Dermatophytosis for veterinary nurses

General workup

Tests are an area the VN can get involved with, starting with general dermatology workups. The full range of skin tests are always advised to ensure elimination of other conditions, even if they are secondary to an underlying problem (Gaudiano, 2005). Skin scrapes and/or hair plucks, for example, can rule out other suspected conditions such as demodicosis; while cytology, in the form of tape strips, impression smears and swabs of primary lesions, can indicate bacterial or yeast infections (Prelaud et al, 2011). This article alone is not sufficient to cover the method for these tests, but it is important to note that they are all tests a VN can perform, where often the VS does not have the time (Robinson et al, 2014).

Wood's lamp

It is common in practice for VSs to use the Wood's lamp technique to look for ringworm — again this is something a VN can do. There are a few key points to note: make sure the room is dark and that the lamp is given at least 5 minutes to warm up; in addition using a lamp with a magnifier is helpful in finding any dermatophytes that are present (Gaudiano 2005). Also note: only M. canis will fluoresce; this makes up about 50–70% of dermatophytosis cases in dogs and cats, however it is not a certainty that all of these will fluoresce, and in addition, identifying dermatophytosis using this technique requires practice (Duclos, 2012). So, the Wood's lamp is far from an elimination test. A positive test is indicated by an apple green fluorescence of the hair shaft; but care is required as creams and scale can fluoresce as well — amongst other things — leading to false positives (Caplan, 1967). It is still accepted as a good screening tool in combination with further testing (Bernard, 2013).

Microscopic examination

Microscopic examination of hair plucks or skin scrapes from the edge of lesions can certainly be done by a VN, looking for fungal hyphae or spores, especially after a suspected positive result with a Wood's lamp. This can be performed by plucking fluorescing hairs and mounting them onto a slide with liquid paraffin for examination; it should be noted this requires practice (Figure 3a) (Paterson, 2017).

Fungal culture

The best way to test for dermatophytosis is with culture (Duclos, 2012) and dermatophyte test medium (DTM) can be purchased to perform in-house dermatophyte cultures (Figure 3b); external labs also offer this service. It is important that samples are gathered correctly and with care (Sparkes et al, 1993), and as such this is another area VNs can be involved with. Hair can be plucked, preferably by rolling them out with a pair of forceps in order to retain the debris needed (Figure 4), from the edge of active lesions; dermatophyte spores if present will be found in this debris. Crusts can also be taken by scalpel scrapes from the same area of lesions, with several, if possible, being sampled (Gaudiano, 2005). If sampling companion animals that are not symptomatic, or a generalised infection is suspected, a Denman brush or toothbrush (Figure 5) can be used, combed through the hair for at least 2 minutes to take the sample. Brush non affected areas first and then lesions if present (Duclos, 2012).

These DTM kits work by growing the culture in medium. The samples should be pressed but not imbedded into the medium (brushes pressed into firm contact), and then incubated with the lid loose at 26°C (Gaudiano, 2005). The dermatophyte grows and as it metabolises proteins, released alkaline metabolites which change the pH of the medium; pH indicators then change colour. For example DTM which is commonly used, changes to red (Figure 3b). This normally happens within 10 days, which should be noted as non pathogenic fungi (not ringworm) which prefer a carbohydrate substrate will start consuming proteins if these run out of carbohydrates, causing alkalisation and a late colour change; a late colour change may, therefore, be a false positive (Salkin, 1973).

Other things to be aware of with in-house culture include difficulty with sampling, incubation, and interpretation; these mean that false negatives and positives are common (Sparkes et al, 1993). In addition, the kits do not detect all species. If dermatophytes do grow, it is best to examine colonies at the end of culture to identify the exact type present. This is done by sampling the colony from the culture medium with clear tape, then sticking it down onto a slide with a drop of lactophenol cotton blue stain, then another drop of this on top of the tape followed by a coverslip; the colonies are then examined for shape and colour. The colour is affected by DTM agar however, as is the colony shape — so this is another limiting factor in-house, unless using a split plate with Sabaruraud's medium. In-house can, therefore, be challenging and best practice is to send the samples to an external laboratory for interpretation (Duclos, 2012). If speed is of concern laboratories often now report the positive (or negative) first, when the colour change occurs, then the type later once the colony has grown; the initial report is usually back within 3–4 weeks.

Some animals may test positive for culture, but not actually be infected, instead acting as a transient mechanical carrier (Moriello et al, 2017). This culture result, along with the patient history, will enable the VS to determine the overall infection status of each pet. This is particularly important in multi-pet households, where all in-contact pets should be cultured and then treated where positive (Duclos, 2012). An informed VN may be able to offer guidance and information on testing methods to the pet owner so they understand how a diagnosis is being achieved, and why tests may need to be performed on other pets.

Systemic treatment

The VS will always decide on the treatment options, but it is vital the VN has an understanding of them. They will generally choose one of three oral treatments to target the active site of the fungal infection, helping to prevent the spread of further lesions (Paterson, 2017). Itraconazole is the most popular and should be given with a meal; it can be hepatotoxic so bloods may be done at the start and possibly during therapy, something a VN can do while also explaining the reasons for this to the client. Recommended protocols vary, and those provided by Carlotti (2010) and Newbury et al (2011) are often used. Carlotti suggests 5 mg/kg orally for a week on and a week off until mycological cure is obtained; in his study this was at 56 days (Carlotti et al, 2010). Newbury et al (2011) used itraconazole at a dose of 10 mg/kg daily for 21 days with either lime sulphur or a chlorhexidine/miconazole product topically (see below) twice weekly. Mycological cure was achieved in 36 days (Newbury et al, 2011). In both cases the treatment took some time to achieve cure, and it is worth informing owners that this may be the case, but that treatment regimens must be adhered to.

Another common choice is terbinafine, this is is not licensed for the treatment of dermatophytosis in dogs and cats; again pre bloods are advised. It can cause vomiting and carries a risk of teratogenicity (Carlotti, 2010; Newbury et al, 2011).

Topical therapy: general considerations

When it comes to treatment in dermatology, the area a VN can really contribute to is topical therapy, both in aiding compliance by discussing it with the owner and also on occasion in application of the product. With dermatophytosis start by discussing the principle of topical therapy with the owner, so they are aware that topical treatment is critical to reduce the risk of spread, by removing and neutralising spores on the coat (Duclos, 2012). Transmission of dermatophytosis occurs via direct contact with infective material; topical therapy acts to decrease the infectious, contagious, and zoonotic risks associated with this disease by disinfecting the hair coat and minimising contamination of the environment (Paterson, 2017).

Clipping the coat prior to application of treatment is controversial (Bernard, 2013), although clipping 5 cm around lesions seems to be generally suggested to remove contaminant and help the topical treatment penetrate (Moriello et al, 2017). Whole body clips in a matted cat may be needed, but otherwise these are not as suggested as they once were (Paterson, 2017). However, if the VS does suggest clipping, the VN will need to perform this and it is essential that personal protective clothing is worn, followed by thorough disinfection of the environment (see below), and disinfection of the clippers. If thorough disinfection is not achieved, other patients and staff are at risk of catching dermatophytosis due to its contagious nature (Gaudiano, 2005).

Topical therapy: treatments

There are three main types of topical therapy currently recommended: enilconazole (Imaverol, Elanco), which is a dip that can leave the coat quite greasy and cause a reaction in cats; lime sulphur (Lime Sulfur Dip, Vetoquinol, USA) which smells like rotten egg and stains many things yellow and is currently not available in the UK; and a miconazole/chlorhexidine shampoo (Malaseb, Dechra) (Perrins and Bond, 2003). The latter is most popular in general practice, however lime sulphur or enilconazole have been shown to be most effective in recent studies (Moriello et al, 2017). All of these should be used twice weekly and have their frustrations, so the VN spending time with the owner talking through application is essential to aid compliance. There are also creams and ointments (clotrimazole, miconazole and enilconazole); these are not reccomended for sole therapy, but as concurrent treatments to systemic therapy (Moriello et al, 2017).

Other pets

Another serious consideration with these cases is the need to screen all in-contact pets — these should be isolated if they test negative, and treated if they test positive (Duclos, 2012). This can be extremely difficult for clients due to the difficult nature of treatment as described previously, and the difficulty in isolating those not infected, especially where cats are involved, so talking through the contagious nature of the disease, the existence of latent carriers and risk of reinfection is critical.

The environment

Owners should be talked to at length about the need and method for cleaning the environment. This is primarily to prevent spores from the environment getting on the coat and causing false positives, as infection from the environment alone is rare. False positive fungal culture results lead to prolonged systemic and/or topical therapy and excessive confinement of pets (Paterson, 2017). That said decontamination is always advised by dermatologists (Moriello et al, 2017) and effectively consist of cleaning thoroughly with an appropriate disinfectant.

When cleaning the practice environment, thoroughly vacuum any hair clippings and dispose of the vacuum bag, clean and disinfect clipper blades (if you have been clipping) then scrub the area thoroughly, preferably with a detergent to begin with before disinfecting using bleach at concentration of at least 1:10 (Moriello, 2014). Then educate owners on following the same procedure at home. Talk to them about what things could act as fomites and on ensuring these are cleaned regularly. They must launder bedding at at least 60°C, along with thoroughly vacuuming furnishings and carpets (Gaudiano, 2005).