Page 826 - Veterinary Toxicology, Basic and Clinical Principles, 3rd Edition

Terrestrial Zootoxins Chapter | 58 785

VetBooks.ir treated symptomatically with control of hypertension, paralysis in Europe and Asia has been reported due to bites
from Hyalomma punctata and Ixodes ricinus.
heart rate changes, and neurologic signs. Some antive-
noms in the United States are produced locally; however,
Tick paralysis has occurred following the bite a single
because these are not approved by the US Food and Drug tick, and heavily infested animals may succumb quickly
Administration, they cannot legally be transported to (Fowler, 1993). Clinical signs include an ascending ataxia
other states (Goddard, 2003). In addition, their use in vet- that progresses to paresis and flaccid paralysis. Early in
erinary patients is considered controversial (Dalefield and the intoxication, animals remain bright, alert, and able to
Oehme, 2006). eat and drink if properly supported. Eventually, paralysis
of the respiratory muscles leads to respiratory failure and
death. Paralysis produced by I. holocyclus, the Australian
Ixodida: Ticks
tick, generally occurs more rapidly and tends to persist
Background following removal of the tick.
Ticks are well known as being vectors for many human
and animal diseases, with the first reports of tick paralysis Treatment
originating in Australia in 1890 and British Columbia in
The main goal of treatment is to remove the ticks and pro-
1912 (Sonenshine et al., 2002). Worldwide, 43 species of
vide supportive care (especially respiratory support) until
ticks from nine different genera have been associated
recovery occurs. Recovery can occur quite rapidly follow-
with tick paralysis: Amblyomma, Argas, Dermacentor,
ing complete removal of the ticks, or it may take a few
Haemaphysalis, Hyalomma, Ixodes, Ornithodoros,
days (Fowler, 1993). The use of topical insecticides may
Otobius, and Rhipicephalus (Dipeolu, 1976; Fowler,
aid in the removal of ticks and can be especially helpful in
1993). Tick paralysis has been reported in North America,
cases in which numerous ticks are embedded. Heavily
Europe, Africa, Australia, and the former Soviet Union.
coated animals may need to be shaved to ensure that
all embedded ticks are found and removed. Removal of
Mechanism of Action
embedded ticks should be performed carefully to avoid
The exact mechanism(s) of action of tick toxins is not expressing additional toxin into the wound or leaving the
well known, but in most tick species it is suspected that head embedded in the skin. Forceps may be used to grasp
the toxin interferes with the synthesis and/or release of the tick as close to the skin as possible and gentle traction
acetylcholine at the neuromuscular junctions, resulting in should be used to remove the tick. In most cases in which
lower motor neuron paresis and paralysis very similar to ticks are removed before bulbar paralysis has occurred, the
that produced by botulinum toxin (Fowler, 1993). The prognosis for full recovery is very good. A short-term
Australian tick, Ixodes holocyclus, toxin may differ immunity develops following recovery from tick paralysis.
because it appears to have more of an effect on central
nerve centers rather than on peripheral (Fowler, 1993).
Myriapoda: Centipedes and Millipedes
Toxicity Centipedes and millipedes are distantly related to lobsters,
Tick paralysis has been reported in a large variety of ani- crayfish, and shrimp. These arthropods are widely distrib-
mal species, including dogs, cats, cattle, sheep, goats, lla- uted throughout the world, and they are characterized by
mas, poultry, wild antelope, bison, foxes, wolves, mice, a long, flat, multisegmented body with one (centipede) or
ground hogs, black-tailed deer, and several species of wild two (millipede) legs emerging from each body segment.
birds (Daly et al., 1992; Fowler, 1993; Beyer and Although most centipedes and millipedes are less than 1.5
Grossman, 1997; Sonenshine et al., 2002). In North in. long, centipedes from the genus Scolopendra may
America, most cases of tick paralysis in livestock occur in grow to be 4 6 in. long. All centipedes have a pair of
the Pacific Northwest due to Dermacentor andersoni, modified front legs (forcipules) that serve as fangs and
whereas most cases in dogs are due to Dermacentor varia- that are connected to venomous glands directly under the
bilis (Fowler, 1993; Sonenshine et al., 2002). Dermacentor head (Norris, 2004). Larger centipedes can inflict painful
occidentalis occasionally causes tick paralysis in cattle, bites resulting in local swelling, erythema, and lymphan-
ponies, and deer but not dogs (Sonenshine et al., 2002). In gitis. In addition, the legs of Scolopendra spp. are tipped
the southeastern United States, Ixodes brunneus has been with sharp claws that are capable of penetrating skin, and
associated with tick paralysis in wild passerine birds toxin produced at the attachment point of each leg may
(Luttrell et al., 1996). In Australia, tick paralysis is caused drop into these wounds, causing inflammation and irrita-
by I. holocyclus, whereas Ixodes rubicundus and tion due to mast cell degranulation (Tavora et al., 2016).
Rhipicephalus evertsi are the primary species responsible Centipede venom has been poorly studied, but compo-
for tick paralysis in Africa (Sonenshine et al., 2002). Tick nents identified in various centipedes include a