Mixed-species Plasmodium infections of humans

Abstract

We analyzed point-prevalence data from 35 recent studies of human populations in which Plasmodium falciparum and one other Plasmodium species were the reported causes of malaria infections. For the P. falciparum-Plasmodium vivax pair, higher overall prevalence in a human population is associated with fewer mixed-species infections than expected on the basis of the product of individual species prevalences. This is not true for P. falciparum-Plasmodium malariae.

FIGURE 1

Relationships between overall prevalence of infection (horizontal axis) and frequency (vertical axis) of tables that show significant (solid bars) or nonsignificant (hollow bars) differences in mixed-species infections from the expected values for Plasmodium falciparum-Plasmodium vivax. Parts a–d show the results for levels of analysis A, B, C, and D, respectively (see text). The numbers on the horizontal axis represent midpoints of percentage prevalence intervals, e.g., 14.5 represents the interval 10–19%; numbers on the vertical axis represent percentages of the total number of tables within the relevant group (significant or nonsignificant) at that level.

FIGURE 2

Relationships between overall prevalence of infection (horizontal axis) and frequency (vertical axis) of tables that show significant (solid bars) or nonsignificant (hollow bars) differences in mixed-species infections from the expected values for Plasmodium falciparum-Plasmodium malariae for level of analysis A (see text). Conventions are as in Figure 1.

FIGURE 3

An infection-history curve from the malariotherapy treatment of a neurosyphilis patient, case 220–1085 (Boyd and Kitchen, 1937). The vertical axis measures log 10 parasitized-erythrocyte (PE) density (per cc, from microscopy-based estimates); the horizontal axis counts days. The time course of Plasmodium falciparum asexual parasitemia (solid line) and gametocytemia (dashed line) and Plasmodium vivax asexual parasitemia (dotted line) is shown following inoculation of the patient (on day 0) by simultaneous feeding of 1 cage of Anopheles stephensi infectious for P. falciparum and another infectious for P. vivax (each infected for an unspecified period). The estimated detection threshold was 10 PE per cc (hence log 10 PE = 1).