Impact of malaria on the brain and its prevention

Cerebral malaria induces electrophysiological and neurochemical impairment in mice retinal tissue: possible effect on glutathione and glutamatergic system

Background

Cerebral malaria (CM) is a severe complication resulting from Plasmodium falciparum infection. This condition has usually been associated with cognitive, behavioural and motor dysfunctions, being the retinopathy the most serious consequence resulting from the disease. The pathophysiological mechanisms underlying this complication remain incompletely understood. Several experimental models of CM have already been developed in order to clarify those mechanisms related to this syndrome. In this context, the present work has been performed to investigate which possible electrophysiological and neurochemistry alterations could be involved in the CM pathology.

Methods

Experimental CM was induced in Plasmodium berghei-infected male and female C57Bl/6 mice. The survival and neurological symptoms of CM were registered. Brains and retina were assayed for TNF levels and NOS2 expression. Electroretinography measurements were recorded to assessed a- and b-wave amplitudes and neurochemicals changes were evaluated by determination of glutamate and glutathione levels by HPLC.

Results

Susceptible C57Bl/6 mice infected with ≈ 10⁶ parasitized red blood cells (P. berghei ANKA strain), showed a low parasitaemia, with evident clinical signs as: respiratory failure, ataxia, hemiplegia, and coma followed by animal death. In parallel to the clinical characterization of CM, the retinal electrophysiological analysis showed an intense decrease of a- and-b-wave amplitude associated to cone photoreceptor response only at the 7 days post-infection. Neurochemical results demonstrated that the disease led to a decrease in the glutathione levels with 2 days post inoculation. It was also demonstrated that the increase in the glutathione levels during the infection was followed by the increase in the ³H-glutamate uptake rate (4 and 7 days post-infection), suggesting that CM condition causes an up-regulation of the transporters systems. Furthermore, these findings also highlighted that the electrophysiological and neurochemical alterations occurs in a manner independent on the establishment of an inflammatory response, once tumour necrosis factor levels and inducible nitric oxide synthase expression were altered only in the cerebral tissue but not in the retina.

Conclusions

In summary, these findings indicate for the first time that CM induces neurochemical and electrophysiological impairment in the mice retinal tissue, in a TNF-independent manner.

Unexpected hosts: imaging parasitic diseases

Radiologists seldom encounter parasitic diseases in their daily practice in most of Europe, although the incidence of these diseases is increasing due to migration and tourism from/to endemic areas. Moreover, some parasitic diseases are still endemic in certain European regions, and immunocompromised individuals also pose a higher risk of developing these conditions. This article reviews and summarises the imaging findings of some of the most important and frequent human parasitic diseases, including information about the parasite's life cycle, pathophysiology, clinical findings, diagnosis, and treatment. We include malaria, amoebiasis, toxoplasmosis, trypanosomiasis, leishmaniasis, echinococcosis, cysticercosis, clonorchiasis, schistosomiasis, fascioliasis, ascariasis, anisakiasis, dracunculiasis, and strongyloidiasis. The aim of this review is to help radiologists when dealing with these diseases or in cases where they are suspected. Teaching Points • Incidence of parasitic diseases is increasing due to migratory movements and travelling. • Some parasitic diseases are still endemic in certain regions in Europe. • Parasitic diseases can have complex life cycles often involving different hosts. • Prompt diagnosis and treatment is essential for patient management in parasitic diseases. • Radiologists should be able to recognise and suspect the most relevant parasitic diseases.

Cannabidiol increases survival and promotes rescue of cognitive function in a murine model of cerebral malaria

Cerebral malaria (CM) is a severe complication resulting from Plasmodium falciparum infection that might cause permanent neurological deficits. Cannabidiol (CBD) is a nonpsychotomimetic compound of Cannabis sativa with neuroprotective properties. In the present work, we evaluated the effects of CBD in a murine model of CM. Female mice were infected with Plasmodium berghei ANKA (PbA) and treated with CBD (30mg/kg/day - 3 or 7days i.p.) or vehicle. On 5th day-post-infection (dpi), at the peak of the disease), animals were treated with single or repeated doses of Artesunate, an antimalarial drug. All groups were tested for memory impairment (Novel Object Recognition or Morris Water Maze) and anxiety-like behaviors (Open field or elevated plus maze test) in different stages of the disease (at the peak or after the complete clearance of the disease). Th1/Th2 cytokines and neurotrophins (brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF)) were measured in the prefrontal cortex and hippocampus of experimental groups. PbA-infected mice displayed memory deficits and exhibited increase in anxiety-like behaviors on the 5dpi or after the clearance of the parasitemia, effects prevented by CBD treatment. On 5dpi, TNF-α and IL-6 increased in the hippocampus, while only IL-6 increased in the prefrontal cortex. CBD treatment resulted in an increase in BDNF expression in the hippocampus and decreased levels of proinflammatory cytokines in the hippocampus (TNF-α) and prefrontal cortex (IL-6). Our results indicate that CBD exhibits neuroprotective effects in CM model and might be useful as an adjunctive therapy to prevent neurological symptoms following this disease.

In vivo imaging in NHP models of malaria: challenges, progress and outlooks

Animal models of malaria, mainly mice, have made a large contribution to our knowledge of host-pathogen interactions and immune responses, and to drug and vaccine design. Non-human primate (NHP) models for malaria are admittedly under-used, although they are probably closer models than mice for human malaria; in particular, NHP models allow the use of human pathogens (Plasmodium falciparum, Plasmodium vivax, Plasmodium malariae and Plasmodium knowlesi). NHPs, whether natural hosts or experimentally challenged with a simian Plasmodium, can also serve as robust pre-clinical models. Some simian parasites are closely related to a human counterpart, with which they may share a common ancestor, and display similar major features with the human infection and pathology. NHP models allow longitudinal studies, from the early events following sporozoite inoculation to the later events, including analysis of organs and tissues, particularly liver, spleen, brain and bone marrow. NHP models have one other significant advantage over mouse models: NHPs are our closest relatives and thus their biology is very similar to ours. Recently developed in vivo imaging tools have provided insight into malaria parasite infection and disease in mouse models. One advantage of these tools is that they limit the need for invasive procedures, such as tissue biopsies. Many such technologies are now available for NHP studies and provide new opportunities for elucidating host/parasite interactions. The aim of this review is to bring the malaria community up to date on what is currently possible and what soon will be, in terms of in vivo imaging in NHP models of malaria, to consider the pros and the cons of the various techniques, and to identify challenges.

Therapy of falciparum malaria in sub-saharan Africa: from molecule to policy

The burden of falciparum malaria remains as great as ever, and, as has probably always been the case, it is carried mainly by tropical Africa. Of the various means available for the control of malaria, the use of effective drugs remains the most important and is likely to remain so for a considerable time to come. Unfortunately, the extensive development of resistance by the parasite threatens the utility of most of the affordable classes of drug: the development of novel antimalarials has never been more urgently needed. Any attempt to understand the vast complexities of falciparum malaria in Africa requires an ability to think "from molecule to policy." In consequence, the review ambitiously tries to examine the current pharmacopeia, the process by which new drugs are developed and the ways in which drugs are actually used, in both the formal and informal health sectors. The informal sector is particularly important in Africa, where around half of all antimalarial treatments are bought from informal outlets and taken at home without supervision by health care professionals: the potential impact of adherence on clinical outcome is discussed. Given that the full costs are carried by the patient in a large proportion of cases, the importance of drug affordability is explored. The review also discusses the splicing of new drugs into national policy. The various parameters that feed into deliberations on changes in drug policy are discussed.

Epilepsy and comorbidity: infections and antimicrobials usage in relation to epilepsy management

Infections are probably the most common preventable cause of epilepsy worldwide. There are concerns that endemic infections and infestations, such as malaria and neurocysticercosis, could be responsible for the increased incidence of epilepsy in the developing world. Cases of epilepsy associated with neurocysticercosis are also being seen increasingly in developed countries due to migration from, and travel to, endemic areas. When prescribing antimicrobial agents in patients with epilepsy a number of issues need to be considered, such as potential adverse effects on seizure control and interactions with concomitant antiepileptic drugs (AEDs). Some antimicrobial agents, including penicillins, cephalosporins, carbapenems, quinolones and antimalarials, can have proconvulsant activity and may precipitate seizures, even in patients who do not have epilepsy. Moreover, many antimicrobials increase or decrease the plasma levels of AEDs, whereas some AEDs may adversely affect the efficacy of antimicrobials.

Imported malaria in southern Taiwan from 1991 to 2002: a single hospital's experience

Malaria, a major public health problem worldwide, is a predominant infectious disease in most tropical and subtropical countries. Before 1965, Taiwan was a hyperendemic area, but most cases are now imported. We present our experience of dealing with various malaria infections. Charts of malaria patients visiting university hospitals in southern Taiwan between January 1991 and June 2002 were available for review. All diagnoses were made by positive blood smear and detailed history that included countries visited, paroxysm of symptoms, and medical treatment. Seventeen patients, 6 women and 11 men (mean age, 32.3 +/- 11.8 years), were enrolled. Six were infected with Plasmodium falciparum, eight with Plasmodium vivax, two with a combination of P. falciparum and P. vivax, and one with an unidentified infection. All Taiwanese patients infected with P. falciparum (n = 5) contracted the disease in Africa or Indonesia. All Taiwanese patients infected with P. vivax (n = 4) contracted the disease in Southeast Asia or Oceania. Fever and chills were the leading symptoms of malaria. P. falciparum infection was treated with quinine and doxycycline/tetracycline, with the addition of artesunate for cerebral malaria. P. vivax infection was treated with chloroquine and primaquine. Maintaining a high degree of suspicion in patients with a history of travel to malaria-endemic areas is the major cornerstone of malaria diagnosis. Erroneous diagnosis and improper treatment leads to greater morbidity and even mortality.

Routine anticonvulsants for treating cerebral malaria

BACKGROUND

Cerebral malaria is a common complication of Plasmodium falciparum infection, and kills over a million people every year. People with cerebral malaria become unconscious, and often have protracted convulsions. It is unclear whether giving anticonvulsant drugs routinely to people with cerebral malaria will improve the outcome of treatment and prevent death.

OBJECTIVES

To evaluate the effect of routine anticonvulsant drugs in people with cerebral malaria.

SEARCH STRATEGY

We searched the Cochrane Infectious Diseases Group specialized trials register (November 2001), The Cochrane Controlled Trials Register (Issue 4, 2001), MEDLINE (1966 to November 2001), EMBASE (1988 to October 2001), LILACS (2001, 40a Edition CD-ROM), Science Citation Index (November 2001), African Index Medicus (1999), reference lists of articles, and research organizations. We also contacted the authors for addtional information.

SELECTION CRITERIA

Randomized and quasi-randomized controlled trials of people with cerebral malaria. The trials compared anticonvulsant drugs started on admission to hospital with no anticonvulsant drug or placebo.

DATA COLLECTION AND ANALYSIS

Two reviewers independently extracted data from those trials eligible for inclusion. We assessed the methodological quality of the included trials by considering allocation sequence, concealment of allocation, blinding, and inclusion of all randomized participants. We used Review Manager (version 4.1) for the meta-analysis and also explored possible sources of heterogeneity.

MAIN RESULTS

Three trials with a total of 573 participants met the inclusion criteria. These trials all compared phenobarbitone with placebo or no treatment. In the two trials with adequate allocation concealment, death was more common in the anticonvulsant group (Relative Risk 2.0; 95% confidence interval 1.20 to 3.33; fixed effect model). In all three trials, phenobarbitone compared with placebo or no treatment was associated with fewer convulsions (Relative Risk 0.30; 95% confidence interval 0.19 to 0.45; fixed effect model).

REVIEWER'S CONCLUSIONS

Routine phenobarbitone in cerebral malaria is associated with fewer convulsions but possibly more deaths. Further trials with adequate design, more participants, and different doses of anticonvulsant drugs are needed.