key: cord-0040459-hfoni1zo authors: Jong, Elaine C.; Mayer, Jonathan D. title: Emerging Diseases and the International Traveler date: 2009-05-27 journal: The Travel and Tropical Medicine Manual DOI: 10.1016/b978-141602613-6.10003-5 sha: 7a2dfc11fe9a6143562c74deb043bbea3973aadb doc_id: 40459 cord_uid: hfoni1zo nan and globalization of food markets. Human behavior contributes to emerging zoonoses through wildlife trade and translocation, live animal and bush meat markets, consumption of exotic food, development of ecotourism, and ownership of exotic pets, as noted by Chomel et al. (2007) . Travelers are an important factor in the global dissemination of EIDs due to the increased frequency and speed of both local and international travel. International travel related to tourism, commerce, relief efforts, work and study means that humans are increasingly in direct or indirect contact with previously isolated, remote populations and ecosystems. The challenge is that travelers returning home may harbor exotic infections that are still in the incubation stage. During the acute stage of illness, non-specific flu-like clinical signs and symptoms and locally available laboratory tests may not suggest the correct diagnosis to local healthcare providers. Thus, infections acquired during travel may be transmitted to others in the community by returned travelers before the diagnosis of disease can be made. In addition to international travelers, imported animals, birds, foods and insects from abroad, especially from tropical developing countries, can also pose a significant threat to the public health of receiving countries by serving as means of transportation for pathogens into new geographic areas. Local, national, and international surveillance and reporting systems are necessary to detect and track new or EIDs, educate the public, and control outbreaks on local and global scales. Awareness of exotic, emerging and re-emerging infections diseases all over the world allows healthcare providers to focus advice and interventions on prevention of serious illnesses with individual travelers during the pre-travel medical encounter. However, surveys have shown that the majority of international travelers do not seek pre-travel advice, and thus, may be unaware of specific risk factors and appropriate steps to protect themselves at travel destinations. Given slow progress to date of health education efforts, commitment to and acceptance of recommended prophylactic interventions (vaccines, chemoprophylaxis, personal protection equipment, etc.) and adoption of positive behavior changes by international travelers, the burden of detection for imported infectious diseases among returning travelers will fall on individual healthcare providers and the public health officials to whom they report. Many individuals in our global society have traveled to developing countries and tropical areas, or have originated in developing countries where there is transmission of infectious agents not usually present in industrialized urban environments. In the 21st century, all persons presenting for diagnosis and treatment of an acute illness should be asked 'where have you traveled?' as part of the routine medical history. Diseases related to past-travel itineraries and geographical exposures should be considered in any differential diagnosis where the etiology of an acute illness is not obvious. The information should be as specific as possible in terms of the cities or areas of the country visited, and if possible, the patient or other knowledgeable person should be asked about the specific types of geographic environments with which the patient has had contact. Activities and exposures, such as swimming in freshwater lakes or rivers, walking barefoot on beaches or muddy trails, receiving many insect bites, eating raw or exotic foods, drinking untreated groundwater or even tap water or beverages with ice cubes in countries with low sanitation, and close/intimate contact with other travelers and foreign residents through work or social activities should also be subject to inquiry. Since most of the emerging and resurgent diseases are specifically discussed in other chapters of this book, the purpose of this chapter is to provide a general framework for their recognition, understanding, and treatment. Many factors are responsible for emergence of infectious pathogens that originate in wild animals. These include travel into previously uninhabited areas, changes in land use and demographic patterns with disruption of stable ecosystems, greater contact with previously isolated animal populations, changing agricultural practices that allow transfer of pathogens between wild and domestic animals, and food customs that involve hunting, butchering and ingesting wild game including non-human primates (bush meat). Numerous epidemiologic studies suggest an upward trend in the incidence of reported cases of zoonoses over the past decade. Two transmission patterns have been described for transmission of pathogens from wild animals to humans by Bengis et al. (2004) . One pattern consists of rare events when direct animal-to-human transmission of an animal pathogen occurs, but then direct human-to-human transmission maintains the infection in the human population for a limited time or permanently. Examples of diseases with this transmission pattern are human immunodeficiency virus (HIV), influenza A, Ebola virus, and severe acute respiratory syndrome (SARS). The second pattern of transmission is where human infections with animal pathogens result from repeated episodes of direct animal-to-human transmission, or of repeated vector-mediated animal-to-human transmission, and the infections are not usually propagated by human-to-human transmission. Examples of diseases with this transmission pattern are rabies and other lyssa viruses, Nipah virus, West Nile virus, Hantavirus, and the agents of Lyme borreliosis, plague, tularemia, leptospirosis and ehrlichiosis. Antimicrobial resistance has emerged through genetic adaptation of microbes to prophylactic and treatment agents. Causal factors are complex, but include the overprescription of broad-spectrum antibiotics for human illnesses, and the increased and mostly unregulated use of antimicrobials in poultry and livestock feeds, leading to emergence of multi-drug resistant bacteria in the human food chain with a significant impact on human health. Drug-resistant Salmonella and Campylobacter strains are prime examples of this phenomenon. Many of the diseases caused by emerging infections are vectored diseases. When competent vectors, such as mosquitoes, ticks, and fleas pre-exist in a geographic environment, movement of infected human or animal hosts into that area can lead to rapid expansion of transmission. An example of this was the spread of West Nile virus in North America, transmitted from birds to humans and horses by Culex mosquito vectors. Following the initial 1999 detection of the agent in Queens, New York, the new pathogen (thought to have been introduced inadvertently through an infected human traveler or migrant bird) spread rapidly across the continental USA from coast-to-coast within 5 years -affecting human activities, veterinary practices, and blood-banking guidelines in the wake of its spread (Fig. 3.1) . A large outbreak of chikungunya virus (CHIKV) emerged in 2005 in the Indian Ocean islands of Mayotte, Mauritius, the Seychelles, and particularly in Reunion Island where 35% of 770 000 inhabitants were infected in 6 months. The virus is transmitted to humans by the bite of infected Aedes and Culex mosquitos, including the daytime-biting Aedes aeypti and Ae. albopictus species. Circulation of this virus has been documented in Madagascar, India, and Sri Lanka, where CHIKV is spreading rapidly. The disease has been reported among travelers returning from endemic areas as a cause of acute illness characterized by sudden onset of fever, chills, headache, nausea, vomiting, joint pain with or without swelling, low back pain and rash, similar to the symptoms of dengue fever (Chapter 20). In some patients, residual joint pain and impairment persisted for months after the acute illness. Relatively recent dengue fever virus outbreaks in the Hawaiian Islands, and Ningbo, People's Republic of China, were linked to importation of the virus in infected travelers from Samoa and Thailand, respectively, and the presence of Aedes aegypti mosquitoes in the local environment that promoted subsequent human-to-human spread in the local populations. Malaria is considered to be an emerging disease because there is some evidence that it is undergoing northward and southward movement into more temperate areas, possibly related to global environmental changes, and because its incidence and prevalence rates are increasing in many areas. Whereas malaria appeared to have been almost eradicated in the 1960s, re-emergence of this has occurred over the following decades due to a combination of factors, including parasite resistance to antimalarial drugs, decreased effectiveness of insecticides used for mosquito control, and changes in social/financial infrastructures necessary for treatment and prevention programs in highly endemic areas. There have been several reports of 'airport malaria' in the USA and Europe, where individuals who live within several kilometers of major international airports contract malaria. This is despite the fact that they have not been in areas where malaria is endemic. Experimental studies show that infected Anopheline mosquitoes can survive in the wheel wells of commercial aircraft, and the putative mode of transmission is that after landing, the mosquitoes are able to fly several kilometers and infect individuals who live near the airports. It is well to remember that many competent anopheline vectors are already present in the USA, and that as recently as the 1930s, malaria was endemic in the Tennessee River Valley. In 19th century summers, malaria was present as far north as upstate New York and Oregon. The prevention and treatment of malaria is discussed in Chapters 6 and 19. From the viewpoint of malaria as an emerging disease, it is crucial to note that strains of both P. vivax and P. falciparum have demonstrated relatively rapid development of resistance to new antimalarial drugs employed for prophylaxis and treatment in recent history, and will continue to do so. Chloroquine-resistant P. falciparum (CRPF) strains emerged in Thailand and the Amazon region of South America, but the spread of CRPF to sub-Saharan Africa, where 90% of the malaria cases now occur, has had the biggest impact on morbidity and mortality. Effective vaccines against CRPF malaria are still under development, so prophylaxis with antimalarial drugs such as atovaquone/proguanil, mefloquine, and doxycycline, and personal insect precautions will remain the mainstay of malaria prevention in the traveler. Increased cases of Lyme borreliosis (B. burgdorferi) in North America have been reported over the past decade. Causal factors include increasing populations of humans as well as animal reservoirs (white-footed mice, white-tailed deer, Ixodes ticks) and mutual encroachment on traditional habitats. These have resulted in expanded opportunities for tick-borne transmission of Lyme disease in rural suburban areas close to human dwellings as well as in the recognized transmission risk environment of grasslands and shrubs at the edge of forests (see Chapter 23). Pathogens that are transmitted directly or indirectly through aerosolized droplets have huge potential for rapid global spread. Examples of pathogens in this group are avian (H5N1) influenza virus, extremely drug-resistant tuberculosis (XDR TB) (Chapter 24), and severe acute respiratory syndrome (SARS) coronavirus. Protective vaccines, personal protection equipment, rapid screening tests, and effective drugs for prophylaxis and treatment are needed against these diseases. Continued public health guidance and a legislative framework for implementation of mandatory screening, isolation and quarantine of individuals meeting infectious case definitions are necessary to prevent transmission and prevent outbreaks. There is a general misconception that airplane cabins provide a unique environment for transmission of air-borne infectious agents: however, human factors rather than strictly environmental factors promote transmission of infectious diseases during long airplane flights (Chapter 4). Disease transmission of respiratory pathogens occurs whenever a susceptible person is in close proximity to an infectious person, and wherever large groups of people are crowded together in confined spaces, be that in classrooms, offices, movie theaters, shopping malls, convention halls, train stations, airports, etc. Direct inoculation from contaminated fingers to mucosal surfaces of the mouth, nose, and eyes is probably as significant as droplet inhalation in transmission of respiratory viruses. Changes in animal production systems and in the food production chain are thought to be among the main factors causing emergence of food-borne zoonoses. The most important emerging food-borne zoonotic pathogens include Salmonella species, Campylobacter species, enterohemorrhagic Escherichia coli, Toxoplasma gondii and Cryptosporidium parvum. New pathogens of fecal origin can lead to water-borne outbreaks when water supplies are contaminated through wildlife or domestic animal feces. If contaminated water supplies are used for agricultural production, transmission of pathogens of zoonotic origin can occur through human ingestion of contaminated fruits and vegetables. Prevention of food-borne and water-borne diseases involves personal precautions and further development and implementation of food safety programs. Individual travelers can reduce their personal risk of exposure by selection of safe foods and beverages, e.g., using water disinfection techniques (Chapter 8), and selecting freshly prepared fully cooked foods (Chapters 7, 27 and 28). Nations can improve the safety of their food and water supplies by adopting integrated approaches to food safety and designating a responsible authority to assure compliance. The Food and Agriculture Organization (FAO)/World Health Organization (WHO) have recently established a new framework of microbiologic risk assessment to guide efforts of member countries in reducing pathogen contamination at relevant points in food production chains. International efforts to implement this approach are necessary to reduce risks to human health in the global food market that prevails at this time. Numerous EIDs, some of which constitute potential risks to international travelers, are discussed in the journal Emerging Infectious Diseases, published by the Centers for Diseases Control and Prevention (CDC) in the United States. (This valuable journal is available at: http://www.cdc.gov/ncidod/EID/index.htm and also available on hard copy). Several hundred emerging infections have been mentioned in the Federation of American Scientists' Program for Monitoring Emerging Diseases (ProMED), which is a simple bulletin board system that contains the most upto-date reports of disease outbreaks. (The archives for ProMED are available at: http://www.healthnet.org/programs/promed.html. Bulletins are sent out via electronic mail, and free subscriptions are available by registering your e-mail address at the above website). The world is dynamic, and what happens in one area can rapidly affect other areas at great distances. This has enormous implications for travel medicine, since a disease that is endemic in one area can rapidly become epidemic in another area through the movements of global travelers. Those providing pre-travel counseling and post-travel treatment need to be aware of potential hazards and outbreaks in regions in which the traveler will be visiting, or from which the traveler is returning. 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