Understanding how ENSO cycles impact immunity and outbreak patterns

Variations in temperature, precipitation, and humidity can influence the spread of infectious diseases, including by altering the habitats of disease transmitters such as mosquitoes. Extreme weather events can disrupt health care responses as well. Previous studies have shown that the El Niño–Southern Oscillation (ENSO), with its alternating warm (El Niño) and cold (La Niña) phases, alters extreme weather and may also influence the spread of infectious diseases, such as cholera, dengue, malaria, respiratory syncytial virus (RSV), and Rift Valley fever.

Though ENSO events can be forecast months in advance, few successful public health interventions, such as vaccine campaigns and vector control efforts, have resulted from these predictions.

Geographic variability, differences in timing between ENSO and disease cycles, and population immunity resulting from previous outbreaks are all factors that complicate linking ENSO events directly to disease outbreaks.

Published in GeoHealth, Chung and collaborators built upon previous locally focused and disease-specific studies to model longer-term interactions between ENSO cycles and various infectious diseases. They used two modeling approaches to investigate how ENSO’s influence on disease outbreaks may change from year to year.

First, the team modeled how back-to-back ENSO events could directly and indirectly affect populations susceptible to disease outbreaks over multiple years for a generic seasonal disease. The second modeling effort focused on an airborne human coronavirus, HCoV-HKU1. Using global humidity data from 1981 to 2017, the researchers examined how humidity variations associated with ENSO influenced disease transmission.

When analyzing population data, the team repeatedly found that immune responses for infectious diseases lagged behind the initial El Niño and La Niña events, sometimes by more than a year. When ENSO events occurred in consecutive years, the effects could therefore lead to longer-lasting and larger disease effects a year or more later.

The researchers suggest that on the basis of these findings, risk managers should consider how population immunity may be a predictor of ENSO’s influence on the spread of infectious diseases. Further improving the understanding of climate and disease interactions could mean planning interventions several months in advance and improving health outcomes, the authors say.

This story is republished courtesy of Eos, hosted by the American Geophysical Union. Read the original story here.