Histological Identification of Sequestered Parasitized Red Cells.

The performance of complete post-mortem examinations of children with severe malaria has helped to explain the cause of death in cerebral malaria as well as show the global phenomenon of sequestration in tissues throughout the body, beyond the brain and eye. The pathology of the brain and other organs has been well described and shows a systemic disease with the most catastrophic features found in the brain (i.e., fatal cerebral edema).This chapter describes the materials and methods needed to study the pathological features of tissues outside of the eye, including the brain and other organs. The bulk of these techniques are standard to pathology including gross examination, histology, special stains, and immunohistochemistry.

Neurovascular sequestration in paediatric P. falciparum malaria is visible clinically in the retina.

Retinal vessel changes and retinal whitening, distinctive features of malarial retinopathy, can be directly observed during routine eye examination in children with P. falciparum cerebral malaria. We investigated their clinical significance and underlying mechanisms through linked clinical, clinicopathological and image analysis studies. Orange vessels and severe foveal whitening (clinical examination, n = 817, OR, 95% CI: 2.90, 1.96-4.30; 3.4, 1.8-6.3, both p<0.001), and arteriolar involvement by intravascular filling defects (angiographic image analysis, n = 260, 2.81, 1.17-6.72, p<0.02) were strongly associated with death. Orange vessels had dense sequestration of late stage parasitised red cells (histopathology, n = 29; sensitivity 0.97, specificity 0.89) involving 360° of the lumen circumference, with altered protein expression in blood-retinal barrier cells and marked loss/disruption of pericytes. Retinal whitening was topographically associated with tissue response to hypoxia. Severe neurovascular sequestration is visible at the bedside, and is a marker of severe disease useful for diagnosis and management.

Trypanosoma brucei-Induced apoptosis of leucocytes as a factor of trypanosusceptibility in infected goats.

White blood cell apoptosis has been demonstrated and is suspected to contribute to the decrease in peripheral leukocyte count and the severity of the disease during acute T. brucei infection in rats. Thus, an investigation of blood and tissue leukocyte apoptosis during T. brucei infections in two natural hosts (Red Sokoto (RS) and West African dwarf (WAD) goats (12 per group)), with differing levels of trypanosusceptibility was conducted. Nine out of 12 animals in each breed group were infected intraperitoneally with 104 parasites/mL and euthanized over time points. Blood and tissues were collected for detection and quantitation of apoptosis by three methods (DNA gel electrophoresis, light microscopy and transmission electron microscopy). T. brucei infected RS animals (trypanosusceptible) showed a significant increase in apoptosis of white blood cells (p=0.0092) and splenocytes (p=0.0239). The infected WAD animals (trypanotolerant) also showed a relatively lower but yet still significant (p=0.0022) increase in white blood cell apoptosis. Apart from the liver, significant increase (P<0.05) in tissue cell apoptosis was recorded in infected RS compared to non-infected controls. The mean white blood cell and splenocyte apoptosis was significantly higher (p=0.0072) in RS compared to WAD. In addition, the peak blood cell apoptosis tallied with peak parasitemia and anemia as well as with the lowest leukocyte count in RS animals. Our data support a relationship between peripheral and tissue white blood cell apoptosis and susceptibility to T. brucei infections. The molecular mechanisms mediating apoptosis of host cells during trypanosoma infections may reveal novel therapeutic or vaccine targets.

Severity of retinopathy parallels the degree of parasite sequestration in the eyes and brains of malawian children with fatal cerebral malaria.

BACKGROUND: Malarial retinopathy (MR) has diagnostic and prognostic value in children with Plasmodium falciparum cerebral malaria (CM). A clinicopathological correlation between observed retinal changes during life and the degree of sequestration of parasitized red blood cells was investigated in ocular and cerebral vessels at autopsy. METHODS: In 18 Malawian children who died from clinically defined CM, we studied the intensity of sequestration and the maturity of sequestered parasites in the retina, in nonretinal ocular tissues, and in the brain. RESULTS: Five children with clinically defined CM during life had other causes of death identified at autopsy, no MR, and scanty intracerebral sequestration. Thirteen children had MR and died from CM. MR severity correlated with percentage of microvessels parasitized in the retina, brain, and nonretinal tissues with some neuroectodermal components (all P < .01). In moderate/severe MR cases (n = 8), vascular congestion was more intense (ρ = 0.841; P < .001), sequestered parasites were more mature, and the quantity of extraerythrocytic hemozoin was higher, compared with mild MR cases (n = 5). CONCLUSIONS: These data provide a histopathological basis for the known correlation between degrees of retinopathy and cerebral dysfunction in CM. In addition to being a valuable tool for clinical diagnosis, retinal observations give important information about neurovascular pathophysiology in pediatric CM.