Immunization of albino mice using chloroquine attenuated Plasmodium yoelli nigeriensis.

In an attempt to induce chloroquine resistance in Plasmodium yoelii nigeriensis by the method of drug pressure, it was found that the mice continued to be infected until the fourth passage when they became refractory or immune to the infection. When the immune mice were challenged at four weekly intervals, they remained refractory to the infection until week 12 when one of them became infected. However, by the sixteenth week, the rest of the mice became susceptible to the infection. Four of the mice which received a booster dose of the parasite which had been exposed to chloroquine in three passages, that is, chloroquine-attenuated at the sixteenth week, did not pick up a challenge infection two weeks later while the controls did.