186 OTHER SPOROZOA 



ticks (Dermacentor) , and undoubtedly will be found in other ar- 

 thropods. Their occurrence in non-bloodsucking insects, aside 

 from the fact that no vertebrate disease is known to be associated 

 with many of these infections in parasitic insects, is evidence for 

 the fact that these organisms, like the intestinal flagellates of 

 insects (see p. 75), are primarily parasites of arthropods, a com- 

 paratively few species of which have become adapted to live in 

 the blood of vertebrate animals, where they may cause disease. 



The human diseases with which Rickettsia-like bodies have been 

 definitely associated are typhus, trench fever, and Rocky Mountain 

 spotted fever. In the Japanese disease, kedani or tsutsugamushi, 

 which shows some affinities with spotted fever, parasites have been 

 described which may be referable to this group. 



Typhus Fever. This deadly disease, which so frequently 

 breaks out when human beings are crowded together where per- 

 sonal care and cleanliness are either neglected or impossible, 

 has for ages been associated with wars and prison camps. In 

 some parts of Europe and North America typhus persists in an 

 endemic or mild epidemic state, ready to burst into flame when 

 opportunity comes, giving rise to terrible epidemics. The dis- 

 ease is endemic on the Mexican plateau, where it is known as 

 tabardillo. 



Typhus has a sudden onset, and is characterized by high fever, 

 headache, aches in the bones and muscles, bronchial troubles, 

 congestion of peripheral blood-vessels and a red rash later giving 

 rise to dark blotches. In an endemic state the mortality is very 

 low, but when an epidemic breaks out there may be 50 to 79 per 

 cent mortality. 



Typhus has been conclusively shown to be transmitted prin- 

 cipally, and perhaps solely, by body lice. Details of the role of 

 the lice, and an account of some recent epidemics, will be found 

 on pp. 397 to 399. 



Attention was first directed to minute granules associated with 

 typhus fever by Ricketts in 1909, but these bodies were first 

 described in detail from typhus-infected lice by Rocha-Lima in 

 1916 and named Rickettsia prowazeki. The organism occurs in 

 abundance in the gut of infected lice as single granules, diploid 

 bodies, or in clumps evidently resulting from continued multi- 

 plication without separation of the individuals; occasionally 

 bacillus-like or thread forms occur. Multiplication seems to 



