Page 1121 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

1096 CHAPTER 10

VetBooks.ir 10.53 10.54

Fig. 10.53 Weak
tongue tone and
dysphagia in a foal with
type B botulism.

Fig. 10.54 A mare
that was dysphagic and
had weak palpebral
tone. The mare had
botulism secondary to
forage poisoning. Eight
other horses on the
farm were affected.

Death from botulism is almost inevitable in but the amount of BoNT present in serum of even
untreated patients and results from paralysis of severely affected horses may still be insufficient to
diaphragmatic and intercostal musculature, which cause mortality in mice (horses appear to be exqui-
causes respiratory failure. sitely sensitive to BoNT), leading to false-negative
results. ELISA and PCR tests for BoNT can be
Diagnosis performed in the USA, although neither is available
A presumptive diagnosis of botulism can be made on commercially in Europe.
the basis of history and clinical examination findings;
that is, abrupt onset of diffuse, symmetrical weakness Management
that gradually progresses to recumbency in 1–4 days Treatment of botulism can be summarised in terms
with normal mentation, concurrent dysphagia and of neutralising circulating BoNT, nursing care and
decreased tongue tone. Dynamic tests may support judicious use of antimicrobials.
a clinical diagnosis of botulism (Table 10.8). A diag-
nosis of botulism also requires the exclusion of other Neutralising circulating BoNT (passive
diseases that cause profound muscle weakness, dys- immunisation)
phagia or muscle fasciculations, such as equine grass Botulism is generally fatal unless treated promptly
sickness, viral encephalitides (equine herpesvirus-1, with antitoxin (specific or multivalent antiserum).
WNV disease), atypical myopathy and EMND. Occasionally, horses with mild, slowly progressing
Attempts to confirm a clinical diagnosis of botu- clinical signs do survive without antitoxin adminis-
lism are frequently unrewarding. A definitive diag- tration. If antitoxin is administered prior to recum-
nosis requires the detection of BoNT in forage, bency in an adult horse, survival rates may exceed
serum, GI contents or faeces. BoNT is stable in fro- 70%. Clinical signs may deteriorate for hours after
zen tissue and can be stored for several weeks. The administration of the antitoxin, because the antise-
mouse bioassay is the most sensitive test available, rum has no effect on BoNT inside the motor neuron.