Tropical Neurology

Tropical neurology refers to those diseases of the nervous system which prevail in between the Tropics of Cancer and Capricorn. Developments in speed and ease of travel and globalisation of economy have resulted in large scale migration rendering the boundaries of tropical regions less distinct. Wars, famines, natural disasters and economic sanctions have added to the problem of infection and aggravated the preexisting nutritional deficiency disorders in many tropical countries. This book is aimed at residents, practicing physicians, health workers and physicians from western countries who are visiting the tropical countries.

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.

Tropical neurology refers to those diseases of the nervous system which prevail in between the Tropics of Cancer and Capricorn. Developments in speed and ease of travel and globalisation of economy have resulted in large scale migration rendering the boundaries of tropical regions less distinct. Wars, famines, natural disasters and economic sanctio

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

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.

Filarial infections cause a huge public health burden wherever they are endemic. These filaria may locate anywhere in the human body. Their manifestations and pathogenic mechanisms, except the most common ones, are rarely investigated systematically. Their neurological manifestations, however, are being increasingly recognized particularly with onchocerciasis or Loa loa infections, Wuchereria bancrofti, or Mansonella perstans. The risk of developing these manifestations may also increase in cases that harbor multiple filariasis or coinfections, for instance as with Plasmodium. The microfilaria of Onchocerca and Loa loa are seen in cerebrospinal fluid. The pathogenesis of neurological manifestations of these infections is complex; however, pathogenic reactions may be caused by mechanical disruption, e.g., degeneration often followed by granulomas, causing fibrosis or mass effects on other tissues, vascular lesions, e.g., vascular block of cerebral vessels, or disordered inflammatory responses resulting in meningitis, encephalitis or localized inflammatory responses. The chances of having neurological manifestations may also depend upon the frequency and“heaviness”of infection over a lifetime. Hence, this type of infection should no longer be considered a disease of the commonly affected areas but one that may produce systemic effects or other manifestations, and these should be considered in populations where they are endemic.

About three-fourths of the total world population live in the tropics but consume only 6% of worldwide food production and contribute 15% of the world's net revenue explaining the short life expectancy, high infantile mortality, and poor daily caloric intake; moreover, lack of clean drinking water and deficient sanitation promote water-borne infections, diarrhea, and risk of malabsorption that contribute to the prevalence of malnutrition in the tropics. One-third of the world's population consumes insufficient iodine increasing the risk for mental retardation and deafness due to maternal hypothyroidism. The main nutritional syndromes comprise protein-energy malnutrition (marasmus and kwashiorkor); nutritional neuropathies, myelopathies and neuromyelopathies, as well as specific deficiencies of vitamins and micronutrients including iodine, iron, zinc, and selenium.