discard contaminated vacuum bags immediately. Scrub and disinfect surfaces tolerating potent disinfectants, such as bleach. Make sure to disinfect (or change) shoes so as not to tract potential fungal spores into the environment.
More information on monitoring and maintaining a fungal-free cat house-hold can be found here: (Outline of Dermatophytosis)
- 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.
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