EQUINE CLINICAL PATHOLOGY - Rossdale & Partners

T h e B e a u f o r t c o t t a g e l a b o r a t o r i e s
a fresh sterile scalpel blade. The hairs
and the scraped skin layers, down to
haemorrhage, should be collected into a
sterile universal container and submitted
for laboratory examination without delay.
The hairs and scraped skin layers should
be incubated for 15 minutes in warm
40% potassium hydroxide (KOH) and then
examined for clear ringworm spores in
broken hair shafts and free whole or
fragmented ectoparasitic mites, including
Sarcoptes, Psoroptes, Chorioptes and
Demodex spp. (differentiated on the basis
of their anatomical appearance).
If negative for dermatophyte spores after
KOH incubation, skin scrapings are
incubated overnight in blue/black ink
and then examined for blue/black stained
spores in clear broken hairs.
Skin scraping samples should be incubated
for bacterial and fungal growth. The latter
(taking up to 3 weeks) will differentiate the
different ringworm-causing dermatophytes,
including Trichophyton and Microsporum
spp.
Microscopic and fungal culture results for
dermatophytes do not always correlate.
Positive microscopic findings but negative
culture results may suggest that the spores
were not viable at the time of scraping.
Negative microscopic findings but positive
culture results may suggest that too few
spores were present in the sample to be
detected in spite of careful examination.
If Dermatophilus congolensis (‘rain scald’
or ‘mud fever’) infection is suspected on
clinical grounds, moist lesions should be
collected and submitted for impression
smear stained with methylene blue to look
for characteristic chains (‘piles of pennies’)
of flattened spores, sometimes in branched
conformation.
clostridial toxin tests
ELISAs to detect the toxins produced
by pathogenic forms of Clostridium
perfringens and Clostridium difficile are
indicated in horses and foals with acute
diarrhoea, particularly where the problem
may be associated with antimicrobial
administration. Faecal samples should be
taken before the drug metronidazole is
given and should be chilled if delivery to
the laboratory is likely to take more than
an hour or two.
Virology
Fluid diarrhoea samples may be examined
by latex particle agglutination for the
presence of Rotavirus antigen.
Specialist virology laboratory facilities and
expertise are required for testing for the
following equine viruses:-
Equine Influenza: paired serum samples
(acute and convalescent phases, collected
14 days apart) are examined for signs
of seroconversion (a four-fold or greater
rise in titres between the acute and
convalescent samples). Nasal discharge or
40