INTRODUCTION — Southeast Asia encompasses the region from southern China through the Indochina peninsula and islands bordering the South China Sea to the island of New Guinea. The countries within this region are Brunei, Cambodia, Indonesia, Laos, Malaysia, Myanmar (Burma), the Philippines, Singapore, Thailand, Timor-Leste, and Vietnam. The region straddles the equator between latitudes of 30ºN and 10ºS and comprises rain forests, savanna, tropical beaches, and volcanic islands.
The health risks vary considerably between regions within Southeast Asia. There are a few places (eg, Singapore) where the food and waterborne risks do not differ appreciably from Western Europe, North America, and Australia.
SURVEILLANCE DATA — The largest contemporary experience in travel-related disease comes from GeoSentinel, the global surveillance network of the International Society of Travel Medicine and the United States Centers for Disease Control and Prevention [1,2]. A 2013 report from 53 GeoSentinel sites provided clinical-based surveillance information on more than 42,000 ill travelers who returned unwell from a trip between 2007 and 2011 [1]. Among over 6800 diagnoses made in travelers who returned from Southeast Asia, over 90 percent of diagnoses fell into one of three categories: gastrointestinal (30 percent), febrile illness (26 percent), and dermatologic (35 percent):
●Among patients with a systemic febrile illness, dengue, P. falciparum and P. vivax malaria, and chikungunya virus were the top specific diagnoses.
●Among patients with diarrhea, Campylobacter, Giardia, and Salmonella were the three most common organisms isolated.
●Among patients with dermatologic disorders, an animal bite requiring rabies prophylaxis, cutaneous larva migrans, and scabies were the three most common specific etiologic diagnoses made.
ARTHROPOD-BORNE DISEASES
Malaria — Malaria-endemic areas exist in all countries in this region except Singapore and Brunei. Transmission occurs year round in endemic areas. Country-specific risk areas are as follows:
●Cambodia – Nationwide risk except no risk in Phnom Penh. Risk within the tourist area surrounding Angkor Wat is negligible.
●Indonesia – Risk in all areas of eastern Indonesia (Maluku, Maluku Utara, Nusa Tenggara Timur, Papua, and Papua Barat), including the town of Labuan Bajo and Komodo Islands in the Nusa Tengarra region, and rural areas of Kalimantan (Borneo), Nusa Tenggara Barat (including Lombok), Sulawesi, and Sumatra. Low transmission in rural areas of Java, including Pangandaran, Sukabumi, and Ujung Kulong. No risk in the cities of Jakarta and Ubud, resort areas of Bali and Java, and Gili Islands and the Thousand Islands (Pulau Seribu).
●Laos – Nationwide risk except no risk in Vientiane.
●Malaysia – The highest risk is in Sabah and Sarawak but also in remote areas of Malaya (especially the Cameron Highlands). Urban and coastal areas (including resorts) are risk free.
●Myanmar – The risk exists throughout the year in remote rural, hilly, and forested areas of the country and in some coastal areas in Rakhine State. There is no transmission in cities and urban areas. The central plains and the dry zone are generally free of malaria, but some areas of transmission still exist.
●The Philippines – The risk exists throughout the year in Palawan and Mindanao Islands. No risk in metropolitan Manila and other urban areas.
●Thailand – The risk is largely confined to the borders with Cambodia and Myanmar. There is no risk in the major cities and tourist resorts (Bangkok, Chiang Mai, Pattaya, Phuket, and Samui).
●Timor-Leste – Risk in Oecusse District. Rare cases in other districts.
●Vietnam – Nationwide risk, excluding urban centers, the Red River delta, and the coastal plain areas of central Vietnam. High-risk areas are the highland areas below 1500 meters (particularly south of latitude 18ºN), including the three central highland provinces of Dak Lak, Gia Lai, and Kon Tum and the southern provinces of Ca Mau, Bac Lieu, and Tay Nimh.
Plasmodium knowlesi is a malaria parasite found in monkeys that can infect humans, with a geographical distribution that extends throughout Southeast Asia [3]. Human cases of P. knowlesi infection have been reported from Malaysia, Thailand, the Philippines, Myanmar, Singapore, Vietnam, Indonesia, Brunei, Laos, and Cambodia [3]. (See "Non-falciparum malaria: Plasmodium knowlesi".)
Drug-resistant malaria has been a major problem in Southeast Asia, with chloroquine-resistant Plasmodium falciparum predominating in virtually all endemic areas. Mefloquine resistance occurs in the Thai-Myanmar and Thai-Cambodian border regions. (See "Prevention of malaria infection in travelers".)
Dengue fever — Dengue fever is an arboviral disease endemic throughout Southeast Asia. The main vector is the daytime biting mosquito Aedes aegypti, which typically breeds near human habitation. Most cases are reported from urban areas with high population densities. High levels of dengue fever activity have been experienced by many countries in Southeast Asia including Singapore, Malaysia, Cambodia, Vietnam, Thailand, the Philippines, Indonesia, and Myanmar. The high incidence of dengue transmission in Singapore since 2013 highlights the need for precautions against mosquitoes in that country [4]. (See "Dengue virus infection: Epidemiology".)
Japanese encephalitis — Japanese encephalitis is an arboviral encephalitis that is endemic throughout much of tropical Asia. Issues related to Japanese encephalitis are discussed in detail separately. (See "Japanese encephalitis".)
Chikungunya fever — Chikungunya is an arbovirus transmitted by mosquitoes that causes acute febrile polyarthralgia and arthritis. The name chikungunya is derived from a local language of Tanzania meaning "that which bends up" or "stooped walk" because of the incapacitating arthralgia caused by the disease. Chikungunya fever is discussed in detail separately. (See "Chikungunya fever: Epidemiology, clinical manifestations, and diagnosis".)
Typhus — Both scrub typhus (caused by Orientia tsutsugamushi) and murine typhus (caused by Rickettsia typhi) are endemic in some regions of Southeast Asia. Scrub typhus occurs in certain rural areas with scrub vegetation but has also been acquired in suburban Bangkok [5]. Most cases of murine and scrub typhus reported to GeoSentinel between 2006 and 2011 were acquired in Southeast Asia [6]. (See "Scrub typhus: Treatment and prevention".)
Murine typhus is transmitted to humans by rat or cat fleas and occurs most commonly in urban settings; there have been several reports of travelers acquiring murine typhus in Southeast Asia [7]. (See "Murine typhus".)
Yellow fever — There is no risk for yellow fever in Southeast Asia. However, due to the presence of the mosquito vector of yellow fever (Aedes aegypti), all countries in the region require travelers to have a yellow fever vaccination certificate if they are coming from areas in South America or sub-Saharan Africa where yellow fever is endemic [8]. (See "Yellow fever: Epidemiology, clinical manifestations, and diagnosis".)
FOODBORNE AND WATERBORNE DISEASES
Travelers' diarrhea — Southeast Asia (with the exception of Singapore) is a high-risk area for the development of travelers' diarrhea [9]. (See "Travelers' diarrhea: Epidemiology, microbiology, clinical manifestations, and diagnosis".)
Enterotoxigenic Escherichia coli is the most common pathogen identified. Vibrio parahaemolyticus, which is common in the region, is associated with seafood ingestion [10]. In Thailand, enteric pathogens have developed resistance to most classes of antibiotics used to treat diarrhea, including the newer fluoroquinolones and macrolides [11].
Typhoid — Typhoid is endemic throughout most of Southeast Asia. The risk is very low for travelers to Singapore. (See "Enteric (typhoid and paratyphoid) fever: Epidemiology, clinical manifestations, and diagnosis".)
Hepatitis A and hepatitis E — Hepatitis A virus is endemic throughout Southeast Asia, although there is a very low risk for travelers to Singapore. (See "Hepatitis A virus infection in adults: Epidemiology, clinical manifestations, and diagnosis".)
Foci of epidemic hepatitis E virus transmission have been recognized throughout Southeast Asia, including Vietnam, Indonesia, and Thailand [12-14]. In addition, a seroprevalence of 10 to 15 percent has been found among Singaporeans [15]. (See "Hepatitis E virus infection".)
Schistosomiasis and other fluke infections — Schistosomiasis due to Schistosoma japonicum is endemic in southern Philippines and Sulawesi (Indonesia), and there are small foci of Schistosoma mekongi in the Mekong River delta. (See "Schistosomiasis: Epidemiology and clinical manifestations" and "Schistosomiasis: Diagnosis".)
Fasciolopsiasis (giant intestinal fluke) and paragonimiasis (lung fluke) can be acquired in most countries of the region. Clonorchiasis (liver fluke) is particularly common in Indochina, while opisthorchiasis (cat liver fluke) is found in Indochina, the Philippines, and Thailand. (See "Liver flukes: Fascioliasis" and "Liver flukes: Clonorchis, Opisthorchis, and Metorchis" and "Paragonimiasis".)
Leptospirosis — Transmission of leptospirosis to humans usually occurs by either direct or indirect contact of mucous membranes or breaks in the skin with infected water surfaces or animals [16]. Various animals serve as reservoirs; rats are probably the most important in tropical areas such as Southeast Asia, where the disease is endemic. Most notable was an Eco-Challenge race associated with a major leptospirosis outbreak [17]. Most cases of leptospirosis reported to GeoSentinel between 2006 and 2011 were acquired in Southeast Asia [6]. (See "Leptospirosis: Epidemiology, microbiology, clinical manifestations, and diagnosis".)
Cholera — In 1999, over 2500 cases of cholera were reported from countries of Southeast Asia, including Cambodia, Malaysia, the Philippines, Singapore, and Vietnam; the number of cases has fallen since that time. The risk for travelers is low and, under normal circumstances, cholera vaccination is not recommended for travelers to the region. (See "Cholera: Clinical features, diagnosis, treatment, and prevention".)
OTHER INFECTIONS
HIV infection — The number of people in Southeast Asia infected with HIV has increased dramatically; commercial sex work has played an important role in the spread of HIV in the region. (See "Global epidemiology of HIV infection".)
Other sexually transmitted diseases — Sexually transmitted diseases other than HIV infection are a major public health problem in parts of Southeast Asia. Contact with sex workers involves high risk.
Hepatitis B and hepatitis C — Hepatitis B virus is highly endemic throughout Southeast Asia. (See "Epidemiology, transmission, and prevention of hepatitis B virus infection".)
The prevalence of hepatitis C among residents of the region ranges from 0.54 percent in Singapore to 6.1 percent in Vietnam [18]. (See "Clinical manifestations, diagnosis, and treatment of acute hepatitis C virus infection in adults" and "Clinical manifestations and natural history of chronic hepatitis C virus infection".)
Respiratory virus infections — Respiratory virus epidemics, including avian influenza and severe acute respiratory syndrome (SARS), have occurred in this region. Avian influenza (H7N9) has been reported in 2014 in China but not in Southeast Asia.
Melioidosis — Melioidosis is caused by Burkholderia pseudomallei, a gram-negative bacillus that can be isolated from soil and water. It is endemic throughout Southeast Asia, especially in rural communities, with seasonal peaks occurring during the rainy seasons. Melioidosis has been reported in travelers to endemic areas [19]. (See "Melioidosis: Epidemiology, clinical manifestations, and diagnosis".)
Penicillium marneffei infection — Penicillium marneffei is a fungus that is endemic in Southeast Asia. It causes disseminated infection in immunocompromised individuals, especially those with HIV infection [20]. In some parts of the region, it is the third most common opportunistic infection in HIV-infected individuals. The exact route of transmission has not been determined; the fungus is closely associated with bamboo rats. (See "Epidemiology and clinical manifestations of Talaromyces (Penicillium) marneffei infection".)
Plague — Cases of plague are being reported from Myanmar and Vietnam, although travelers are rarely affected. (See "Epidemiology, microbiology and pathogenesis of plague (Yersinia pestis infection)".)
Rabies — Rabies is endemic throughout Southeast Asia. Through the efforts of rabies control programs, the prevalence of human and canine rabies has decreased significantly in some countries. However, in Thailand, the proportion of dogs testing positive for rabies averaged 54 percent in one report, indicating that rabies is still a major public health threat [21]. Furthermore, 42 percent of rabid dogs were less than six months old; this is the age group most likely to interact with humans and the group least likely to have received rabies vaccination. Thus, postexposure treatment is recommended following all potential exposures, and prophylaxis should be considered by travelers spending significant periods of time in the region. (See "Rabies immune globulin and vaccine" and "Indications for post-exposure and pre-exposure rabies prophylaxis".)
Tuberculosis — Tuberculosis is relatively common in some parts of Southeast Asia; short-term travelers from countries of low endemicity are generally not considered at increased risk of infection.
Sarcocystosis — Acute muscular sarcocystosis has been described in travelers returning from Malaysia. Symptoms include fever and muscle pain; eosinophilia and elevated serum creatine phosphokinase may occur [22]. This protozoan infection is usually acquired through ingestion of food or water contaminated with oocysts/sporocysts [23]. (See "Sarcocystosis".)
Nipah virus infection — Nipah virus is a member of the Paramyxoviridae and was initially isolated and identified in 1999 during an outbreak of encephalitis and respiratory illness among pig farmers and people with close contact with pigs in Malaysia and Singapore [24]. Flying foxes of the genus Pteropus were subsequently identified as the reservoir. Since this outbreak, no subsequent cases (in neither swine nor human) have been reported in either Malaysia or Singapore, although outbreaks still occur in neighboring Bangladesh [25]. (See "Nipah, Hendra, and other henipaviruses".)
OTHER HAZARDS
Motor vehicle accidents — Injury caused by motor vehicles is one of the greatest health hazards and a leading cause of death in travelers, although data specific to travelers to Southeast Asia is lacking.
Snake bites — Venomous snakes are present throughout Southeast Asia. The Malayan pit viper (Calloselasma rhodostoma), Russell's viper (Daboia russelii), green pit vipers (eg, Trimeresurus albolabris), and the monocellate cobra (Naja kaouthia) are responsible for most bites and deaths. (See "Snakebites worldwide: Clinical manifestations and diagnosis".)
Marine hazards — There are many potential marine hazards in the waters around Southeast Asia. Envenomation by marine creatures (including jellyfish, sea snakes, blue-ringed octopus, cone shells, stingrays, and stone fish) accounts for many fatalities and severe morbidity in humans [26,27].
High-altitude disease — There are several mountainous regions in Southeast Asia at altitudes over 2500 meters in which acute mountain sickness is possible. Carstensz Pyramid (5030 m) in Irian Jaya is the region's highest point, but the most likely places for high-altitude exposure are volcanoes in other parts of Indonesia and Kinabalu (4094 m) in Malaysia. (see "High-altitude illness: Physiology, risk factors, and general prevention")
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Travel medicine".)
INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, “The Basics” and “Beyond the Basics.” The Basics patient education pieces are written in plain language, at the 5th to 6th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10th to 12th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.
Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on “patient info” and the keyword(s) of interest.)
●Basics topics (see "Patient education: Vaccines for travel (The Basics)")
●Beyond the Basics topics (see "Patient education: General travel advice (Beyond the Basics)")
SUMMARY
●Southeast Asia encompasses the region from southern China through the Indochina peninsula and islands bordering the South China Sea to the island of New Guinea. The countries within this region are Brunei, Cambodia, Indonesia, Laos, Malaysia, Myanmar (Burma), the Philippines, Singapore, Thailand, and Vietnam. The health risks vary considerably from region to region within Southeast Asia, although there are only a few places (eg, Singapore) where the risks do not differ appreciably from Western Europe, North America, and Australia. (See 'Introduction' above.)
●Among returned travelers from Southeast Asia, manifestations generally fall into four major syndrome categories: systemic febrile illness without localizing findings, acute diarrhea, dermatologic disorders, and nondiarrheal gastrointestinal disorders.
●Malaria endemic areas exist in all countries in Southeast Asia except Singapore and Brunei. Within endemic areas, transmission occurs year round. Drug-resistant malaria has been a major problem in Southeast Asia, with chloroquine-resistant Plasmodium falciparum predominating in virtually all endemic areas. Mefloquine resistance occurs in the Thai–Myanmar and Thai–Cambodian border regions. (See 'Malaria' above.)
●Other arthropod-borne diseases that are endemic in Southeast Asia include dengue fever, Japanese encephalitis, chikungunya fever, and typhus. (See 'Arthropod-borne diseases' above.)
●Southeast Asia (with the exception of Singapore) is a high-risk area for travelers' diarrhea. Enterotoxigenic Escherichia coli is the most common pathogen identified. Vibrio parahaemolyticus, which is common in the region, is associated with seafood ingestion. In Thailand, enteric pathogens have developed resistance to most classes of antibiotics used to treat diarrhea, including the newer fluoroquinolones and macrolides. (See 'Travelers' diarrhea' above.)
●Other foodborne and waterborne diseases in Southeast Asia include typhoid, hepatitis A, hepatitis E, schistosomiasis, leptospirosis, and cholera. (See 'Foodborne and waterborne diseases' above.)
●Other infections that travelers in Southeast Asia may be exposed to include avian influenza, HIV, other sexually transmitted diseases, hepatitis B, hepatitis C, melioidosis, penicilliosis, plague, rabies, and tuberculosis. (See 'Other infections' above.)
●Other hazards for travelers include motor vehicle accidents, snake bites, envenomation by marine creatures, and high-altitude disease. (See 'Other hazards' above.)
