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ADF Health September 2003 - Volume 4 Number 2

Travel Medicine

Travel medicine: profiling an emerging specialty

• Lieutenant Colonel Peter A Leggat, BMedSc, MB BS, DipEd, DTM&H, MMedEd, DIH, MPH, PhD, FAFPHM, FACTM, FFTM, FACRRM, RAAMC

INTERNATIONAL TRAVEL is increasingly common. 1 Ease of air transportation has ensured that an estimated 660 million people currently travel internationally each year to every part of the globe. 2 More than three million Australians also travel abroad each year, 3 which includes thousands of Australian Defence Force (ADF) personnel.

Travellers are potentially exposed to diseases for which they have no immunity, as well as other serious threats to well-being, such as accidents. It is conservatively estimated that 30%-50% of travellers become ill or are injured while travelling. 4 Relative estimated monthly incidence rates of various health problems have been compiled elsewhere. 5 The risk of severe injury is thought to be greater for people when travelling abroad. 1,6 Both injury and infectious diseases, such as respiratory tract infection and travellers' diarrhoea, are important concerns for travellers. 1,4,6 The main health complaints of returned Australian travellers reported in a recent survey of travel insurance claims were respiratory (20%), musculoskeletal (17%), gastrointestinal (14%), ear, nose and throat (12%), and dental conditions (7%). 7 Fortunately, few Australian travellers die abroad and those who do tend to die of pre-existing conditions, such as heart disease, but accidents are also a major contributor. 8

This review highlights some of the current issues in travel medicine, with special reference to the ADF.

Definition of travel medicine

Travel medicine is a new multidisciplinary specialty emerging in response to the needs of the travelling population worldwide.

Travel medicine seeks to prevent illnesses and injuries occurring to travellers going abroad and manages problems arising in travellers coming back or coming from abroad. It is also concerned about the impact of tourism on health and advocates for improved health and safety services for tourists. 9

The latter aspect recognises the impact of travel on ecosystems around the world, particularly the introduction and spread of diseases and disease resistance.

Specialists in travel medicine consider and advise on various aspects of travel-related health, including fitness to travel and the health risks of travelling in itself, as well as considering the implications of exposure to a variety of infectious diseases and managing diseases arising from travel. This may require providing chemoprophylaxis for malaria and other diseases and various vaccinations. The areas that may be covered in the pretravel health consultation are listed in Box 1.

Developments in travel medicine

Several key developments in the past decade have ensured the continuing emergence of travel medicine as a specialty. The Australian Government's Travel Safe program, including the development of Australian guidelines for travel medicine, 11 was an important advance, as this recognised the need for a consensus strategy for combating infectious diseases and other problems commonly encountered by travellers. These guidelines were directed to the major providers of travel health advice, which were general practitioners and public health agencies, but also travel clinics.

Australia has also seen an explosion in the establishment of dedicated specialist travel clinics operated commercially and within teaching hospitals and general practice. These travel clinics are usually designed to provide comprehensive pre-travel and post-travel health services, providing advice and chemoprophylaxis as well as vaccination and other commercial items, such as travellers' medical kits, mosquito nets and repellents, and water purifiers.

The first difficulties for all travel health advisers is to ensure that travellers recognise the need for travel health advice. The second is ensuring that travellers seek travel health advice in a timely manner (usually 6-8 weeks before travel) and then obtain this advice from a qualified source. One of the decisive factors in whether travellers seek health advice is the perceived risk and severity of tropical diseases. 1

As well as preventing potentially lethal diseases and injuries among travellers abroad, travel medicine services are also increasingly recognised as important in relation to early detection and reporting of imported infections.

Professional and academic initiatives

The International Society of Travel Medicine (ISTM), established in 1991, has taken the lead in establishing a professional base for travel medicine globally. Among its initiatives are travel health alerts to subscribers, a journal, biennial conferences, a global listing of travel health practitioners, a collaborative disease reporting network (GeoSentinel) with the Centers for Disease Control and Prevention (CDC) in Atlanta, 12 and most recently a certification program based on a detailed body of knowledge in travel medicine. 13

GeoSentinel is an excellent example of the contribution of travel medicine to early detection and reporting of imported infections. 12 ISTM also collaborates with the Asia Pacific Travel Health Association to conduct biennial conferences in travel medicine in the Asia-Pacific region, in alternate years to the ISTM's Biennial Conference. The two major journals in the travel medicine area are presently the ISTM's Journal of Travel Medicine, published by BC Decker, and Travel Medicine and Infectious Diseases, published by Elsevier Science. In Australia, the development of a professional body in travel medicine, the Australasian Faculty of Travel Medicine (FTM), was recently achieved in 2000, as part of The Australasian College of Tropical Medicine. The FTM works in close association with the New Zealand Society of Travel Medicine, established in 1997.

Comprehensive guidelines in travel medicine were last published by the Australian Government in 1994. 11 The key Australian government, World Health Organization (WHO), commercial and related publications that provide travel medicine guidelines and advice are listed in Box 2. There are also several valuable Internet and related resources that provide information on disease distribution and prevention (Box 3). The ADF publishes a wide range of Health Directives relating to travel medicine for the Defence Health Services. Access to policy guidelines and up-to-date health intelligence, usually provided from Internet-based resources, is essential. The research undertaken by the ADF, such as that conducted by the Australian Army Malaria Institute, 19 contributes substantially to the development of more effective countermeasures to infectious diseases associated with travel and the development of guidelines in travel medicine.

Training in travel medicine is available both nationally and internationally through certificate, diploma, or masters' degrees. In Australia, training is available at James Cook University at subject level for postgraduate programs in public health and tropical medicine and also at the level of a postgraduate certificate of travel medicine. Civil aviation medicine courses are available at several institutions in Australia, including Monash University, Griffith University, and Edith Cowan University. Military training in aviation medicine is available through the Institute of Aviation Medicine. In New Zealand, the University of Otago Medical School at Wellington offers both postgraduate certificate and diploma courses in travel and migrant medicine, as well as a related subject in airport and travel health as part of its aviation medicine courses. As previously mentioned, ISTM awards a certificate in travel medicine to successful examination candidates. 13 Other international programs in travel medicine have been listed elsewhere. 20

Vector-borne diseases

Vector-borne diseases remain among the great problems for operational deployment of the ADF. Some vectorborne diseases also represent a potential public health problem when returning home. Malaria remains the single most important vector-borne disease problem of travellers, including the military, but arboviral diseases, such as dengue and Japanese encephalitis, are also of increasing importance. Some vector-borne diseases are important for local travel within Australia as well as overseas (eg, scrub typhus, which affected military personnel in north Queensland). 21

Malaria

Malaria is a serious disease caused by a protozoan parasite largely confined to the tropics. WHO estimates that malaria "causes more than 300 million acute illnesses and at least one million deaths annually". 22 Most cases and deaths occur due to infection with Plasmodium falciparum species of malaria, however infection due to P. vivax also remains important, especially as dormant liver stages can cause relapses for months after returning home. Standard malaria countermeasures will be considered as part of planning for operational deployment based on Defence Health Service Health Directives and disease patterns in the area of operations. Civilian guidelines for malaria chemoprohylaxis and treatment are described elsewhere. 14

Current countermeasures against malaria include the use of malarial chemoprophylaxis, personal protective measures, environmental health measures against disease vectors, and malaria eradication treatment for liver stages, including hypnozoites, and gametocytes on return to Australia. Growing chloroquine and multidrug resistant P. falciparum and, more recently, P. vivax, have limited the antimalarial drug options for malaria chemoprophylaxis. Current recommended malaria chemoprophylaxis regimens are doxycycline (one 100mg tablet daily), or mefloquine (one 250mg tablet weekly), or Malarone (one tablet daily, which consists of 250mg of atovaquone and 100mg of proguanil). 14 Chloroquine continues to be recommended as malaria chemoprophylaxis for malaria in the few areas where there is no chloroquine resistance. Current eradication treatment for malaria is primaquine (two 7.5mg tablets twice daily for 2 weeks), although tafenoquine has recently been trialed in ADF personnel in East Timor as both an alternative eradication treatment (400mg daily for three days) and as a weekly dose chemoprophylactic agent. 23

Due to the incidence of neuropsychiatric side-effects, such as anxiety and nightmares, it is advisable for soldiers taking mefloquine for the first time to take several trial doses, commencing as early as three weeks before departure. 24 It is also advisable that soldiers who are taking other antimalarials, such as doxycycline and Malarone, are given trial doses well before departure. This is to ensure that there is time to consider alternatives if an adverse reaction is produced. 24 If the deployment is at short notice, modification to antimalarial regimens may have to be done in the field.

There are varying opinions on how long antimalarials should be continued after leaving a malarial area, but for drugs which have no pre-erythrocytic effects on the liver stages of the malarial parasite, such as doxycycline and mefloquine, prophylaxis should continue for up to four weeks after leaving the malaria-endemic area. This relates to the time it takes for parasites to develop in the liver and infect the blood stream. Malarone has some effect on the hepatic stages of P. falciparum parasites and may be given for shorter periods after return, (eg, one week). 25

For travellers to more remote areas, standby treatment may also be useful. "Standby treatment consists of a course of antimalarial drugs that travellers to malaria endemic areas can use for selftreatment if they are unable to gain access to medical advice within 24 hours of becoming unwell". 24 In these situations, a traveller's medical kit may be supplied with a thermometer, possibly an immunochromatographic test (ICT) malaria diagnostic kit with written instructions, and an appropriate malaria treatment course with written instructions. Travellers who use standby treatment must seek medical advice as soon as possible. Newer antimalarials, which may be useful for standby treatment, include Malarone and Riamet (20mg artemether and 120mg lumefantrine). 26

Arboviral diseases

There are many arboviral diseases that may affect travellers and military deployments. Two of the most important arboviral diseases for the ADF are dengue and Japanese encephalitis, as a number of deployments in recent years have been to areas where these diseases are endemic. Both of these diseases are transmitted by various species of mosquitoes, some of which are known to exist in Australia, especially in north Queensland, where major military bases are located.

• Dengue is a major global public health problem. WHO estimates that there may be 50 million cases per year. 27 Dengue is a viral illness transmitted by Aedes spp. of mosquito. Infection may be subclinical, or produce an illness with fever, arthralgia and rash, or be complicated by haemorrhagic diatheses or shock syndromes. Treatment is supportive, while management of the problem is directed towards preventing transmission upon return to Australia. Numerous outbreaks of dengue in north Queensland have been attributed to travellers returning with the disease. A recent study of soldiers returning from East Timor during the incubation period of the disease showed that a collaborative effort by military and civilian public health authorities to contain and prevent the transmission of the disease among the local population was vital. 28 Until a vaccination becomes available, the mainstays of dengue prevention are personal protective measures and environmental health measures against disease vectors. (For more on dengue, see the review by Aaskov in this issue of the journal.) 29
• Japanese encephalitis is the leading cause of viral encephalitis in Asia. WHO estimates that there are more than 70000 cases annually in south east Asia. 30 Up to a third of patients with clinical infection die and about half have permanent residual neurological sequelae. 30 Vaccines against Japanese encephalitis are available, but their immunogenicity has recently been questioned and concerns have been raised regarding adverse reactions. 31 The development of safer and more immunogenic Japanese encephalitis vaccines 30 will be important for future ADF deployments in the region.

Preventing other infectious diseases

Many infectious diseases of travellers can be prevented by immunisation. In some circumstances, certified vaccination is required before travel. Yellow fever vaccination is required for all travellers entering or returning from a yellow fever endemic area, which is prescribed by WHO. 18 Meningococcal vaccination is required for travellers to Mecca. 18

Various other vaccinations may be required for travellers to particular destinations. It is prudent to vaccinate against diseases that might be acquired through food and water, such as hepatitis A, typhoid and polio, 24 as well as using other measures to combat these diseases. The most common vaccine-preventable disease among travellers to date is hepatitis A. 32 Typhoid vaccination should also be considered for travel to many developing countries. Polio vaccination is rarely required these days, after a concerted campaign for global eradication, but it may be required in situations where polio outbreaks have been reported. 24 Other vaccine-preventable infectious diseases that may afflict travellers to certain destinations are listed in Box 1.

For travellers aged 65 years or more, pneumococcal and influenza vaccinations should also be considered. 15

The development of combination vaccines, such as hepatitis A plus typhoid and hepatitis A plus B, may greatly reduce the number of injections required. 24 The development of rapid schedules for travellers departing at short notice has been useful in providing protection within four weeks. 24

The travel medicine consultation is also an opportunity to update routine and national schedule vaccinations against diseases that may afflict travellers anywhere.

Non-infectious hazards of travel

Despite the emphasis on infectious disease in travel medicine, the most common preventable causes of death among travellers are accidents and injuries. 8,32 In 1995 it was reported that about 35% of Australian deaths abroad were the result of ischaemic heart disease, with all natural causes accounting for some 50% of deaths. 8 Trauma (including homicide, suicide and execution) accounted for 26% of deaths of Australians abroad. Injuries were the reported cause of 18% of deaths, with the major injury group being motor vehicle accidents, accounting for 7% of deaths. 8 A similar pattern of mortality has been observed in Swiss, 32 American, 33 and Canadian 34 travellers abroad. Deaths of Australian tourists overseas have also resulted from air crashes, drowning, boating accidents, skiing accidents, bombs and electrocution. 8 Homicides, suicides and executions combined accounted for about 8% of all deaths. 8 Most fatal accidents in American and Swiss travellers were traffic or swimming accidents. 32,33 Infectious disease was reported as the cause of death in only 2.4% of Australians who died while travelling abroad. 8

Issues in aviation medicine

Some travel medicine specialists are also certified by the Civil Aviation Safety Authority as Designated Aviation Medical Examiners of pilots, air traffic controllers and, in some instances, flight attendants, but all practitioners of travel medicine need to be aware of the potential health effects of modern airline travel. These include the effects of reduced atmospheric pressure, low humidity, closed environment, inactivity, disrupted circadian rhythm, alcohol, and aircraft motion. 35 These effects can produce barotrauma, dehydration, jet lag, motion sickness, claustrophobia, panic attacks and air rage, and contribute to the development of deep venous thrombosis (DVT) and venous thromboembolism (VTE). 35 Aircraft are also environments conducive to the spread of infectious disease. There have been concerns raised about the transmission of tuberculosis through close proximity to infected travellers on commercial aircraft. 36 Providing travel health advice and countermeasures for these conditions also largely falls to the specialist in travel medicine.

Some travellers need special clearance to fly in cases of aeromedical evacuation on commercial aircraft and in certain prescribed circumstances, such as serious physical or mental incapacity or after recent surgery. 35 Liaison with the airline's medical department is usually advisable.

Travel medicine is also a key component of the activities of many health professionals working in aviation medicine. In addition to undertaking aviation medical examinations and advising their own staff, airline medical departments review passengers' clearances to fly and provide advice to travel health advisers. They are also involved in developing policies and guidelines for managing in-flight emergencies involving travellers and for training flight attendants in first aid. Physicians working in aviation medicine have their own professional organisation, the Aviation Medical Society of Australia and New Zealand, which holds regular conferences and produces a journal, Avmedia.

Recently, considerable attention has been focused on DVT and VTE, but it remains uncertain what the contribution of air travel is to the development of this condition among travellers. What seems to be clear is that the development of DVT and VTE is multifactorial. 37 While the identification of travellers with predisposing risk factors would seem useful, it is only an option where the risks of side-effects of the screening procedure do not outweigh the risks of developing DVT after a long haul flight, which is estimated to be about 1 in 200000 for travellers on a 12- hour flight. 38 In the meantime, conservative measures should be recommended, such as in-flight exercises, restricting alcoholic and caffeinated beverages and drinking lots of water. For some travellers with an increased risk of DVT, other preventive measures, such as subcutaneous heparin, are worthy of investigation. 38 Current epidemiological research and pathophysiological studies are helping to establish which travellers are at greatest risk, which will in turn lead to appropriate intervention studies.

Issues in refugee and migrant medicine

In 1997, the United Nations High Commission for Refugees (UNHCR) estimated that there were more than 20 million refugees and internally displaced persons who came under the UNHCR mandate. 39 Illegal migration and trafficking in migrants, usually from poor countries to rich countries, is a worldwide phenomenon. Many successfully gain asylum in their host countries. Rarely are migrants properly prepared for travel to their new homes, and greater co-operation and health planning is needed between their home and host countries.

Migration has important health implications. Migrants often have a higher rate of various infectious diseases than other travellers, as well as psychological disorders as a result of previous ordeals and the stress of leaving their homeland. 40 Refugees and illegal migrants should be screened for various infectious and parasitic diseases such as tuberculosis, hepatitis B and C, schistosomiasis, malaria, and sexually transmitted infections (including syphilis and HIV). 40 Chronic diseases also need to be considered, such as diabetes, cardiovascular disease, malignancies, asthma and other chronic respiratory conditions. 40 Health services, including those provided by the ADF, need to understand and respond to the wide and varied travel health problems of refugees and migrants, especially illegal immigrants.

Competing interests

None declared.

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Lieutentant Colonel Peter Leggat, RAAMC, joined the Australian Regular Army in 1987. He was posted to various units, including the historic 2 Field Ambulance in Townsville. Lieutenant Colonel Leggat is currently serving as a Consultant, Defence Health Services, Army Reserve, Queensland. In 2002, he was awarded the Major General John Pearn Surgeon General's Medal for outstanding contributions to tropical medicine.

School of Public Health and Tropical Medicine, James Cook University, Townsville, QLD.

Peter A Leggat, BMedSc, MB BS, DipEd, DTM&H, MMedEd, DIH, MPH, PhD, FAFPHM, FACTM, FFTM, FACRRM, RAAMC, Associate Professor. Correspondence: Lieutenant Colonel Peter A Leggat, School of Public Health and Tropical Medicine, James Cook University, Townsville, QLD 4811. Peter.Leggat@jcu.edu.au