INSECTS AS AGENTS IN SPREAD OF DISEASE 549 



can not be said, and the same is true to a greater or less degree of 

 cholera, pink-eye, yaws, syphilis, and many other diseases which can 

 not be considered as typically insect-borne. 



One other disease which has been increasing at an alarming rate in 

 our own country during the past several decades is infantile paralysis. 

 This malady occurs in certain parts of Europe, whence it is prob- 

 able that it was brought to America. As a rule it affects children dur- 

 ing the first few years of life and, although the mortality is not so very 

 great, a majority of the children affected are left permanently lame after 

 recovery. The virus of this disease is an ultramicroscopic organism 

 which causes lesions of the spinal cord that sometimes lead to paralysis. 

 At the present time it appears probable that infantile paralysis is 

 insect-borne, and it has been suggested by Brues and Sheppard that 

 the stable fly, Stomoxys calcitrans, acts as a carrier of the virus, 1 

 although it is quite possible that some other insect also may be con- 

 cerned. 



No account of insect-borne diseases, however brief, could be com- 

 plete without some reference to animal diseases. A few of these have 

 already been referred to incidentally as affecting both man and animals, 

 and it is quite likely that other human diseases whose etiology is at 

 present obscure, will in the future be shown to bear some relation to 

 those of animals. Apart from this, the economic loss occasioned by 

 such affections of domestic animals is enormous, although it is in great 

 part preventable. 



A wide-spread disease of cattle in the southern part of the United 

 States, known as splenetic fever, or "Texas fever," is the most important 

 insect-borne animal disease that occurs in this country, and is particu- 

 larly interesting since it was the first disease of any kind shown to be 

 carried exclusively by insects or ticks. It occurs very generally through- 

 out the gulf states as far north as the thirty-sixth parallel of latitude and 

 is the cause of immense pecuniary loss to this region, not only on 

 account of the cattle lost, but as a result of the greatly weakened condi- 

 tion of the animals in general. Southern cattle are usually immunized 

 by an attack at an early age, but northern animals die in large numbers 

 when exposed to the disease. 



Smith and Kilborne showed, in 1893, that the protozoan blood-para- 

 site, Piroplasma bigeminum,, which Smith had discovered several years 

 earlier to be the cause of the disease, is carried by ticks. The common 

 cattle-tick of the southern United States, Margaropus annulatus, acts 

 as the exclusive vector, becoming infected during its period of engorge- 

 ment when feeding on the blood of a diseased animal and then trans- 



1 Since the above was written, it has been shown by experiments with 

 monkeys by Eosenau and Brues, that Stomoxys can actually transmit this dis- 

 ease, and their results have been confirmed by Anderson and Frost. 



