Neuroparasitology And Tropical Neurology

Neuroparasitology and Tropical Neurology, a new volume in The Handbook of Clinical Neurology, provides a comprehensive and contemporary reference on parasitic infections of the human nervous system. Parasitic infections are varied and some are resolved by the host’s immune system, other infections may become established even though unnoticed, and some cause severe disease and death. In our modern world, neuroparasitoses are no longer geographically isolated and these infections now appear worldwide. Outside of a very few well understood pathologies, most parasitic infections have been neglected in the neurological literature and most neurologists have never diagnosed such an infection. This volume details how, with the advent of modern neuroimaging techniques, improved diagnostic applications of molecular biology, more accurate immunodiagnosis, and minimally invasive neurosurgery, human nervous system parasitoses are now diagnosed and treated, with increasing frequency. The book is divided into six sections, and begins with an introduction to the mechanisms of infection, diagnosis, and pathology of parasitic diseases. Subsequent chapters detail protozoan diseases and a section covering each of the major classes of human-infecting helminths: nematodes (roundworms), trematodes (flukes), and cestodes (tapeworms). The final section contains chapters on other important areas of tropical clinical medicine including the neurological complications of venomous bites and tropical nutritional deficiencies. Neuroparasitology and Tropical Neurology will be of interest to neurologists, neurosurgeons and other health professionals encountering patients with parasitic infections. A comprehensive reference resource on the diagnosis and treatment of parasitic infections of the human nervous system Focuses on the impact of modern neuroimaging techniques, improved diagnostic applications of molecular biology, more accurate immunodiagnosis, and minimally invasive neurosurgery to diagnose parasitoses International list of contributors including the leading workers in the field

Cysticercosis, an infection caused by the cystic larvae of the pork tapeworm Taenia solium, is one of the most frequent parasitic infections of the human nervous system (neurocysticercosis). It is endemic in most of Latin America, the sub-Saharan Africa, and vast parts of Asia, including the Indian subcontinent. It has also been increasingly diagnosed in developed countries because of migration of people from endemic zones and exposure in travelers. The life cycle involves the development of the adult tapeworm in the human small intestine (after ingesting infected pork with cysts) and larval infection in pig tissues (after ingesting human stools containing the eggs of the tapeworm). Humans get infected by the fecal-oral route, most often from a direct contact with an asymptomatic Taenia carrier. Most common clinical presentations are seizures (particularly late-onset seizures), chronic headaches, and intracranial hypertension. However, cysticerci can locate anywhere in the human nervous system, thus potentially causing almost any neurological syndrome and making clinical diagnosis a difficult task. Neuroimaging is the main diagnostic tool, and specific serology confirms the diagnosis and helps to define the diagnosis when images are unclear. Factors such as location (extraparenchymal versus intraparenchymal), number, size and evolutive stage of the parasites determine the clinical manifestations, therapeutic approach, and prognosis. Management includes symptomatic drugs (analgesics, antiepileptic drugs, anti-inflammatory agents) and in many cases cysticidal drugs, either albendazole or praziquantel. In recent years, efforts have focused on transmission control and potential elimination in endemic regions.

Human African trypanosomiasis or sleeping sickness is a neglected tropical disease that affects populations in sub-Saharan Africa. The disease is caused by infection with the gambiense and rhodesiense subspecies of the extracellular parasite Trypanosoma brucei, and is transmitted to humans by bites of infected tsetse flies. The disease evolves in two stages, the hemolymphatic and meningoencephalitic stages, the latter being defined by central nervous system infection after trypanosomal traversal of the blood–brain barrier. African trypanosomiasis, which leads to severe neuroinflammation, is fatal without treatment, but the available drugs are toxic and complicated to administer. The choice of medication is determined by the infecting parasite subspecies and disease stage. Clinical features include a constellation of nonspecific symptoms and signs with evolving neurological and psychiatric alterations and characteristic sleep–wake disturbances. Because of the clinical profile variability and insidiously progressive central nervous system involvement, disease staging is currently based on cerebrospinal fluid examination, which is usually performed after the finding of trypanosomes in blood or other body fluids. No vaccine being available, control of human African trypanosomiasis relies on diagnosis and treatment of infected patients, assisted by vector control. Better diagnostic tools and safer, easy to use drugs are needed to facilitate elimination of the disease.

Trichinellosis is a parasitic zoonosis caused by the nematode Trichinella spp. Neurotrichinellosis represents one of the most important complications of severe trichinellosis in humans and is sometimes fatal, especially when Trichinella spiralis is involved. There are numerous mechanisms responsible for the involvement of the nervous system through direct or indirect involvement of the parasite. In the latter, inflammatory cells, especially eosinophils, appear to play a crucial role. Encephalopathy, neuromuscular disturbances, and ocular involvement represent the most frequent presentations of neurotrichinellosis, with the first being the most responsible for fatalities. The diagnosis is based on imaging (CT or MRI), which shows nodular multifocal hypodensities in serologically positive individuals with relevant epidemiological factors (e.g., consumption of raw pork). However, only direct diagnosis by muscle biopsy can give the absolute certainty of infection. Albendazole and mebendazole are the anthelminthic of choice and should be used with corticosteroids to prevent allergic manifestations.

Fascioliasis is a worldwide, zoonotic disease caused by the liver trematodes Fasciola hepatica and Fasciola gigantica. Neurological fascioliasis has been widely reported in all continents, affecting both sexes and all ages. Two types of records related to two physiopathogenic mechanisms may be distinguished: cases in which the neurological symptoms are due to direct effects of a migrating juvenile present in the brain or neighboring organ and with cerebral lesions suggesting migration through the brain; and cases with neurological symptoms due to indirect immuno-allergic and toxic effects at distance from flukes in the liver. Neurological manifestations include minor symptoms, mainly cephalalgias, and major symptoms which are nonspecific, extremely diverse, varying from one patient to another and even within the same patient, and comprising meningeal manifestations and impressive neurological manifestations. The puzzling neurological polymorphism leads to confusion with cerebral tumors, multiple sclerosis, lesions of the brainstem, or cerebro-meningeal hemorrhages. Only blood eosinophilia and information on infection source guide toward correct diagnosis by appropriate coprological and/or serological techniques. Although neurological patients usually recover after fasciolicide treatment or surgical worm extraction, sequelae, which are sometimes important, remain in several patients. The need to include possible neurological complications within the general frame of fascioliasis becomes evident.

Toxoplasma gondii, an Apicomplexan, is a pathogic protozoan that can infect the central nervous system. Infection during pregnancy can result in a congenial infection with severe neurological sequelae. In immunocompromisedindividuals reactivation of latent neurological foci can result in encephalitis. Immunocompetent individuals infected with T. gondii are typically asymptomatic and maintain this infection for life. However, recent studies suggest that these asymptomatic infections may have effects on behavior and other physiological processes. Toxoplasma gondii infects approximately one-third of the world population, making it one of the most successful parasitic organisms. Cats and other felidae serve as the definite host producing oocysts, an environmentally resistant life cycle stage found in cat feces, which can transmit the infection when ingested orally. A wide variety of warm-blooded animals, including humans, can serve as the intermediate host in which tissue cysts (containing bradyzoites) develop. Transmission also occurs due to ingestion of the tissue cysts. There are three predominant clonal lineages, termed Types I, II and III, and an association with higher pathogenicity with the Type I strains in humans has emerged. This chapter presents a review of the biology of this infection including the life cycle, transmission, epidemiology, parasite strains, and the host immune response. The major clinical outcomes of congenital infection, chorioretinitis and encephalitis, and the possible association of infection of toxoplasmosis with neuropsychiatric disorders such as schizophrenia, are reviewed.

Parasitic infections of the central nervous system (CNS) have increased over the last couple of decades, partly due to a drop in the living conditions of large populations in the world and the AIDS epidemic. Parasitic infections of the CNS are indolent and often life threatening, hence, an early diagnosis is imperative. While brain biopsy and laboratory analysis remain the gold standard for diagnosis, neuroimaging contributes significantly to diagnosis and follow-up. Imaging can demonstrate the extent of infection and complications and possibly, the type of parasitic infection when characteristic features are evident. The disappearance of the parasite or inflammation, gliosis, and/or calcification suggest a therapeutic response. The initial experience of the CT scan has been greatly enhanced by MRI which is currently the imaging modality of choice. This has been due to the greater tissue contrast resolution of MRI and its ability to detect subtle changes in the tissue parenchyma. Advanced techniques such as diffusion-weighted imaging (DWI), perfusion imaging (PI), MR angiography (MRA), and MR spectroscopy (MRS) have been used to improve the sensitivity for characterizing the type, viability, and burden of the parasites and the host tissue response. Additionally, it is possible to demonstrate the complications of the primary infection and those secondary to treatment, in some cases.

Neglected tropical diseases are a group of mostly infectious diseases that thrive among poor populations in tropical countries. A significant proportion of the conditions affecting the neurological system in such countries can be attributed to neglected tropical diseases of helminth, protozoan, bacterial, or viral origin. The neurological burden of neglected tropical diseases has not been thoroughly investigated yet, but is expected to be significant; its full appreciation, estimation, and recognition present significant challenges, as shown by the case of the “silent epidemic” of epilepsy. While tropical infections involving the nervous system are today largely preventable or treatable, as vaccines or chemotherapeutic agents are available to kill or neutralize the responsible agents, associated morbidity – when established – cannot be cured. In resource-poor settings it is likely that many infections will not be treated and will therefore progress into their advanced and severe stages, thus being increasingly associated with irreversible morbidity; this is also the case for neurological morbidity, which often entails permanent disability. Public health should aim at reducing the burden of tropical neurological diseases through interventions addressing the infection, the associated morbidity, and the disability deriving from it.