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Neuroepidemiology in Tropical Health

By: , Posted on: November 6, 2017

This book fills the existing void resulting from the lack of publications in two major areas of interests to neurologists worldwide: neuroepidemiology and tropical neurology. It provides substantial and updated information on the peculiar epidemiology and clinical manifestations of the diseases of the nervous system that occur predominantly or exclusively in the tropics.

A large majority of the inhabitants of the world live in the tropics, in regions situated along the Equator, extending 30 degrees latitude North and South between the Tropics of Cancer and Capricorn. Most of South America, Central America and the Caribbean islands, Africa, the Indian subcontinent, Southeast Asia, Papua New Guinea, and parts of Australia and the Pacific islands are situated in the tropics. The tropical climate is characterized by high daytime temperatures and abundant direct sunlight; days and nights of equal length, and absence of four seasons. Mountain ranges, jungles, and deserts provide wide variations in temperature and humidity, and a multitude of ecosystems for a large number of neurologic infections, poisonous animals, and neurotoxic plants capable of affecting the nervous system.

Free Article: “Is Tropical Neurology Specific?”

Although three-quarters of the total world population—or 5.55 billion of the current estimate of 7.4 billion people—live in the tropics, they consume a meager 6% of the worldwide food production. Not surprisingly, malnutrition affects more than 35% of the population in tropical Africa, about 25% of the people in India, and 5%–20% of Latin America and Caribbean populations. Hunger remains a widespread worldwide problem due to drought, famine, poverty, war, displacement of populations, and social unrest. Poverty is the best correlate of undernutrition; half of the world population lives on less than US$2 per day and 20% survive on less than US$1 per day. For this reason, hunger and neurologic problems linked with malnutrition and consumption of drought-resistant neurotoxic plants continue to occur since time immemorial. Contemporary epidemic outbreaks in the tropics, such as the Cuban blindness that affected over 50,000 patients in 1993–94 resulted from economic, political, nutritional, and toxic factors (Román, 2016). Research on this epidemic eventually led to better knowledge of the fragile equilibrium that exists between energy-providing nutrients and the failure of energy-dependent neurons of the optic nerve maculo-papillary bundle.

This book was planned and edited by the Maître–Élève team formed by two of the most prominent experts in the field, Profs. Michel Dumas and Pierre-Marie Preux. Honored in 2015 by the World Federation of Neurology with the Gold Medal for Services to International Neurology, Prof. Michel Dumas is the recognized creator of the specialty of Tropical Neuroepidemiology and Founding Director of the Institute of Neuroepidemiology and Tropical Neurology (IENT) which he launched in 1982 in Limoges, France. Prof. Dumas is a living legend: born in Bamako, Mali (Africa) in 1934, he became a neurologist specializing in tropical medicine under Prof. Henry Collomb in Dakar, Senegal, whom he succeeded as Chairman of Neurology. He trained innumerable generations of neurologists in Francophone Africa, the Pan-Arab nations, Latin America, and Asia. The result of Prof. Dumas’ unfailing teaching and research activities in tropical neurology, parasitic diseases of the nervous system, and epidemiology was the eventual creation of one of the largest networks of tropical neurologists around the world. His disciple and co-editor, Prof. Pierre-Marie Preux MD PhD (Epidemiology and Public Health) is a clinical neurologist specialized in Epidemiology, Biostatistics, Clinical Research, and Tropical Medicine. Prof. Preux succeeded his mentor, Prof. Dumas, as Head of the IENT at the University of Limoges, where he also directs the INSERM UMR1094 Unit on Tropical Neuroepidemiology, and is Head of Clinical Research and Biostatistics at Limoges University Hospital. He has conducted research on numerous tropical diseases with emphasis on epilepsy throughout the tropical world including Africa, South East Asia, and Latin America. P.M. Preux is Professor of Epidemiology and Vice President for Research of the University of Limoges. He is an advisor to the World Health Organization (WHO) and to numerous research organizations in France and other countries. For this book, Preux and Dumas secured the collaboration of an international panel of distinguished experts that provided up-to-date information on their topics of expertise.

Many neurologists practicing in temperate areas of the world in North America and Europe may ask what is the need for a practicing neurologist to obtain information on the epidemiological distribution and the pattern of presentation of tropical neurological diseases. The answer is simple: neurologists around the world are now confronted with formerly “exotic” tropical diseases among travelers, foreign workers, and migrants. In these times of rapid air travel, the exponential increase in international travel and, in particular, ecologic tourism to the tropics, makes it far from exceptional to find neurologic cases of a tropical disease such as malaria in the midst of a heavy snowfall (Román, 2011). Moreover, global warming has recently extended the traditional ecological niche of many arthropod-borne diseases such as West Nile, Dengue, Chikungunya, and Zika. Despite claims to the contrary, global warming is changing the distribution of diseases formerly confined to the tropics.

Hospitals cater for the needs of millions of international business travelers and migrants from tropical countries. Tropical conditions mimic common ailments such as headache, seizures, or low-back pain. Isolated cases of parasitic tropical diseases may occur in recipients of blood transfusions or even organ donations from foreign-born asymptomatic carriers. Therefore, unless the neurologist obtains a history of travel, the correct diagnosis and treatment may be delayed with tragic consequences. Contemporary neurologists must be aware of the manifestations of diseases that are common in other regions of the world, as presented here.

Many tropical countries are underdeveloped producing only 15% of the world’s net revenue. Health indicators such as life expectancy at birth, infantile mortality, and daily caloric intake, access to clean drinking water, literacy, and health expenditures are significantly lower in tropical countries than in industrial nations. These factors explain in part the neuroepidemiological pattern of tropical neurology resulting from problems of illiteracy, malnutrition, deficient sanitation, overcrowding, pollution with neurotoxins and other environmental pollutants, high human immunodeficiency virus (HIV) seroprevalence, as well as frequent waterborne and arthropod-transmitted infections of viral, bacterial, and parasitic origin. The two main determinants of neurological diseases in underdeveloped countries are lack of education and poor socioeconomic conditions (Toro et al., 1983).

Finally, the tropics continue to provide a fertile ground for research on neurological diseases. Two examples of novel neurological conditions recently reported in the tropics are the unexpected neurotropism of the Zika virus and the Nodding Syndrome described in Uganda, currently considered a post-measles brain disorder triggered by malnutrition (Spencer et al., 2016).

Zika virus is a striking example of a true tropical neurological disease producing a pandemic in tropical and temperate regions worldwide. Described 70 years ago, in 1947, in the Zika forest in Uganda, this Flavivirus was considered clinically unimportant given that only 14 human symptomatic cases were reported between 1947 and 2006 ( Smith et al., 2016). The first Zika case in the United States was reported in 2007 in Alaska, in a person infected during the epidemic outbreak in Yap Island in Micronesia. Local transmission of Zika in South America was reported in Brazil in 2015. Transmission was by the bite of mosquitoes Aedes aegypti and Aedes albopictus, who are also carriers of chikungunya and dengue viruses. Rapid spread of the virus throughout the Western Hemisphere resulted in over 650,000 reported cases. On February 1, 2016, the WHO declared Zika a Public Health Emergency of International Concern. In addition to mosquito bites, sexual transmission has been demonstrated and the virus has been isolated in blood, semen and maternal milk. Zika infection is manifested by fever, maculopapular rash, conjunctivitis and rare uveitis, arthralgias, muscle pain, and headache, but about 80% of infections are asymptomatic.

Although other Flaviviruses such as West Nile, yellow fever, Saint Louis encephalitis, dengue, and Japanese encephalitis are capable of producing neurological disease, the broad spectrum of neurological manifestations of Zika virus was unprecedented. Zika virus infection of pregnant women causes microcephaly probably because the virus infects pluripotent neural stem cells. Also, ocular macular abnormalities have been reported in association with microcephaly. Adults may develop Guillain–Barré syndrome (Parra et al., 2016), meningoencephalitis, and myelitis. Preventive measures to avoid mosquito bites and avoidance of unprotected sex are recommended when traveling to endemic areas. Currently there is no treatment available for Zika infection.

FOREWORD written by Gustavo C. Román

Neuroepidemiology in Tropcial Health

This article is an excerpt from the FOREWORD written by Gustavo C. Román in the new book Neuroepidemiology in Tropcial Health, edited by Michel Dumas and Pierre-Marie Preux. We are pleased to offer you a further look into this book with this complimentary chapter called Is Tropical Neurology Specific?”.

 If you would like to view additional chapters, you can do so online via ScienceDirect. If you prefer, you can purchase a print or e-copy from the Elsevier Store. Apply discount code STC317 at checkout and receive up to 30% off the list price and free global shipping. If you are attending the Society for Neuroscience meeting in Washington DC, the book will be on display at Elsevier booth 301.

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