Mention the Black Death and visions of overcrowded 14th-century European cities teaming with rats come to mind. Despite the association of plague with crowded cities the disease didn’t originate there. Plague is caused by a bacterium regularly found in flea and rodent populations across Central Asia’s rural areas, where it first appeared.
An interdisciplinary and international team of researchers, including Susan Jones and Marlene Zuk from the College of Biological Sciences, recently published an article in the Proceedings of the National Academy of Sciences detailing secret plague eradication efforts in the USSR — and the fact that they failed. The authors also present a framework to mitigate the spread of diseases with similar ecologies to plague.
The bacterium that causes plague infects fleas that then bite their animal hosts, typically wild rodents. When conditions are right infected fleas can bite domesticated rodents, pets, livestock and humans. Depending on the type of plague and treatment, infected humans die 35% to 95% of the time. Plague, a zoonotic disease, persists naturally in animal populations only occasionally impacts humans.
Beginning in the 1920s and lasting several decades, the USSR attempted to eradicate the disease. Pledges to “sanitize” landscapes and “liquidate” all wild rodents and fleas over thousands of square miles led to extensive scorched-earth campaigns. This included spraying DDT from airplanes, mobilizing tens of thousands of people to manually place poisons into rodents’ burrows, and burning the landscape.
A document from the World Health Organization in the mid 20th century, claimed no sources of plague existed in the USSR following this campaign. Jones, who is trained as a veterinarian and science historian, encountered this document a few years ago and knew this couldn’t be the case. With strong collaborations in place, she learned a bit of Russian and requested access to archives in St. Petersburg and elsewhere.
Even though the campaigns were no longer a “state secret,” documents were challenging to find — securing a single photo from a medical military museum took two years. She credits her Ph.D. student and study co-author Anna Amramina as instrumental in making connections and translating documents. During this era in the USSR, “The science was entangled with the political situation,” Jones says. The concept of scientific discovery was pitted against the pressure to find what the government wanted scientists to unearth.
Plague returned to “sanitized” areas. In the 1970s, the USSR turned away from complete eradication. Scientists began to monitor and control flea densities. Complete eradication is not a plausible option to battle animal-to-human diseases like plague. Instead, monitoring disease build-up in nature and controlling its spread is the best option for preventing spillover to humans.
Ongoing research aims to increase understanding of the complex ecologies of the disease, including the bacterium, fleas and burrowing rodents. Zuk hopes to study how the social behavior of burrowing disease-harboring rodents will better inform on the ground surveillance efforts.
Jones notes that “The plague story is central to the globalization of our disease ecology histories.” Because of this, plague is an incredibly powerful case study and provides insights into how scientific discoveries and political influences can become intertwined. — Claire Wilson