A retrospective examination of secondary sporozoite- and trophozoite-induced infections with Plasmodium falciparum: development of parasitologic and clinical immunity following secondary infection.

A retrospective study was made of clinical records to determine parasitemia and episodes of fever of 59 patients reinfected with Plasmodium falciparum for treatment of neurosyphilis, which was considered standard medical care at the time. Records were collected at the National Institutes of Health laboratories in Columbia, South Carolina and Milledgeville, Georgia during the period 1940 to 1963. Nineteen patients were infected via the bites of Anopheles albimanus, An. quadrimaculatus, or An. freeborni mosquitoes; the median prepatent period was 11.5 days. It was evident that clinical immunity, as measured by the frequency of fever, particularly high intensity fever (> or = 104 degrees F), was increased following reinfection. The parasitologic immunity, as measured by the frequency of asexual parasite counts and gametocyte counts, was also evident. In general, in secondary infections with homologous and/or heterologous strains of P. falciparum, fever episodes > or = 101 degrees F and > or = 104 degrees F were reduced in number, parasitemia was reduced, and gametocyte production was reduced. However, despite long courses of parasitemia during their primary infections, most patients developed fever and, in some cases, high-density parasitemia and gametocytemia following reinfection. The intensity of the secondary response did not appear to be associated with the length of the previous course of parasitemia. In addition, current infection with heterologous strain parasites did not prevent the development of fever or higher density parasite counts following imposition of the new strain of parasite.