The distribution and intensity of parasite sequestration in comatose Malawian children

Abstract

Background: The sequestration of Plasmodium falciparum-infected erythrocytes in capillary beds is a characteristic feature of severe malaria and is believed to be central to disease pathogenesis. Sequestration occurs in all P. falciparum infections, including those in asymptomatic individuals. Therefore, sequestration cannot be the sole determinant of severe disease; the intensity or distribution of infected erythrocytes may also contribute. Discerning the relationship between sequestration and well-defined clinical syndromes may enhance understanding of disease mechanisms.

Methods: We measured the concentration of parasite-derived lactate dehydrogenase (pLDH) in tissue samples obtained at autopsy from patients with clinically defined cerebral malaria. On the basis of the autopsy findings, patients were divided into 2 groups: those with an identifiable, nonmalarial cause of death and those without, who were presumed to have died of cerebral malaria. The concentration of pLDH, as determined by enzyme-linked immunosorbent assay, was used to estimate parasite load in different organs.

Results: When pLDH could be detected, the parasite load was higher in patients with presumed cerebral malaria than in parasitemic patients with assumed cerebral malaria with a nonmalaria cause of death identified at autopsy (P<.05 for brain, intestine, and skin).

Conclusions: These findings suggest that sequestration in patients with fatal cerebral malaria occurs in multiple organs and does not reflect a predilection in the parasite for the cerebral vasculature.

Figure 1

Reproducibility of parasite-derived lactate dehydrogenase (pLDH) ELISA assay. Twelve known quantities of parasites were assayed for pLDH concentrations on 5 consecutive days (as denoted by each line). Samples were measured in triplicate on each day.

Figure 2

Comparison of parasite loads in the brain, estimated by parasite counting and parasite-derived lactate dehydrogenase (pLDH) ELISA methods. Parasite count reflects the no. of parasites seen per 100 cross-sectional capillaries, whereas pLDH ELISA represents parasite protein per milligram of tissue.

Figure 3

Comparison of concentrations of parasite-derived lactate dehydrogenase (pLDH) in various organs. Autopsy nos. are classified as presumed cerebral malaria (CM) or assumed cerebral malaria with nonmalaria causes of death (NMCD). Colors denote different tissues, and pLDH levels per milligram of each tissue are represented by lengths of bars.

Figure 4

Dot plots comparing parasite-derived lactate dehydrogenase concentrations in brain cortex (A), intestine (C), and skin (E) of patients with presumed cerebral malaria (CM) or with assumed cerebral malaria with nonmalaria causes of death (NMCD). The means are represented numerically (i.e., 64, 39, and 25) and by horizontal bars. Shown are hematoxylin-eosin–stained sections of brain cortex (B), intestine (D), and skin (F) of a patient with cerebral malaria showing abundant sequestration (×200, with ×1000 inset).