HUMAN DISEASES 54 1 



south as Southern Rhodesia and the Cape. Rat-flea typhus, 

 though relatively uncommon among human beings, appears to be 

 enzootic among rats over an extensive area. The reason for this 

 is that, unlike plague infection, the virus of typhus does not kill 

 the rats and hence the rat-fleas do not often overflow on to man. 

 Louse-typhus is much the commonest type, and although milder 

 in South Africa than the classical old-world typhus, some 35,000 

 cases have been reported during the past thirteen years, resulting 

 in about 4,660 deaths. These figures give a case mortality of 1 3 per 

 cent, though the actual mortality is certainly much lower, since in 

 a primitive community fatal cases come to the notice of authorities 

 much more frequently than mild ones. Among Europeans in the 

 same period there have been 686 cases with 32 deaths, a case 

 mortality of 4' 7 per cent. Louse-typhus has probably been preva- 

 lent in South Africa for a very long time, but did not come into 

 prominence until about 191 9. From then until 1923 reported 

 cases averaged over 8,000 annually, the worst year being 1920, 

 with 11,000. After 1924 the number fell below 2,000 until 1933, 

 since when it had increased to nearly 7,000 in 1935. The endemic 

 area is now roughly triangular in shape, embracing about one 

 half of the Union, including the Transkei, Giskei, and the Orange 

 Free State. The recent increase in the disease is in some measure 

 due to its spread in the interior in a north-westerly direction, but 

 the economic distress of recent years has probably been still more 

 important in that the standard of living has been reduced and the 

 body louse has become more prevalent. Typhus will eventually 

 disappear from South Africa, as it has done in Europe, with advan- 

 cing civilization and an increased standard of living, but mean- 

 while direct preventive measures against lice succeed in arresting, 

 but not eradicating the disease. The detailed work of Pijper and 

 Dau summarized (1935) the immunological relationship of the 

 three typhus-like diseases as follows: the rat-flea virus immunizes 

 against tick-bite fever, but not against louse-typhus; tick-bite fever 

 does not immunize against rat-flea typhus, but louse-typhus im- 

 munizes against rat-flea typhus. 



The possibility of typhus fever being present elsewhere in Africa 

 to a greater extent than supposed is a matter for examination. 

 This is suggested particularly by the evidence of Tonking (1932) 



