Effect of Continuous Passage of Endamoeba Histolytica through Experimental Dogs. ∗

Abstract

Since the development of a satisfactory technic for the cultivation of Endamoeba histolytica in vitro 1 it has been shown 2 , 3 that such cultivation gradually reduces the virulence of this organism and renders it less and less capable of infecting experimental animals. On the other hand, the effect of its successive passages through the experimental host has remained a matter for controversy. Some workers 4 , 5 , 6 have claimed that the organism becomes less virulent with passage. On the other hand, Baetjer and Sellards 7 state that in 11 direct transfers of an active inoculum through kittens they increased the virulence of the amebæ. Dale and Dobell, 8 after 43 passages through kittens, concluded that evidence of increased virulence was lacking. Cleveland and Sanders 3 believed that the increased incidence of infection was due to an increased virulence in the bacteria accompanying the amebæ. All serious attempts to solve this problem have been carried out thus far on experimental kittens.

The present study is based on the successful passage of a single human strain of Endamoeba histolytica through a direct line of 20 dogs and subsidiary infection of 40 additional dogs. The original inoculum, obtained in February, 1934, from a case of amebic dysentery contracted in Louisiana, contained an abundance of active amebæ which were immediately introduced intracecally into 2 young dogs according to the technic previously described. 9 One of the 2 became infected and from it adequate material was obtained to continue direct passage of the strain to the present time. All subsequent animals inoculated became infected. All were carefully studied during the course of the infection and all were carefully examined post-mortem.