Population dynamics, health, and labor migration in Micronesia during the Japanese occupation, 1919–1945

Abstract

A pressing global health concern in the 21^st century is the risk of rapid and widespread disease transmission and its negative demographic consequences. The interface between migration, disease transmission, and demography is of central importance today; however, understanding the interrelationships among these factors is difficult due to confounding factors. Much can be learned from historical case studies, particularly in island populations. First, the role of migration in disease transmission can be more readily disentangled than in contemporary populations. Second, changes in the health and demography of populations were often drastic after foreigners arrived and clearly related to introduced disease. Episodes of colonialism allow for a clear picture of how the movement of people and social and environmental change are associated with population health and demographic change.

This dissertation focuses on the interplay between gonorrhea and tuberculosis transmission, labor migration, and demography in Micronesia during the Japanese colonial period (1919–1945). It also identifies lessons for more complex and contemporary settings involving other diseases and cultural norms.

First, this dissertation illustrates the potential demographic consequences of uncontrolled epidemics. Although disease is not usually thought of as having a large impact on fertility, this work shows that it should not be discounted. Especially before treatment, gonorrhea epidemics could be large and devastating, and could trigger depopulation. Fertility usually has a larger impact on population growth than mortality. However, in a situation of an uncontrolled epidemic such as tuberculosis on Yap during the Japanese occupation, increases in mortality rates were a greater determinant of population growth than were depressed fertility rates from gonorrhea infections.

Second, this dissertation uses a simulation model to clarify the role of migration in disease transmission. A general assumption is that return migrants are responsible for spreading infection. This work shows that the assumed association between circular migration and STD transmission at home depends on the etiology of disease and social climate. Migrants should not be blamed for inciting epidemics without detailed research. One needs to look closer at (1) the specific characteristics of the disease, and (2) the behaviors of the migrants before conclusions can be drawn.