696 PATHOGENIC MICROORGANISMS 



PATHOGENICITY OF THE PARATYPHOID GROUP FOR MAN 



Organisms of this class may be the causative agents of a number of 

 clinically varying conditions of man. In general, it may be said that 

 two main types of disease can be caused by this group, 1, that in 

 which the disease simulates a mild or severe typhoid fever recognizable 

 as different from true typhoid fever only by isolation and identification 

 of the paratyphoid organisms; and 2, those which fall into the category 

 of "meat poisoning" in which, after a very short incubation time, one 

 to two days or even less, there are symptoms of gastroenteritis which 

 may be mild, but more frequently are explosive and severe. 



1. True paratyphoid fever, or a typhoid-like fever, may be caused 

 by members of the paratyphoid "A" or "B" group. 



The paratyphoid "A" group may be regarded as standing somewhat 

 apart from the other microorganisms of this large and heterogeneous 

 family in being quite sharply distinguishable from the others, both by 

 cultural and agglutinative reactions. The organism, unlike other para- 

 typhoid and enteritidis bacilli, fails to ferment xylose, as shown by 

 Krumwiede and his coworkers, and fails to give a positive reaction on 

 the lead acetate media. By agglutination reactions the organisms of the 

 "A" type are found to be more homologous than others and a power- 

 ful "A" serum usually agglutinates "A" organisms in general, a con- 

 dition which is quite unlike that existing among the "B" and other 

 members of the group. Paratyphoid "A" is probably conveyed in 

 exactly the same way as is typhoid fever, namely, by water, milk and 

 direct and indirect contact, food contamination, carriers and the agency 

 of flies. 



The disease itself may take the form either of a very mild and short- 

 lived enteric disturbance with slight fever, or it may take the form of a 

 moderately severe typhoid fever with rose spots, enlargement of the 

 spleen and positive blood culture. Paratyphoid "A" cases are not a 

 very large percentage of the ordinary sick rate of communities, but 

 occasionally small group epidemics have been studied; and during 

 recent years in the United States, military epidemics have occurred. 

 Upon the recent return of some American militia regiments from 

 the Mexican Border, there appeared among them an epidemic of para- 

 typhoid which consisted largely of the "A" type. We had the privilege 

 of studying a good many of these cases, and found a most varied clinical 

 picture. The severe cases were practically indistinguishable from 

 typhoid fever, rjut there were at the same time cases of very mild fever 

 with nothing but a little diarrhea, in which diagnosis was made only by 



