Ethnography of a parasite [electronic resource] : a study of malaria in Colombia

This dissertation employs an innovative mixed methods approach to address distinctive aspects of malaria transmission in Colombia. My overarching objective is to characterize populations living near epidemic thresholds of malaria (when malaria becomes endemic), describing disease intensity with demographic and behavioral profiles. First, at a national level, I used statistical analysis (time series analysis and a spatial scan statistic) to identify populations living under intense malaria exposure. To do so, I characterized malaria intensity by region, and ethnic membership based on case reports collected by the government based on passive (individuals seeking health care) and active (health officials actively scouting cases) surveillance. This malaria intensity study was conducted at the national level and included 5,615 populations. Second, a case study in a Nükak population of 108 individuals experiencing endemic malaria was conducted to examine behavioral and demographic aspects associated with malaria endemicity in Colombia. Census data were collected in this endemic population and reproductive patterns of all females in the community were described, using available data for other populations from ethnographic observations as controls. Within the case study village/population, behavioral data were collected to explore behavioral risk profiles for malaria using behavioral activity budget scans, not commonly used in epidemiological studies. All Colombian populations were classified according to two distinctive malaria characteristics. Whether they were experiencing intense malaria, and, whether the intensity was endemic or epidemic within each population. Results indicate malaria persists in highly concentrated yet hyperdispersed sites of endemicity in Colombia, and is epidemic in populations where an occupational risk hazard prevails. My focal case study was then conducted in the Nükak population of San José del Guaviare, where malaria endemicity was most intense. I found that malaria among the Nükak followed a different pattern than those described for populations at risk of contracting the disease. Furthermore, I found that malaria among the Nükak underwent a transition, from non-endemic to epidemic, crossing an epidemic threshold. This epidemic threshold was associated with their changes in subsistence patterns, and also correlated with a demographic transition from hunter-gathers to sedentary means of production, where women increased their reproductive rates. I detected and found a statistical association between birth intervals and subsistence patterns using a Cox proportional regression model. Furthermore, using a Poisson regression model, I found that the risk of contracting malaria prevailed at a population level, but not at an individual level. My research showed that malaria persists in endemic pockets with sustained household transmission. I suggest that this occurred via livelihood modifications that affect malaria epidemiology by altering two critical parameters. First, susceptible individuals increased within this population as female reproductive rates increased. Second, the presence of asymptomatic individuals, who remain untreated and infective to mosquitoes for prolonged periods decreased the necessary number of infected individuals to maintain the epidemic. Altering these parameters imparts critical interactions of susceptible and infected groups for malaria dynamics, whereby populations cross an epidemic threshold and, in turn, malaria becomes endemic (R0 > 1). These findings may have potential public health applications for malaria control. First, in this case study region, using bed nets is not an effective means to prevent malaria where it persists endemically. Second, my research suggests that public health measures should also focus on treating asymptomatic individuals, and controlling the increased risk of malaria endemicity due to the density of young vulnerable individuals.

Keywords: Anthropology.
Advisor: Jones James Holland primary advisor. Thesis advisor
Curran Lisa Marie
Lambin Eric F. advisor. Thesis advisor