Q02 MICROBIOLOGY OF DISEASES OF MAN AND DOMESTIC ANIMALS 



the similarity among these spirochaetes in method of transmission 

 and because of practical identity in the symptoms and treatment of 

 the diseases which they produce, it is better to describe the relapsing 

 fevers as one disease caused by Spirochcrtd recurrentis. 



Spiroch&ta duttoni is a slender organism measuring from 14/1 to i6ju in length; its 

 thread-like body lies in a number of waves, which vary greatly in number, according 

 to the way in which the preparation is made; consequently, the number of waves is 

 not a constant character which can be relied upon for the identification of these 

 spirochaetes. This spirochaete is composed of an outer ectoplasmic sheath, and of 

 an interior composed largely of chroma tin; the sheath extends at either end into 

 flagellum-like prolongations. Multiplication is usually 

 accomplished by transverse binary division, sometimes by 

 longitudinal division. Sometimes, perhaps most often 

 toward the end of an attack of fever the spirochaetes coil up 

 tightly, within a cystlike matrix. Such encysted forms 

 may lie within cells, i.e., liver cells, and spleen cells; they 

 are seen most frequently in the liver and spleen, and they 

 are always present in the alimentary canal of ticks which 

 have ingested spirochaete-infected blood. The chromatin 

 . of both free and encysted spirochaetes may be fragmented, 



chata'duttonL (After more or less re g ularlv - In the tick > cysts, containing a 



Doflein.) spirochaete with fragmented chromatin, burst and set free 



the granules of chromatin. Some investigators believe 



that each granule develops into a spirochaete, others that this represents a degenera- 

 tion and destruction of the parasite. It is not impossible that some such method of 

 multiplication occurs in man. 



The form and exact way in which the spirochaetes are transmitted is not com- 

 pletely known. Ticks can transmit the disease by their bites. Lice, which have 

 become infected from feeding on patients, do so only when they are crushed and 

 their bodies are rubbed into the wounded skin by scratching fingers. Similarly, 

 infection may result when spirochaetes contained in coxal fluid or faeces, dropped 

 upon the skin by a feeding tick, find their way into the wound made by the 

 tick's bite. It is probable that a tick, once infected, never loses its power to 

 transmit the disease; the infection may be transmitted, from mother to daughter, 

 through at least three generations of ticks. 



An incubation period of about five days intervenes between infection and the 

 appearance of symptoms. The fever is characteristic; it rises rapidly to, perhaps, 

 105 and it remains high for from three to five days. It then falls suddenly and 

 there is no fever for from five days to two weeks. Then the temperature rises 

 again. There may be from three to six such recurrences of fever before the 

 illness ends. The definite periodicity of the relapses probably depends upon some 

 more or less regular developmental change in the spirochaetes since the latter are 

 always most numerous in the blood during the height of the fever. The disease 



