CHAPTER XXIX 



Diseases Caused or Carried by Mites and Ticks ^ 

 W. Dwight Pierce 



The Arachnid order Acarina, composed of mites and ticks, contains 

 many of the most serious carriers of causative agents of disease. As 

 all ticks are parasitic on animals and derive their entire nourishment from 

 the blood of their hosts, it is naturally to be expected that in this group 

 we will find a great proportion of the carriers of animal blood diseases. 

 The mites are not all parasitic, but there are quite a number of families 

 in which parasitic mites are found, and some of the families are parasitic 

 exclusively in their habits. 



The most familiar of all the tick-borne diseases is the disease known 

 as TEXAS FEVER OF CATTLE which has cost the southern states 

 millions of dollars, and has been the cause of restricting the shipment 

 of cattle from southern to northern states. The discovery of the role of 

 the tick in the transmission of Texas Fever by Smith and Kilbome of 

 the Bureau of Animal Industry, was one of the earliest discoveries in 

 medical entomology. Since that time the Department of Agriculture, 

 through the investigations of the Bureaus of Animal Industry and 

 Entomology has devoted a great deal of attention to this problem. The 

 Bureau of Animal Industry has had charge of the eradication of the 

 cattle tick in America and has succeeded in eliminating this pest from 

 large areas and from at least one state, the State of Mississippi. 



In South Africa tick-borne diseases are the principal limiting factors 

 to animal industry. The RELAPSING FEVERS of man in Africa are 

 carried almost exclusively by ticks. In our own country one of the most 

 serious local diseases is ROCKY MOUNTAIN SPOTTED FEVER in 

 the northern Rocky Mountains. The relationship of the ticks and mites 

 to disease can best be shown by an arrangement of these diseases accord- 

 ing to their causative organism. 



DISEASES CAUSED BY DIRECT ATTACK OF TICKS AND MITES 



ACARINE DERMATOSIS or ACARIASIS. A great many different 

 species of mites are capable of causing various types of DERMATOSIS 



'This lecture was prepared for the present edition. 



403 



