Lifestyle change, hormone levels, and parasitic disease risk among the Shuar in Ecuador
by Theresa Gildner
Despite medical advances, infectious diseases continue to have substantial health consequences for people worldwide. The negative effects of these diseases are disproportionally high among economically developing nations in tropical regions. While some diseases like malaria receive significant attention from public health initiatives, the so-called neglected tropical diseases do not, even though they affect over 1.4 billion people globally. Neglected tropical diseases, especially parasitic infection, commonly occur in less affluent countries resulting in impaired physical and cognitive function, limited economic productivity, and even death, effectively trapping these groups in a cycle of disease and poverty.
This pattern has been observed in tropical South America, where previously isolated indigenous communities are now undergoing rapid urbanization characterized by the adoption of agricultural technology and market foods. These changes have profound health effects: some, like improved healthcare access, may lead to decreased disease risk; others, such as greater reliance on domesticated animals and increased population density, can raise disease burden. Still, surprisingly little research has been conducted among indigenous South American societies to examine how lifestyle factors affect parasite infection risk and determine how to reduce disease burden. The goal of my research is to address this public health issue by identifying the social and biological factors most strongly linked to parasitic disease risk among the Shuar, a large indigenous group of Amazonian Ecuador experiencing a varied but rapid increase in urbanization.
Previous research has demonstrated that shifts in diet and activity patterns (the result of urbanization) have the potential to influence hormone levels and health outcomes, yet this issue has not been well studied. For instance, evidence suggests a sex difference exists in immune function with women generally responding more effectively to infections, including parasites. This may in part reflect the immunosuppressive effects of the hormone testosterone in men, including reduced white blood cell response to infection; although this remains poorly tested in humans, especially those experiencing high rates of parasite infection.
To test these hypothesized interactions, my project examines how testosterone levels and economic change influence parasitic disease by comparing rural and urban areas with respect to testosterone profiles and parasite load. The primary goal of my preliminary dissertation research last summer, partially supported by the summer graduate student research grant from CLLAS, was therefore to measure testosterone levels among Shuar men to determine how these measures vary compared to other populations. Testosterone levels were measured using saliva samples collected from 39 Shuar men during previous field seasons. Peak testosterone levels were then compared between Shuar and U.S. men using NHANES data. This pilot study indicates that U.S. men have significantly higher overall testosterone levels than Shuar men, suggesting that Shuar testosterone levels are generally lower than those in industrialized populations. Given that high testosterone levels are associated with several energetically expensive traits (e.g., increased musculature), this pattern may reflect a decreased ability among Shuar men to maintain elevated testosterone levels due to lower caloric intake, higher physical activity levels, and increased disease exposure.
Building upon these initial results, my future work will examine how lifestyle factors and testosterone levels influence the immune system and parasite infection among the Shuar. Clarifying interactions among social factors, hormone levels, and infection risk have the potential to improve public health policy in the region. With this goal of improving health outcomes, my research seeks to alleviate the burden of parasitic disease in participant communities. During previous field seasons I have collected and analyzed fecal samples to measure parasite load among the Shuar. I have subsequently used this information to treat infected participants, at no cost to them, through a collaborative effort with local healthcare providers. I also plan to develop an education program with the Shuar Federation to provide culturally appropriate community education about locally feasible infection prevention methods, including: water purification, proper food preparation, and other hygiene practices. It is my hope that this project will alleviate the burden of parasitic disease among the Shuar and other indigenous South American populations, both through infection treatment in participant communities and the identification of the lifestyle factors most strongly linked with parasitic disease risk.
—Theresa Gildner is a Ph.D. candidate in the UO Department of Anthropology. Her research focuses on the effects of human behavior and the environment on infectious disease, especially parasitic infection. She is also interested in understanding how these interactions can be used to design more effective disease intervention programs.