Dust in the Wind: Climate and Meningococcal Meningitis in Africa
By Elisabeth Gawthrop, Climate and Society ’13
For many of us, dust is just an annoyance. It’s the coating that accumulates on our picture frames, and, for some, it may trigger unwelcome allergies. Dust is increasingly garnering interest, however, in the scientific community, including the role it plays in the climate system. And for many in sub-Saharan Africa, better understanding of dust could be a helpful tool in mitigating the risk of meningococcal meningitis epidemics.
Meningococcal meningitis (MM) is a cerebrospinal infection caused by the bacterium Neisseria meningitidis, and its severity of symptoms, 10% fatality rate (with treatment), and often debilitating effects for survivors make it a priority research and intervention target. This summer, I’ve been working as a NASA DEVELOP intern with Pietro Ceccato and Madeleine Thomson at the International Research Institute for Climate and Society (IRI), Carlos Perez at NASA’s Goddard Institute for Space Studies (GISS), and fellow C+S student Tammy Tran to study the relationship between humidity, temperature, and meningitis in what’s known as the Meningitis Belt in sub-Saharan Africa (see figure).
This region has the highest rates of MM in the world, and epidemics occur almost exclusively in the dry season. This has led researchers to hypothesize that dry, dusty, and windy conditions are conducive to the spread of the disease, with the possible explanation of such conditions irritating the membrane of the nasal cavity and allowing the bacteria to more easily enter the body.
Although this seasonal tendency is well established, the relationship between year-to-year variability of climate and MM incidence is less well understood. For most countries in the Meningitis Belt, there is always a dry season, and yet there is not an epidemic every year. Much research in this field has focused on case studies at the subnational level. Our project this summer compared satellite and model-based humidity and temperature data with MM incidence at the national level for six countries along the periphery of the Meningitis Belt. Our ultimate goal was to examine the potential for more widespread predictability using these climate variables.
The selected countries were chosen because, unlike the countries in the heart of the belt, the climate of the dry season is more variable each year, with some years being drier than others. Our hypothesis was that the hotter, drier years in these areas would correlate with the years of higher MM incidence, and if this relationship is validated, one could potentially use climate to predict which areas on the edge of the belt are at high risk for a MM outbreak.
Our results thus far indicate that the climate variable most correlated with MM differs by locality. For some of the countries we studied, widespread low humidity was significantly correlated with MM incidence, while for others there was a stronger, and negative, correlation between nighttime temperatures and MM. While our findings suggest that widespread predictability of MM using climate variables will require more research before use by decision makers, the significant correlations for some areas are promising. Furthermore, though the variables we studied are certainly related to dust, further research will include modeling dust itself, as well as wind, and look for consequent relationships with MM incidence.
Researchers at the IRI have developed online tools for decision makers that use satellite measures of climate conditions to estimate risk of malaria in Africa, and they, in concert with the Meningitis Environmental Risk Information Technologies (MERIT) program, hope to provide similar tools for meningitis risk. Results from our work this summer point these scientists to areas where predictability is strongest and future studies can be targeted. If correlations found by this study are further confirmed, climate conditions that indicate high-risk for meningitis epidemics can be used in early warning systems, vaccination programs, and other strategies by MERIT to mitigate the risk of humans contracting the disease.