Climate Variability, Extremes Allow Emergence and Propagation of Cholera Strains

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According to new research published in PLOS Neglected Tropical Diseases, climate anomalies may create opportunities for the emergence of new cholera strains. Since 1961, over 1 million people worldwide have died in an ongoing cholera pandemic. The drivers of previous cholera pandemics were unclear, but this new finding suggests that climate conditions may act synergistically with the genetic changes of the bacterium that causes cholera, Vibrio cholerae, to facilitate spread and new strains.¹

For this study, the investigators evaluated the roles of climate and putative strain for the sixth choler pandemic (from 1899 to 1923) using newly assembled historical records for climate variables and cholera deaths in the provinces of former British India. Additionally, this was compared with the seventh pandemic along with the temporary emergence of the O139 strain.²

The investigators examined the regional synchrony of outbreaks as well as associations of the disease with regional temperature, rainfall, and the El Niño Southern Oscillation (ENSO). Further, climate projections were generated using multimodel climate solutions for different 50-year periods to help establish future expectations and evaluate climate anomalies that may accompany historical strain replacements.²

According to the investigators, the results support a role of climate acting as a major driver of the 1904 to 1907 anomalous cholera episode, which would have expedited the novel strain. Additionally, this strain was found to be related to unusually cold conditions and high precipitation. Further, higher mortality in the dominant winter peaks would have therefore been facilitated but the anomalous monsoon season of the prior summer, and the very low temperatures helped to abruptly end the winter peak.²

Additionally, the authors note that excessive rainfall during the monsoon season could have disrupted sanitation systems, therefore promoting bacterial propagation. Both effects, according to the authors, would have generated a larger pool of susceptible individuals and/or lower levels of temporary acquired immunity, contributing to a larger winter outbreak in the transmission season following the monsoons. Heavy rains could have also played an important role by disrupting sanitation systems, promoting a delay in the proliferation of bacteria in the environment, possibly because of increased nutrients. The authors note that the anomalies in rainfall and temperature support a role of ENSO during the 1904 to 1907 event, which is consistent with prior studies of more recent cholera and climate variability.²

“Variation in climate conditions or the evolutionary change of a pathogen can be important drivers of major epidemics and pandemics. But these 2 drivers are typically considered separately in studies seeking to explain the emergence of unusually large outbreaks…here, we present indirect evidence that the 2 can act together to synergistically underlie the establishment and widespread transmission of a new strain,” said the study authors in a press release.¹

The CDC recommends that individuals get vaccinated for cholera if traveling to an area where cholera is present, or where the water and food are considered unsafe to eat. Additionally, the CDC suggests individuals are vaccinated if there is a humanitarian crisis with a high risk of cholera.³

Currently, Vaxchora (Bavarian Nordic A/S) is the only FDA-approved cholera vaccine in the US. It is a single dose administered orally and is indicated for individuals aged 2 to 64 years of age who are traveling to an area where cholera is present. It is recommended that individuals get vaccinated at least 10 days prior to travel. It reduces the chance of moderate and severe diarrhea in people aged 18 to 45 years by approximately 90% at 10 days post-vaccination, and by about 80% at 3 months; however, it is currently unknown how long protection lasts beyond 3 months.³

References

1. PLOS. Climate anomalies may play a major role in driving cholera pandemics. News release. August 1, 2024. Accessed August 14, 2024. https://www.eurekalert.org/news-releases/1052971

2. Rodó X, Bouma MJ, Rodríguez-Arias MÀ, Roy M, De Yebra P, et al. (2024) Strain variation and anomalous climate synergistically influence cholera pandemics. PLOS NTDs 18(8): e0012275 doi:10.1371/journal.pntd.0012275

3. Cholera vaccines. Centers for Disease Control and Prevention. Accessed August 14, 2024. https://www.cdc.gov/cholera/prevention/cholera-vaccines.html