Infectious disease. Siberia's deadly stalker emerges from the shadows

Cerebral Toxocariasis: Silent Progression to Neurodegenerative Disorders?

Toxocara canis and T. cati are highly prevalent nematode infections of the intestines of dogs and cats. In paratenic hosts, larvae do not mature in the intestine but instead migrate through the somatic tissues and organs of the body. The presence of these migrating larvae can contribute to pathology. Toxocara larvae can invade the brains of humans, and while case descriptions of cerebral toxocariasis are historically rare, improved diagnosis and greater awareness have contributed to increased detection. Despite this, cerebral or neurological toxocariasis (NT) remains a poorly understood phenomenon. Furthermore, our understanding of cognitive deficits due to toxocariasis in human populations remains particularly deficient. Recent data describe an enhanced expression of biomarkers associated with brain injury, such as GFAP, AβPP, transforming growth factor β1 (TGF-β1), NF-L, S100B, tTG, and p-tau, in mice receiving even low doses of Toxocara ova. Finally, this review outlines a hypothesis to explore the relationship between the presence of T. canis larvae in the brain and the progression of Alzheimer's disease (AD) due to enhanced AD-associated neurodegenerative biomarker expression.

Communicating hydrocephalus following eosinophilic meningitis is pathogenic for chronic Viliuisk encephalomyelitis in Northeastern Siberia

BACKGROUND

Viliuisk encephalomyelitis (VE) is an endemic neurological disease in Northeast Siberia and generally considered to be a chronic encephalomyelitis of unknown origin actually spreading in the Sakha (Yakutian) Republic.

METHODOLOGY AND PRINCIPLE FINDINGS

In search for the pathophysiology and causative agent of VE, we performed a cross-sectional study on clinical, serological and neuroimaging data on chronic VE patients during two medical expeditions to three villages within the Viliuiski river basin in the Republic of Sakha in 2000 and to the capital Yakutsk in 2006. The severity of the core clinical picture with predominant sensory ataxia, gait apraxia, lower limb spasticity, cognitive impairment and bladder dysfunction correlated with the degree of MRI findings showing enlargement of inner ventricular spaces as in communicating hydrocephalus. Laboratory studies revealed transient eosinophilia during the preceding acute meningitis-like phase, but no ongoing inflammatory process in the CSF. We found immune reactions against Toxocara canis in the majority of chronic VE patients but rarely in controls (P = 0.025; Fisher's exact test). Histological analysis of subacute to subchronic VE brain samples showed eosinophilic infiltrations with no signs of persistent Toxocara canis infection.

CONCLUSIONS AND SIGNIFICANCE

Our data showed that pressure by the communicating hydrocephalus as a mechanical factor is the major pathogenic mechanism in chronic VE, most likely triggered by eosinophilic meningitis. There are no signs for an ongoing inflammatory process in chronic VE. The past eosinophilic reaction in VE might be caused by Toxocara ssp. infection and might therefore represent the first hint for an initial cause leading to the development of chronic VE. Our data provide a framework for future studies and potential therapeutic interventions for this enigmatic epidemic neurological disease potentially spreading in Sakha Republic.

Viliuisk encephalomyelitis in Northeastern Siberia is not caused by Borrelia burgdorferi infection

Viliuisk encephalomyelitis (VE) is an endemic neurological disease in Northeastern Siberia and generally believed to be a chronic encephalomyelitis of unknown origin. We investigated 17 patients with a clinical diagnosis of VE within the Viliuiski region of Sakha (Yakutian) Republic to explore the core clinical syndrome of chronic VE and subsequently whether VE is caused by Borrelia burgdorferi infection. We found a chronic myelopathy as the core of the syndrome, often following an acute phase with a meningo-radiculo-neuropathy, suggestive of chronic neuroborreliosis. A search for inflammatory parameters in a larger cohort in blood (39 VE patients and 41 controls) and CSF samples (10 VE patients and 7 controls) excluded an ongoing chronic infection, but revealed evidence for an immunological scar or a chronic inflammatory ("autoimmune") response in the CSF. In addition, we detected signs of a previous exposure to Borrelia burgdorferi antigens in a subset of chronic VE patients with positive serological results using ELISA/immunoblot in 54/10% and 22/0% of VE patients and controls, respectively (p values of 0.003/0.034; Fisher's exact test). However, CSF analyses did not show a link between exposure or at least immunological reaction against Borrelia and the risk of suffering from VE. Our data provide the first evidence of the presence of Borrelia burgdorferi or similar pathogens in Northeastern Siberia, but do not support a causative role of these pathogens in the aetiopathogenesis of VE.

Evaluating association and transmission of eight inflammatory genes with Viliuisk encephalomyelitis susceptibility

Since the discovery of Viliuisk encephalomyelitis (VE) in 1887, scientists have tried to understand the natural history and aetiology of this endemic neurological disorder among the native Sakha population of Central Siberia. Familial aggregation and segregation analysis suggested a genetic influence on VE incidence. However, recent studies have implicated an unknown virus, possibly from the alpha herpesvirus family, as a possible cause for this disease. As VE is a neurological disease characterized by the inflammatory reactions systematically observed in the spinocerebellar fluid and in the brain tissue of deceased patients, we examined 17 single nucleotide polymorphisms (SNPs) across seven inflammation-related candidate gene regions, including chemokine receptors type 2 and 5 (CCR2/CCR5), interferon-gamma (IFN-gamma), interleukin-4 (IL-4), IL-6, IL-10, stromal cell-derived factor (SDF) and chemokine regulated upon activation, normal T-cell expressed and presumably secreted (RANTES). Our main objective was to analyse the degree of genetic association between VE and candidate genes that have been previously implicated in other inflammatory diseases. Samples were collected from 83 affected families comprising 88 verified VE cases, 156 family members, and an additional 69 unrelated, unaffected inhabitants of the same geographical area. This collection included substantially all of the cases that are currently on the VE Registry. The experimental design included both case-control and transmission/disequilibrium test (TDT)-based familial association analyses. None of 17 SNPs analysed was significantly associated with VE occurrence. Exclusion of these eight genes based on the lack of association has important implications for identifying the disease agent, as well as prescribing therapy and understanding Viliuisk encephalomyelitis.