Page 1129 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

1104 CHAPTER 10

VetBooks.ir Clinical presentation the lysosomal enzyme mannosidase, resulting in
Swainsonine and swainsonine N-oxide inhibit
Tick paralysis is characterised by ascending paresis
followed by paralysis. The progression of disease can
charides. The cellular vacuolation that results from
be rapid and horses may die within 24 hours in some lysosomal accumulation of mannose-rich oligosac-
cases. the inhibition of mannosidase leads to cellular dys-
function, comparable to hereditary mannosidosis of
Differential diagnosis humans and cattle. Locoweed is initially ingested
The main differential diagnosis is botulism. when other foodstuffs are scarce, but horses appar-
Differentiation based on clinical signs is impossible. ently acquire a taste for the plant once ingestion has
started. Horses are more susceptible to the effects of
Diagnosis locoweeds than other species.
Diagnosis is based on characteristic clinical signs
and identification of ticks on the body. There is no Clinical presentation
other means of diagnosis. Clinical signs appear 2 weeks to 2 months after inges-
tion commences. Continuous ingestion is required
Management to cause disease. The signs can appear abruptly and
If tick paralysis is suspected based on clinical signs are indicative of a diffuse CNS disorder. Periods of
and geographical region, a thorough search should depression alternating with frenzy and overreaction
be performed for the presence of ticks on the body. to stimulation are common features. Other signs
All ticks must be removed. It is very easy to overlook that can be seen are gait abnormalities (including
a small number of ticks, so careful examination is a stringhalt-like gait), head nodding, visual impair-
required. Heavily haired areas should be very closely ment and dysphagia. Weight loss occurs quickly
examined. Clipping may be required. Supportive and can lead to emaciation and death. Other organs
care beyond tick removal is similar to that described are frequently affected, and reproductive problems
for botulism (see p. 1097). Prevention of disease such as abortion and limb deformities in foals are
involves avoiding tick infested areas and inspection common.
and prompt removal of ticks from horses that have
had access to potentially infested areas. Differential diagnosis
EPM; WNV encephalitis; trauma; aberrant para-
Prognosis site migration (Halicephalobus deletrix); metabolic
The prognosis is good with Dermacentor infestations, derangement; hepatic encephalopathy; rabies; drug
provided ticks are identified and removed, but poor reaction (reserpine, fluphenazine).
with Ixodes infestation.
Diagnosis
LOCOWEED INTOXICATION Clinical presentation and a history of possible
chronic ingestion of locoweeds are suggestive.
Definition/overview Identification of cytoplasmic vacuolation in lympho-
Locoweed intoxication is a geographically important cytes is supportive of locoweed intoxication.
cause of neurological disease associated with chronic
ingestion of locoweeds, plants of the Astragalus and Management
Oxytropis genera. There is no effective treatment for chronic locoweed
intoxication. Sedation is usually ineffective in hyper-
Aetiology/pathophysiology excitable horses.
Astragalus and Oxytropis spp. are found in the range-
lands of western North America and Australia. Prognosis
These are perennial plants that contain a variety of Mildly affected horses recover in 1–2 weeks if the
toxic compounds. source of locoweed is removed. However, there is