EQUINE CLINICAL PATHOLOGY - Rossdale & Partners

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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
G u i d e t o e q u i n e c l i n i c a l p a t h o l o g y nasopharyngeal swabs collected during the acute phase into viral transport medium are cultured specifically for the virus. A direct ELISA test is available for the rapid detection of the virus in acute-phase nasal discharge or nasopharyngeal swab samples. Equine Herpesviruses (EHV-1, EHV-3, EHV-4): paired serum samples (acute and convalescent phases, collected 14 days apart) are examined for signs of seroconversion (significant rise in titres between the acute and convalescent samples). Nasal discharge or nasopharyngeal swabs collected during the acute phase into viral transport medium are cultured specifically for EHV-1 and EHV-4. Aborted foetal, placental and neurological tissues may be examined for EHV-1 and EHV-4 DNA by specific polymerase chain reaction (PCR) test. Equine Viral Arteritis (EVA): paired serum samples (acute and convalescent phases, collected 14 days apart) are examined for signs of seroconversion (significant rise in titres between the acute and convalescent samples). Nasal discharge or nasopharyngeal swabs collected during the acute phase into viral transport medium are cultured specifically for the virus. Aborted foetal and placental tissues may be examined for the virus DNA by specific PCR test. For the screening of equine aborted foeti for EHV and EVA infections, please see postmortem examinations (see page 48). NOTES 41
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EQUINE CLINICAL PATHOLOGY - Rossdale & Partners

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