Date Published: May 24, 2011
Publisher: Public Library of Science
Author(s): Brian D. Gushulak, Douglas W. MacPherson
Abstract: In the second article in a six-part PLoS Medicine series on Migration & Health, Brian Gushulak and Douglas MacPherson discuss the pre-departure phase of migration and the specific health risks and policy needs associated with this phase.
Partial Text: This is one article in a six-partPLoS Medicine series on Migration & Health.
The flow of populations within and across international boundaries is an important element in today’s globalized world. Recent estimates of migration patterns place the combined numbers of international migrants and internal migrants at nearly a billion people . Although migrant populations are extremely diverse, the processes of migration include certain characteristics shared by all migrants. All migrants have a place of origin. Experiences and exposures at a place of origin can influence migrants’ health throughout the process of mobility , which may include transition, temporary residence, and arrival at a destination. After arrival or settlement, some migrant cohorts may experience ongoing or return migrations that can also have health consequences.  As indicated in Table 1, rates of departure from origin countries are markedly different between global areas and countries, with rates in Europe, Latin America, and Oceania more than double those of Africa, Asia, and North America . It is important to note, however, that even low rates of departure from highly populated countries of origin can produce large health impacts at destinations.
The observation that one’s origin, in terms of physical location and the determinants of health (socioeconomics, genetics and biology, behaviour, and environment), influences one’s current and future response to events is widely appreciated across the spectrum of social and physical sciences . In the context of migration and population mobility, the pre-departure phase can be considered as the beginning of the migration process and as such affects the rest of the migratory journey. The health characteristics of pre-departure migrant populations can be very diverse, reflecting disparities in the determinants of health at both individual and societal levels. The interaction between those pre-existing determinants of health and the forces that create migration affect many health outcomes in migrants.
These push and pull pressures are unequally distributed across pre-departure migrant populations, and together they both influence and affect migrant demography. An illustration is provided by comparing rural to urban migration and international migration from the same area. Rural to urban internal migration often represents the movement of workers, either with or without their families, from less affluent areas to metropolitan centers where jobs are perceived to be more plentiful. This broad pattern of migration has its own set of health issues and examples have been observed in several locations including child health in Africa, where death in those younger than 5 years old was greater for children of rural–urban migrants . Other examples include the acquisition of less healthy determinants associated with urban living related to diet, activity, body weight, and access to preventive health services. Studies have noted increases in body mass index and diabetes in rural–urban migrants in India , increased cardiovascular risk factors in urban migrants in Latin America , and reduced rates of immunization in children of urban migrants .
Pre-departure health status affects both individual and population health outcomes . As described in Table 3, the magnitude of those influences is dependent upon the diversity (differences) and/or disparity (differences with a disadvantage) in the determinants of health and their outcomes between their new destination and those at the migrants’ origin. People moving between regions of high endemicity for a disease can carry that epidemiology to low incidence, migrant-receiving nations . Pre-departure differences in chronic disease epidemiology between migrant origin and destination locations can have long-term effects . Over time and with sustained migration from high prevalence to low prevalence areas, migrants can come to represent specific disease risk groups in destination countries  for non-prevalent conditions such as tuberculosis , hepatitis B , strongliodaiasis , malaria , cystercercosis , South American trypanosomiasis , diabetes , renal failure , cardiovascular disease , and certain malignancies , among others.
Historically, the pre-departure influences affecting the health of migrants were approached in terms of the potential risks migrants were believed to pose to the domestic host population. Attempts to control the admission of epidemic diseases grew to include the medical screening of arriving migrants . Practiced by nations with organized immigration selection programs, medical screening may be an element of a formal regulated process used to determine the eligibility of entry on health grounds . Additional or supplemental screening is often recommended for clinical or public health benefit . Screening is also a frequent component of organized migrant labor or temporary workers programs in Asia  and the Middle East .
Migration health policies, when they exist, are frequently based on traditional considerations of immigration/emigration. Those frameworks often categorize mobile populations of increasingly diverse origin into a limited number of administratively determined immigrant categories. Health concerns in mobile populations have often been addressed in terms of traditional migrant classification (refugee, immigrant, temporary worker, visitor, etc.). While those categories may reflect historical migration flows, they are often not representative of modern migrant diversity or disparity, nor may they reflect the current reality of health differences relevant to receiving nations. An example is provided by the demographic, experiential, and personal differences present in current refugee populations. Depending on location and national practice, a wealthy, educated political refugee originating in a developed metropolitan area who filed an asylum claim versus an economically and educationally deprived laborer forced from his or her home into a refugee camp by conflict, could be administratively classified identically. Yet, their health status and needs may be significantly different.
The determinants of health present during the pre-departure phase of migration are crucially important factors affecting the existing and future health outcomes of migrants and host populations. The effects of these factors extend throughout the remaining phases of the migratory process and apply at both the individual and population level. Appreciating and dealing with these issues at operational and policy levels requires global focus, rapid and flexible response to change, and current information on the composition and nature of the migrants themselves as opposed to traditional administrative migrant-classification- or disease-based paradigms. Increasingly, the challenges of dealing with migrant health are being addressed through collaborating centers of reference and experience ,. Bringing together multidisciplinary sectors that include providers, migrant communities, and educational institutions, these centers allow for the effective preparation of migrant-focused policies, programs, and services using shared knowledge, research, and resources. Collaboration of this type reduces duplication of activities, allows for the expedient extension of best practices, and supports comparative research.