Tick paralysis

The paralysis tick, Ixodes holocyclus, is the main cause of tick paralysis of cattle. Paralysis tick is native to Australia’s east coast from Cape York Peninsula in Queensland to southern Victoria. Other paralysis tick species are not as common but do extend into Tasmania (Figure 1).

Paralysis ticks are a 3-host tick and the most common host is the bandicoot although many native species are infested.

Adult paralysis ticks, which are responsible for causing paralysis, are more active in late winter to mid-summer (August to December) but cases can be seen all year round in some areas. A drop in barometric pressure and rain events can stimulate activity in pasture-based unattached adults resulting in movement to areas (higher parts of plants) that increase likelihood of attachment to a host.

The adult tick is found mainly in areas that are less likely to get rubbed off, so most attach to the head, neck, ventral abdomen and escutcheon (under the tail area) of the host. As the tick feeds on the blood of the host, saliva from the tick is injected into the host animal (Figure 2). The saliva contains toxins that cause paralysis. Paralysis does not occur immediately. Sufficient tick toxin may be injected to cause signs in the host after an adult tick has fed for about 3 days. Young calves are more prone to the effects of the toxin. Natural immunity to the toxin can develop with repeated exposure.

Signs

• Paralysis starting with hind limb ataxia (weakness) is usually the first symptom.
• Paralysis is ascending (progressively moving forward) until the animal is unable to rise.
• Increased respiratory effort and difficulty swallowing may become evident as paralysis increases.
• As paralysis continues to increase, an animal may not be able to maintain sternal recumbency (sitting up) and death is usually from aspiration of gut contents and pneumonia complications.
• Mis-adventure and an inability to move from environmental extremes may also contribute to the death toll.

Diagnosis

Diagnosis is based on the presence of signs of paralysis as described above and the presence of paralysis ticks, or craters left in the skin where paralysis ticks have been.

See tick paralysis treatment and management pages for more information.

Figure 1. Distribution of Australian paralysis ticks. Image courtesy of Virbac.

Figure 2. Paralysis ticks feeding on the blood of a cow. Image courtesy of Lex Turner.