178 OTHER SFOROZOA 



Oroya fever has been constantly confused with other diseases 

 and it was not until the South American expedition of the 

 Harvard School of Tropical Medicine, under the leadership of 

 Dr. R. P. Strong, made an investigation of the disease that 

 some order was brought out of the confusion. Malaria, para- 

 typhoid, and particularly verruga peruviana are the diseases 

 which have been most frequently confused with Oroya fever. 

 Mixed infection of these diseases and others such as yaws and 

 tuberculosis with true Oroya fever has still further complicated 

 matters. From the time of the Incas verruga peruviana and 

 Oroya fever have been associated and regarded as different phases 

 of the same disease, and this view is still held by some investi- 

 gators. The fact that the characteristic nodules of verruga were 

 usually associated with a very mild form of fever and sometimes 

 with none at all, while oroya fever was of very severe type caus- 

 ing very high fatality, raised some question as to the distinctness 

 of the diseases. To settle this point a Peruvian medical stu- 

 dent, Daniel Carrion, vaccinated himself with blood from a 

 verruga nodule. Five or six weeks later he died of a severe 

 fever, and the question of the identity of the disease was ap- 

 parently settled, and the fever was called " Carrion's Fever " 

 in his honor. The notes regarding Carrion's illness have been 

 lost and it is now believed that he may have died of some other 

 disease or that the patient from whom he inoculated himself 

 may have been suffering from some other disease in addition to 

 verruga. 



As a result of their own studies, Dr. Strong and his colleagues 

 believe that the diseases are quite distinct. They have shown 

 that Oroya fever is caused by a very minute parasite living in 

 the red blood corpuscles and multiplying in the endothelial cells, 

 and that it cannot be inoculated into animals; verruga peruviana, 

 on the other hand, is caused by a virus which is ultra-microscopic, 

 probably related to the smallpox virus, and can be successfully 

 inoculated into laboratory animals. It is easy to understand 

 how the two diseases were confused, since to a large extent their 

 ranges overlap and a visitor to endemic regions would be likely 

 to contract both. Verruga, being less quickly contracted and 

 having a longer incubation period, would tend to appear later 

 than Oroya fever, and would therefore be looked upon as a later 

 stage of the same disease. The native belief that a general erup- 



