220 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 6 



The close parallelism existing between verruga and Rocky Mountain 

 spotted-fever is especially significant. It is possible that both diseases 

 are either ordinary or bizarre forms of piroplasmosis. Both are al- 

 most certainly caused by endoglobular hsematozoans; both consist of 

 a breaking up of the erythrocytes during the fever phase, with re- 

 sultant anemia; both begin with a very variable fever phase and later 

 develop profound dermatic disorganization; both are confined to cer- 

 tain restricted valleys in the mountainous regions of America; both 

 exist through a wide range of altitude; both exhibit manj" graduated 

 forms and degrees of virulence; both cause swelling and congestion of 

 the spleen and liver; both may be contracted in localities uninhabited 

 by man; both have their primary reservoir of infection in the native 

 fauna; the specific pathogenic agent of neither is j^et known, but in- 

 dications in both point to a sporozoan allied to Piroplasma; both are 

 almost certainly transmitted only by ticks. 



It seems strongly indicated that verruga is transmitted by ticks in 

 practically the same manner as is Rocky Mountain spotted-fever — 

 that is to say, that the early stages of the tick live upon the small native 

 mammals, while the adults attach to large animals and man for en- 

 gorgement during which process they transmit the disease. This 

 explains the mular eruption in mules in the verruga districts. The 

 native reservoir fauna should be largely immune to the disease but 

 carries in its blood from one generation to the next the pathogenic 

 organism of verruga in its infective sporozoite stage. Immunity seems 

 to be transmitted through only one generation, the third generation be- 

 coming again susceptible. The sporozoite is unable to develop at all 

 in the native immunes, their erythrocytes being proof against its at- 

 tack. It is able to develop and reproduce asexually in the erythrocytes 

 of susceptible animals, and later to reproduce sexually in their subcuta- 

 neous tissues where it inaugurates the requisite environment. When 

 the ultramicroscopic infective sporozoite stage of the pathogenic or- 

 ganism escapes in the ingested blood from the immune animals to the 

 gut of the tick, it evidently leaves the gut and lodges in both the 

 salivary glands and the ovaries, where it awaits unchanged an oppor- 

 tunity to gain access to the blood of a susceptible animal. From the 

 salivary glands it escapes during the bite of the tick. From the ovaries 

 it is transmitted in the ova to the succeeding generation of young ticks, 

 in which it takes up its position in the salivarv glands. It is reasonable 

 to suppose that it always seeks the salivary glands in immature ticks 

 and adults not yet fully engorged, but seeks the ovaries in fully en- 

 gorged females which have no further occasion to feed. It evidenth' 

 remains unchanged in the salivarj^ glands through the transformation 

 of the tick to adult stage, awaiting the engorgement of the adult to 

 gain access to susceptible blood. Mules are evidently more or less 



