Page 268 - The Veterinary Laboratory and Field Manual 3rd Edition

Microbiology 237

the pathogen involved. For systemic infections, • Skin scales: collect by scraping the surface
the appearance of stained fungal hyphae in his- of the margin of the lesion using a sterile
tological sections may help in the identification scalpel blade.
of fungal pathogens but this is more likely to be • Crusts: collect by removing part of the
at necropsy vs. ante-mortem. crust nearest to healthy skin using sterile
scissors and tweezers.
• Nail, horn or hoof piece: collect by taking
Laboratory diagnosis a small section of the infected part of the
nail or hoof/horn using sterile tweezers
Fungal diseases are diagnosed in a similar way and scissors.
to bacterial diseases, that is, starting with asep- • Hair: pluck complete hairs with the sur-
tic collection of specimens from affected tissues rounding skin segment if possible.
followed by culture on specialized media (for
example, Sabouraud dextrose agar). The specific After collecting representative specimens place
approach will depend on the location and type them in a labelled envelope or plastic container.
of lesions seen. For necropsy cases the approach The label should indicate the name of the sub-
followed is outlined in Chapter 8. mitter, the identity and species of the infected
animal, the source of the sample material and
Fungal infections of the skin the date.
One of the most common fungal diseases seen
in temperate regions is ringworm. Although this Examples of specific fungal diseases
skin condition is caused by a fungus it is often
discussed along with parasitic skin diseases. Ringworm
Confirmatory diagnosis of ringworm and other
cutaneous fungal infections involves clinical Ringworm is a skin disease caused by a group
examination, collection of skin scrapings and of fungal species known as dermatophytes.
hair, microscopic examination of samples and The most common dermatophytes in tem-
(potentially) culture. In cases where an unusual perate countries include Microsporum sp. and
fungal pathogen is involved samples may need Trichophyton sp. Depending on the severity of the
to be sent to a mycology reference centre for infection and the presence or absence of concur-
identification. rent disease and predisposing factors, clinical
The collection of skin specimens is described signs may or may not be present. In mild cases,
below and in Chapter 3 (section 3.9) along with there may only be evidence of minor hair loss
the diagnosis of diseases caused by ectoparasites. over specific regions of the body. In severe cases
the animal may suffer significant hair loss due to
secondary bacterial infections and resultant irri-
Specimens to collect
tation and rubbing. A percentage of Microsporum
1 Cleanse the affected area with 70% alcohol. sp. infected hairs fluoresce under a Wood’s lamp
2 Collect skin scales, crusts, and pieces of nail (UV light). Although this is a popular diagnos-
or hair on a clean piece of paper. If avail- tic test for domestic pets a negative result does
able use dark coloured paper because the not necessarily mean that no fungus is present
specimen will be easier to see against a dark because many other dermatophyte fungi do not
background. fluoresce.

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