Page 267 - The Veterinary Laboratory and Field Manual 3rd Edition

236 Susan C. Cork and Roy Halliwell

Figure 4.14b Diagrammatic
representation of some
fungal species.

The rate of growth, the colour and the form of Clinical importance
the fungal colony is distinct for each species and
these characteristics are important in identifica- Fungi are common in the environment but rarely
tion. cause significant mortality in healthy animals.
Single cell fungi that reproduce by budding Mycoses (and mycotoxins) can nevertheless be
are generally referred to as yeasts. In the yeasts a cause of morbidity in animals. The range of
hyphae are absent or represented only by pseudo- diseases that can be caused by fungi are numer-
hyphae which are elongated budding cells often ous and potentially complex. Fungal infections
linked in branching chains. Some opportunistic are especially common in tropical countries
fungal pathogens are dimorphic, that is, they where humidity is high. Some fungal diseases
occur in two different forms. Dimorphic fungi are caused by primary pathogens but most are
are filamentous (mycelial) in culture and yeast- opportunistic, that is, they are ordinarily harm-
like in infected tissues. Most fungi reproduce less but may infect an animal when predisposing
by forming spores, which may be produced in factors, such as immune-suppression or concur-
many different ways. The size, shape and colour rent disease, are present.
of spores and their manner of production are A confirmatory diagnosis of fungal infection
also of value in identifying fungal species (Figure is usually achieved by direct microscopy of sam-
4.14b). ples (usually skin scrapings or tissue smears) but
culture may be required to definitively identify

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