This year marks the 100th anniversary of one of the deadliest natural disasters in human history - The 1918 influenza pandemic, also known as the “Spanish Flu”, which killed about 50 million people worldwide.
Pandemic influenza is different than typical, seasonal influenza that circulates every winter, and it only happens when a new influenza virus emerges and spreads globally. In the past century, there have only been four influenza pandemics, with the "Spanish Flu" being the deadliest. When examining the spread of a pandemic and the likelihood of it happening again, it is important to first understand what sparks these types of events.
What’s Important to Know About Influenza and Spark Risk:
- Novel influenza viruses occur when a typical human influenza virus exchanges genetic information with an influenza virus from another species, most commonly a bird or pig.
- The influenza virus that caused the 1918 pandemic virus contained genes from an avian influenza virus.
- Because of the interaction between human and animal viruses, today’s researchers can look for areas where new viruses are likely to originate, and more specifically the location of origin, more commonly known as “the spark site.”
The spark site for the 1918 influenza pandemic has been a topic of extensive debate and there are many conflicting hypotheses about the virus’s geographic origin. The name “Spanish Flu” appears to be a misnomer. The leading hypothesis, asserted first by historian Alfred Crosby and later by John Barry, author of The Great Influenza, claims that the virus originated in the U.S., and was first observed among military recruits reporting for duty at Fort Riley, Kansas. Under that hypothesis, recruits from throughout the surrounding rural areas likely brought the virus to Fort Riley in the winter of 1918 towards the end of World War I, and over the next month, the virus spread to other Army camps, ultimately causing over 11,000 hospitalizations. Soon after, the virus began making its way across the Atlantic along with U.S. soldiers.
If the 1918 influenza pandemic happened today, the initial spark site could be much different. The increase in the human population, changes in land use, and differences in agriculture can all contribute to where the spark site is likely to occur. For better insight into spark risk, researchers can create spark risk maps, which predict the probability of a virus originating at any given location. They are constructed by collecting all the known locations that the virus has been detected and using that information to look for the attributes that these locations have in common.
What are Disease Attributes:
- For pandemic influenza viruses, these attributes could include poultry or wild bird density, proximity to pig farms, average annual temperature or rainfall, and types of vegetation or land cover.
- For example, a study published in 2016 showed that poultry production was the strongest predictor for occurrence of a highly pathogenic avian influenza (HPAI) virus known as H5N1.
- From the global map below, it is evident that areas in southern and Southeast Asia have the highest spark risk. That said, HPAI is not the only threat. The 2009 influenza pandemic, known as "Swine Flu", originated in Mexico and quickly made its way to the U.S., with the first identified cases in southern California and then Texas.
Figure: Predicted probability of occurrence of highly pathogenic avian influenza (HPAI) H5N1.
From: Global mapping of highly pathogenic avian influenza H5N1 and H5Nx clade 126.96.36.199 viruses with spatial cross-validation. MS Dhingra, et al. 2016, eLife.
In an effort to better understand and mitigate against these massive global pandemics in the future, Metabiota has created a model incorporating spark, spread, and preparedness risks, in order to simulate influenza pandemics. This model shows that a future pandemic with similar characteristics to the “Spanish Flu” could spark anywhere in the world, with devastating human and economic impacts. Many countries lack the resources and capacity to tackle an event of this magnitude and severity, contributing a large preparedness gap. Most worryingly, many of these countries happen to be in areas that also have high spark risk. These areas are especially important to target for increased monitoring to more quickly detect when viruses have jumped from animals to humans and could spark the next pandemic.
- Although it has been 100 years since the “Spanish Flu” pandemic sparked, the risk that another influenza pandemic will occur still exists today.
- Areas where humans, pigs, poultry, and wild birds interact are expected to have the greatest spark risk.
- Due to the large global preparedness gap, a pandemic similar to the 1918 pandemic is a real possibility.
- We must accurately estimate this risk to be prepared.