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 (^ 104 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> 101 F and S: 104 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.

Previously, 1 we reported on a retrospective study of the clinical records of 318 neurosyphilitic patients who were treated by infection with the El Limon, Santee Cooper, and McLendon strains of Plasmodium falciparum either via sporozoite or trophozoite inoculation. No records indicated that these patients had been infected previously with Plasmodium. Here, we report a similar examination of the clinical records of patients reinfected with homologous and heterologous strains of P. falciparum. These studies were conducted at the National Institutes of Health laboratories in Columbia, South Carolina and Milledgeville, Georgia during the period 1940 to 1963.