ringworm
In Humans

Ringworm - a persistent fungus

Dermatophytosis and Dermatophilosis – what’s the difference?

Many species of animals, including humans, are susceptible to fungal skin infections. Cats, dogs and domestic livestock, including horses, are the most commonly affected animals

Contrary to popular opinion, Ringworm is the collective name given to fungal infections of the hair and skin which can be caused by a series of fungal species which we will outline below. Thus, Ringworm is better described as a condition, not a specific disease with only one specific cause.

The scientific description for fungal skin infections is Dermatomycosis, and this term covers infections by all fungal species (each fungus is scientifically known as a dermatophyte).

Ringworm, or dermatophytosis, is a highly contagious infection of the keratinised tissue (skin, hair and claws) of domestic animals and man by one of the three common disease causing genera of fungi collectively called Dermatophytes;

Microsporum canis, M.gypseum – this genus infects mainly animals, and M.canis is the most common cause of Ringworm in dogs and cats, and can cause infection in humans. It is less common in other animals including goats, cattle & swine. M.gypseum causes ringworm infection in rodents, horses and dogs

Trichophyton mentagrophytes, T. verrucosum, T.equinum – this genus also infects mainly animals, with T.equinum causing ringworm mainly in horses, as well as Tinea in humans. T.mentagrophytes can cause ringworm in rodents, dogs, cats, horses, cattle, swine and humans. T.verrucosum causes ringworm in cattle and occasionally in sheep, horses and humans.

Epidermophyton – causes problems primarily in humans, and is virtually non- existent in domestic animals.

These pathogenic fungi are found worldwide, and some have regional geographic distributions.

Several of these organisms of animal origin are responsible for the fungal skin infections in humans, and Ringworm is known to be a zoonosis (disease transferable from animal to man). The particular ability of these three genera to be transmissible to animals as well as humans signifies their importance as a veterinary and human health problem worldwide. Microsporum canis is one of the most important fungi in both animals and humans.

In humans, ringworm forms a ring-shaped raised red rash, but this presentation is very uncommon in animals, where ringworm can look like anything.

Most people get ringworm infections from cats or kittens. Studies show that in 30-70% of households where the cat has ringworm, at least one person will contract ringworm infection. Having said that, it is important to understand that humans have their own forms of ringworm as well- Tinea and Athlete’s Foot are the human ringworm infections. Only about 3.5% of all human cases are caused by the same fungus that infects dogs and cats, so humans are far more likely to obtain ringworm (tinea) from a school playground, gym, or communal shower facility.

Transmission to humans is also highly possible from ringworm in other species, including horses, camels, sheep and cattle, so the real treatment objective with domestic animals is to maintain effective hygiene to reduce transmission from, or between, infected animals, and to man.

New Zealand 1955 research in confirmed that about 40% of scalp and body ringworm in children was due to contact with cats, and that cats were responsible for 63% of human infections in total, with the majority being caused by M.canis. Further research in 1981 confirmed that of a total of 774 specimens from dogs and 227 from cats submitted for examination in Norway in 1973 to 1979. Microsporum canis accounted for all infections in cats, and for 95.8% of infections in dogs

In developed countries, the greatest economic and human health impact comes from the fungal infections of cats and cattle (particularly Microsporum canis infections of domestic cats and Trychophyton verrucosum infections of cattle and lambs), but infections from dogs, horses, camels and other species to man are still commonly encountered.

Ringworm is transmitted primarily through direct contact with infected individuals and/or contaminated grooming tools or saddlery. Contact with a fungus does not always result in an infection.

Whether infection becomes established depends, to some degree, on a number of factors including the species, age, state of competence of the immune system, condition of the exposed skin, grooming behaviour and nutritional status of the host animal. Disruption of the intact skin surface appears to be important to allow the invasion of hair follicles by Microsporum and Trichophyton organisms, and these organisms then require actively growing hairs for survival ( although infectious spores can remain for very long periods on hair shafts after the active infection has ceased).

In most cases Ringworm only grows in tissues containing keratin (skin, hair and claws), and an infection usually stops once it reaches living cells or inflamed tissue. While this should effectively limit Ringworm infections rapidly, the organisms actually produce elaborate metabolic products which diffuse to surrounding cells causing inflammatory and hypersensitivity reactions that are responsible for the development of characteristic lesions seen commonly and most obviously in humans.

Infection begins in a growing hair or on the skin surface, where threadlike hyphae develop from the infective fungal spores. These hyphae (like tentacles) penetrate and weaken the hair shafts, and create some inflammation in the hair follicles, leading to patchy hair loss. As the infection ages, clusters of infective spores then develop on the outer surface of the hair shafts. Broken hairs (plus the infective spores found on the hairs) are important sources of infection and spread of the disease.

Ringworm is usually self limiting in healthy animals – as inflammation and the immunity of the host develops, further spread of the infection is inhibited, although this process may take several weeks or longer. In young or otherwise debilitated animals, and in longhaired domestic cats, infections can be persistent and widespread.

The surface of the skin separates during infection, forming a scab. The moisture in wet scabs is particularly effective at enhancing the proliferation of fungal spores

Few animals exhibit itching with Ringworm infections, and uncomplicated skin lesions heal without scarring, and have little effect on general health. Animals with more severe generalised infections commonly have a loss of condition or develop secondary skin infections or fly irritation.

After treatment appears to be effective it must be continued for some time, even though animals may look better. Hair re-grows long before the fungus is exterminated. In a single cat household, treatment may be required for 3-8 weeks, and multiple cat households it may require much longer periods.

Fungal spores can persist in the environment, including the home carpet, for up to 2 years, so re-infection is always a concern. Similarly, spores can survive on horse or camel saddlery and rugs for well over 12 months. Getting rid of any hair shed is of major importance in limiting spread of ringworm.

Sunlight is effective at killing spores, so wherever possible put saddlery, rugs and tack out in sunlight for as long as possible to prevent re-infection from contaminated gear. In a household situation, vacuum carpets thoroughly, and be very aware that the vacuum bag is a wonderful haven for ringworm spores to survive, so make sure vacuum bags are destroyed after thorough cleaning.

Let’s have a look at the variations between ringworm in various species of domestic animals.

Ringworm in Cats
 

Three species of ringworm (dermatophytes) are commonly found to infect felines. These are Microsporum canis (by far the most common cause of ringworm in cats and dogs), Trychophyton mentagrophytes (usually contracted through contact with rodents), and Microsporum gypseum (usually contracted through contact with spores in the soil). Over 98% of infections in cats are caused by M.canis infection.

Ringworm is spread through contact with another infected animal, or through contact with infective spores. Spores are scattered through the environment after cats are infected, and can be found in carpets, furniture, cat bedding and even air filters in the home. The spores are highly resistant and can last in the environment for up to 18 months, so treatment of ringworm in cats must include a thorough house cleaning to clean up any spores that could reinfect the cat.

As well as being contagious to other cats and dogs, ringworm is a common zoonotic disease, infecting humans readily, particularly children.

The clinical appearance of ringworm in cats is quite variable. Kittens are most commonly affected. Lesions usually consist of focal hair loss, scaling and crusting, mostly around the ears and face or on the extremities of the legs.

Cats are well known to be able to be asymptomatic carriers of ringworm, hosting and spreading the disease without any obvious symptoms themselves. This can be a serious issue in multiple cat households, or in homes with other animals and children.

Ringworm is generally seen in kittens and young cats before their immune systems are fully developed, or in adults with suppressed immune systems from other age or disease related issues.

While ringworm can clear up in cats spontaneously, particularly in short haired cats, the ability of cats to carry the disease without symptoms can complicate ringworm treatment and management. Medication is highly recommended in cats to prevent spread. Long haired cats in particular may require systemic medication for long periods.

Vets are often faced with diagnosis of ringworm in cats, and many owners will be aware of the Woods Lamp test, which illuminates infected hairs/skin/nails under the light as a positive diagnosis. It is important to recognise that the Woods Lamp will only illuminate Microsporum canis infections, which glow green under the lamp. Other fungal species will not illuminate.
Skin and hair may also be directly examined under a microscope as a rapid test for ringworm by the vet, and in many cases the vet may choose to perform a skin scraping and fungal culture by sending the sample to a laboratory.

Ringworm in Dogs

Over 70% of cases are caused by Microsporum canis, and 20% by M.gypseum, 10% by Trichophyton mentagrophytes.

Definitive diagnosis is often confirmed by skin scraping and fungal culture. The Woods Lamp will fluoresce M.canis infections (and M.equinum in horses) only.

Dog lesions are classically those of hair loss, with scaly patches and broken hairs. Circular, bald patches 1 to 4cm diameter are commonly seen. Lesions often give the impression of having been shaved, and can occur on any part of the body. Dogs may develop folliculitis with papules and pustules. Generalised ringworm in adult dogs is uncommon, except in immune deficient animals. Lesions are generally more conspicuous in young animals, while older animals have more discrete lesions, or none at all. Ringworm in dogs generally clears spontaneously, but there is a risk of spread to other animals and children, so treatment hastens response. Local lesions respond to topical treatment with creams or ointments, and whole body washes may be used.

Most dog ringworm infections come from cat contamination initially.

Ringworm in Horses

Trichophyton equinum and T. mentagrophytes are the primary causes of ringworm in horses, although M.gypseum, M.canis and T.verrucosum are also seen in some cases.

Transmission in horses is by direct contact with infected animals or infected gear, rugs and saddlery. Most lesions are seen in the saddle and girth regions, producing “girth itch”.

Diagnosis is often confirmed by culture, as there are several diseases in horses which can produce similar skin lesions, including bacterial folliculitis and dermatophilosus (another fungus-like organism which produces rain scald and greasy heel). – See later in this article

Ringworm treatment in horses is usually topical because systemic treatment is expensive and often of unproven efficacy. Shampoos and rinses are often used to wash the whole body, and antifungal creams and ointments can be of value on discrete lesions. Grooming equipment, rugs and saddlery should be disinfected and placed in direct sunlight regularly, and affected horses should be isolated until treatment if effective.

Australian research by Pascoe (1976) surveyed 560 horses in training and 2535 horses in breeding farms in Queensland, to find that 32% of horses in training and 1.1% of breeding horses showed clinical ringworm infections. The majority of lesions were in the girth region, and Trichophyton equinum var autotrophicum, M.canis and M.equinum were restricted to racing horses, while M.gypseum occurred in racing, riding and breeding horses.

The same researcher reported in 1973 that Trichophyton equinum var autotrophicum has been consistently isolated from lesions of girth itch as well as girth rugs and brushes from affected horses, and that this fungus was the most common cause of skin lesions in thoroughbred horses in Queensland in 1979.

While the fungus could survive on saddle girths for 12 months, mild abrasions from the saddle during work favoured the development of lesions and prolonged the recovery period.

Ringworm is most common in horses in Australia in periods of high relative humidity between November and April (summer). Clinical signs generally appear between 5-10 days following contact, and the hair within lesions becomes erect, and lesions become visible from a distance. The hair is easily plucked from the horse, occasionally in tufts where the hair is matted at the base by exudate to leave a grey, moist, glistening lesion. Single lesions may spread to about 35mm diameter. Hair regrowth generally starts about 30 days after infection. Itching is uncommon in horses.

It is reported by Al-Ani (2002) that Trichophyton and Microsporum species are the main causes of ringworm in Saudi Arabia and Sudan. Of 316 horses examined in Jordan, 57 (18%) had ringworm infection. Microsporum equinum was the most common isolate, representing 40% of total identified fungi. Horses younger than 2 years were found to be most susceptible to ringworm infection in the region.

Ringworm in Cattle

Trichophyton verrucosum is the usual cause of ringworm in cattle, but T.mentagrophytes, T.equinum, Microsporum gypseum, M.nanum and M.canis may also be isolated.

Dermatophytosis is most commonly seen in calves, particularly in the region around the eyes, although generalised skin lesions on the body can develop. Cows and heifers develop lesions on the chest and limbs most often. Lesions are usually discrete, scaly patches of hair loss with a grey crust formation. Some become thickly crusted with pus.

Ringworm is more common as a herd health problem in winter months, and also in temperate or tropical climates, and in British Breeds rather than zebu breeds

Spontaneous recovery is common in cattle, but valuable animals are commonly treated to limit progression of the disease to other herd members. Any thick crusts and hair removed should be burned or destroyed to prevent reinfection

A worthwhile 2002 reference reporting the incidence of ringworm in cattle and horses in Jordan stated that limited studies on ringworm infection in cattle had been published from Arab countries to date, and that T.verrucosum, T.mentagrophytes and Microsporum species were the most common fungi isolated. In this study, 375 calves were examined, and 115 (30.6%) had clinical ringworm lesions, with farm to farm prevalence varying from 10% to 100%, and calves aged 3-7 months developing clinical lesions on head, neck, dewlap and chest regions.

Trichophyton species accounted for 69% of total fungi isolated, with T.verrucosum most common at 47.8%, T.mentagrophytes second at 12.7%

The author confirmed that ringworm is a common disease of calves at weaning in this region. In countries bordering Jordan, the disease is frequently reported in Saudi Arabia, Iraq, Syria and Egypt, occurring through the year with a higher prevalence during winter due to high humidity. All treated calves responded to topical treatment within one month.
(FK Al-Ani, FA Younes, OF Al-Rawashdeh. Ringworm Infection in Cattle and Horses in Jordan. Acta Vet.Brno 2002, 71:55-60)

Ringworm in Pigs, Sheep & Goats

Dermatophytosis in pigs is usually caused by Microsporum nanum. Lesions are rings of inflammation or brown discoloration that spread, up to a 6cm diameter. Ringworm in pigs is of little economic significance.

In lambs, ringworm is a common, troublesome problem in show stock. The primary species is Trichophyton verrucosum, and lesions in lambs are usually on the head as well as under the wool. T.verrucosum is contagious to man. Infections are self-limiting in healthy lambs.

Ringworm in Domestic Rabbits

This is commonly a problem in Europe, and is generally associated with poor husbandry. Lesions appear on the head, then spread to any skin area. Areas are circular, raised, reddened, and capped with a flaky, white material. The most common cause is Trichophyton mentagrophytes granulare, which also affects man, guinea pigs, mice and rats.

Ringworm in Camels and Camelids

Alpacas

Trichophyton verrucosum is the common cause of dermatophytosis in alpacas and llamas, as well as T.mentagrophytes var.mentagrophytes. lesions caused by both organisms are similar to lesions in cattle, with raised, crusty, circular plaques around the poll and face. Plaques vary from 2-4cm diameter. Spores of T.verrucosum and T.mentagrophytes may remain viable for up to 4.5 years in hair and cellular debris scraped off the animal and left attached to barn walls, fence posts, trees and other fixtures, blankets, leads, grooming apparatus, etc, (Murray E. Fowler, DVM. Medicine and Surgery of South American Camelids. 2nd Edition. Blackwell Publishing, pp156-8).

Treatment of affected camelids is suggested as iodine 2% tincture applied directly to lesions daily for 2 weeks. The less caustic Povidone-Iodine preparation diluted 1:4 may be equally effective.

Camels

A 1994 survey of camel ringworm in Eastern Sudan found that 217 out of 498 young camel calves under two years old examined during one year (43.5%) were diagnosed with ringworm. The peak incidence of disease was autumn and winter, with incidence highest in young growing calves (1-2 years). Lesions were observed primarily on head, neck and shoulder, with frequent extension to the flanks and limbs. Trichophyton verrucosum was isolated as the primary causal organism. (Fadlelmula A., Agab H., le Horgne JM, Abbas B., Abdalla AE. First isolation of Trichophyton verrucosum as the aetiology of ringworm in the Sudanese camels (Camelus dromedarius). Rev Elev. Med. Vet pays Trop. 1994;47(2):184-7 )

A second 1993 study reported that, among 75 camels showing skin lesions, 48% were positive for fungal infection, with younger individuals more susceptible. Trichophyton and Microsporum were the most commonly diagnosed genera, with T.verrucosum the primary causal agent in young camels, and T.mentagrophytes most commonly isolated in older camels. (Mahmoud AL. Dermatophytes and other associated fungi isolated from ringworm lesions of camels. Folia Microbiol (Praha). 1993;38(6):505-8)

An earlier 1986 study showed that in a survey of ringworm in camels, over 25% of young animals suffered from T.verrucosum infection, and fewer than 0.5% had T.mentagrophytes. (Kuttin ES, Alhanaty E., Feldman M, Chaimovits M, Muller J. Dermatophytosis of camels. J.Med. Vet. Mycol. 1986 Aug;24(4):341-4

Prevention in the home

Cat and dog owners are likely to have pets in the home, and any infected pet is likely to contaminate furniture, bedding and carpets with resistant ringworm spores which may persist for up to 18 months.

While it is commonly believed that ringworm (dermatophyte) spores are highly resistant to disinfection, this is not actually the case. It is well known that these fungi require keratin to survive, so it is therefore advised that all material containing keratin is removed from animal and home living areas. While spores may remain in the environment for 18 months or more in protected circumstances, spores are susceptible to several common disinfectants such as benzalkonium chloride, dilute (1:10) chlorine bleach, and strong detergents. Mechanical removal (vacuum cleaner with filter) of hair and skin cells from areas inhabited by infected animals in homes is vital, then followed by disinfection.

Treatment of pets

Treatment can be difficult and frustrating, especially in multiple pet households or kennels, but treatment helps accelerate recovery and reduce environmental contamination. Long haired cats appear to suffer more persistent infections

Other Similar Conditions in Animals

There are conditions very similar to Dermatophytosis (Ringworm) which need to be discussed, as the presenting signs can sometimes appear quite similar.

DERMATOPHILOSUS

Dermatophilosis has many common names, including Rain Scald, Greasy Heel, Mud Fever, Swamp Fever, Rain Rot, Cutaneous Streptothricosis, Lumpy Wool, and Mycotic Dermatitis, depending on the species affected and region of the body where lesions appear.

This is an infection of the skin which is seen worldwide, but is most prevalent in the tropics. The lesions are characterised by an exudative dermatitis with scab formation.

The causal organism is Dermatophilus congolensis, a bacteria (actinomycete)with many similar actions to fungi. Dermatophilus is found in many species of domestic animals – cattle, sheep, & goats are most commonly affected; horses and camels occasionally.

Dermatophilus has hyphae, or branching filaments similar to fungi, and also produces spores. The natural habitat is still unknown, as attempts to isolate this organism from soil have consistently failed, yet it has been regularly isolated from the skin of various animals.

Factors including prolonged wetting from rain, high humidity, high temperature, and various ectoparasites that can damage the skin surface are required to influence the development, seasonal incidence and transmission of dermatophilosis. This organism can survive on skin until climatic conditions favour its development. Epidemics usually occur in the rainy season, where moisture facilitates the release of spores from pre-existing lesions. High humidity contributes indirectly to the spread of lesions by encouraging increases in the numbers of biting insects, particularly flies and ticks, that act as mechanical carriers. Infections can be spread by shearing, dipping, introducing infected animals to a herd, and even by contaminated rugs, tack and grooming equipment.

In most acute infections the invasion of skin by the filamentous hyphae occurs in 2-3 weeks.

Rain Scald in Horses See Ranvet

Rain Scald (Rain Rot) in horses is a common skin infection in warm, damp conditions where high temperature and humidity are present, and has been described in most regions of the world.

Appearing as large crust-like scabs generally on the topline of horses, but also on the back of the fetlock and canon bone (Greasy Heel), the scabs have embedded hair and exudate forming a crust which can be easily pulled off to reveal pink skin and pus.

Horses become infected from contaminated saddle blankets, leg wraps and grooming equipment when conditions of extreme moisture are present, and when the skin is damaged or cut. It is very difficult to prevent the spread in groups of horses, as simple contact is sufficient. This is a common disease in horses kept in yards and paddocks without shelter

Dermatophilus grows best without oxygen, and is protected within a scab of hair and exudate, so any treatment will require removal of scabs and exudate to reveal underlying skin and allow the use of antiseptics, shampoos and rinses

Scratches and continued moisture around the pastern of horses can result in typical “Greasy Heel” infections.

The scabs can be extremely painful when removed, especially from the fetlock region. If under saddles or gear the skin can become quite sensitive in affected areas

It is vital to remove (and destroy) infected scabs, hair and debris to prevent further transmission, and use antiseptics to thoroughly clean affected areas.

This is a self limiting disease and will disappear as the horse loses its long hair coat in most cases, but treatment is preferred to limit the discomfort to the horse, as well as the likely transmission to other horses.

Dermatophilosis in Sheep

Also known commonly as Lumpy Wool, or Mycotic Dermatitis, this is a common disease in sheep, caused by the same organism responsible for Rain Scald and Greasy Heel in horses, Dermatophilus congolensis..
Causing an exudative dermatitis on persistently wet skin, it causes matting of wool. This disease is widespread in Australia & New Zealand, and has been reported in Canada, northern USA, UK, South Africa and India.

The difference between this disease and ringworm is that dermatophilus attacks living skin, not the keratin in hair, nails and claws, as with ringworm.. Moist conditions favour the disease, particularly when there is high winter or spring rainfall
Seen in most breeds of sheep, it is most commonly seen in medium to strong woolled Merinos, as well as in horses, cattle, deer and goats

Dermatophilosis in Cattle

Seen mostly in young cattle, lesions of typical exudative dermatitis are seen on the head, neck, body or udder and may extend down the sides of the body. Brown or creamy thick scabs about 2.5cm diameter cover an exudative raw skin surface. In many cases in cattle, tick infestation has provided the requisite skin damage for initial entry of the organism

Dermatophilosis in Camels

Dermatophilus congolensis and Microsporum gypseum infections have both been recorded in camels, including as mixed infections in a camel dairy farm in Saudi Arabia, where a total of 131 out of 559 camels were affected (23.4%). 48 camels less than one year old had discrete, circumscribed crusty, hairless lesions on neck and forelegs, and 83 camels of varying ages had extensive hair matting with crusty, hairless lesions, especially on the flanks. Young camels generally displayed a greater amount of skin lesions. (CG Gitao, H.Agab & AJ Khalifalla/ An outbreak of a mixed infection of dermatophilus congolensis and Microsporum gypseum in camels (Camelus dromedaries) in Saudi Arabia. Rev. Sci. Tech. Off. Int. Epiz. 1998, 17(3), 749-755)

Similarly, natural Dermatophilus congolensis infections of camels has been reported in Kenya in semi-arid conditions, where severe infections were found in two camel herds of which 50-75% of animals were infected. Of other herds examined, camel calves were more likely to be infected (34%) than adults (8.9%). Lesions began as hair matting and later developed hard crusts. Fatality ranged from 10-30%. Camel dermatophilosis was found to be one of the most serious problems faced by camel herders in the region (CG Gitao, H.Agab & AJ Khalifalla. Outbreaks of dermatophilus congolensis infection in camels (camelus dromedaries) from the Butana region in Eastern Sudan. Rev.Sci.Tech.Off.Int.Epiz. 1998, 17(3), 743-748)

Although only recently described, camel dermatophilosis is recognised as widespread, and incidence may be related to the presence of ticks which cause initial skin damage.