Chronic malarial infection of mice: A comparison of single and multiple infections with Plasmodium berghei following P. yoelii.

Chronic malarial infection was induced in two groups of BALB/c mice by injection of Plasmodium yoelii followed by either one or repeated injections of P. berghei. Both groups showed a continuing but fluctuating splenomegaly, and a considerably increased reticulocyte count which also varied regularly, over a period of six months. During this time many mice had a very low grade parasitaemia demonstrable by subinoculation of blood into uninfected recipients. Mice infected with P. yoelii alone did not show any of these changes. One year after the first malarial attack all the infected mice had higher fluorescent antibody titres to P. yoelii than to P. berghei, titres against which were very low. Infected mice showed an increase in plasma cell proliferation in the red pulp of the spleen. There was a significant difference between mice which had received multiple injections of P. berghei and the other infected animals; the former had many germinal centres in the spleen, while the other infected groups did not.