by Dr. Nita Bharti

Movement and Health

Human movement and human health:

pathogen transmission and access to health care

 
Road to Etengua, Namibia

Road to Etengua, Namibia

We can’t separate studies of human health from studies of human populations
 

We study the links between human health and human movement

Movement is a critical element of human contact and connectivity, which drive pathogen transmission. We work to measure human movement to understand pathogen transmission and access to health care, particularly in areas where a lack of understanding of human contact has limited progress in public health.

 
A schematic of population dynamics for seasonally mobile populations. In agriculturally driven economies, such as Niger, population density, measles transmission, and access to health care simultaneously increase during the dry season as urban populations grow. These populations decline during the rainy season, leading to decreased measles transmission as well as reduced access to health care and measles prevention. From Bharti et al 2016 Nature Scientific Reports.

A schematic of population dynamics for seasonally mobile populations. In agriculturally driven economies, such as Niger, population density, measles transmission, and access to health care simultaneously increase during the dry season as urban populations grow. These populations decline during the rainy season, leading to decreased measles transmission as well as reduced access to health care and measles prevention. From Bharti et al 2016 Nature Scientific Reports.

It’s impossible to vaccinate a population adequately without knowing how many people make up a population.

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Populations change over years, seasons, and weeks. Sometimes, they change regularly or predictably, which can help inform vaccination efforts. Our work measures these changes and quantifies how predictable they are to help close gaps in vaccination coverage. Our work in this area is primarily in Niger and Namibia.

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We use satellites to measure anthropogenic lights

Nighttime lights and urban populations: Annual seasonal fluctuations of brightness across each of five cities in Niger and Nigeria. The top plot for each city in Niger shows the estimated measles transmission curves for each city in Niger on a scale of 0 (center) to 2 (perimeter) by month (January to December) from measles case reports from 1995-2005 (citations 4,18); data unavailable for Katsina, Nigeria. Each pixel in the animation reflects the local maximum of the quantified brightness value from DMSP-OLS satellite images at the time indicated by transmission plot. This nighttime lights animation, was created in D3.js (https://d3js.org/) by Patrick Dudas. Basemap: Map tiles by Carto (https://carto.com/), under CC BY 3.0, data by OpenStreetMap, under ODbL. Bharti et al 2018 Nature Scientific Data.

 

There are lot of sources for official population size numbers and they’re never the same. This creates uncertainty when vaccination programs calculate how many to administer to a population to achieve ~92% coverage, to break local chains of measles transmission.

( A ) Point estimates of coverage of reinforcement activities in the city of Niamey, Niger from survey responses (left, black) and as calculated from doses distributed and city population size estimates from MSF, MoH, and the UN (left to right, faded points). Bright points and CI: Estimated coverage of reinforcement activities with CI including model estimates from posterior distribution of population flux using city population size estimates (bright points and lines). ( B ) Above: reported daily measles cases in Niamey. Below: estimated population fluxes of each commune by calendar day calculated from model. Vertical dashed line indicates start of reactive immunization campaign. Central solid lines indicate estimates for population flux based on posterior mean; shaded polygons indicate prediction intervals for flux based on central 95% of posterior distribution. From Bharti et al 2016 Nature Scientific Reports.

(A) Point estimates of coverage of reinforcement activities in the city of Niamey, Niger from survey responses (left, black) and as calculated from doses distributed and city population size estimates from MSF, MoH, and the UN (left to right, faded points). Bright points and CI: Estimated coverage of reinforcement activities with CI including model estimates from posterior distribution of population flux using city population size estimates (bright points and lines). (B) Above: reported daily measles cases in Niamey. Below: estimated population fluxes of each commune by calendar day calculated from model. Vertical dashed line indicates start of reactive immunization campaign. Central solid lines indicate estimates for population flux based on posterior mean; shaded polygons indicate prediction intervals for flux based on central 95% of posterior distribution. From Bharti et al 2016 Nature Scientific Reports.

Desert in Niger just outside of Niamey

Desert in Niger just outside of Niamey

 

Otjitanda, Namibia

Etengua, Namibia