PREVENTIVE MEDICINE 355 



TICKS. 



Ticks belong to the Natural Order Acarina and to the family 

 Ixodoidae. Of the many species and sub-species which are known 

 throughout the world, two are of importance in this country, 

 Ixodes ricinus and Hamaphysalis punctata. 



Ticks are of great economic importance as they act as carriers 

 of various diseases in the Tropics, and in the British Isles are solely 

 responsible for the spread of bovine redwater and apparently play 

 an important part in the transmission of louping-ill of sheep. 

 Their life-cycle* is of interest to the hygienist, and that of /. ricinus, 

 which is a three-host parasite, is as follows : The female lays her 

 eggs, of which there may be as many as 2000, in the grass in groups, 

 and having completed her egg-laying she dies. From the eggs 

 develop in from 2 to 5 months small hexapod larvae, or " seed ticks," 

 which attach themselves to the first available host. The seed ticks 

 may have to wait for months before a suitable host passes within 

 reach. Having gorged themselves on the host, the seed ticks drop 

 to the ground and moult to octopod nymphs, and still further moult- 

 ing when on the ground brings them to adult ticks. The female 

 becomes impregnated when on the body of a host and when fully 

 gorged drops off and begins to lay her eggs. The male tick is not 

 a blood sucker. The life-cycle is not the same for all species of 

 ticks, some requiring three hosts while others are satisfied with 

 and complete their metamorphosis on one. 



During any stage of their life-cycle ticks may live for many 

 months away from a host, for six to ten months or even longer. 



Ixodes is parasitic on cattle, sheep, horse, dog, goat and cat, 

 and sometimes on man ; in the summer time seed ticks often fasten 

 themselves on to children when they sit on the grass. Both /. 

 ricinus and H. punctata transmit redwater in Great Britain. 



PREVENTIVE MEASURES. It is easy to suggest measures for 

 the eradication of ticks, but very difficult to put them into effective 

 operation. In countries where ticks play an important part in 

 transmitting disease drastic measures are called for in order to 

 eradicate them. Large tracts of land known to harbour ticks are 

 fenced off from cattle, and by this means the ticks are starved 

 out or are cleaned of disease as they are unable to suck blood con- 

 taining bovine piroplasms. Burning and clearing the land destroys 

 a large number of ticks and removes the cover that is necessary for 

 them. Converting pasturage into tillage ground is an effective 

 * See also under Redwater. 



