390 Microbes and You 



Because agglutination differences between typhus fever and 

 Rocky Mountain spotted fever are only a matter of degree, these 

 reactions in themselves are not enough to differentiate these dis- 

 eases. Another more complicated serological test, called the com- 

 plement FIXATION REACTION, may be employed to separate them. 

 This test will not be described here. 



METHODS FOR CONTROLLING RICKETTSIAL DISEASES 



One of the most effective means for preventing rickettsial dis- 

 eases is the elimination, if possible, of the vectors and the animals 

 upon which these vectors thrive. This is usually a herculean task, 

 but progress has been made in this direction not only in the United 

 States but also in many endemic areas throughout the world. 



Prophylactic vaccination has proven very effective in man's 

 fight against diseases of rickettsial etiology. The dramatic drop 

 in the number of cases of typhus during World War II as com- 

 pared with the first World War is proof that the combination of 

 effective vaccines and the liberal use of DDT and other substances 

 to kill lice can be employed to control this disease. The Germans 

 were reported during the closing stages of World War I to be 

 manufacturing typhus vaccine by the intra-rectal injection of lice 

 with living rickettsiae. The intestines of lice serve as excellent 

 locations for the growth of these microorganisms, but such a manu- 

 facturing process is difficult and dangerous, to say nothing of the 

 relatively small yield of vaccine per man-hours expended. Vac- 

 cines for both typhus fever and Rocky Mountain spotted fever can 

 be prepared by employing either the yolk sac method of Cox or the 

 chorio-allantoic membrane of the developing chick. After separat- 

 ing the rickettsial bodies from the egg material, the microorgan- 

 isms are inactivated with phenol and preserved with formalin. 

 Active immunity induced by injections with these vaccines lasts 



