TRANSMISSION OF DISEASES 359 



is usually accompanied by little or no fever, makes this seem 

 unlikely. A single attack of tick paralysis seems to confer 

 immunity and it is probable that many children are naturally 

 immune. The most reasonable explanation is that the ticks 

 secrete a toxic substance, especially when rapidly engorging, 

 which has a specific action on the motor nervous system. Pos- 

 sibly the bite must pierce or come in contact with a nerve or 

 nerve ending in order to produce the effect. 



Numerous cases of tick paralysis in children have occurred 

 in British Columbia and in the Blue Mountains of Eastern 

 Oregon. One doctor in the vicinity of Pendleton reported no 

 less than 13 cases. The disease begins with paralysis of the 

 legs and usually results in complete loss of their use; the paraly- 

 sis ascends in the course of two or three days, affecting the arms 

 and finally the thorax and throat. Unless the heart and respi- 

 ration are affected, recovery follows in from one to six or eight 

 days after removal of the ticks. The latter, often in pairs, are 

 usually found on the back of the neck or along the middle line 

 of the head, especially just at the base of the skull. If the ticks 

 are not removed, the disease may result in death or in spon- 

 taneous recovery after a few days or a week. 



Unfortunately in most of the cases of tick paralysis in chil- 

 dren the ticks have not been identified, but it is Avell known 

 that the spotted fever tick is the most frequent cause of paralysis 

 in sheep and the only species by which such a disease has been 

 reproduced experimentally. In South Africa, however, a similar 

 paralysis in sheep results from the bites of Ixodes pilosus, and 

 paralysis in children in Australia from the bites of other but 

 undetermined species. The scrub-tick, Ixodes holoajclus, is said 

 to be troublesome as a cause of paralysis in j^oung stock in New 

 South Wales. In the regions of Oregon and British Columbia 

 where tick paralysis is especially prevalent there occur a number 

 of different ticks, and there is no evidence that any tick which 

 attacks man along the spinal cord or on the head may not cause 

 paralysis. 



Ticks and Disease 



The role of ticks as disease carriers has been well established 

 since Button and Todd in 1905 proved that African relapsing 

 fever was transmitted by a species of tick known as the tampan, 



