PAEASITES 417 



of which the two following are the most important from a 

 hygienic point of view, viz., the I.wdidce (Ticks), and Sar- 

 coptidce (Mange acari). 



IxoDiD^. — The Tick family has recently become of special 

 interest, as some members have been found to act as carriers 

 of specific disease, of which the following are at present 

 known : Ehodesian Eed Water (East Coast Fever) is 

 carried by a brown tick very widely distributed in Africa, 

 and known as the Rhipicephalus appendiculatus. Texas 

 Fever, or ordinary Infectious Haemoglobin aria of cattle, is 

 conveyed by the E. annulatus ; the tick fever of Australia 

 is carried by the R. Australis, while another variety trans- 

 mits the ' Tristezza ' disease of the Argentine. All these 

 diseases are due to an intra-corpuscular micro-organism, 

 and it is most likely that other varieties of tick than those 

 mentioned may act as carriers, for example. East Coast 

 Fever may also be carried by the Black-pitted Tick (Theiler). 



Other tick-transmitted diseases are Bilious Fever of the 

 horse, and Malignant Jaundice of the dog, seen in South 

 Africa, the latter carried by the Hcemaphysalis leachi. 

 ' Heart-Water ' in cattle, sheep, and goats (also a South 

 African disease), is inoculated by the AmUyoimna hehrcsum, 

 which besides acting as a carrier produces suppurating 

 sores on the udders of cows. The Hsemoglobinuria of 

 European cattle is produced by the Ixodes reduvius, while 

 ' Louping-ill ' of sheep is popularly connected with the bite 

 of a tick. 



Thus, there is quite a list of formidable diseases in 

 which these blood-sucking parasites play a part of supreme 

 importance. Further, though some of these diseases may 

 be reproduced by the direct inoculation of virulent blood, 

 or even the blood of the recovered animal — Texas Fever 

 for example — others, like African Coast Fever, must pass 

 through the tick as an intermediate host before infection 

 can result, and in this particular case it must pass through 

 a special species of tick. 



But the behaviour of the tick in all cases is not quite 

 the same. In Texas Fever, ' Trestezza,' Tick fever, and 



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