Paralysis of domestic stock by the paralysis tick is primarily a disease of young animals (especially calves) and of non-habituated stock introduced into tick-infested country in spring.
The paralysis tick has a wide host range, but its principal hosts are bandicoots. The tick has one generation per year and the adult female, which causes almost all paralysis, is abundant in spring and early summer and occurs most commonly in overgrown or regrowth country where bandicoots are abundant.
Calves from immune mothers receive temporary protection (maternal antibody) from the colostrum (first milk) which prevents tick paralysis. Calves exposed to ticks when the maternal or age resistance is high, rarely show clinical symptoms but develop a solid, long lasting immunity. It is therefore frequently only cattle that have not been previously exposed to ticks and especially their new-born calves that are affected. In fact, cattle and sheep losses of over 50 per cent have sometimes occurred when previously unexposed stock have grazed in infested country.
Often few ticks are found on cattle dying from paralysis and this had led to the belief that small numbers of ticks can kill even adult cattle. The likely explanation is that the engorged ticks have dropped off before the animal became paralysed. Research suggests that ten female ticks are required to paralyse 2 to 3 week old calves while older calves are paralysed by 20 ticks, but not by 10 ticks.
It has been suggested that to reduce tick paralysis in cattle, the calving time should be in winter rather than spring and cows should be put in "clean" paddocks to calve.
More information can be found in the general Tick section.
Contributed by R. Brooks. Last updated: October 2007
