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Background Information

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Which dermatophytes?

Dermatophyte infections in pets and horses are caused exclusively by members of the  Microsporum and Trichophyton families. The last family also harbours Arthroderma benhamiae, which is difficult to identify in culture and has recently been found in animals (especially guinea pigs) in the Netherlands and elsewhere.

The susceptibility for developing skin lesions varies per individual, but young individuals are generally more susceptible.

Note : Dermatophytes are not host species specific. However, Microsporum  mainly (but not exclusively) infects cats and dogs, and Trichophyton mainly infects rodents.


How does the infection come about?

  In most cases, the source of infection is another animal with which direct or indirect physical contact has occurred. A rare exception to this is mainly found in horses where the soil can be the source. 


Carriers

Cats, rabbits, and guinea pigs can also be so-called carriers, which appear perfectly healthy but are infected and do spread the infection. Dermatophytes form spores (similar to plant seeds), which can survive for a long period of time in the environment (house / stable etc.), and thus remain a source of infection for susceptible animals. Therefore, the environment of the patient must always be an integral part of the treatment (see ' Rules of thumb treatment). 


Contaminated animal environment


 The fact that the immediate environment of a patient is contaminated implies that the coat of healthy animals in that environment can consequently be contaminated and thus positive when tested. Lack of expertise in interpreting test results may thus lead to incorrect conclusions.


Often hard to recognize

  Because the clinical picture of a dermatophyte infection is often not typical,  laboratory testing is needed for a reliable diagnosis.


 

Culture was the common approach

 With culture, a sample from the patient is placed on special culture media and then incubated for at least 10 days. Daily checks for suspect growth  have to be performed. This can be done by the local veterinarian, but requires some expertise and strict following of the guidelines.  Alternatively, the sample can be submitted to an external laboratory with proven expertise in this field.


Knowledge is obligatory

  It is important to be aware of false results. It is therefore essential that practices who perform in-house testing have a protocol describing the method and responsibilities. Additionally, a certain level of expertise is essential but this may even be lacking in some laboratories.  


The reliability of the result is essential

  A reliable result is important, both because dermatophyte infections in animals are contagious (also to humans) and because the treatment of an infection is a burden for the animal and requires a lot of energy and time from the owner. Notably, prescribing anti-mycotic drugs must be based on a proper diagnosis. In situations with dense animal populations, e.g. catteries and shelters, a dermatophytosis outbreak is an true disaster for humans and animals, and therefore should be avoided at any cost.  


Reliable testing starts with a good sample

  The reliability of a test result depends greatly on the quality of the sample.  A good quality sample is representative for the patients skin (disorder) and contains sufficient material.


Sensitivity and Specificity

  The diagnostic reliability of a test result is determined by two factors; the sensitivity -essentially: how reliable is a negative result?- and the specificity -essentially: how reliable is a positive result?  These factors strongly depend on the method used and the expertise of the investigator. In general, a specialised -'dedicated'- laboratory is more accurate than a practicing veterinarian or a general laboratory.  The sensitivity of 'culture' greatly affected by the extent to which the sample material is in contact with the culture medium. The sample -usually hair- is extremely difficult to handle in this respect. The specificity depends greatly on the available expertise. The most commonly used culture media contain 'color indicators'. However, the color change is not entirely specific; the required microscopic identification is sometimes omitted. In short, 'culture' may suffer from uncertainties.


 Culture is Time Consuming 

Another problem with 'culture' is its duration. Due to the slow growth of dermatophytes, a reliable negative result may take up to 2-3 weeks. In contrast, a relatively reliable positive result may come as soon as 5 to 7 days, but it usually takes longer. So, it is hard to predict when the result will be available, which is frustrating all those involved.


 

 

The new VdQd test

 VdQd has developed a test that resolves the issues above. The sampling is optimised by using a special brush, whereas the sensitivity and specificity are maximised by a unique lysis and extraction method of the entire sample, followed by an analysis at the DNA level with the aid of a so-called real-time PCR. The test detects all common veterinary dermatophytes and distinguishes between the  two major families. And finally, performing the test only takes us a few hours.  


Maximum reliability

  An extensive validation study (> 200 field samples) showed that this new test is as sensitive as the culture carried out by an expert, while the specificity is 100%. These results demonstrated that the new VdQd test yields maximum reliability for both negative and positive results. Notably, it also performed well with post-treatment samples. 


VdQd: unique expertise

  VdQd boasts unique expertise in the field of veterinary dermatophyte diagnostics and has long standing experience with the treatment of dermatophytosis in animals (also see 'About us' and' Rules of thumb treatment).