14 



CIRCULAR 4 2 3, U. S. DEPARTMENT OF AGRICULTURE 



known as sylvatic plague, has been gradually spreading and has been 

 identified in several thousand rodents in California, Oregon, Idaho, 

 Wyoming, Utah, Nevada, and Montana, including ground squirrels, 

 wood rats, deer mice, and woodchuck. The sylvatic form of the 

 plague is apparently not highly contagious to man, as an average of 

 only about one human case each year has been reported. The 

 menace, however, remains a most disturbing one because of the ever- 

 present possibilities that house rats may become reinfected in the pop- 

 ulation centers and that human cases of bubonic plague contracted 

 from native rodents may develop the secondary, or pneumonic, form, 

 which is highly contagious directly from person to person. 



Figure 12. — Tubes of oil paint ruined by rats. 

 TYPHUS FEVER 



Another rat-borne disease that is assuming serious proportions in 

 the United States is endemic typhus fever, or Brill's disease. This is 

 related to Old World typhus but is not identical with it. The death 

 rate is not high, but the disease is extremely disabling. Like plague, 

 it is transmitted from the rat to man by means of the rat flea, and 

 may also be carried by the tropical rat mite. These fleas and mites in 

 feeding on infected rats ingest the disease organism and in turn 

 transmit it through biting other rats or human beings. Typhus fever 

 has increased alarmingly in recent years. State health departments 

 reported 332 cases in 1931, 995 cases in 1932, and 1,345 cases in the 

 first 10 months of 1933. At the close of 1933, antirat campaigns to 

 control typhus fever were undertaken by the Bureau of Biological 

 Survey in Georgia, Alabama, and Texas as a Civil Works Adminis- 

 tration project in cooperation with the United States Public Health 

 Service. Rat bait and traps were put out on more than three-quar- 

 ters of a million premises and the disease, which was there assuming 

 epidemic proportions, was successfully checked. 



