Genetic welfare problems of companion animals
Related terms: ringworm; Microsporum canis infection; fungal skin infection
Persian cats are believed to be predisposed to fungal skin infections and to forms of the disease that tend to be more severe and persistent than are usual in other cats. It is thought that this is related to their long coats. The Persian cat’s abnormally long coat is due to it being homozygous for a mutant gene (ie having two copies of it). If mild, the skin infection may have only minor welfare effects but, if severe, the disease can cause prolonged discomfort. The disease usually requires treatment and this – including prolonged administration of oral medicines and repeat shampooing – is stressful to many cats. It seems likely that breeding for normal coat length would solve or ameliorate the problem.
Summary of Information
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1. Brief description
Dermatophytosis is infection of the skin, including hair and claws, by one or more of a group of fungi that are adapted to invade these structures. The species that most commonly affects cats and the one that is relevant to the predisposition in Persian cats is Microsporum canis. Hair is infected after exposure to fungal spores in the environment or from another animal – usually a cat. The disease usually affects younger cats, and it is presumed that the lower prevalence in older ones is because of acquired immunity through repeated exposure (Sparkes et al 1993).
Infection with these fungi can cause a wide range of skin problems. These commonly start one to three weeks after exposure. The skin lesions vary from mild to severe. Typically, the head and feet are especially affected (Lewis et al 1991) but lesions can occur anywhere and can affect large parts of the body in some cats. Usually there is loss of hair (alopecia) where this has been invaded and damaged by the fungus. Often there is scaling (dandruff). In some cases, mycetomas and psedomycetomas form which are nodules under the skin often with an ulcerated area or discharge of fluid. This form of disease is severe and difficult to treat and rarely seen in any cats other than Persians (Bond et al 2001, Zimmerman et al 2003, Nuttall et al 2008, Chang et al 2011).
Treatment does not quickly eliminate the fungus but does reduce the time taken for recovery, and also reduces environmental contamination and thus the risk of spread to other animals and humans (Scott et al 1995).
2. Intensity of welfare impact
Dermatophytosis usually is not itchy and it can be argued that the disease itself causes relatively few welfare problems to affected animals (Nuttall et al 2009). When welfare problems do arise it is partly due to the side effects of the treatment that is considered necessary, in order to reduce contamination of the environment with fungal spores shed by the animal and to lessen the risk of in-contact humans and animals becoming infected. Treatment usually involves clipping of fur, many months of oral medication and medicated shampoos. These procedures cause cats stress as most cats dislike this degree of handling and interference.
3. Duration of welfare impact
Although other animals are usually only affected for a few weeks or months, in Persians dermatophytosis can be difficult to cure and can persist and require treatment for months to years (Balda 2009).
4. Number of animals affected
It is recognised that Persian cats are predisposed to dermatophytosis (Lewis et al 1991, Sparkes et al 1993, DeBoer & Moriello 1995) and to the more aggressive forms of the disease (Bond et al 2001, Zimmerman et al 2003) but, as far as we are aware, there are no data on the proportion affected.
A diagnosis of dermatophytosis may be suggested because of the typical appearance of the skin lesions, especially when seen in a young cat, but unusual forms of the disease may also be seen therefore further tests are required for a definitive diagnosis. Examination of hairs under the microscope, skin biopsies, and Wood’s lamp (ultra violet light) examination of the hair are all useful, but culture of the fungus from hair is the key diagnostic test. Culture also enables determination of the species of the dermatophyte involved.
Persian cats have two copies of the mutant version of the gene for fibroblast growth factor 5 which causes abnormally long hair growth, and having long hair seems to make it more likely that the affected animal will more likely suffer from the disease. The disease may also involve a genetic defect in cell-mediated immunity that may be linked to the inheritance of the mutant gene for long hair, but this is not fully understood at present.
7. How do you know if an animal is a carrier or likely to become affected?
All Persian cats are long haired, this being part of the breed standard. As this is likely to be associated with their predisposition to dermatophytosis, there may be no way to avoid the risk of the disease without selecting for shorter fur. The genetics of any cell-mediated immunity defect that might also be part of the problem is not understood. Breeding only from animals that have not had the problem and whose close relatives have not had the problem, might help to select for animals with a higher level of natural immunity and thus, to reduce the prevalence of the condition.
8. Methods and prospects for elimination of the problem
Long hair is part of the Persian breed standard. If the predisposition to, and difficulty in treating, dermatophytosis in Persian cats is linked to the inheritance of the genes that cause the long coat, as seems quite likely, then it may not be possible to overcome these problems except by changing the breed standard and selecting for shorter hair. As far as we are aware, there are no breeding programmes aimed at tackling the problem of dermatophytosis in this breed.
For further details about this condition, please click on the following:
- Clinical and pathological effects
- Intensity of welfare impact
- Duration of welfare impact
- Number of animals affected
- How do you know if an animal is a carrier or likely to become affected?
- Methods and prospects for elimination of the problem
Dermatophytosis is infection of the skin, including hair and claws, by one or more of a group of fungi that are adapted to invade these structures. The species that most commonly affect cats and the one that is relevant to the predisposition in Persian cats is Microsporum canis. (Other dermatophytes that are important in veterinary species include additional Microsporum species such as M. mentagrophytes and persicolor and species from the genus Trichophyton such as T. Mentagrophytes (Nuttall et al 2009)).
Ringworm is an old-fashioned name for this condition. It is commonly used but misleading as it is not caused by a worm and the lesions are not necessarily round.
Infection occurs through exposure of the hair to fungal spores in the environment or from another animal – usually a cat. The spores can survive in the environment for 18 months (Mancianti et al 2003, Sparkes et al 1994). Exposure to spores does not necessarily lead to infection, partly because the spores may be removed as the cat grooms. The relatively high proportion of cases of this disease seen in which the head is affected may reflect that cats are unable to groom their own heads so thoroughly. The spores grow in living hairs, claws and skin. The disease occurs more commonly in younger cats, and it is presumed that this is because older animals have acquired a level of immunity over time and repeated exposure (Sparkes et al 1993).
Infection by these fungi can cause a wide range of skin problems. Clinical symptoms may be seen one to three weeks after exposure and skin lesions may vary from mild to severe. The disease can present in a variety of ways but the most common symptoms are alopecia (hair loss) and scaling of affected skin. Typically, the head and feet are especially affected (Lewis et al 1991) but lesions can occur anywhere and may affect large parts of the body. In some cases deeper infection of the skin occurs, causing folliculitis (inflammation of the hair follicle(s)), furunculosis (persistent, reoccurance of furuncules (boils)), granulomas (small lesions made up of inflammatory cells) or kerions (raised, exudative, spongy lesions caused through secondary infection of hair follicles).
Mycetomas and pseudomycetomas may also occur. These are nodules of infection under the skin often with an ulcerated area or with fluid discharge. This form of the disease is rarely seen in any cats other than Persians. It is severe and does not always respond well, even to aggressive treatments (Bond et al 2001, Nuttall et al 2008, Chang et al 2011).
Infections of the claws and claw beds are quite common and show as swollen, broken or easily shed claws: one or more may be affected. Dermatophytosis can also cause otitis externa (Godfrey 2001, Nuttall et al 2009). Except in unusual circumstances, the fungi cause no internal diseases (Black et al 2001).
Having long hair and being pedigree have both been found to be factors predisposing to dermatophytosis in cats. Living in, or having come from, a larger group of cats is also a risk factor (Nuttall et al 2009) and pedigree cats are often bred in catteries that hold relatively large numbers of individuals. Persian cats are predisposed to dermatophytosis and several reasons for this have been suggested (Miller and Goldschmidt 1986, Nuttall et al 2009), as listed below:
1. Dermatophytes are more often found in colonies of cats, and pedigree cats are more likely than others to have come from colonies.
2. The long hair of Persians makes effective grooming to mechanically remove fungal spores impossible.
3. The long, thick coat means that the spores are more hidden from sunlight which, on cats with normal hair, tends to kill spores exposed to it.
4. The large volume of hair provides a larger habitat for the fungus than in short-haired cats
5. There may be a defect in cell-mediated immunity in this breed (this has been shown to be an important underlying factor in human cases in which fungal diseases fail to resolve [Odom 1993]).
6. Shampooing therapies may be less effective in Persians because of the length of coat.
7. Drug treatments that rely on uptake of drugs from the bloodstream into the growing hair may work more slowly as it will take a very long time for the full length of the hairs to be protected..
As well as being predisposed to dermatophytosis, the Persian breed is also more likely to have a form of it that is difficult to eliminate (Bond et al 2001, Zimmerman et al 2003).
After infection most cats will (without treatment) recover and eliminate the fungus in around 2-3 months. The production of antibodies against dermatophytes does occur but this appears not to be important in their elimination. Rather, it is effective cell-mediated immunity (direct activity of the white blood cells) that is crucial (Sparkes et al 1995). In long-haired cats the time it takes to spontaneously eliminate the fungus from their skins may take up to four years (Medleau and White-Weithers 1992, Moriello and DeBoer 1991).
Effective anti-fungal medications are available. However, these treatments do not quickly eliminate the fungus but do reduce the time taken for recovery and also reduce environmental contamination and thus the risk of spread to other animals and humans (Scott et al 1995).
Humans in contact with a cat affected by M canis commonly also develop the disease. It may spread to them directly from the cat or from the contaminated environment. About 50% of humans exposed to a cat with signs of dermatophytosis, or that is carrying the spores on its fur, develop skin lesions (Pepin & Oxenham 1986, Foil 1993).
Dermatophytosis is not usually itchy in mildy affected animals and it can be argued that the disease causes relatively few welfare problems in these individuals (Nuttall et al 2009). However, those with widespread or deep infections may suffer from prolonged discomfort and pain.
Additional welfare problems are associated with treatments used to try to resolve the disease in the cat and to reduce contamination of the environment with fungal spores and thus the risks to humans and other animals. In attempting to treat the disease it is considered necessary to treat all affected animals (Nuttall et al 2009). Treatment usually involves clipping fur, the administration of oral medication, and shampooing. Most cats dislike the degree of handling and interference that these procedures involve, and the frequent visits to a veterinary practice. The medications used to treat dermatophytosis can have side effects that cause significant welfare problems, for example, the antifungal agent itraconazole may cause nausea, abdominal pain and liver damage (Ramsey 2011). Some cats are euthanased because their owners cannot cope with treating their cat for financial reasonsor because managing the disease becomes impossible for them (Bond et al 2001).
Over time (2 to 3 months) most develop immunity to the fungus, recover naturally from the infection and retain some degree of resistance to future infections. This immunity is not so reliable in Persian cats.
Although other animals are usually only affected for a few weeks to a few months, dermatophytosis in Persian cats can be difficult to cure and the infection can persist and require treatment for months to years (Balda 2009).
Persian cats are recognised to be predisposed to dermatophytosis (Lewis et al 1991, Sparkes et al 1993, DeBoer & Moriello 1995) and to the more aggressive forms of the disease (Bond et al 2001, Zimmerman et al 2003). However, we are unaware of data on the proportion of Persians that are affected and on how this compares with other breeds.
A diagnosis of dermatophytosis may be suggested because of the typical appearance of the skin lesions, especially when seen in a young cat, but unusual forms of the disease may also be seen therefore further tests are required for a definitive diagnosis.
Examination of hairs under the microscope will often confirm dermatophytosis and sometimes it can be detected in skin biopsies – especially if special staining procedures are used. Illuminating the fur with a Wood’s lamp, which emits ultraviolet light, can be helpful because some dermatophyte-infected hairs fluoresce. However, not all dermatophyte species cause fluorescence and only around 50% of Microsporum canis strains do so (Nuttall et al 2009).
The most important method to confirm diagnosis is culture of a sample of hair and scale (Scott et al 1995). However, culturing M. canis from a Persian cat does not necessarily mean that it has the disease as it may just be carrying spores on its coat in the same way that they can be found on carpets, rugs etc (Sparkes et al 1994). Culture enables identification of the species of fungus involved.
The genetic basis of the long hair of Persian cats is known (Drogemuller et al 2007). A mutant form of the gene for fibroblast growth factor 5 causes the abnormally long hair growth in the Persian (and most other long-haired cats). The gene is recessive to that for normal hair length and long hair occurs only in cats that are homozygous for the recessive gene (ie have inherited two copies of the gene). All Persian cats are homozygous for this mutant gene.
It has been suggested that a defect in cell-mediated immunity may also be part of the dermatophytosis problem in this breed, and the inheritance of this may be closely linked to the inheritance of the gene for long hair (ie cats that inherit one are very likely to inherit the other). But this is unclear and its genetic basis has not been explored.
All Persian cats are long haired: that feature is part of the breed standard. As this is likely to be associated with their predisposition to dermatophytosis, and of a form that is difficult to eliminate, there may be no way to avoid the risk of the disease without breeding for shorter fur. The genetics of any cell-mediated immunity defect that might also be part of the problem is not understood. Breeding only from animals that have not had the problem, and whose close relatives have not had the problem, might help to select for animals with a higher level of natural immunity and thus, to reduce the prevalence.
Long hair is part of the Persian breed standard (eg see http://www.cfa.org/documents/standards/persian.pdf, http://www.acfacat.com/persian_standard.htm). Assuming that the predisposition of Persian cats to dermatophytosis, and to forms of the disease that are difficult to resolve, is due to their coat type then it may not be possible to reduce the prevalence except by breeding for shorter hair (and altering the breed standard accordingly). Short-haired “Persians” do exist as a separate breed called Exotic Shorthairs.
As far as we are aware, there are no breeding programmes aimed at decreasing the prevalence of dermatophytosis in this breed. It may be that avoiding breeding from animals that have the disease (or severe forms of it) or whose close relatives have, would help select for reduced susceptibility.
UFAW is grateful to Rosie Godfrey BVetMed MRCVS and David Godfrey BVetMed FRCVS for their work in compiling this section.
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© UFAW 2011