key: cord-0750040-2l9hyhq0 authors: Zumla, Alimuddin; Ustianowski, Andrew title: Tropical Diseases: Definition, Geographic Distribution, Transmission, and Classification date: 2012-04-23 journal: Infect Dis Clin North Am DOI: 10.1016/j.idc.2012.02.007 sha: fce58a99363504edbe30a4ccc234e84cdb398e13 doc_id: 750040 cord_uid: 2l9hyhq0 The term tropical diseases encompasses all diseases that occur principally in the tropics. This term covers all communicable and noncommunicable diseases, genetic disorders, and disease caused by nutritional deficiencies or environmental conditions (such as heat, humidity, and altitude) that are encountered in areas that lie between, and alongside, the Tropic of Cancer and Tropic of Capricorn belts. In tropical countries, apart from noncommunicable diseases, a severe burden of disease is caused by an array of different microorganisms, parasites, land and sea animals, and arthropods. syndrome (AIDS), and poor health systems (consequential on poverty, mismanagement, and corruption) that afflict a large proportion of developing countries across the tropics. Although, in the past decade, lifestyle issues and changes in diet have led to an increase in the number of noncommunicable disease such as hypertension, diabetes, chronic obstructive airways disease, myocardial infarction, and cerebrovascular accidents in resource-poor tropical countries, tropical infectious diseases remain one of the major causes of preventable morbidity and mortality. 5 Tuberculosis, HIV/AIDS, and malaria alone are currently responsible for an estimated 6 million deaths annually. [1] [2] [3] [4] Schistosomiasis is the second most important parasitic disease after malaria, with 200 million people infected and 779 million at risk in more than 70 countries. In addition to these, leishmaniasis, onchocerciasis, filariasis, Chagas disease, African trypanosomiasis, rickettsioses, enteric fever, helminthiases, viral hemorrhagic fevers, and diarrheal diseases have extremely high public health impacts, and cause significant morbidity and mortality in adults and children. These diseases share population targets, ecological niches, and wide geographic distribution. [1] [2] [3] [4] Respiratory tract infections (RTIs) are caused by a variety of bacterial, viral, and fungal pathogens. RTIs remain major causes of morbidity and mortality in adults and children worldwide, causing millions of deaths each year. 6, 7 The identification and diagnosis of acute and chronic bacterial (including tuberculosis), viral, and fungal respiratory infections remain an important challenge in medical inpatient and outpatient practice in Europe, the United States, and developing countries. Respiratory infectious diseases such as severe acute respiratory syndrome (caused by coronavirus) and the avian influenza 8 are frequently causes of major concern. The Global Surveillance Network of the International Society of Travel Medicine (ISTM) and the Centers for Disease Control (CDC) established a worldwide communications and data collection network of travel/tropical medicine clinics in 1995, and their valuable Web site gives regularly updated information on geographic and temporal trends in disease-associated morbidity among travelers, immigrants, and refugees. 9 Tropical diseases are not restricted to the tropics. Increasing migration, international air travel, tourism, and work visits to tropical regions have contributed to an increased incidence of such diseases being seen in the United States, United Kingdom, and Europe. 9,10 Climate change and global warming (with a resulting increase in average and nadir temperatures) may be causing tropical diseases and vectors to spread to higher altitudes in mountainous regions, and to higher latitudes that were previously spared, such as the southern United States and the Mediterranean area. The last decade of the twentieth century was marked by a resurgence in tropical diseases being encountered in countries outside the tropics, such as the United States, including Chagas disease, a chronic, systemic, parasitic infection caused by the protozoan Trypanosoma cruzi, and vector-borne viral encephalitides. 3, 9 Other previously rare, but presently emerging, diseases from particular geographic areas include leptospirosis, trypanosomiasis, giardiasis, and viral hemorrhagic fever. Bites from several animal species, including snakes, scorpions, and jellyfish, cause much morbidity and mortality from envenomation and secondary infections. Skin diseases are common in travelers returning from the tropics. 3 The increasing success rates of solid organ and hematopoietic stem cell transplantations, with advances in immunosuppression, make transplants an early therapeutic option for many diseases affecting a considerable number of people worldwide. Thus, transplant programs in Western countries, as well as those in developing countries, have started to face the impact of neglected tropical diseases transmitted via the donor tissue. 11 More posttransplantation respiratory viral, bacterial, protozoal, and fungal infections are being recognized. It is imperative that physicians globally are aware of the wide spectrum of tropical, infectious, and parasitic diseases to which their patients may have been exposed. It is prudent to enquire about travel history and geographic origins early in consultations, to aid early diagnosis and treatment and thereby prevent poor outcomes in many patients. An extensive enquiry into the travel history is prudent because certain tropical infectious diseases can first present years or even decades after the last tropical travel, including malaria (Plasmodium ovale and Plasmodium vivax), trypanosomiases (T cruzi and Trypanosoma brucei gambiense), strongyloidiasis (Strongyloides stercoralis), filariases, and schistosomiasis (any Schistosoma spp). It is imperative to consider the possibility of a tropical disease in cases that are difficult to diagnose, even potentially in those without a suggestive travel history. For example, malaria can occur in patients who have not traveled overseas, being acquired near city airports where mosquitoes imported on aircraft arriving from the tropics can survive and transmit the infection during the summer months. 12 A high degree of clinical awareness of the possibility of a tropical disease enables an early diagnosis to be made and enables effective treatment measures to be initiated, reducing morbidity and mortality. The number and range of tropical and infectious diseases prevalent globally is extremely large and broad ranging. 1-3 Thus, for practical purposes, specific listings and classifications are useful for streamlining the microbiological and clinical assessment of the patient's illness. Classification of tropical diseases can also serve as aidemé moires or checklists for guiding clinicians, microbiologists, pathologists, and laboratory staff. For the practicing infectious diseases physician, there are several ways in which tropical/infectious diseases are presented in century-old classic tropical diseases textbooks like Manson's Tropical Diseases or other major treatises that present the classification of tropical diseases with a combination of clinical and microbiological approaches. The classification of infectious and tropical diseases, and their treatment, control, and prevention, have historically involved the joint efforts of epidemiologists, microbiologists, and clinicians. Table 1 gives a basic classification of common infectious pathogens for clinical use. Physicians also tend to classify infectious diseases according to the most important organ or organ system to be affected, or the important clinical manifestations of the specific disease ( Table 2) . 13, 14 Microbiologists tend to prefer classifying infectious diseases according to the classic microbiological nomenclature codes of kingdom, phylum, class, order, family, genus, and species and have large standard textbooks that give detailed classification and nomenclature. 15 They relate information according to microscopic appearance after staining or culture characteristics, to advise the clinician on the most appropriate antibiotic therapy and management. However, with advances in molecular technology, microorganisms are frequently being reclassified and renamed. For example Rickettsia tsutsugamushi, the causal agent for scrub typhus, has been reclassified into the genus Orientia. DF-2 is now known as Capnocytophaga canimorsus. 16 Epidemiologists usually describe tropical disease in terms of person, place, time, and exposure, with a view to developing control and prevention strategies to limit the spread of the diseases in the community. They often classify infectious diseases according to their distribution, their means of transmission, and according to their reservoirs in nature. Such classifications use the routes of transmission or acquisition of the infectious disease ( Table 3) . Many tropical infectious diseases are characterized by chronic inflammation as the battle between the host and pathogen becomes protracted. Pathologic reports often describe the presence of a granuloma in biopsy tissue and the tissue may be processed with special stains, molecular methods, or culture to try to identify further. A granuloma [17] [18] [19] is defined as a chronic, compact collection of inflammatory cells in which mononuclear cells predominate, usually formed as a result of an undegradable product, in the case of tropical infectious diseases; examples are given in Table 4 . Some of the organisms contained within the granuloma remain viable, and these can reactivate to cause active disease when the patient becomes immunosuppressed from HIV or immunosuppressive therapy. Tuberculosis in HIV-infected individuals or in those on anti-TNF-a therapy, and Chagas disease in transplant recipients, are classic examples. Infectious diseases transmitted through medical procedures (eg, transfusion of blood or blood-related products 20 and via transplantation) can also be classified microbiologically according to the type of microorganism (Box 1). There are geographic differences in the distribution and intensity of tropical infectious diseases and knowledge of these in relation to travel history or country of origin may increase the likelihood of making an accurate and rapid diagnosis. The incidence and prevalence of each disease varies with time, and therefore published World Health Organization data and map resources can rapidly become outdated because of the lag between data collection and publication. The Global Health Observatory (GHO) 21 is a unique and useful service providing a gallery of global maps illustrating the prevalence of an extensive list of major health topics including tropical diseases, which are updated on a regular basis. These maps are classified by disease themes, including all major infectious and parasitic diseases. Each theme page provides information on the global situation, prevalence, and trends, using core indicators, database views, publications, and links to relevant Web pages. The GHO also issues analytical reports on the current situation and trends for priority health issues. A key output of the GHO is the annual publication World Health Statistics, which compiles statistics for key health indicators and also includes a brief report on progress toward health-related Millennium Development Goals. In addition, the GHO provides analytical reports on cross-cutting topics such as the report on women and health and burden of disease. Ongoing research and surveillance continues to yield new information. Advances in tropical medicine, as with all clinical specialties, tend to be distributed throughout the general medical and scientific literature, and sole reliance on such sources for specialist tropical medicine information does not usually suffice. There are several major textbooks focusing on clinical and laboratory aspects of tropical and parasitic diseases. [1] [2] [3] The information they contain is comprehensive, but some details may become outdated rapidly because of new developments, and readers are advised to look up more current sources of literature on each subject area. 22 It is important that any comprehensive search encompasses general and specialist sources, including journals, books, databases, and Web sites. Many traditional print resources, such as journals, indexes, and, increasingly, books, are now available online. This issue of Infectious Diseases Clinics of North America on tropical diseases covers the epidemiologic, clinical, laboratory, and management aspects of most of the common tropical infectious and parasitic diseases that may present to the physician in the west. Diseases caused by venomous bites, stings, and poisoning are also described to emphasize that not all tropical diseases are caused by microorganisms. Manson's tropical diseases Tropical infectious diseases. Principles, pathogens and practice Hunters tropical medicine and emerging infectious diseases The Global Burden of Disease 2004 update: 1. Cost of illness. 2. World health -statistics. 3. Mortality -trends. I. World Health Organization. Geneva: World Health Organization Principles of medicine in Africa Infectious Diseases Clinics of North America. Emerging respiratory infections of the 21st century Emerging respiratory infections of the 20th century Pandemic planning in China: applying lessons from severe acute respiratory syndrome The Global Surveillance Network of the ISTM and CDC. A worldwide communications and data collection network of travel/tropical medicine clinics Travel-related imported infections in Europe Parasitic infections in solid organ transplant recipients Why aircraft disinsection? Lecture notes in tropical medicine Oxford handbook of tropical medicine Bergey's manual of systematic bacteriology DF-2 infection (may follow dog bites and hazardous to the immunosuppressed) Granulomatous infections -aetiology and classification Granulomatous disorders 616 Granulomatous infections -an overview Manson's tropical diseases Sources of literature on tropical medicine. Manson's Tropical Diseases. International Edition