An ultrastructural study of the brain in fatal Plasmodium falciparum malaria.

Cerebral malaria (CM) is a major cause of death in severe Plasmodium falciparum malaria. We present quantitative electron microscopic findings of the neuropathologic features in a prospective clinicopathologic study of 65 patients who died of severe malaria in Thailand and Vietnam. Sequestration of parasitized red blood cells (PRBCs) in cerebral microvessels was significantly higher in the brains of patients with CM compared with those with non-cerebral malaria (NCM) in all parts of the brain (cerebrum, cerebellum, and medulla oblongata). There was a hierarchy of sequestration with more in the cerebrum and cerebellum than the brain stem. When cerebral sequestration was compared with the peripheral parasitemia pre mortem, there were 26.6 times more PRBCs in the brain microvasculature than in the peripheral blood. The sequestration index was significantly higher in CM patients (median = 50.7) than in NCM patients (median = 6.9) (P = 0.042). The degree of sequestration of P. falciparum-infected erythrocytes in cerebral microvessels is quantitatively associated with pre-mortem coma.

Redox-dependent apoptosis in human endothelial cells after adhesion of Plasmodium falciparum-infected erythrocytes.

During Plasmodium falciparum infection leading to cerebral malaria, mechanisms such as cytokine generation and cytoadherence of parasitized red blood cells (PRBC) to post-capillary venules are clearly involved. We demonstrated that PRBC adhesion to human lung endothelial cells (HLEC) upregulated TNF-alpha superfamily genes and genes related to apoptosis and inflammation. Apoptosis was confirmed by standard techniques (annexin-V binding, genomic DNA fragmentation, and caspases activation). This apoptotic process involved the cytoplasmic pathway from a death receptor (DR-6, Fas, TNF-R1) through caspase 8, and the mitochondrial pathway though Bad and caspase 9 activation. Oxidative stress has been implicated in apoptosis induction in various pathological models. Superoxide anion (O(2)*(-)) is a key molecule in the oxidative stress pathway which can form peroxynitrites (ONOO(-)) in association with nitric oxide (NO*). Even though the role of NO* in malaria physiopathology is still a matter of controversy, we demonstrated that PRBC-induced apoptosis in endothelial cells is mediated through an oxidative stress pathway. The inhibition of NO* synthesis protected the endothelial cells suggesting a deleterious role for NO*. In addition, the superoxide dismutase mimetic, MnTBAP, also protected the HLEC against PRBC-induced apoptosis, revealing the role of O(2)*(-) and ONOO(-).

Invasion of skin by Schistosoma cercariae.

Schistosomiasis caused by Schistosoma spp. remains a major global health problem affecting >200 million people. The success of these parasites is a result of their adaptation to several different environments, including snail tissue, fresh water and mammalian blood; and their ability to switch between these environments rapidly. The initial step in infection of the human host involves penetration of the human skin by the aquatic form of Schistosoma, the cercaria. This aspect of host invasion is remarkable because no wounds or insect vectors are required and cercariae can penetrate through intact skin rapidly. The mechanisms of host finding and invasion represent fascinating and complex biological phenomenon, which are discussed here.

Lesions caused by cardiovascular flukes (Digenea: Spirorchidae) in stranded green turtles (Chelonia mydas).

Evidence of infection with spirorchid flukes (Digenea: Spirorchidae) was sought at necropsy of 96 stranded green turtles, Chelonia mydas, that were examined during the course of a survey of marine turtle mortality in southeastern Queensland, Australia. Three species of spirorchid (Hapalotrema mehrai, H. postorchis, and Neospirorchis schistosomatoides) were identified. Severe disease due to spirorchid fluke infection (spirorchidiasis) was implicated as the principal cause of mortality in 10 turtles (10%), and appeared to be one of multiple severe problems in an additional 29 turtles (30%). Although flukes were observed in only 45% of stranded C. mydas in this study, presumed spirorchid fluke infection was diagnosed in an additional 53% of turtles, based principally on characteristic necropsy lesions and to a lesser extent on the histopathological detection of spirorchid eggs. Characteristic necropsy lesions included miliary spirorchid egg granulomas, which were observed most readily on serosal surfaces, particularly of the small intestine. Cardiovascular lesions included mural endocarditis, arteritis, and thrombosis, frequently accompanied by aneurysm formation. Resolution of thrombi was observed to occur via a combination of granuloma formation about indigestible components (spirorchid fluke egg shells) and exteriorization through the vessel wall, which resulted in granulomatous nodules on the adventitial surface. Septic aortic thrombosis complicated by disseminated bacterial infection, observed in five turtles, was recorded for the first time. Egg granulomas were ubiquitous in turtle tissues throughout this study. Although they generally appeared to be mild or incidental lesions, they were occasionally associated with severe multifocal granulomatous pneumonia or meningitis.

Cerebral malaria in mice: demonstration of cytoadherence of infected red blood cells and microrheologic correlates.

To understand the microcirculatory events during cerebral malaria, we have studied the lethal strain of rodent Plasmodia, Plasmodium yoelii 17XL, originally described by Yoeli and Hargreaves in 1974. The virulence of P. yoelii 17XL is caused by intravascular sequestration of infected red blood cells (IRBCs), especially in the brain vessels and capillaries. This mouse model resembles human P. falciparum infection more closely than P. berghei ANKA infection since it shows little, if any, inflammation of the brain. In vivo microcirculatory studies on cytoadherence of IRBCs were performed using the cremaster muscle preparation, which is an easily accessible vasculature for intravital observations. Ex vivo assay of cytoadherence was carried out in the artificially perfused mesocecum preparation of the rat. The results in either preparation demonstrated cytoadherence of IRBCs that was restricted to postcapillary venules. Furthermore, the in vivo measurements showed the prevalence of cytoadherence in small-diameter (< 40 microns) venules in accordance with the local wall shear rates. The parasitized animals demonstrated significantly reduced red blood cell velocities and wall shear rates in the small-diameter postcapillary venules of the cremaster. The relationship between cytoadherence and venular wall shear rates was also reflected in the inverse correlation between the number of adhered cells and the venular diameter in the ex vivo mesocecum preparation. In the ex vivo preparation, cytoadherence of IRBCs was accompanied by a higher peripheral resistance. Transmission electron microscopy of the cremaster muscle and brain tissues showed a tight association of IRBCs with the endothelium of small venules. These observations demonstrate that cytoadherence of P. yoelii 17XL-infected mouse red blood cells is very similar to that of P. falciparum-infected cells. Thus, this model should allow a detailed analysis of the molecular mechanisms involved in the generation of cerebral malaria by cytoadherence of the infected red blood cells to the vascular endothelium.

Clinical diagnosis of schistosomiasis in Sudanese cattle.

This study was done in the White Nile Province to characterise the history and signs of naturally occurring Schistosoma bovis infection in cattle (Gorag). Necropsy and laboratory examinations were performed on 10 animals six to 30 months of age which were in poor condition. They were selected because of a history suggestive of schistosomiasis. All the animals showed some degree of S. bovis infection; eight had a moderate or heavy degree of infection. Also all had liver damage due to either past or active Fasciola gigantica infection. Although concurrent infection with these two trematodes is common an owner who diagnoses Gorag is most likely referring to the syndrome caused by S. bovis as being the major cause of the poor performance observed. Fasciolicide treatment may eliminate active fascioliasis as the principal damaging agent. Also differentiating signs of haemorrhagic diarrhoea, severely sunken eyed appearance and only moderate inappetence are common in animals with acute schistosomiasis.